Novel bio-based and biodegradable block copolymers were synthesized by "click" reaction between poly(L-lactide)(PLLA) and polyamide 4(PA4). Upon tuning the molar mass of PLLA block, the properties of copolym...Novel bio-based and biodegradable block copolymers were synthesized by "click" reaction between poly(L-lactide)(PLLA) and polyamide 4(PA4). Upon tuning the molar mass of PLLA block, the properties of copolymers and electrospun ultrafine fibers were investigated and compared with those of PLLA and PA4 blends. PLLA and PA4 were found incompatible and formed individual crystalline regions, along with reciprocal inhibition in crystallization. Electrospun fibers were highly hydrophobic, even if hydrophilic PA4 was the rich component. The crystallinity of either PLLA or PA4 decreased after electrospinning and PLLA-rich as-spun fibers were almost amorphous. Immersion tests proved that fibers of block copolymers were relatively homogeneous with micro-phase separation between PLLA and PA4. The fibrous structures of copolymers were different from those of the fibers electrospun from blends, for which sheath-core structure induced by macro-phase separation between homopolymers of PLLA and PA4 was confirmed by TEM, EDS, and XPS.展开更多
Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ra...Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from sub- microns to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU.展开更多
The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw ...The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw respectively. The results indicated that five variables, namely purity of monomer, initiator to monomer ratio, vacuum level, polymerization temperature and polymerization time had different influences on the molecular weight and molecular weight distribution of poly(D. L-lactide).展开更多
The non-isothermal crystallization of poly（L-lactide） （PLLA） under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy （POM） with a hot shear stage and wide...The non-isothermal crystallization of poly（L-lactide） （PLLA） under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy （POM） with a hot shear stage and wide-angle X-ray diffraction （WAXD）. The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.展开更多
Antibacterial poly（D,L-lactide） （PDLLA） fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridi...Antibacterial poly（D,L-lactide） （PDLLA） fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine （4VP） and quaternization of the grafted pyridine groups with hexylbromide. The success of modification with quaternized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy （XPS）. The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus （S. aureus） and Gram-negative Escherichia coli （E. coli）. The PDLLA fibrous membranes modified with quatemized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%. The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage.展开更多
Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as ...Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.展开更多
In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resol...In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resolved Fourier transform infrared spectroscopy （FTIR）. It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time （t0.5） of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents （n） for the kinetics of mesophase formation are -0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.展开更多
Porous hybrid microspheres were fabricated by the synthesized calcium gluconate-g-poly（D,L-lactide） （CG-g- PDLLA） composites. These hybrid microspheres were treated with an alkaline solution for different period o...Porous hybrid microspheres were fabricated by the synthesized calcium gluconate-g-poly（D,L-lactide） （CG-g- PDLLA） composites. These hybrid microspheres were treated with an alkaline solution for different period of time to control the amount of generated carboxylate groups and remained CG on the surface. The microspheres were then incubated in a supersaturated simulated body fluid （1.5 SBF） solution for different time to investigate their biomimetic mineralization behavior. The depositions were found to have a fine cluster morphology, a similar crystal structure and chemical structure to natural hydroxyapatite, and a medium Ca/P of approximately 1.30. The effect of surface treating time on the structure and mineralization behavior of these microspheres has been discussed in detail. The results indicate that the nucleation and growth of apatite on the surface are influenced by the induced carboxylate groups and the remained CG. The hybrid CG-g- PDLLA microspheres have the potential as a novel alternative in bone tissue engineering.展开更多
