Living/controlled cationic ring-opening polymerization(ROP)of L-lactide is a promising approach to isotactic-rich and crystalline poly(L-lactide).In contrast with the unsubstituted lactones,L-LA can not be polymerized...Living/controlled cationic ring-opening polymerization(ROP)of L-lactide is a promising approach to isotactic-rich and crystalline poly(L-lactide).In contrast with the unsubstituted lactones,L-LA can not be polymerized by organic Lewis acids or carbenium ions,and the state of the art in this field is the cationic ROP of L-LA catalyzed by BrФnsted acid/alcohol system via activated monomer mechanism.Herein,we reported the first example of controlled cationic ROP of L-LA by using Meerweintype ion pair[Me_(3)O]^(+)[B(C_(6)F_(5))_(4)]^(-)as the catalyst.[Me_(3)O]^(+)[B(C_(6)F_(5))_(4)]^(-)promoted rapid L-LA cationic polymerization in the absence of alcohol,producing isotactic-rich and crystalline PLLA without transesterification and epimerization side reactions.An activated chain end mechanism,involving twice S_(N)2 substitution and configuration-inversion(S→R→S)with the assistance of released Me_(2)O,was proposed and further verified by density functional theory and control experiments.This work expands the catalytic toolbox of isotactic-rich and crystalline polylactide synthesis.It represents a unique example of cationic-controlled polymerization of L-LA catalyzed by an organic ion pair.展开更多
基金supported by the National Natural Science Foundation of China(52222302)。
文摘Living/controlled cationic ring-opening polymerization(ROP)of L-lactide is a promising approach to isotactic-rich and crystalline poly(L-lactide).In contrast with the unsubstituted lactones,L-LA can not be polymerized by organic Lewis acids or carbenium ions,and the state of the art in this field is the cationic ROP of L-LA catalyzed by BrФnsted acid/alcohol system via activated monomer mechanism.Herein,we reported the first example of controlled cationic ROP of L-LA by using Meerweintype ion pair[Me_(3)O]^(+)[B(C_(6)F_(5))_(4)]^(-)as the catalyst.[Me_(3)O]^(+)[B(C_(6)F_(5))_(4)]^(-)promoted rapid L-LA cationic polymerization in the absence of alcohol,producing isotactic-rich and crystalline PLLA without transesterification and epimerization side reactions.An activated chain end mechanism,involving twice S_(N)2 substitution and configuration-inversion(S→R→S)with the assistance of released Me_(2)O,was proposed and further verified by density functional theory and control experiments.This work expands the catalytic toolbox of isotactic-rich and crystalline polylactide synthesis.It represents a unique example of cationic-controlled polymerization of L-LA catalyzed by an organic ion pair.
