In this manuscript,we conveniently prepared a series of polyester-polycarbonate copolymer(PPC-P)/polybutylene adipate terephthalate(PBAT)blends that exhibit both flame-retardant properties and toughness.Piperazine pyr...In this manuscript,we conveniently prepared a series of polyester-polycarbonate copolymer(PPC-P)/polybutylene adipate terephthalate(PBAT)blends that exhibit both flame-retardant properties and toughness.Piperazine pyrophosphate(PAPP),melamine phosphate(MPP)and ZnO were used as synergistic flame retardants for PPC-P/PBAT blends.The effects of synergistic flame retardants on thermal stability,combustion behavior and flame retardancy of PPC-P/PBAT blends were investigated.The results showed that when the ratio of PAPP/MPP/ZnO was 18.4:9.2:2.4,the LOI of PPC-P/PBAT composite was 42.8%,and UL-94 reached V-0 level.The results of cone calorimetry showed that the mass loss rate(MLR),the peak value of the biggest smoke production rate(pSPR)and total smoke production(TSP)of the material decreased,and a continuously expanded carbon layer with a compact structure was formed after combustion.The carbon layer formed after surface combustion protects the material from decomposition over a long temperature range.In terms of mechanical properties,compared with the composites with only PAPP and MPP,PAPP/MPP/ZnO composites can improve the mechanical properties.After adding 2.4 wt% ZnO,the tensile strength and impact strength of the polymer increased to 34.2 MPa and 28.5 kJ/m^(2),respectively.The results showed that the use of non-toxic,environmentally friendly,halogen-free flame retardants to enhance the flame retardant properties of biodegradable polymer composites is a promising direction in the future.展开更多
In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a ...In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers.The matrix material is composed of a blend of NR and BR,which is widely used in tire manufacturing.By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene)(TBIR)rubber powder(pVTPR)with different cross-linking densities and contents,significant improvements in the gas barrier properties and CO_(2)permselectivity of the NR/BR/pVTPR composites were observed.The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR,BR,and TBIR,the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties.Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite.For example,the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m^(3)resulted in a 79%improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR,achieving a value of 5.47×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1).Similarly,the nitrogen barrier property improved by 76%compared to NR/BR,reaching 2.4×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1),which is 28%higher than the conventional inner liner material brominated butyl rubber(BIIR,PN2=3.32×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1)).Owing to its low cost,exceptional gas barrier properties,superior adhesion to various tire components,and co-vulcanization capabilities,the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires.Furthermore,by fine-tuning the cross-linking density of pVTPR,the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO_(2)permselectivity,with a CO_(2)/N2 selectivity of 61.4 and a CO_(2)/O_(2)selectivity of 26.12.This innovation provides a novel strategy for CO_(2)capture and separation,with potential applications in future environmental and industrial processes.The multifunctional NR/BR/pVTPR composite,with its superior gas barrier properties and CO_(2)permselectivity,is expected to contribute to the development of safer,greener,and more cost-effective transportation solutions.展开更多
Living cationic polymerization of 4-acetoxystyrene(STO)was conducted in CH_(2)Cl_(2) at-15℃ using a dicumyl chloride(DCC)/SnCl_(4)/nBu_(4)NBr initiating system.Impurity moisture initiation was inhibited by adding pro...Living cationic polymerization of 4-acetoxystyrene(STO)was conducted in CH_(2)Cl_(2) at-15℃ using a dicumyl chloride(DCC)/SnCl_(4)/nBu_(4)NBr initiating system.Impurity moisture initiation was inhibited by adding proton trap 2,6-di-tert-butylpyridine(DTBP),and the controlled initiation of DCC was confirmed by ^(1)H nuclear magnetic resonance(^(1)H-NMR)spectroscopy and matrix-assisted laser desorption ionization time-offlight mass(MALDI-TOF-MS)spectrometry.The polymerization kinetics were analyzed to for optimizing the polymerization rate.Allyl-telechelic PSTOs(allyl-PSTO-allyl)with molecular weight(Mn)range of 3540–7800 g/mol and narrow molecular weight dispersity(Mw/Mn)about 1.25 were prepared through nucleophilic substitution with allyltrimethylsilane(ATMS)at approximately 40%monomer conversion.The experimental results indicate that the substitution efficiency of ATMS increased with higher ATMS concentration,temperature,and extended reaction time.Nearly unity ally-functionality for allyl-PSTO-allyl was achieved by adding sufficient SnCl_(4) prior to the substitution.展开更多
Herein,a simple method for preparing poly(vinylidene fluoride)(PVDF)films with controlledβ/γratios by spin-coating assisted by potassium bromide(KBr)is proposed.The results show that the relative fraction of theβph...Herein,a simple method for preparing poly(vinylidene fluoride)(PVDF)films with controlledβ/γratios by spin-coating assisted by potassium bromide(KBr)is proposed.The results show that the relative fraction of theβphase(denoted as Fβ)for the films prepared on the KBr surface first decreased until a critical temperature(denoted as Tc)was reached,and then increased with increasing spin-coating temperature.This was related to the dissolved K and Br ions in the films.Further experiments showed that below Tc,high humidity can enhance Fβbut exhibit an adverse effect at and above Tc.The high content of K and Br ions in the PVDF/KBr blend film and larger shear stress can facilitate the formation of theβphase,leading exclusively to the formation ofβ-andγ-phases.The mechanism responsible for the change in Fβwith temperature was proposed:below Tc,the decrease in water intake with increasing temperature results in the decline of Fβ,whereas above Tc,the increase in Fβwith temperature is attributed to the synergistic effect of ions and shear stress.Ultimately,this paves the way for fabricating PVDF films with tailoredβ/γratios for electroactive and energy-harvesting applications.展开更多
Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ult...Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ultrathin films induced by stretching was investigated using transmission electron microscopy(TEM)and Fourier transform infrared(FTIR)spectroscopy.The results show that stretching can enhance the crystallinity and increase the average thickness of the lamellae.A fullα-βphase transition can be achieved for PVDF ultrathin films of 20.6%βphase stretched to aλ(stretching ratio)of 1.5,while fewαphases still exist for ultrathin films of 35.0%βphase,together with bent and tilted lamellae.Compared to thicker PVDF films undergoing stretching-inducedα-βphase transition,the higherα-βphase transition efficiency of the PVDF ultrathin films can be attributed to the parallel aligned lamellar structure.Moreover,a higherβ-phase content can suppressα-βphase transition because of the stress concentration effect ofβ-phase.Ultimately,these results provide valuable insights into the stretching-inducedα-βphase transition of PVDF ultrathin films.展开更多
As a naturally occurring terpenoid that is abundant in essential oils,citronellal remains largely unexplored in polymer science.Herein,we present a novel strategy for converting bio-based citronellal into the diene mo...As a naturally occurring terpenoid that is abundant in essential oils,citronellal remains largely unexplored in polymer science.Herein,we present a novel strategy for converting bio-based citronellal into the diene monomer 6,10-dimethyl-1,3,9-undecatriene(DMUT),which under-goes neodymium-catalyzed coordination polymerization to yield poly(6,10-dimethyl-1,3,9-undecatriene)(PDMUT),a bio-derived polydiene poly-mer.This provides a facile and sustainable route for transforming renewable citronellal into functional polymers.The effects of polymerization conditions on the catalytic performance and polymer characteristics,including molecular weight,polydispersity,and microstructure,were sys-tematically investigated.In addition,DMUT was successfully copolymerized with isoprene(IP)and 1,3-butadiene(BD),yielding copolymers with tunable compositions and microstructures.These results demonstrate the versatility of DMUT as a renewable building block for both homopoly-mers and copolymers,paving the way toward bio-based elastomeric materials with customizable properties.展开更多
High catalytic efficiencies in ring opening polymerization(ROP)of a large ring-sized macrolactone,ω-pentadecalactone(PDL),by using transition metal Fe(II)-based catalysts were achieved for the first time in this stud...High catalytic efficiencies in ring opening polymerization(ROP)of a large ring-sized macrolactone,ω-pentadecalactone(PDL),by using transition metal Fe(II)-based catalysts were achieved for the first time in this study.Benefited from the bulky nature of the ligatedα-diimine ligands,as evidenced from single-crystal structures,as well as the weakly oxophilic nature of the metal centers,chain transesterification reactions could be partially suppressed,allowing the polymerization proceed in a living-like and semi-controllable manner,i.e.good linear dependence of propagation rates on catalyst concentration and PDL concentration as observed in the detailed kinetics studies.The whole polymerization proceeds via a“coordination-insertion”mechanism,and with the aid of density functional theory(DFT)calculation studies,a“slow insertion→fast elimination”manner was demonstrated for the monomer propagation step,suggesting the insertion of Fe-OR into the carbonyl group C=O as the rate-determining step.The present catalytic system also showed fast chain transfer reactions to alcohol compounds,affording quasi-immortal characteristics.DFT calculations showed that such a transfer reaction only required an energy barrier of 6.4 kcal/mol,performing a good consistency with the fast chain transfer rates.展开更多
Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distr...Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene （Bd to Ip） on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition tempera^re by changing Bd content and temperature.展开更多
Polypropylene （PP）/polybutene-1 （PB） alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were ca...Polypropylene （PP）/polybutene-1 （PB） alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were carried out to form isotactic polypropylene （iPP） particles containing active catalyst. Then, butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles. Finally, iPP/PB alloys with spherical shape and adjustable PB content were synthesized. The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed. The composition and physical properties of the PP alloys were characterized by FT-IR, 13C-NMR, SEM, DSC and XRD. It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly（butene- co-propylene） random copolymers and poly（butene-block-propylene） block copolymers. SEM measurements verified that the PB phases with size in the range of 300-400 nm dispersed in the PP matrix uniformly. The incorporation of PB upon the PP matrix affects the properties of final products greatly.展开更多
A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calcul...A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tiid6s （K-T） method and the Mao-Huglin （M-H） method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers＇ composition distribution.展开更多