Miscibility, isothermal crystallization kinetics, and morphology of poly（L-lactide）/poly（trimethylene carbonate） （PLLA/PTMC） crystalline/amorphous blends were studied by differential scanning calorimetry （DSC）...Miscibility, isothermal crystallization kinetics, and morphology of poly（L-lactide）/poly（trimethylene carbonate） （PLLA/PTMC） crystalline/amorphous blends were studied by differential scanning calorimetry （DSC） and optical microscopy （OM）. The heterogeneity of OM images and an unchanged glass transition temperature showed that PLLA was immiscible with PTMC. During isothermal crystallization, the crystallization rate of PLLA improved when the PTMC content was low （≤ 20%）. However, when the PTMC content was high （≥ 30%）, the crystallization rate decreased significantly. The reason of these nonlinear changes in crystal kinetics was analyzed according to the nucleation and growth process by virtue of a microscope heating stage. The isothermal crystallization morphologies of the blends were also studied by polarized optical microscopy and the results confirmed the conclusions obtained from crystallization kinetics.展开更多
The effect of exogenous hydroxyl,carboxyl groups and/or Sn^(2+) on pyrolysis reactions of poly(L-lactide)(PLLA)was investigated by thermogravimetric analysis(TGA).The activation energy(fa)of pyrolysis reactions was es...The effect of exogenous hydroxyl,carboxyl groups and/or Sn^(2+) on pyrolysis reactions of poly(L-lactide)(PLLA)was investigated by thermogravimetric analysis(TGA).The activation energy(fa)of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose method.The kinetic models were also explored by the Malek method,and the random degradation behavior was determined by comparing the plots of ln{-ln[1-(1-w)05]}versus 1/7for experimental data from TGA with model reactions.The pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65-70 mg·kg^(-1)but increased appreciably in the presence of extraneous Sn^(2+),-COOH/Sn^(2+),or-OH/Sn^(2+).The Ea values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn2+in different chemical environments because Sn^(2+) can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups,which were different in steric hindrance for the formation of activated complex between Sn^(2+) and PLLA.Under the catalysis of Sn^(2+),a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains,and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of lactide.However,it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol^(-1).展开更多
Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lac...Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates＇ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents＇ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.展开更多
This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MP...This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MPs)for oral controlled drug delivery.The XRD patterns,thermal and spectroscopic analyses indicated intercalation of drugs into the MMT interlayer that was stabilized by electrostatic interaction.No significant changes in structural and functional properties of drugs were found in the MMT layers.In vitro drug release studies showed controlled release pattern.展开更多
In this work, hydroxyl-terminated oxalamide compounds N^(1),N^(2)-bis(2-hydroxyethyl)oxalamide(OXA1) and N^(1),N^(1)′-(ethane-1,2-diyl)bis(N^(2)-(2-hydroxyethyl)oxalamide(OXA2) were synthesized to initiate the ring-o...In this work, hydroxyl-terminated oxalamide compounds N^(1),N^(2)-bis(2-hydroxyethyl)oxalamide(OXA1) and N^(1),N^(1)′-(ethane-1,2-diyl)bis(N^(2)-(2-hydroxyethyl)oxalamide(OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide)(PLA_(OXA)), i.e., PLA_(OXA1) and PLA_(OXA2). The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA_(OXA) which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by HoffmanLauritzen theory and it revealed that the nucleation energy barrier of PLA_(OXA1) and PLA_(OXA2) was lower than that of PLA. Consequently, PLA_(OXA) could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5%(T=125 ℃), respectively. In addition, the final crystallinity of PLA_(OXA1) and PLA_(OXA2) was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 ℃/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments(PLA_(OXA2) compared with PLA_(OXA1)) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.展开更多
For monomer reactivity ratios study, the copolymerization of D,L-3-methylglycolide (MG) with glycolide (GA) or D,L-lactide (LA) was carried out in bulk to a certain low conversion in the presence of stannous octoate a...For monomer reactivity ratios study, the copolymerization of D,L-3-methylglycolide (MG) with glycolide (GA) or D,L-lactide (LA) was carried out in bulk to a certain low conversion in the presence of stannous octoate at 140 degrees C. The copolymer compositions were determined by H-1 NMR spectroscopy. The monomer reactivity ratios were evaluated by Fineman-Ross method, Kelen-Tudos method and linear least-squares method. The monomer reactivity ratios of D,L-3-methylglycolide and glycolide or D,L-lactide are r(mg)= 0.73, r(ga)= 1.47; r(mg)= 1.71, r(la)= 0.92, respectively.展开更多
Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The e...Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated.The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator,and the molecular weight dist...展开更多
