Preparation And Properties Of Aliphatic Polycarbonate-Based Self-Healing Materials

Self-healing materials are regarded as materials that can self-heal to the original state under specific conditions when they are damaged by external stress.This will make the materials to possess self-healing abilily,and at the same time can extend their service life and reduce their potential harm.The aliphatic polycarbonate has the advantages of good biocompatibility,degradability,non-toxic and degradation products.It can also enhance or improve its own performance by introducing side chain groups.In the field of self-healing materials,it has important application prospects.In recent years,researchers have prepared multi-functional self-healing materials according to the needs of different fields.However,self-healing materials have many drawbacks in practical applications,such as poor mechanical properties of materials and long self-healing time,which will limite its actual application range.In view of the above problems,the thesis aims at constructing polymer materials with excellent mechanical and highefficiency self-healing properties.Through the regulation of the polymer molecular structure and the introduction of dynamic non-covalent bond forces,it has successfully developed a polymer material with excellent mechanical and high-efficiency self-healing properties.In the second chapter,polyethylene glycol monomethyl ether(mPEG₁₁₃)was used as the macroinitiator and Sn（Oct）₂ was used as the catalyst to carry out the ring-opening polymerization of the monomer 5-methyl-5-benzyloxycarbonyl trimethylene carbonate（MBC）and caprolactone（CL）.The molar ratio（M₁:M₂）,reaction time and reaction temperature were changed to tailor the properties of the obtained mPEG₁₁₃-b-P（MBC-b-CL）n hydrogel.Through FT-IR characterization,it is confirmed that the chemical structure conforms to the molecular design.The experimental results show that the crosslinking mechanism of the network is physical cross-linking due to the formation of hydrogen bonds between the terminal hydroxyl group of mPEG₁₁₃-b-P（MBC-b-CL）n and the ester carbonyl group of the side chain.The thermal properties of the materials were characterized by differential scanning calorimeter（DSC）and thermogravimetric analyzer（TGA）.The results show that the glass transition temperature of the materials decreased with the increase of CL content,and the thermal decomposition temperature increased with the CL content.The dynamic thermomechanical analyzer（DMA）shows that the maximum modulus of mPEG₁₁₃-b-P（MBC-CL）_n is 6 MPa,and the optical microscope shows that the fastest repair time for scratches is 4 hours.It can be concluded that the monomer ratio plays an important role in improving the physical and chemical properties of the obtained materials.Meanwhile,the prepared hydrogel has excellent mechanical and excellent self-healing properties.In the third chapter,the mPEG₁₁₃ and Sn（Oct）₂ were used as the initiator and catalyst,respectively.The monomer MBC and 5-benzyloxy-trimethylene carbonate（BTMC）were used for the polymerization reaction,and the molar ratio of monomers MBC and BTMC was adjusted（M₁:M₂）,reaction time,reaction temperature for ring-opening polymerizationand was also adjusted to tailor the mPEG₁₁₃-b-P（MBC-BTMC）_n elastomers under different reaction conditions.The chemical structure was confirmed to conform to the molecular design by FTIR characterization.The results show that the crosslinking mechanism of the network is that the terminal hydroxyl group of mPEG₁₁₃-b-P（MBC-BTMC）_n and the ester carbonyl group of the side chain form hydrogen bonds,and the benzene ring groups between the polymer side chains form the hydrophobic associative interaction.The synergic effect of these non-covalent bonds finally forms dual physical cross-linked network.In addition,the thermal properties of elastomers were characterized by DSC and TGA.The results show that the glass transition temperature of the material increases with the decrease of BTMC content,and the thermal decomposition temperature increases with the decrease of BTMC content.Meanwhile,it can be determined from DMA that the maximum modulus of the elastomer is 6.3 MPa.Then the scratches on the surface of the material were self-repaired by an optical microscope.The repair results showed that the fastest repair time for the elastomer to achieve complete self-healing was 0.5 h.Compared with mPEG₁₁₃-b-P（MBC-CL）_n hydrogel,mPEG₁₁₃-b-P（MBC-BTMC）_n elastomer has better self-healing properties.