The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer.Trans-1,4-poly(butadiene-co-isoprene)multi-block copolymer rubbers(TBIR)exhibit o...The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer.Trans-1,4-poly(butadiene-co-isoprene)multi-block copolymer rubbers(TBIR)exhibit outstanding fatigue resistance,low heat build-up and good abrasion resistance,and are expected to be desirable candidate for high performance tire.Study on the influence of TBIR with different molecular weights on the structure and properties of TBIR and natural rubber(NR)/TBIR blends is essential to understand its contribution to the greatly improved dynamic properties of the rubber vulcanizates.TBIR with different molecular weights characterized by 1H-NMR,13C-NMR,GPC,and DSC were highly trans-1,4-copolymers with similar chain sequence distribution and crystalline trans-1,4-polyisoprene(TPI)blocks.The green strength and modulus of TBIR increased with the increasing molecular weight.The NR/TBIR compounds filled with 40 phr carbon black were chemically cured by sulfur for the preparation of NR/TBIR vulcanizates.The compatibility between NR and TBIR,filler distribution,crosslinking bond and density,and properties of NR/TBIR vulcanizates were studied.The NR/TBIR vulcanizates showed increasing tensile strength,hardness,modulus,rebound,abrasion resistance,and flexural fatigue properties with increasing molecular weight of TBIR.Furthermore,they presented significant improvement in flexural fatigue resistance when compared with that of NR vulcanizate.The contribution mechanism of TBIR on the NR/TBIR blends was discussed.The TBIR with a wide range of molecular weight are ideal rubbers for high performance tires.展开更多
To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer ru...To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer rubber (EPDM) is reported, which was designed by graft-polymerization of zinc dimethacrylate (ZDMA) onto rubber chains to form a reversible ionic cross-linked network. Single ionic cross-linked network and dual network, combining covalent and ionic cross-links, could be tuned by controlling vulcanization process to achieve tailorable mechanical and self-healing properties. It was found that ionic cross-linked EPDM showed a recovery of more than 95% of the original mechanical strength through a healing process of 1 h at 100 °C. The covalent cross-links could improve mechanical properties but block self-healing. Adding 50 wt% liquid rubber to “dry” EPDM could effectively enhance self-healing capability of the dual cross-linked network and the healed tensile strength could reach 0.9 MPa. A compromise between mechanical performance and healing capability could be potentially tailored by controlling vulcanization process and liquid rubber content.展开更多
For the solid-solid transformation from formⅡto formⅠof isotactic polybutene-1(iPB),the temperature dependence of formⅠnucleation and growth was deemed to control the transformation process.However,the relationship...For the solid-solid transformation from formⅡto formⅠof isotactic polybutene-1(iPB),the temperature dependence of formⅠnucleation and growth was deemed to control the transformation process.However,the relationship between formⅠformation and formⅡdisappearance in the transformation process is not clear.In this work,the spontaneous crystal transformation from formⅡtoⅠof iPB with 81 mol%mmmm sequence concentration is studied firstly by tracking the two processes,the decay of formⅡand the yielding of formⅠin a wide range of temperature spanning from 0℃to 50℃and in a long transformation time ranging from 5 min to 65 days with in situ FTIR and WAXD.Unlike the literature reports,the decay rate of formⅡis firstly found to be lower than the yielding rate of formⅠat all studied temperatures,especially at low transition temperature.This is attributed to the amorphous chains which locate near crystal lamella participating into the nucleation of formⅡ.The regular chain folding and growth of i PB formⅠfrom amorphous chains containing short isotactic sequences also lead to an increase in crystallinity of formⅠcompared with that of initial formⅡcrystallized at 60℃.An increase in the annealing temperature results in decrease in crystallinity and increase in lamellae thickness of i PB formⅠ.展开更多
Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials.In this paper,we addressed the effects of solvent vapor annealing,including chloroform and w...Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials.In this paper,we addressed the effects of solvent vapor annealing,including chloroform and water vapor,on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1(PB-1)by means of in situ Fourier transform infrared spectroscopy(FTIR).The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity.Also,a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.展开更多
In this work, the crystallization of immiscible polypropylene （PP）/polybutene-1 （PB） blends, in particular the effect of crystal morphology of PP （HTC, high Tm component） on the subsequent crystallization behavi...In this work, the crystallization of immiscible polypropylene （PP）/polybutene-1 （PB） blends, in particular the effect of crystal morphology of PP （HTC, high Tm component） on the subsequent crystallization behavior of PB （LTC, low Tm component） was studied. Herein, we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites, reflected by the decreased crystallization temperature （To） of PB and the formation of form I＇ beside form II. Notably, if PP previously crystallized at high Tc, fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.展开更多
This study presents a direct-writing structure color patterns on electrospun colloidal fibers by inkjet printing. The colloidal fiber was obtained by electrospinning the aqueous mixture of colloidal particles of poly(...This study presents a direct-writing structure color patterns on electrospun colloidal fibers by inkjet printing. The colloidal fiber was obtained by electrospinning the aqueous mixture of colloidal particles of poly(styrene-methyl methacrylate-acrylic acid) and poly(vinyl alcohol). The pattern was obtained by directly inkjet printing water onto the electrospun colloidal fiber. The pattern formation was attributed to the morphological transition of the colloidal fiber from the fiber aggregation to latex aggregation and the corresponding color change due to the dissolution of poly(vinyl alcohol) by water. Interestingly, a clear and clean image was successfully obtained on the ethanol-treated colloidal fibers film in comparison to a confused and blur image onto the freshly-made film. It is because the treatment process can compact the fiber structure and lower the spreading/wetting behavior of ink on the fiber structure, contributing to the formation of high-quality pattern. Various letters or quick response code were flexibly designed and printed on to colloidal fibers.Furthermore, the pattern can be easily transferred onto flexible substrate, i.e., a flexible printed bracelet. This work will be of great significance for the development of novel wearable functional materials/devices based on electrospun colloidal fibers.展开更多
