Effect Of Copolymerized Fumaric Acid On Crystal Behavior Of Aliphatic Polyester

Properties of polymer depend strongly on the crystalline structure.So the study of polymorphism and manipulation of crystal structure is a significant and interesting work.Introducing of copolymerization fumaryl units is an effective way for variation of crystalline structure and intermolecular force,which can be used to regulate polymorphism.A series of random poly(hexamethylene succinate-co-hexamethylene fumarate)(PHSF)and Poly(butylene adipate-co-butylene fumarate)(PBAF)samples were synthesized,and their properties of polymorphism and crystal behaviour were systematically studied.Major work includes:We study the crystal structure,polymorphism and crystal behavior of PHSF with low hexamethylene fumarate content.The PHSF sample only show monoclinic or orthorhombic modification in all Tc range when the CHF is ≤ 6 mol% or ≥ 14 mol%,respectively.However,PHSF shows Tc-dependent polymorphism when CHF ranges from 8 mol% to 12 mol%.FTIR results suggest the polymorphism in PHSF may be related to special hydrogen-bonding interaction.Moreover,PHSF solid-solid-phase transition takes place at a elevated temperature.The morphology of PHSF is various between different crystal modification.Monoclinic modification shows ringless spherulites,while orthorhombic modification and mixed crystal show ring-banded spherulites.On the another hand,BF units can effectly regulate the polymorphism behaviour and crystal transformation of poly(butylene adipate).BF units are found to cocrystallize into both α-and β-form crystal lattices,while β-form lattice shows better accommodation degree for BF units than α-form.Incorporation of BF units alters the formation temperature ranges for polymorphism behavior,and facilitates β-form crystal at high temperature due to their stronger restriction effect on primary and secondary nucleation of α-form crystal than β-form crystal.Furthermore,BF units retards β to α solid-solid crystal transformation,and a novel triple melting phenomenon emerges on DSC curve of β-form PBAF,which is reasonably attributed to the melting of the original β-form crystal and two types of newly-formed α-form crystals during heating.The β to α transformation takes place through both solid-solid and solid-liquid-solid(melt-recrystallization)routes.A special hydrogen-bonding interaction between neighbouring chain stems in crystal phase is suggested to be responsible for the restriction of solid-solid route and the induction of solid-liquid-solid route for β to α transformation.