A Novel Rod−Coil Block Copolymer and Its Compatible Blends

Abstract

A novel rod−coil diblock copolymer, poly(n-hexyl isocyanate)-b-poly(ethylene glycol) (PHIC-b-PEG) was synthesized by using the living titanium(IV)-catalyzed coordination polymerization method. The lyotropic mesophases and mesophases in solid state of the PHIC-b-PEG rod−coil block copolymer were investigated using polarized optical microscopy (POM). The 30 wt % copolymer/toluene solution exhibited birefringence with apparent orientation. The morphology in the solid state showed nematic-like domain structures. The sizes of the domains decreased when the solid film was solution-cast from chloroform rather than toluene. However, the overall dimension of the domain was estimated to be micrometer in scale. The solution-cast PHIC-b-PEG/PMMA blends showed some compatibility between the two components from the DSC measurements. The 5/95 (wt/wt) blend exhibited liquid crystalline domains of 1-μm size. The 40/60 blend indicated improved compatibility. The tensile strength of the more compatible 40/60 blend was significantly improved especially at high temperatures around Tg. The creep experiments at various temperatures above Tg showed reorientation of the rods in the 40/60 blend. These ordered domains in the blend were further confirmed by DSC, where a small sharp endothermic peak appeared at around 140 °C with an enthalpy change about 0.4 J/g. This melting of the stretch-induced ordering of the rods was irreversible.