Structure And Properties Of Biodegradable Shape Memory Poly(L-Lactide) And Its Copolymers

A series of poly(L-lactide) homopolymers (PLLA) and poly(L-lactide)/poly(ε-caprolactone) copolymers (PCLA) with different composition and chemical structure were polymerized by ring opening polymerization and copolymerization, respectively. The microstructure, mechanical property, degradable property and shape memory property of the polymers were investigated systematically by FTIR, 1H-NMR, DSC, XRD, POM and tensile test. The relationship between the microstructure and the properties were illuminated. The mechanism of shape memory effect was revealed.The experimental results show that the PLLA homopolymers show shape memory effect. The PLLA crystal serves as fixed phase, the amorphous acts as reversible phase. The PLLA shows the cold deformation shape memory effect. With the deformation temperature increasing, the shape recovery rate decreases.The molecular weight has obviously affectted on the microstructure and mechanical property, and further affected the shape recovery rate and recovery stress. The shape recovery rate and recovery stress increase with the increase of the molecular weight,The superior shape memory effect can be obtained by modulating the composition of PCLA random copolymers. The shape recovery rate increases, but the shape retention rate decreases with theε-CL content increasing. For the copolymers with similar composition, the shape memory effect can be improved by increasing the molecular weight. In PCLA random copolymers (R90~R70), the PLLA crystal and PCLA amorphous phase act as fixed phase and reversible phase, respectively. However, the entanglements of molecular chains serve as the fixed phase in the fully amorphous R60. The shape memory effect arises from the fixation and recovery of high elastic deformation of amorphous phase.The deformation has apprant effects on the shape memory effect. With the deformation strain increasing, the shape recovery rate decreases, but the recovery stress increases initially and then decreases. With the number of cycles increasing, the shape recovery rate decreases rapidly and then keeps steady. This implies that after destroying some''weak''crosslinks in the initial repeating tests, the...