Isodimorphism And Polymorphic Structure Of Long Chain Aliphatic Polycarbonate Copolymers And Polyether Copolymers

Random copolymerization is the common method to prepare the new polymeric materials and control the material properties.As regarding two crystallizable components,the crystallization behavior of random copolymers can be classified into three categories:noncrystallization,isodimorphism and isomorphism,according to the degree of comonomer inclusion in the crystal lattice.The isodimorphism and isomorphism are the common types of cocrystallization,which requires that the different comonomer units should have good miscibility,and similar chemical structure and crystal structure.In the case of isodimorphic copolymers,the minor comonomer units can enter into the crystalline phase and be regarded as defects.The inclusion and exclusion of comonomer units in the crystal lattice are competed and affected by crystallization conditions and composition.In case of the polymorphic polymers,the comonomer inclusion can affect their crystal polymorphs selection and facilitate the formation of specific crystal polymorphs,due to crystal lattice and chain conformation matching of different comonomer units.However,the crystal polymorphs selection of commoner defect-containing with long carbon chain polymorphic polycarbonate and polyether,with comonomer inclusion degree depending on composition and crystallization temperature,and their underlying mechanism are still unclear.First,we synthesized the poly(octamethylene-ran-decamethylene carbonate)with various compositions from 1,8-octanediol,1,10-decanediol,and dimethyl carbonate by transesterification and melt-polycondensation,and systematically studied their crystallization behavior and crystal transitions in the cooling and heating processes.The random copolycarbonates exhibit isodimorphic crystallization behavior,showing the pseudo-eutectic region at octamethylene carbonate fraction(fC8)of 0.64-0.79.The octamethylene carbonate(C8)-rich copolycarbonates(fC8≥0.79)show reversible solid-solid crystal transitions as poly(octamethylene carbonate)(PC8)homopolymer upon cooling and heating,which are temperature-and composition-dependent.With fC8 decreasing,the δ-α transition is observed at a high temperature with more inclusion of comonomer defects,and the crystals are conformational disordered with development of more gauche conformation in methylene segments at a low temperature when compared to PC8 homopolymer.At a high temperature,the chain conformation in methylene segments of C8-rich copolycarbonates are analogous as that of PC8 homopolymer,thus the α-β transition temperature remains unchanged.Second,we synthesized the poly(oxydecamethylene-ran-oxyhexamethylene)with different compositions from 1,10-decanediol and 1,6-hexanediol,and studied their crystallization behavior,as well as the effect of composition and crystallization temperature(Tc)on their polymorphic structure.The copolyethers display an isodimorphic crystallization behavior,showing the pseudo-eutectic region at decanediol fraction(fC10)of 0.10-0.15.In the case of decanediol-rich(fC10=0.26-0.98)copolyethers,their crystal structure varies from orthomorphic and monoclinic mixed crystal to orthomorphic crystal with fC10 decrasing.The crystal structure of hexanediol-rich(fC10=0.06-0.15)copolyethers changes from monoclinic crystal to orthomorphic crystal.Thus,the orthomorphic crystal is formed at the copolyethers with intermediate composition(fC10=0.26-0.93).The crystal structure of copolyethers with the composition at the critical point of crystal transition strongly depends on the Tc.orthomorphic crystal is preferred to form at a high Tc.