Synthesis and phase behavior of a new 2-vinylbiphenyl-based mesogen-jacketed liquid crystalline polymer with a high glass transition temperature and low threshold molecular weight

Abstract

We have synthesized a new mesogen-jacketed liquid crystalline polymer, poly(4′-(methoxy)-2-vinylbiphenyl-4-methyl ether) (PMVBP) containing a biphenyl core in the side-chain. PMVBP has a smaller monomer molecular weight (MW), a higher glass transition temperature and a lower threshold MW for liquid crystalline (LC) formation. PMVBP was obtained via a nitroxide-mediated living radical polymerization and characterized by gel permeation chromatography, differential scanning calorimetry, polarized light microscopy, and one- and two-dimensional wide-angle X-ray diffraction (WAXD) experiments. The number-average MW (M_n) of the polymers ranges from 0.41 × 10⁴ to 1.64 × 10⁴ g mol⁻¹. A relatively high glass transition temperature is observed, which increases from 173 to 208 °C with increasing MW. The LC phase developed at relatively high temperatures is strongly dependent on the M_n of the polymer. A hexagonal columnar (Φ_H) LC phase is observed above 260 °C when the M_n is only above 0.53 × 10⁴ g mol⁻¹, a low threshold MW for LC formation. All of the LC phases are retained during cooling.