In this study, a series of monodispersed poly（L-lactide）（PLLA） were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight（Mn） o...In this study, a series of monodispersed poly（L-lactide）（PLLA） were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight（Mn） on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry（DSC） and wide-angle X-ray diffraction（WAXD）. The total crystallization rate of PLLA was Mn-dependent, which reached the maximum value for PLLA with Mn of 18.6 kg/mol. In addition, when Mn of PLLA was 18.6 kg/mol, the melting enthalpy（ΔHm） showed a maximum value（87.1 J/g）, which was the highest reported value till now. The critical temperature for change of crystal formation from ？-form to ？-form crystals increased in the isothermal crystallization process with Mn increasing. In the reheating procedure, high-Mn PLLA demonstrated a small exothermal peak prior to the dominant melting peak, corresponding to crystal transition from ？- to ？-form, but low-Mn PLLA didn＇t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different Mn.展开更多
Poly（L-lactide）（PLLA）/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal ...Poly（L-lactide）（PLLA）/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal and mechanical properties were systematically studied. The results show that the dispersion of vermiculite in the matrix is quite well when the loading content does not exceed 3 wt%. Pristine vermiculite can obviously improve the melt-crystallization temperature during the nonisothermal crystallization. Both crystallization time span and spherulitic size of PLLA decrease with the increasing amount of vermiculite under isothermal crystallization condition by enhancing the primary nucleation of PLLA. And the adding vermiculite can also improve the tensile modulus and Izod impact strength of PLLA. The intrinsic mechanism for the nucleating effect of vermiculite on PLLA is proposed to be the epitaxial crystallization and specific interaction between vermiculite and PLLA.展开更多
Block copolyesters of L-lactide and ε-caprolactone were synthesized by melt copolymerization of ε-caprolactone and L-lactide.The degradation performance of copolyesters was investigated by quartz crystal microbalanc...Block copolyesters of L-lactide and ε-caprolactone were synthesized by melt copolymerization of ε-caprolactone and L-lactide.The degradation performance of copolyesters was investigated by quartz crystal microbalance with dissipation(QCM-D).Diisocyanate terminated copolyesters could obtain via the reaction of copolyesters and diisocyanate.Diisocyanate terminated copolyesters could react with polyol resin to prepare degradable polyurethane which can be used in antifouling coatings.In this paper,we also discussed the degradation products release action and antifouling performance of the copolyesters film.展开更多
The effects of graphene oxide（GO） with polar groups and functionalized GO（f GO） with nonpolar groups on the isothermal crystallization of poly（L-lactide）（PLLA） were compared. Functionalized GO was obtained by ...The effects of graphene oxide（GO） with polar groups and functionalized GO（f GO） with nonpolar groups on the isothermal crystallization of poly（L-lactide）（PLLA） were compared. Functionalized GO was obtained by grafting octadecylamine and characterized by FTIR, WAXD and TGA. Isothermal crystallization kinetics of PLLA/GO and PLLA/f GO nanocomposites were investigated by combining DSC data and Avrami equation. The results showed that f GO could improve PLLA crystallization rate more obviously than GO. By analyzing the morphology obtained from POM, SEM and TEM, it was found f GO with large layer space dispersed better in PLLA and supplied more nucleation sites than GO. Therefore, for the multilayer graphene, increasing the layer spaces is important to improve its dispersion in polymers, which will cause the crystal kinetics changing of polymers.展开更多
Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface mod...Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.展开更多
基金financially supported by the National Key Research and Development Program of China (Nos. 2017YFB0309301 and 2017YFB0309302)the Natural Science Foundation of Shanghai, China (No. 17ZR1407200)
文摘Novel bio-based and biodegradable block copolymers were synthesized by "click" reaction between poly(L-lactide)(PLLA) and polyamide 4(PA4). Upon tuning the molar mass of PLLA block, the properties of copolymers and electrospun ultrafine fibers were investigated and compared with those of PLLA and PA4 blends. PLLA and PA4 were found incompatible and formed individual crystalline regions, along with reciprocal inhibition in crystallization. Electrospun fibers were highly hydrophobic, even if hydrophilic PA4 was the rich component. The crystallinity of either PLLA or PA4 decreased after electrospinning and PLLA-rich as-spun fibers were almost amorphous. Immersion tests proved that fibers of block copolymers were relatively homogeneous with micro-phase separation between PLLA and PA4. The fibrous structures of copolymers were different from those of the fibers electrospun from blends, for which sheath-core structure induced by macro-phase separation between homopolymers of PLLA and PA4 was confirmed by TEM, EDS, and XPS.
