Study On Aggregated Structure And Properties Of PCL-PBA-PCL Fully Biodegradable Triblock Copolymer

Aliphatic polyesters,which belong to polymer materials,are usually biodegradable.It is one of the best materials to replace petroleum-based plastics,and has broad application prospects.Physical or chemical modification for aliphatic polyesters to adjust their structure and properties to meet their wider applications has become one of the main research directions in the field of environmentally friendly polymers.In this thesis,a typical biodegradable polycrystalline aliphatic polyester,poly(1,4-butylene adipate)(PBA),was selected as the research object.A new triblock copolyester with PBA as the middle block and another biodegradable polyester poly(?-caprolactone)(PCL)as the terminal block,PCL-PBA-PCL,was synthesized to explore the influence of the physical and chemical properties of each block,the crystallization conditions,and the microphase separation structure between the blocks on the crystal morphology and dynamic evolution of the triblock copolymer system.The relationship and mechanism of“microphase separation structure-confined crystallization-phase transition-properties”were explored and analyzed.The main content contains the following:1.Hydroxyl-terminated PBA was synthesized by esterification and polycondensation,and PBA was used as a macromolecular initiator.The system of triblock copolyester with different molecular weights was synthesized through ring-opening polymerization(ROP).~1H NMR and GPC were used to characterize the synthesized copolyester.2.The thermal properties and crystal morphology of the block copolymer system were investigated.The crystallization of PBA is significantly confined in block copolymers as the chain length of PCL increases.The distribution of the thermal degradation temperature of the block copolymer system is between Neat PBA and Neat PCL.PCL-PBA-PCL did not found ring-band spherulites in the range of the crystallization temperature which may results from the covalent way of PBA and PCL that affect the nucleation and growth of its crystallization.3.The aggregation structure of the block copolymer system and the crystal phase transition of PBA were investigated.Under the confinement of the PCL block,it is difficult for the crystal growth of PBA with the decrease of its crystallization temperature.Even when CB~6C~8 was annealing at 42?for 2 hours,there was no phase transition from the?-crystal form to the?-crystal form.It is attributed to the confinement of the PBA middle block that confine the rearrangement or adjustment of the molecular chain of PBA,which greatly reduced its Phase transition rate.