Study of phase transitions in liquid crystalline side group polymers via photon transmission method

Photon transmission measurements were applied to study the phase transitions of an acrylate monomer, 3-(4-cyanobiphenyl-4′-oxy)propyl acrylate (LC3), its homopolymer (PLC3) and its graft copolymer (GLC3) with polytetrahydrofuran grafts. In PLC3 drastic decrease in the transmitted light intensity was attributed to a first-order isotropic–nematic phase transition. The phase transitions were also confirmed by DSC and polarizing microscopy. No phase transition was observed in GLC3. This method was not able to detect the isotropic–nematic phase transition in GLC3, probably because of the small size of the phase separated domains in this graft copolymer. The isotropic–nematic transition of GLC3 was identified by polarizing microscopy only by the appearance of a weak diffuse birefringence on cooling.