Studies of molecular motions in selected polymer systems

Abstract

Torsional Braid Analysis, TBA, of various polysaccharide derivatives and of members of the poly (di-n-alkylitaconate) series, complemented by a limited number of Differential Scanning Calorimeter thermograms, has enabled the mclecular motions associated with several secondary glass transitions to be tentatively identified. A damping peak observed at less than -190° to -166°C in TBA thermograms for polymers with side groups containing n-alkyl moitiés as large as the n-propyl group has been attributed to the onset of rotational motion of this alkyl group alone. TBA of higher poly (di-n-alkylitaconates) also revealed a large secondary transition between -70° and -45°C; from the relationship between their temperatures these two transitions were identified with the glass and melting transitions of the n-alkyl side-chains and it was suggested that the g-transition for the entire polymer also contributes to the high damping associated with the latter process. Two of the secondary transitions that are visible in TBA thermograms for various polysaccharide derivatives may be associated with absorbed water: the damping maximum occurring between 15° and 33°C has been attributed to the rupture of hydrogen bonds, the increased mobility of bonded water molecules possibly being responsible for the damping variation at about -1U°C. It was suggested that motion of the oxycarbonyl portion of ester groups and/or of the C6 oxymethylene group may be initiated at approximately -55°C. It was concluded that chair-chair conformational interchange of main-chain glucose rings becomes energetically feasible between -90 and -140°C, the temperature of this secondary transition being particularly dependent on the structure of substituent groups. The glass transition temperature was also determined for each available sample, the variety in their structures enabling the relationship between these two parameters to be discussed.