Sulfur-substitution-enhanced crystallization and crystal structure of poly(trimethylene monothiocarbonate)

In this paper,the crystallization behavior of a novel poly(monothiocarbonate),poly(trimethylene monothiocarbonate)(PTMMTC),was investigated and compared with its polycarbonate analogue,poly(trimethylene carbonate)(PTMC).It is found that PTMMTC exhibits strong crystallizability,while un-stretched PTMC is amorphous.DSC and DMA results reveal that PTMMTC possesses higher glass transition temperature(T_(g))andβ-transition temperature(T_(β))than PTMC.Simulation based on density functional theory(DFT)shows that,the bond angle of C-S-C is evidently smaller than that of C-O-C,and thus a larger dipole moment.This leads to the stronger intermolecular interaction and more rigid chain confor-mation in PTMMTC,which is the origin of sulfur-substitution enhanced crystallization.The crystal struc-ture of PTMMTC was preliminarily determined for the first time.PTMMTC has an orthorhombic crystal structure with a planar zig-zag chain conformation.The parameters of unit cell are a=10.74 A,b=4.79 A,and c(fiber axis)=7.74 A.