The structural transformation of mesophase to crystalline phase of strain-induced poly(L-lactic acid) has been investigated by differential scanning calorimetry(DSC) and in situ temperature dependent polarized Fourier...The structural transformation of mesophase to crystalline phase of strain-induced poly(L-lactic acid) has been investigated by differential scanning calorimetry(DSC) and in situ temperature dependent polarized Fourier transform infrared(FTIR) spectroscopy. It is found that, as the drawing temperature increases, melting of strain-induced mesophase in the heating process can remarkably interfere the crystallization behavior subsequently. Coupling with in situ polarized FTIR, from 60 °C to 76 °C, the mesophase melts partially rather than completely melting, and changes immediately to three-dimensional ordered structure. Of particular note, through monitoring the subtle spectral change in the critical phase transformation temperature from 60 °C to 64 °C, it is clearly demonstrated that relaxation of oriented amorphous chains initially takes place prior to the melting of mesophase.展开更多
Natural rubber nanocomposites filled with hybrid fillers of multi-walled carbon nanotubes(CNTs) and carbon black(CB) were prepared. CNTs were ultrasonically modified in mixture of hydrogen peroxide(H2O2) and distilled...Natural rubber nanocomposites filled with hybrid fillers of multi-walled carbon nanotubes(CNTs) and carbon black(CB) were prepared. CNTs were ultrasonically modified in mixture of hydrogen peroxide(H2O2) and distilled water(H2O). The functional groups on the surface of CNTs, changes in nanotube structure and morphology were characterized by Fourier transform infrared spectroscopy(FT-IR), Raman Spectroscopy, and transmission electron microscopy(TEM). It shows that hydroxyl(OH·) is successfully introduced. The surface defects of modified CNTs were obviously higher than those of original CNTs, and the degree of agglomeration was greatly reduced. Thermal conductivity of the composites was tested by protection heat flow meter method. Compared with unmodified CNTs/CB filling system, the thermal conductivity of hybrid composites is improved by an average of 5.8% with 1.5 phr(phr is parts per hundred rubber) of hydroxyl CNTs and 40 phr of CB filled. A three-dimensional heat conduction network composed of hydroxyl CNTs and CB, as observed by TEM, contributes to the good properties. Thermal conductivity of the hybrid composites increases as temperature rises. The mechanical properties of hybrid composites are also good with hydroxyl CNTs filled nanocomposites;the tensile strength, 100% and 300% tensile stress are improved by 10.1%, 22.4% and 26.2% respectively.展开更多
The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_(4)/MgCl_(2)Ziegler-Natta(Z-N)catalysts are determined by the structure and nature of active centers,which are mysterio...The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_(4)/MgCl_(2)Ziegler-Natta(Z-N)catalysts are determined by the structure and nature of active centers,which are mysterious and fairly controversial.In this work,the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers[C*]with different tacticity.SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP)particles.The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS.The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method.The catalytic activity,active centers with different tacticity and propagation rate constant kp,fragmentation of the catalyst,crystalline structure of PP are correlated with temperature and time for propylene polymerizations.The polymerization temperature and time show complex influences on the propylene polymerization.The higher polymerization temperature(60℃)resulted higher activity,kp and lower[C*],and the isotactic active centers Ci*as the majority ones producing the highest isotactic polypropylene(iPP)components showed much higher kp when compared with the active centers with lower stereoselectivity.Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation.This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles,and provide the solutions to the improvement of catalyst activity and isotacticity of PP.展开更多
TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerizati...TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/（mol Ti-h）. Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%, and its melting temperature is about 159℃. The weight-average molecular weight of PP can reach 6.7 × 10^5 - 7.8 × 10^5, and the molecular weight distribution is between 7.7 and 7.9.展开更多
基金Financial support from National Natural Science Foundation of China(Grant No.22075298)National Key R&D Program of China(2022YFD2301204)is gratefully acknowledged.
文摘In this manuscript,we conveniently prepared a series of polyester-polycarbonate copolymer(PPC-P)/polybutylene adipate terephthalate(PBAT)blends that exhibit both flame-retardant properties and toughness.Piperazine pyrophosphate(PAPP),melamine phosphate(MPP)and ZnO were used as synergistic flame retardants for PPC-P/PBAT blends.The effects of synergistic flame retardants on thermal stability,combustion behavior and flame retardancy of PPC-P/PBAT blends were investigated.The results showed that when the ratio of PAPP/MPP/ZnO was 18.4:9.2:2.4,the LOI of PPC-P/PBAT composite was 42.8%,and UL-94 reached V-0 level.The results of cone calorimetry showed that the mass loss rate(MLR),the peak value of the biggest smoke production rate(pSPR)and total smoke production(TSP)of the material decreased,and a continuously expanded carbon layer with a compact structure was formed after combustion.The carbon layer formed after surface combustion protects the material from decomposition over a long temperature range.In terms of mechanical properties,compared with the composites with only PAPP and MPP,PAPP/MPP/ZnO composites can improve the mechanical properties.After adding 2.4 wt% ZnO,the tensile strength and impact strength of the polymer increased to 34.2 MPa and 28.5 kJ/m^(2),respectively.The results showed that the use of non-toxic,environmentally friendly,halogen-free flame retardants to enhance the flame retardant properties of biodegradable polymer composites is a promising direction in the future.