基金financially supported by the National Natural Science Foundation of China(No.51403210)China Postdoctoral Science Foundation(No.2014M550801)President Fund of University of Chinese Academy of Sciences(No.Y35102CN00)
文摘Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from sub- microns to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU.
基金Funded by the Key Project of the Ministry of Science and Technology (No. 96 - 920 - 20 - 21)
文摘The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw respectively. The results indicated that five variables, namely purity of monomer, initiator to monomer ratio, vacuum level, polymerization temperature and polymerization time had different influences on the molecular weight and molecular weight distribution of poly(D. L-lactide).
基金supported by the National Natural Science Foundation of China(No.50527301)
文摘The non-isothermal crystallization of poly（L-lactide） （PLLA） under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy （POM） with a hot shear stage and wide-angle X-ray diffraction （WAXD）. The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.
基金supported by the National Natural Science Foundation of China(Nos.50573011 and 50673019)Southeast University Foundation(Nos.9207040015 and 4022001023)
文摘Antibacterial poly（D,L-lactide） （PDLLA） fibrous membranes were developed via electrospinning, followed by surface modification which involved plasma pretreatment, UV-induced graft copolymerization of 4-vinylpyridine （4VP） and quaternization of the grafted pyridine groups with hexylbromide. The success of modification with quaternized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy （XPS）. The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus （S. aureus） and Gram-negative Escherichia coli （E. coli）. The PDLLA fibrous membranes modified with quatemized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%. The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage.
基金The authors are Indebted to the National Basic Science Rescarch and Development Grants(973)(No.1999054306).
文摘Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.
基金financially supported by the National Natural Science Foundation of China(Nos.51120135002,51203104)the Doctoral Program of the Ministry of Education of China(No.20120181120101)+1 种基金the Program of Introducing Talents of Discipline to Universities(B13040)the Innovation Team Program of Science&Technology Department of Sichuan Province(No.2013TD0013)
文摘In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resolved Fourier transform infrared spectroscopy （FTIR）. It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time （t0.5） of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents （n） for the kinetics of mesophase formation are -0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.
基金supported by the National Natural Science Foundation of China(Nos.51025314 and 21104089)the Fundamental Research Funds for the Central Universities(No.ZY1632)
文摘Porous hybrid microspheres were fabricated by the synthesized calcium gluconate-g-poly（D,L-lactide） （CG-g- PDLLA） composites. These hybrid microspheres were treated with an alkaline solution for different period of time to control the amount of generated carboxylate groups and remained CG on the surface. The microspheres were then incubated in a supersaturated simulated body fluid （1.5 SBF） solution for different time to investigate their biomimetic mineralization behavior. The depositions were found to have a fine cluster morphology, a similar crystal structure and chemical structure to natural hydroxyapatite, and a medium Ca/P of approximately 1.30. The effect of surface treating time on the structure and mineralization behavior of these microspheres has been discussed in detail. The results indicate that the nucleation and growth of apatite on the surface are influenced by the induced carboxylate groups and the remained CG. The hybrid CG-g- PDLLA microspheres have the potential as a novel alternative in bone tissue engineering.
基金financially supported by the Shandong Province High School Science & Technology Fund Planning Project(No.J13LA52)
文摘Miscibility, isothermal crystallization kinetics, and morphology of poly（L-lactide）/poly（trimethylene carbonate） （PLLA/PTMC） crystalline/amorphous blends were studied by differential scanning calorimetry （DSC） and optical microscopy （OM）. The heterogeneity of OM images and an unchanged glass transition temperature showed that PLLA was immiscible with PTMC. During isothermal crystallization, the crystallization rate of PLLA improved when the PTMC content was low （≤ 20%）. However, when the PTMC content was high （≥ 30%）, the crystallization rate decreased significantly. The reason of these nonlinear changes in crystal kinetics was analyzed according to the nucleation and growth process by virtue of a microscope heating stage. The isothermal crystallization morphologies of the blends were also studied by polarized optical microscopy and the results confirmed the conclusions obtained from crystallization kinetics.
