Synthesis,High Performance And Degradation Studies On 2,5-Furandicarboxylic Acid Based Biodegradable Polyesters

Using degradable polymer is one of the effective ways to solve the problem of plastic pollution.With the increasing demand for degradable polymers,it is expected that they will possess physical properties closing to or exceeding those of existing plastics.Up to now,most of the degradable polymers are synthesized by aliphatic monomers,so their mechanical,gas barrier and heat-resistant properties are relatively poor.2,5-Furandicarboxylic acid(FDCA)is a bio-based monomer with large rigidity and polarity.In this thesis,FDCA and various aliphatic monomers are copolymerized for the degradable polyesters with excellent mechanical and gas barrier properties.Specifically,the main contents include 4 aspects: realizing efficient melt polycondensation of glycolic acid and lactic acid with FDCA and further broadening the monomer source of degradable polyesters,using FDCA and short-chain aliphatic monomers to prepare degradable polyesters with excellent mechanical and barrier properties,using FDCA and long-chain monomers to prepare degradable elastomers,and improving the controllability of the degradation behavior.Generally,it is difficult to synthesize high molecular weight copolyesters from α-hydroxyl acid(such as glycolic acid,lactic acid)through melt polymerization,due to the poor thermostability of α-hydroxyl acid.Herein,the oligomer of α-hydroxyl acid is synthesized firstly,and then melt polymerization is performed under relatively low temperature and high vacuum,which can effectively improve the transesterification efficiency between oligomer and obtain random copolyesters with high molecular weight in shorter reaction time.Herein,glycolic acid and lactic acid are successfully introduced into FDCA based polyesters.Short α-hydroxyl acid can retain the rigidity of FDCA based polyesters.They obtain excellent gas barrier properties,good tensile strength and toughness.Moreover,over 30 mol% of hydroxyl acid can significantly improve the degradation rate of copolyesters.Appropriate polymerization method provides technical basis for changing the segment structures and preparing high performance biodegradable polyesters.Aliphatic dicarboxylic acids are often used as the degradation units of aliphaticaromatic copolyesters.We prepare the copolyesters of FDCA,adipic acid,succinic acid and diglycolic acid,respectively.The influences from the content of dicarboxylic acid,length of chain segment and ether bond are discussed.The long-chain dicarboxylic acids can enhance the biodegradability,but inevitably induce the weakness of mechanical and gas barrier properties.Improving these two properties while maintaining the biodegradability is still a big challenge.Through the introduction of neopentyl glycol(NPG)monomer,the side chain methyl groups of NPG fill the space in and between the chains,maintaining a small free volume.According to this principle,introducing 40% succinic acid unit into copolyesters still retain excellent mechanical and gas barrier properties.In addition,dimethyl carbonate is used to keep the rigidity of segments and realize the degradation through the carbonate unit.Both of them have realized the high performance and maintained the biodegradability,revealing great application potential.As for the application of artificial skin and tissue engineering,there is a great demand for degradable elastomer.However,most materials cannot be elastic and degradable at the same time.The ε-caprolactone is introduced into the FDCA based polyesters,and the biodegradable elastomer with good biocompatibility and excellent recovery performance is obtained.They have very high tensile strength(>50MPa)and elongation at break(>720%).PBFCL40 and PBFCL50 show excellent tensile recovery.Crystallization is very important for the elastic resilience.In-situ WAXS and SAXS are used to observe the crystallization evolution during stretching.The structure of the lamellae is stable at the initial stage while melting rapidly after yielding.Melting and recrystallization of crystals coexist at the stress hardening stage.The physical crosslinking point of elastic recovery is composed of the original crystals and newly formed fiber crystals.Nowadays,there is still a wide gap between the actual degradation process and the degradation rate tested from the standard composting environment.So the realization of controlled degradation is an important trend for degradable materials.With the introduction of PEG segments,stable and adjustable hydrolysis rate could be realized.A series of PBF-PEG copolymers are prepared with different mass fraction and molecular weight of PEG segments.The crystallization ability of PBF segment can be maintained by appropriate PEG segments,and the melting temperature of each component is higher than 100 ℃,ensuring good heat resistance.By controlling the molecular weight,mass fraction of PEG segments,the p H of solutions and the time of degradation tests,the controlled hydrolysis of PBF-PEG can be realized.