Controlled Synthesis Of Environment-Friendly Materials Multi-Block Copolymer Poly-L-Lactic Acid-Co-Poly(Butylene Succinate) With Organic Guanidine Catalysts

In the past two decades,large-scale production of petroleum-based plastics has led to increased environmental pollutions,although it has brought convenience to people's lives.Environmentally friendly and biodegradable materials Polylactic acid(PLLA)and polybutylene succinate(PBS)have attracted much attention of scientists owing to their excellent biodegradability and mechanical properties.Poly L-lactic acid(PLLA)possessing favourable biodegradability and biocompatibility is considered to be the most promising biodegradable materials,however,the application of PLLA is limited by its strong brittleness and poor processability.PBS has well shock strength,processability and chemical stability,the modification of PBS and PLLA can combine the advantages of two polyesters and expand the application field.The traditional PLLA-PBS copolymerization has the disadvantages of poor controllability of the reaction and toxicity of the catalyst.In this paper,high molecular weight PLLA-PBS block copolymers were controlled synthesized via melt block copolycondensation(bc-MP)with organic guanidine catalyst(OG).(1)In this thesis,medium molecular weight multi-block copolymers of Poly-L-lactic acid(PLLA)and Poly(butylenes succinate)(PBS),MMW-mb(PLLA-PBS)s,were controlled synthesized via bc-MP of two macromonomers,i.e.oligo-PLLA(OPLLA)and oligo-PBS(OPBS)with four creatinine(CR)based organic guanidine catalysts(OG).The catalytic performance of four OGs is far superior to that of SnOct2 in terms of molecular weight(MW 14.2-28.6kDa vs 12.9kDa),apparent yield of synthesized block copolymers(74.15-82.02%)as well as the by-product(Lactide LA)yield(1.08-6.71%vs 20.7%).Among the OGs,creatininum acetate(CRA)shows the best performance.1HNMR structural characterization of the MMW-mb(PLLA-PBS)synthesized with CRA shows that the measured molar ratio of the two blocks fOPLLA/fOPBS in the MMW-mb(PLLA-PBS)is 89.3/10.7,which is close to the designed value 90/10.A high molecular weight(MW 114.0kDa)block copolymer HMW-mb(PLLA-PBS)was synthesized via bc-MP with CRA.The tensile strength(TS 50.67MPa)of the block copolymer is close to that of PLLA(TS 54.10MPa),the breaking elongation(BE 60.66%)of the copolymer is 15 times greater than that of PLLA.TGA analysis indicates that the original decomposition temperature(Td,0 272 ?)is 22 ? higher than that of PLLA.The molar ratio of two blocks fOPLLA/fOPBS(89.7/10.3)in the HMW-mb(PLLA-PBS),measured by 1HNMR,is very close to the value designed(90/10).According to the above conclusions,this is the first controlled synthesis of HMW-block copolymer of PLLA-PBS via bc-MP with a biogenic guanidine-based catalyst CRA.The mechanism of the bc-MP was proposed on the basis of experimental investigation.(2)In this thesis,the research on the yield of by-product lactide(LLA)in the melt-polycondensation(MP)synthesis of PLLA was studied to improve the yield of mb(PLLA-PBS)copolymer and optimize the process conditions.The yield of LLA decerased from 6%?18%to 1.6%by the following means:optimizing the catalytic system and improving the operation methods.PLLA with high molecular weight(Mw 9.5×104Da),narrow molecular distribution(PDI 1.64)was synthesized via one-step melt polycondensation(MP)with composite catalyst system based on creatinine.It is worth mentioning that the yield of by-product LLA is only 1.45%,which greatly inhibits the formation of LLA side reactions.The above results can be used not only to optimize the synthesis of mb(PLLA-PBS)copolymer,but also to provide data support for the implementation of large-scale industrialization of PLLA by one-step melt polycondensation(MP).(3)In this thesis,difference in structure and performance between the HMW-mb(PLLA-PBS)multi-block copolymer and PLLA/PBS(90/10)blend was compared by thermal degradation experiments,SEM and DSC.According to the conclusions,the PLLA/PBS blends has poor thermal stability,and the degradation rate in the same thermal environment is faster than that of HMW-mb(PLLA-PBS)multi-block polymer;the copolymer is a homogeneous system,and the surface is smooth without phase interface,while PLLA/PBS blend is heterogeneous and has a rough surface.The tensile strength(TS 21.8MPa)of the block copolymer is close to that of PLLA/PBS blend(TS 18.8MPa),the breaking elongation(BE 49.2%)of the copolymer is 2 times greater than that of PLLA/PBS blend.The above research initially explored the application prospects of mb(PLLA-PBS)multi-block copolymer.