基金the National Key Research and Development Program of China(No.2016YFB0302500)the National Natural Science Foundation of China(Nos.51873209,51873210,51773194 and 51973219)Jilin Scientific and Technological Development Program,China(No.20200403022SF).
文摘The effect of exogenous hydroxyl,carboxyl groups and/or Sn^(2+) on pyrolysis reactions of poly(L-lactide)(PLLA)was investigated by thermogravimetric analysis(TGA).The activation energy(fa)of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose method.The kinetic models were also explored by the Malek method,and the random degradation behavior was determined by comparing the plots of ln{-ln[1-(1-w)05]}versus 1/7for experimental data from TGA with model reactions.The pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65-70 mg·kg^(-1)but increased appreciably in the presence of extraneous Sn^(2+),-COOH/Sn^(2+),or-OH/Sn^(2+).The Ea values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn2+in different chemical environments because Sn^(2+) can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups,which were different in steric hindrance for the formation of activated complex between Sn^(2+) and PLLA.Under the catalysis of Sn^(2+),a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains,and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of lactide.However,it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol^(-1).
基金Funded by the Natural Science Foundation of Shanxi Province (No.2006011069)the Opening Foundation of Key Laboratory of Shanxi Province (No.2009011059-7)
文摘Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates＇ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents＇ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.
基金Authors are thankful to Director,CSMCRI,Bhavnagar for pro-viding necessary infrastructure facilities and the Council of Scientific and Industrial Research,Government of India,New Delhi,India(CSIR)for Senior research fellowship awarded to BDK,and funding under Network Project:NWP 0010.
文摘This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MPs)for oral controlled drug delivery.The XRD patterns,thermal and spectroscopic analyses indicated intercalation of drugs into the MMT interlayer that was stabilized by electrostatic interaction.No significant changes in structural and functional properties of drugs were found in the MMT layers.In vitro drug release studies showed controlled release pattern.
基金financially supported by the National Natural Science Foundation of China(No.51873082)the MOE&SAFEA 111 Project(No.B13025)+1 种基金the Opening Project of Beijing Key Laboratory of Quality Evaluation Technology for Hygiene and Safety of Plastics(Beijing Technology and Business University)(No.QETHSP2019003)the Postgraduate Research&Practice Innovation Program of Jiangnan University(No.JNKY19020)。
文摘In this work, hydroxyl-terminated oxalamide compounds N^(1),N^(2)-bis(2-hydroxyethyl)oxalamide(OXA1) and N^(1),N^(1)′-(ethane-1,2-diyl)bis(N^(2)-(2-hydroxyethyl)oxalamide(OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide)(PLA_(OXA)), i.e., PLA_(OXA1) and PLA_(OXA2). The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA_(OXA) which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by HoffmanLauritzen theory and it revealed that the nucleation energy barrier of PLA_(OXA1) and PLA_(OXA2) was lower than that of PLA. Consequently, PLA_(OXA) could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5%(T=125 ℃), respectively. In addition, the final crystallinity of PLA_(OXA1) and PLA_(OXA2) was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 ℃/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments(PLA_(OXA2) compared with PLA_(OXA1)) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.
基金This work was supported by the Key Project of the National Natural Science Foundation of China!(59833 140).
文摘For monomer reactivity ratios study, the copolymerization of D,L-3-methylglycolide (MG) with glycolide (GA) or D,L-lactide (LA) was carried out in bulk to a certain low conversion in the presence of stannous octoate at 140 degrees C. The copolymer compositions were determined by H-1 NMR spectroscopy. The monomer reactivity ratios were evaluated by Fineman-Ross method, Kelen-Tudos method and linear least-squares method. The monomer reactivity ratios of D,L-3-methylglycolide and glycolide or D,L-lactide are r(mg)= 0.73, r(ga)= 1.47; r(mg)= 1.71, r(la)= 0.92, respectively.
