INFLUENCE OF SPACER LENGTH BETWEEN INTERACTING GROUP AND POLYMER BACKBONE ON THE GLASS-TRANSITION TEMPERATURE OF ELECTRON-DONOR ELECTRON-ACCEPTOR BLENDS

Charge transfer interaction (CT-I) between electron-donor/electron-acceptor groups contributes to an enhancement of the miscibility in polymer blends. Typical of polymer blends with charge transfer interaction is an increase of the glass transition temperature, suggesting a decrease of the free volume during mixing of the blend components. Both, ''zip''-like orientation effects of the CT-I onto the polymer backbones and temporary crosslink formation may contribute to the reduction of the free volume. The effect generally decreases with increasing spacer length between the interacting groups and the polymer backbone, although an increased probability of electron-donor/electron acceptor (EDA) association may be accepted due to the enhanced mobility of the interacting endgroups. Thus the increased probability of EDA association is overcome both by the increased mobility of the temporary crosslinks and by the decrease of the induced orientation effect on the polymer backbone of the CT-I due to the enhanced decoupling of the mobile interacting groups from the less mobile polymer backbone. Because of the possibility of D/2A association of the carbazolyl end-group the effect is more complicated. For the same overall spacer length of the interacting EDA groups the deviation from the additivity of the glass transition temperatures of the polymer blend components is always the larger the longer the donor-spacer.