Preparation And Properties Of Self-healing And Shape Memory Elastomers Based On Aliphatic Polycarbonate

Damage such as microcracks can occur in medical polymers and composites during processing and use,leading to a reduction in performance and service life and creating potential problems.Intrinsically repairable materials can use their own dynamic bonds or weak interactions to achieve self-healing under mild conditions.Intrinsically self-healing polymers and materials have received increasing attention from researchers because they can be repaired multiple times after damage.The self-healing properties of polymers depend mainly on physical or chemical interactions at the molecular level,as well as on the combined action of both.By introducing special functional groups（e.g,hydroxyl,mercapto,amino,carboxyl,etc.）into the polymer molecular chain it is possible to provide dynamic chemical cross-linking bonds to the material,making the polymerisation self-healing.However,this reaction usually has many disadvantages,such as harsh reaction conditions and unstable product quality.In addition,polymers with internal cross-linked dots/junctions and reversible molecular transition fragments often have shape memory properties.Aliphatic polycarbonate is indispensable in biomedical and pharmaceutical fields because of its many kinds of biomaterials.Their polymers such as polytrimethylene carbonate（PTMC）typically have a low glass transition temperature.Their functionalisability and ability to copolymerise with a wide range of materials make their copolymers an attractive prospect.Chapter 2 of this paper begins with the melt ring-opening polymerisation of 5-methyl-5-benzyloxycarbonyl trimethylene carbonate（MBC）and D,L-lacticide（DLLA）proprieties,catalyzed by stannous octanoate,using poly（ethylene glycol）monomethyl ether(m PEG₁₁₃)as initiator.A series of m PEG₁₁₃-b-P（MBC-DLLA）_n polycarbonate elastomers were prepared by controlling the feed ratio of the two monomers,reaction time,reaction temperature.Infrared spectroscopy tests showed that the synthesised elastomers conformed to the molecular design and that hydrogen bonding absorption peaks were found in the infrared spectrum.The elastomers only swelled and did not dissolve in solvents such as methylene chloride,trichloromethane,tetrahydrofuran and dimethylformamide,and only marginal melting was observed when heated for a long time at 200 ^oC in a flat vulcaniser mould indicating that the synthesised elastomers have a strong cross-linked structure.The thermal properties of the polymer were characterised by differential scanning calorimetry（DSC）and thermogravimetric analysis（TGA）and it was found that the polymer had only one glass transition temperature.The cross-sectional morphology of the polymer was observed by scanning electron microscopy（SEM）and revealed a relatively regular structure with no defects,bubbles,phase separation etc.,but a more continuous and homogeneous structure.Uniaxial tensile test shows that the introduction of D,L-lactide can make the elongation at break of the material reach 1443%,and the MBC component had a significant effect in improving the mechanical strength of the polymer.A better recovery of scratches on the copolymer was observed under an optical microscope after 150 minutes of repair at room temperature.Shape memory experiments showed that elastomers with more MBC components had better shape memory properties.In Chapter 3 of this paper,a batch of m PEG₁₁₃-b-P（MBC-（DLLA-TMC））_nelastomers was prepared by introducing different monomer ratios of DLLA and TMC components into the material under the synthetic conditions selected in Chapter 2,while keeping the proportion of MBC monomer in the molecular design of the polymer constant.Infrared spectroscopy tests showed that the synthesised elastomers conformed to the molecular design and that hydrogen bonding absorption peaks were found in the infrared spectrum.Swelling experiments in good solvents showed that the elastomers have a strong cross-linked structure.DSC tests show that the polymer has only one glass transition temperature,which decreases with increasing TMC.The cross-sectional morphology of the polymer shows a more regular structure.Shape memory experiments show that the shape memory performance of the polymer is greatly enhanced by the introduction of the TMC component.Self-repair tests showed that the mechanical properties of the elastomer were restored by 67.3%after 240 min of repair at room temperature.Uniaxial tensile tests have shown that the addition of small doses of TMC components improves the mechanical properties of the polymer while providing good elongation at break.This suggests that the properties of the polymer can be controlled by adjusting the ratio of monomers to the polymer,providing a basis for the preparation of multifunctional medical materials.