Synthesis of polyfumarates containing a 4-tert-butylcyclohexyl group and unique solid-state properties based on the orientation of rigid poly(substituted methylene) chains

Poly(dialkyl fumarate)s (PDRFs), which are produced by the radical polymerization of dialkyl fumarates, are highly transparent amorphous polymer materials with excellent heat resistance, mechanical, and optical properties. The physical properties of PDRFs with a rigid poly(substituted methylene) structure discontinuously change at their β transition temperature (T_β) because of restricted local molecular motion, including the rotation of substituents in the side chain. In this study, we performed a radical polymerization of symmetric and asymmetric dialkyl fumarates, including 4-tert-butylcyclohexyl esters with a fixed cycloalkyl conformation, to clarify the thermal and optical properties of the produced PDRFs. The T_β value, refractive index, and density of the PDRFs increased with the introduction of the 4-tert-butylcyclohexyl group. Based on the wide-angle X-ray scattering (WAXS) measurement results, we analyzed the spontaneous aggregation of the PDRF chains in the solid state to discuss their density and optical properties in detail.