Crystallizability Manipulation And Functionlization Of Polyesters

Synthetic polymers have been bringing great convinience to human life due to their excellent properties ever since its coming into being,however,the wide application of nondegradable polymers represented by polyolefins has caused increasingly serious environmental problems.Therefore,it's high time to use degradable polymers as alternatives.Polyester is a kind of degradable polymers,and the development of its new structures and new functions has been paid special attention.The alternating copolymerization of epoxides with cyclic anhydrides is an effective method to prepare polyesters with new structures and novel properties due to the diversities of two monomers.Up to date,the reported polyesters prepared by epoxides and cyclic anhydrides generally face weakness such as amorphous state,poor thermal and tensile properties.Corresponded to the noted issues,the research of this dissertation focus on the stereocomplexation of chiral polyesters,the reversible isomerization or crosslinking reaction,which adjust the thermal property of polyesters or result in functional polyesters.1)11 kinds of isotactic polyesters were synthesized from the regioselective ring-opening copolymerization of various chiral epoxides and cyclic anhydrides,and most of the isotactic polyesters are crystalline,showing Tm values between 92 and 142?.By mixing(R)-and(S)polyester in equivalent mass ratio,8 different kinds sterecomplexes were discovered.Compared with parent polyester,stereocomplexes show better crystallizability and higher melting points.The backbone rigidity,steric hindrance of the pendant chain,molecular weight and tacticity have significant influence on stereocomplexation.Bulky substituent groups in the pendant chain and rigid backbone appear to facilitate stereocomplexation.Taking the polyester from phthalic anhydride and phenyl glycidyl ether as a model,a detailed study was performed to investigate the stereocomplexation.The minimum polymerization degree and tacticity required for stereocomplexation are 5 and 87%respectively.Obvious splitting of the v(C=O)signal was observed in the Raman spectrum of stereocomplex in comparison with that of the component polyester.Solid-state NMR studies indicate that stereocomplexation restricts the mobility of CH and C=O along the backbone,resulting in enhanced spin-lattice relaxation time.Both 1H and 13C downfield shifts were observed owing to the strong intermolecular interactions between(R)-and(S)-chains.2)Poly(ethylene maleate),an amorphous material with a Tg of 7?,was synthesized by the copolymerization of maleic anhydride and ethylene oxide.The complete cis-to-trans isomerization of C=C bond catalyzed by Et2NH transforms poly(ethylene maleate)into poly(ethylene fumarate),which is a semicrystalline material with a Tm of 124?.With catalytic amount of benzophenone as sensitizer,the trans-alkene in poly(ethylene fumarate)was partially(30%)transformed into cis-alkene under the irradiation of 365 nm light,which resulted in an amorphous material with a Tg of 18?.The corresponding amorphous polyester could be transformed into semicrystalline poly(ethylene fumarate)again in the presence of Et2NH.The molecular weight and D of the polyesters remained constant throughout the reversible cis-trans isomerization process.Furthermore,the same strategy was applied to three chiral unsaturated polyesters,which also realized the reversible transformation of polyesters between amorphous and semicrystalline states.3)Polyesters with light responsive property were synthesized by the terpolymerization of glutaric anhydride,propylene oxide and 4-methyl-7-(2,3-epoxypropyl)coumarin(MEC).Taking advantage of the crosslink reaction of coumarin group under the irradiation of 365 nm light,films with different elasticity could be obtained by adjusting the MEC feed ratio of terpolymerization.The self-healing of an amputated film was realized by the irradiation of 254 nm light and sequent 365 nm light for decrosslinking and crosslinking,respectively.Compared with the original film,the healing film show nearly the same maximum strain,indicating the high efficiency of the self-healing process.