基金supported by the National Key Research and Development Program of China (No. 2022YFB3704700(2022YFB3704702))the National Natural Science Foundation of China (No. 52473096)+1 种基金Major Scientific and Technological Innovation Project of Shandong Province (No. 2021CXGC010901)Taishan Scholar Program
文摘In this study,a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber(NR)/polybutadiene rubber(BR)composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers.The matrix material is composed of a blend of NR and BR,which is widely used in tire manufacturing.By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene)(TBIR)rubber powder(pVTPR)with different cross-linking densities and contents,significant improvements in the gas barrier properties and CO_(2)permselectivity of the NR/BR/pVTPR composites were observed.The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR,BR,and TBIR,the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties.Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite.For example,the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m^(3)resulted in a 79%improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR,achieving a value of 5.47×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1).Similarly,the nitrogen barrier property improved by 76%compared to NR/BR,reaching 2.4×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1),which is 28%higher than the conventional inner liner material brominated butyl rubber(BIIR,PN2=3.32×10^(-14)cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1)).Owing to its low cost,exceptional gas barrier properties,superior adhesion to various tire components,and co-vulcanization capabilities,the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires.Furthermore,by fine-tuning the cross-linking density of pVTPR,the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO_(2)permselectivity,with a CO_(2)/N2 selectivity of 61.4 and a CO_(2)/O_(2)selectivity of 26.12.This innovation provides a novel strategy for CO_(2)capture and separation,with potential applications in future environmental and industrial processes.The multifunctional NR/BR/pVTPR composite,with its superior gas barrier properties and CO_(2)permselectivity,is expected to contribute to the development of safer,greener,and more cost-effective transportation solutions.
基金financially supported by the National Natural Science Foundation of China(No.52373011)。
文摘Living cationic polymerization of 4-acetoxystyrene(STO)was conducted in CH_(2)Cl_(2) at-15℃ using a dicumyl chloride(DCC)/SnCl_(4)/nBu_(4)NBr initiating system.Impurity moisture initiation was inhibited by adding proton trap 2,6-di-tert-butylpyridine(DTBP),and the controlled initiation of DCC was confirmed by ^(1)H nuclear magnetic resonance(^(1)H-NMR)spectroscopy and matrix-assisted laser desorption ionization time-offlight mass(MALDI-TOF-MS)spectrometry.The polymerization kinetics were analyzed to for optimizing the polymerization rate.Allyl-telechelic PSTOs(allyl-PSTO-allyl)with molecular weight(Mn)range of 3540–7800 g/mol and narrow molecular weight dispersity(Mw/Mn)about 1.25 were prepared through nucleophilic substitution with allyltrimethylsilane(ATMS)at approximately 40%monomer conversion.The experimental results indicate that the substitution efficiency of ATMS increased with higher ATMS concentration,temperature,and extended reaction time.Nearly unity ally-functionality for allyl-PSTO-allyl was achieved by adding sufficient SnCl_(4) prior to the substitution.
基金support from the National Natural Science Foundation of China(Nos.52203026 and 52027804)。
文摘Herein,a simple method for preparing poly(vinylidene fluoride)(PVDF)films with controlledβ/γratios by spin-coating assisted by potassium bromide(KBr)is proposed.The results show that the relative fraction of theβphase(denoted as Fβ)for the films prepared on the KBr surface first decreased until a critical temperature(denoted as Tc)was reached,and then increased with increasing spin-coating temperature.This was related to the dissolved K and Br ions in the films.Further experiments showed that below Tc,high humidity can enhance Fβbut exhibit an adverse effect at and above Tc.The high content of K and Br ions in the PVDF/KBr blend film and larger shear stress can facilitate the formation of theβphase,leading exclusively to the formation ofβ-andγ-phases.The mechanism responsible for the change in Fβwith temperature was proposed:below Tc,the decrease in water intake with increasing temperature results in the decline of Fβ,whereas above Tc,the increase in Fβwith temperature is attributed to the synergistic effect of ions and shear stress.Ultimately,this paves the way for fabricating PVDF films with tailoredβ/γratios for electroactive and energy-harvesting applications.
基金financially supported from the National Natural Science Foundation of China(Nos.52203026 and 52027804)。
文摘Highly oriented poly(vinylidene fluoride)(PVDF)ultrathin films with differentβ-phase contents were prepared using the melt-draw method.The effect ofβ-phase content onα-βphase transition of highly oriented PVDF ultrathin films induced by stretching was investigated using transmission electron microscopy(TEM)and Fourier transform infrared(FTIR)spectroscopy.The results show that stretching can enhance the crystallinity and increase the average thickness of the lamellae.A fullα-βphase transition can be achieved for PVDF ultrathin films of 20.6%βphase stretched to aλ(stretching ratio)of 1.5,while fewαphases still exist for ultrathin films of 35.0%βphase,together with bent and tilted lamellae.Compared to thicker PVDF films undergoing stretching-inducedα-βphase transition,the higherα-βphase transition efficiency of the PVDF ultrathin films can be attributed to the parallel aligned lamellar structure.Moreover,a higherβ-phase content can suppressα-βphase transition because of the stress concentration effect ofβ-phase.Ultimately,these results provide valuable insights into the stretching-inducedα-βphase transition of PVDF ultrathin films.
