Structural and thermal properties of poly(1,4-cyclohexane dimethylene terephthalate) containing isosorbide†
Poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PICT) copolymers were synthesized by melt condensation with various contents of the corn derived monomer isosorbide (ISB). Since poly(1,4-cyclohexanedimethylene terephthalate) (PCT) has disadvantageous thermal processing properties as well as a high melting temperature, ISB could be used to control Tg and Tm simultaneously. An increased content of ISB can increase the Tg and lower the Tm by affecting the crystallization behavior and structural properties of PCT. The composition of PICT was confirmed using 1H-NMR spectroscopy, and the detailed structure was analyzed with correlation spectroscopy (COSY) and heteronuclear single-quantum correlation spectroscopy (HSQC). 13C-NMR spectroscopy was used for investigating the sequence distribution and from these results, the effect of the ISB-TPA dyad on the thermal properties was revealed. Solid state cross polarization/magic angle spinning (CPMAS) 13C-NMR spectroscopy was used to investigate the free space of an atom due to environment dependent relaxation behavior, which determines whether ISB is excluded from the crystal structure. Then, WAXD was used to analyze the crystal structure, representing the effect of ISB on the crystallization. Finally, polarized optical microscopy and atomic force microscopy were used to visualize the morphological change of the crystallite resulting from ISB.