MOLECULAR MOBILITY OF SUBSTITUTED POLY(P-PHENYLENES) CHARACTERIZED BYA RANGE OF POLYMER RELAXATION TECHNIQUES

The free volume and related mobility properties of substituted poly(p- phenylene) polymers are examined. The techniques used range from posit ron annihilation, dielectric relaxation, and dynamic mechanical spectr oscopy to thermally stimulated currents. Fractional free volume is det ermined for the samples with different substituted side groups and rel ated to the glass transition temperature. Bulkier groups lead to a gre ater fractional free volume and lower glass transition temperatures. C omparison of molecular relaxation times using the different characteri zation techniques demonstrates that there is strong coupling between m otion of the main chain and the side groups, on which the dipoles resi de. Intermolecular coupling between the main chains at the primary rel axation is shown in this work to be related to the nature of the side chains and resultant free volume, as are the temperature locations of local, secondary relaxations. A qualitative model describing the effec t of regiochemistry on the motions and packing of these materials is a lso proposed. (C) 1998 John Wiley & Sons, Inc.