基金supported by the National Key R&D Program of China(No.2022YFC2104702)the National Natural Science Foundation of China(No.22071236)H.L.thanks for the financial support from the Taishan Scholars Program(No.tsqn202211165).
文摘As a naturally occurring terpenoid that is abundant in essential oils,citronellal remains largely unexplored in polymer science.Herein,we present a novel strategy for converting bio-based citronellal into the diene monomer 6,10-dimethyl-1,3,9-undecatriene(DMUT),which under-goes neodymium-catalyzed coordination polymerization to yield poly(6,10-dimethyl-1,3,9-undecatriene)(PDMUT),a bio-derived polydiene poly-mer.This provides a facile and sustainable route for transforming renewable citronellal into functional polymers.The effects of polymerization conditions on the catalytic performance and polymer characteristics,including molecular weight,polydispersity,and microstructure,were sys-tematically investigated.In addition,DMUT was successfully copolymerized with isoprene(IP)and 1,3-butadiene(BD),yielding copolymers with tunable compositions and microstructures.These results demonstrate the versatility of DMUT as a renewable building block for both homopoly-mers and copolymers,paving the way toward bio-based elastomeric materials with customizable properties.
基金financially supported by the National Natural Science Foundation of China(Nos.21901020 and 22003076)China Postdoctoral Science Foundation(No.2021M701818)+1 种基金Shandong Provincial Natural Science Foundation(No.ZR2022QE237)the Qingdao Postdoctoral Applied Research Project.H.Liu sincerely acknowledges financial support from the Taishan Scholars Program(No.tsqn202211165)。
文摘High catalytic efficiencies in ring opening polymerization(ROP)of a large ring-sized macrolactone,ω-pentadecalactone(PDL),by using transition metal Fe(II)-based catalysts were achieved for the first time in this study.Benefited from the bulky nature of the ligatedα-diimine ligands,as evidenced from single-crystal structures,as well as the weakly oxophilic nature of the metal centers,chain transesterification reactions could be partially suppressed,allowing the polymerization proceed in a living-like and semi-controllable manner,i.e.good linear dependence of propagation rates on catalyst concentration and PDL concentration as observed in the detailed kinetics studies.The whole polymerization proceeds via a“coordination-insertion”mechanism,and with the aid of density functional theory(DFT)calculation studies,a“slow insertion→fast elimination”manner was demonstrated for the monomer propagation step,suggesting the insertion of Fe-OR into the carbonyl group C=O as the rate-determining step.The present catalytic system also showed fast chain transfer reactions to alcohol compounds,affording quasi-immortal characteristics.DFT calculations showed that such a transfer reaction only required an energy barrier of 6.4 kcal/mol,performing a good consistency with the fast chain transfer rates.
基金financially supported by the National Basic Research Program of China(No.2015CB654700(2015CB654706))Shandong Province Natural Science Fund for Distinguished Young Scholars(No.JQ201213)the National Natural Science Foundation of China(No.51473083)
文摘Abstract Two series of trans-1,4-poly（butadiene-co-isoprene） copolymers （TBIR） were prepared using the catalyst system TiCl4/MgCl2-Al（i-Bu）3 at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to 13C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene （Bd to Ip） on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition tempera^re by changing Bd content and temperature.
基金financially supported by the National Natural Science Foundation of China(Nos.21174074,20774098)National Scientific Supporting Program from Ministry of Science and Technology of China(No.2011BAE26B05)
文摘Polypropylene （PP）/polybutene-1 （PB） alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were carried out to form isotactic polypropylene （iPP） particles containing active catalyst. Then, butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles. Finally, iPP/PB alloys with spherical shape and adjustable PB content were synthesized. The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed. The composition and physical properties of the PP alloys were characterized by FT-IR, 13C-NMR, SEM, DSC and XRD. It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly（butene- co-propylene） random copolymers and poly（butene-block-propylene） block copolymers. SEM measurements verified that the PB phases with size in the range of 300-400 nm dispersed in the PP matrix uniformly. The incorporation of PB upon the PP matrix affects the properties of final products greatly.
基金financially supported by the National Key Technology R&D Program of China(No.2011BAE26B05)the Shandong Province Natural Science Fund for Distinguished Young Scholars(No.JQ201213)+2 种基金National Natural Science Foundation of China(No.21174074)Shandong Province Science and Technology Development Plan(No.2012GGA05042)the Major Projects of Independent Innovation Achievements Transformation in Shandong Province(No.2013ZHZX1A0207)
文摘A series of trans-1,4-butadiene/isoprene copolymers were prepared using the catalyst system TiCl4/MgCl2-Al（i- Bu）3 with bulk precipitation technology at different temperatures. Monomers reactivity ratios were calculated based on the Kelen-Tiid6s （K-T） method and the Mao-Huglin （M-H） method. The influence of temperature on copolymer composition and polymerization rate was discussed in detail. The increase of reaction temperature brought the decrease of butadiene reactivity ratio rBd and supplied an effective adjustment on copolymers＇ composition distribution.
