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. (C) 2002 Elsevier Science B.V. All rights reserved.