Preparation And Properties Of Fe₃O₄/Poly(l-lactic-co-glycolic Acid) Shape Memory Nanocoposites

Shape memory polymer is a new kind of functional polymers. It has broad application prospects in biomedical and engineering field. Polylactide (PLA) is a kind of shape memory polymers which has good mechanical properties. However, it is crisp, hard, hydrophobic, and it has low degradation rate and high glass transition temperature. So it could be possible to improve its properties by copolymerizing it with polyglycolide (PGA).Nanoparticles have special surface effect and high reaction activities. They can be easily combined with polymers at molecular level. So they are often used to fill polymers to optimize their properties. Most shape memory polymers which have been investigated so far are thermally induced shape memory polymers. However, in some special occasions such as human body which can't be heated directly, we should use non-contact induction heating to heat the polymers to their shape transition temperatures. Base on the above backgrounds, we have done some research works as follows:1. A series of poly(1-lactic-co-glycolic acid) (PLLGA) with different compositions were synthesized by ring opening copolymerization. Chemical structure, phase structure, thermal property, mechanical property and shape memory property of the prepared PLLGA were investigated and their shape memory mechanisms were analyzed. The results showed that good mechanical and shape memory properties can be observed through changes of PLLGA compositions. For PLLGA90/10 and 80/20, the fixed phase was acted by their crystals and the entanglements of molecular chains, while the reversible phase was acted by their amorphous phase. However, for PLLGA 70/30 and 60/40, the fixed phase was only acted by the entanglements of molecular chains. In general, the best shape memory properties were showed by PLLGA 80/20.2. Fe3O4/PLLGA shape memory nanocomposites were synthesized with solution blending method, and the affect of different nanoparticles contents on the thermal, mechanical, magnetic and shape memory properties of the nanocomposites were investigated. The results showed that the size distribution of Fe3O4 nanoparticles was narrow and the nanoparticles were dispersed well in PLLGA. With the increase of nanoparticles contents, the glass transition temperatures, magnetic properties, shape recovery rates and forces of the nanocomposites were raised, while their mechanical properties, shape fixation rates, magnetic response time and shape recovery time were reduced. What is more, their shape memory properties induced by magnetic fields were as good as the shape memory properties induced by directly heating.3. Fe3O4/PLLGA shape memory nanocomposites were synthesized with in situ polymerization method, and compared with the nanocomposites synthesized by solution blending method. The results showed that their variation trends of properties were similar. However, compared with the nanocomposites synthesized by solution blending, the nanocomposites synthesized by in situ polymerization had better dispersion, magnetic and shape memory properties and worse mechanical properties.