基金financially supported by the National Basic Research Program of China(No.2015CB654700(2015CB 654706))Major Program of Shandong Province Natural Science Foundation(No.ZR2017ZA0304)Taishan Scholar Program
文摘The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer.Trans-1,4-poly(butadiene-co-isoprene)multi-block copolymer rubbers(TBIR)exhibit outstanding fatigue resistance,low heat build-up and good abrasion resistance,and are expected to be desirable candidate for high performance tire.Study on the influence of TBIR with different molecular weights on the structure and properties of TBIR and natural rubber(NR)/TBIR blends is essential to understand its contribution to the greatly improved dynamic properties of the rubber vulcanizates.TBIR with different molecular weights characterized by 1H-NMR,13C-NMR,GPC,and DSC were highly trans-1,4-copolymers with similar chain sequence distribution and crystalline trans-1,4-polyisoprene(TPI)blocks.The green strength and modulus of TBIR increased with the increasing molecular weight.The NR/TBIR compounds filled with 40 phr carbon black were chemically cured by sulfur for the preparation of NR/TBIR vulcanizates.The compatibility between NR and TBIR,filler distribution,crosslinking bond and density,and properties of NR/TBIR vulcanizates were studied.The NR/TBIR vulcanizates showed increasing tensile strength,hardness,modulus,rebound,abrasion resistance,and flexural fatigue properties with increasing molecular weight of TBIR.Furthermore,they presented significant improvement in flexural fatigue resistance when compared with that of NR vulcanizate.The contribution mechanism of TBIR on the NR/TBIR blends was discussed.The TBIR with a wide range of molecular weight are ideal rubbers for high performance tires.
基金financially supported by the National Basic Research Program of China (Nos. 2015CB654700 and 2015CB654706)the National Natural Science Foundation of China (No. 51403115)the Key Laboratory of Rubber-Plastics, Ministry of Education/ Shandong Provincial Key Laboratory of Rubber-plastics of Qingdao University of Science & Technology (KF2017008)
文摘To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer rubber (EPDM) is reported, which was designed by graft-polymerization of zinc dimethacrylate (ZDMA) onto rubber chains to form a reversible ionic cross-linked network. Single ionic cross-linked network and dual network, combining covalent and ionic cross-links, could be tuned by controlling vulcanization process to achieve tailorable mechanical and self-healing properties. It was found that ionic cross-linked EPDM showed a recovery of more than 95% of the original mechanical strength through a healing process of 1 h at 100 °C. The covalent cross-links could improve mechanical properties but block self-healing. Adding 50 wt% liquid rubber to “dry” EPDM could effectively enhance self-healing capability of the dual cross-linked network and the healed tensile strength could reach 0.9 MPa. A compromise between mechanical performance and healing capability could be potentially tailored by controlling vulcanization process and liquid rubber content.
基金financially supported by the Major Science and Technology Innovation Project of Shandong Province(No.2019JZZY010352)Natural Science Foundation of Shandong Province(ZR2019MB072)Taishan Scholar Program
文摘For the solid-solid transformation from formⅡto formⅠof isotactic polybutene-1(iPB),the temperature dependence of formⅠnucleation and growth was deemed to control the transformation process.However,the relationship between formⅠformation and formⅡdisappearance in the transformation process is not clear.In this work,the spontaneous crystal transformation from formⅡtoⅠof iPB with 81 mol%mmmm sequence concentration is studied firstly by tracking the two processes,the decay of formⅡand the yielding of formⅠin a wide range of temperature spanning from 0℃to 50℃and in a long transformation time ranging from 5 min to 65 days with in situ FTIR and WAXD.Unlike the literature reports,the decay rate of formⅡis firstly found to be lower than the yielding rate of formⅠat all studied temperatures,especially at low transition temperature.This is attributed to the amorphous chains which locate near crystal lamella participating into the nucleation of formⅡ.The regular chain folding and growth of i PB formⅠfrom amorphous chains containing short isotactic sequences also lead to an increase in crystallinity of formⅠcompared with that of initial formⅡcrystallized at 60℃.An increase in the annealing temperature results in decrease in crystallinity and increase in lamellae thickness of i PB formⅠ.
基金financially supported by the Special Foundation of Taishan Mountain Scholar Constructive Programthe National Natural Science Foundation of China(No.21174074)+3 种基金Shandong Provincical Key R&D Program(No.2015GGX102019)Shandong Provincial Natural Science Fund for Distinguished Young Scholars(No.JQ201213)the Nature Science Foundation of Shandong Province(No.ZR2013BM004)the Yellow River Delta Scholar program(Office of National University Science&Technology Park Administrative Committee(China University of Petroleum))
文摘Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials.In this paper,we addressed the effects of solvent vapor annealing,including chloroform and water vapor,on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1(PB-1)by means of in situ Fourier transform infrared spectroscopy(FTIR).The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity.Also,a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.
基金financially supported by Shandong Provincial Key R&D Program (No. 2015GGX102019)the Taishan Scholar Program
文摘In this work, the crystallization of immiscible polypropylene （PP）/polybutene-1 （PB） blends, in particular the effect of crystal morphology of PP （HTC, high Tm component） on the subsequent crystallization behavior of PB （LTC, low Tm component） was studied. Herein, we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites, reflected by the decreased crystallization temperature （To） of PB and the formation of form I＇ beside form II. Notably, if PP previously crystallized at high Tc, fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.