基金This work was financially supported by the National Natural Science Foundation of China(No.20404007)and many thanks for the assistance of Instrumental Analysis Center of SJTU.
文摘Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated.The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator,and the molecular weight dist...
基金financially supported by the National Natural Science Foundation of China(Nos.5130317651373169+3 种基金5103300351473166 and 51403089)Innovative Research Group(No.51321062)The National High-tech R&D Program of China(863 program)(No.2011AA02A202)
文摘In this study, a series of monodispersed poly（L-lactide）（PLLA） were synthesized by the ring-opening polymerization with Schiff base aluminum catalyst, and the effects of the number-average molecular weight（Mn） on the crystallization and melting behaviors of PLLA were investigated by differential scanning calorimetry（DSC） and wide-angle X-ray diffraction（WAXD）. The total crystallization rate of PLLA was Mn-dependent, which reached the maximum value for PLLA with Mn of 18.6 kg/mol. In addition, when Mn of PLLA was 18.6 kg/mol, the melting enthalpy（ΔHm） showed a maximum value（87.1 J/g）, which was the highest reported value till now. The critical temperature for change of crystal formation from ？-form to ？-form crystals increased in the isothermal crystallization process with Mn increasing. In the reheating procedure, high-Mn PLLA demonstrated a small exothermal peak prior to the dominant melting peak, corresponding to crystal transition from ？- to ？-form, but low-Mn PLLA didn＇t show the peak of crystal transition. These different crystallization and melting behaviors were attributed to the different chain mobility of PLLA with different Mn.
基金financially supported by the National Natural Science Foundation of China(No.21304108)the Science Foundation of China University of Petroleum-Beijing(No.YJRC-2013-142462013BJRC001)
文摘Poly（L-lactide）（PLLA）/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal and mechanical properties were systematically studied. The results show that the dispersion of vermiculite in the matrix is quite well when the loading content does not exceed 3 wt%. Pristine vermiculite can obviously improve the melt-crystallization temperature during the nonisothermal crystallization. Both crystallization time span and spherulitic size of PLLA decrease with the increasing amount of vermiculite under isothermal crystallization condition by enhancing the primary nucleation of PLLA. And the adding vermiculite can also improve the tensile modulus and Izod impact strength of PLLA. The intrinsic mechanism for the nucleating effect of vermiculite on PLLA is proposed to be the epitaxial crystallization and specific interaction between vermiculite and PLLA.
文摘Block copolyesters of L-lactide and ε-caprolactone were synthesized by melt copolymerization of ε-caprolactone and L-lactide.The degradation performance of copolyesters was investigated by quartz crystal microbalance with dissipation(QCM-D).Diisocyanate terminated copolyesters could obtain via the reaction of copolyesters and diisocyanate.Diisocyanate terminated copolyesters could react with polyol resin to prepare degradable polyurethane which can be used in antifouling coatings.In this paper,we also discussed the degradation products release action and antifouling performance of the copolyesters film.
基金financially supported by the National Natural Science Foundation of China(Nos.51503117 and 51403119)Promotive Research Fund for Excellent Young and Middle-aged Scientisits of Shandong Province(No.BS2013CL032)
文摘The effects of graphene oxide（GO） with polar groups and functionalized GO（f GO） with nonpolar groups on the isothermal crystallization of poly（L-lactide）（PLLA） were compared. Functionalized GO was obtained by grafting octadecylamine and characterized by FTIR, WAXD and TGA. Isothermal crystallization kinetics of PLLA/GO and PLLA/f GO nanocomposites were investigated by combining DSC data and Avrami equation. The results showed that f GO could improve PLLA crystallization rate more obviously than GO. By analyzing the morphology obtained from POM, SEM and TEM, it was found f GO with large layer space dispersed better in PLLA and supplied more nucleation sites than GO. Therefore, for the multilayer graphene, increasing the layer spaces is important to improve its dispersion in polymers, which will cause the crystal kinetics changing of polymers.
基金supported by the National Natural Science Foundation of China(Nos.50425309,0711351501,50733033)National Fund for Distinguished Young Scholar(No.50425309).
文摘Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.
