DYNAMIC-MECHANICAL BEHAVIOR OF RANDOM COPOLYMERS OF A LC-METHACRYLATEAND OCTYL METHACRYLATE

The dynamic mechanical behaviour of random copolymers of LC monomer - 1-(hexyloxycarbonyl)ethyl 4-[4-(methacryloyloxy)benzoyloxy]benzoate (H B) and octyl methacrylate (OMA) was studied in the main transition and flow regions. Even though the aliphatic end groups of the side chain of HB and OMA are roughly the same, the T-g temperature of poly(HB) is similar to 80 K higher than that of poly(OMA); this fact is due to th e presence of the stiff phenyl benzoate mesogenic group in the side ch ain of HB. With increasing content of OMA in the copolymer the superim posed curves of the storage G'(p) and loss G ''(p) moduli at a constan t temperature shift towards shorter frequencies. It has been shown tha t this shift is mainly due to an increase of the free volume in the co polymers with increasing content of OMA. While HB monomer shows liquid crystalline (LC) properties, its polymer (poly(HB)) and random copoly mers with OMA show only isotropic thermal behaviour because no flexibl e spacer is present in the side chain of HB which would decouple the m ain chain and mesogenic group motions. This means that neither the hom opolymer of HB, nor its copolymers with a flexible comonomer retain th e LC properties of the starting LC monomer, HB.