基金financial support by National Key R&D Program of China (Nos. 2016YFA0200803, 2017YFA0204 504, 2016YFB0402004)the National Natural Science Foundation of China (Nos. 51873221, 51673207, 51373183)
文摘This study presents a direct-writing structure color patterns on electrospun colloidal fibers by inkjet printing. The colloidal fiber was obtained by electrospinning the aqueous mixture of colloidal particles of poly(styrene-methyl methacrylate-acrylic acid) and poly(vinyl alcohol). The pattern was obtained by directly inkjet printing water onto the electrospun colloidal fiber. The pattern formation was attributed to the morphological transition of the colloidal fiber from the fiber aggregation to latex aggregation and the corresponding color change due to the dissolution of poly(vinyl alcohol) by water. Interestingly, a clear and clean image was successfully obtained on the ethanol-treated colloidal fibers film in comparison to a confused and blur image onto the freshly-made film. It is because the treatment process can compact the fiber structure and lower the spreading/wetting behavior of ink on the fiber structure, contributing to the formation of high-quality pattern. Various letters or quick response code were flexibly designed and printed on to colloidal fibers.Furthermore, the pattern can be easily transferred onto flexible substrate, i.e., a flexible printed bracelet. This work will be of great significance for the development of novel wearable functional materials/devices based on electrospun colloidal fibers.
基金financial supports from the National Natural Science Foundation of China(Nos.21774068 and 21704053)Natural Science Foundation of Shandong Province(No.ZR2017BB069)
文摘The structural transformation of mesophase to crystalline phase of strain-induced poly(L-lactic acid) has been investigated by differential scanning calorimetry(DSC) and in situ temperature dependent polarized Fourier transform infrared(FTIR) spectroscopy. It is found that, as the drawing temperature increases, melting of strain-induced mesophase in the heating process can remarkably interfere the crystallization behavior subsequently. Coupling with in situ polarized FTIR, from 60 °C to 76 °C, the mesophase melts partially rather than completely melting, and changes immediately to three-dimensional ordered structure. Of particular note, through monitoring the subtle spectral change in the critical phase transformation temperature from 60 °C to 64 °C, it is clearly demonstrated that relaxation of oriented amorphous chains initially takes place prior to the melting of mesophase.
基金Supported by the National Natural Science Foundation of China(51606107,51576102)the Collaborative Innovation Project of Green Tire and Rubber(0200501436)
文摘Natural rubber nanocomposites filled with hybrid fillers of multi-walled carbon nanotubes(CNTs) and carbon black(CB) were prepared. CNTs were ultrasonically modified in mixture of hydrogen peroxide(H2O2) and distilled water(H2O). The functional groups on the surface of CNTs, changes in nanotube structure and morphology were characterized by Fourier transform infrared spectroscopy(FT-IR), Raman Spectroscopy, and transmission electron microscopy(TEM). It shows that hydroxyl(OH·) is successfully introduced. The surface defects of modified CNTs were obviously higher than those of original CNTs, and the degree of agglomeration was greatly reduced. Thermal conductivity of the composites was tested by protection heat flow meter method. Compared with unmodified CNTs/CB filling system, the thermal conductivity of hybrid composites is improved by an average of 5.8% with 1.5 phr(phr is parts per hundred rubber) of hydroxyl CNTs and 40 phr of CB filled. A three-dimensional heat conduction network composed of hydroxyl CNTs and CB, as observed by TEM, contributes to the good properties. Thermal conductivity of the hybrid composites increases as temperature rises. The mechanical properties of hybrid composites are also good with hydroxyl CNTs filled nanocomposites;the tensile strength, 100% and 300% tensile stress are improved by 10.1%, 22.4% and 26.2% respectively.
基金financially supported by the Major Scientific and Technological Innovation Project of Shandong Province(No.2019JZZY010352)Natural Science Foundation of Shandong Province(No.ZR2019MB072)Taishan Scholar Program。
文摘The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_(4)/MgCl_(2)Ziegler-Natta(Z-N)catalysts are determined by the structure and nature of active centers,which are mysterious and fairly controversial.In this work,the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers[C*]with different tacticity.SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP)particles.The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS.The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method.The catalytic activity,active centers with different tacticity and propagation rate constant kp,fragmentation of the catalyst,crystalline structure of PP are correlated with temperature and time for propylene polymerizations.The polymerization temperature and time show complex influences on the propylene polymerization.The higher polymerization temperature(60℃)resulted higher activity,kp and lower[C*],and the isotactic active centers Ci*as the majority ones producing the highest isotactic polypropylene(iPP)components showed much higher kp when compared with the active centers with lower stereoselectivity.Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation.This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles,and provide the solutions to the improvement of catalyst activity and isotacticity of PP.
基金financially supported by the National Natural Science Foundation of China(Nos.20774098,50973123, 50503023)the Scientific Research Startup Foundation of Qingdao University of Science and Technology
文摘TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/（mol Ti-h）. Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%, and its melting temperature is about 159℃. The weight-average molecular weight of PP can reach 6.7 × 10^5 - 7.8 × 10^5, and the molecular weight distribution is between 7.7 and 7.9.
