Heterocyclic polymers with high glass transition temperatures

Abstract

Glass transition temperatures (T gs) of polymers have been correlated with the concept of free volume so that the relationship between T g and the molecular mass M $$ {T_g} = T_{_g}^\infty - \frac{K}{M} $$ where T ∞ g is the glass transition temperature for infinite molecular weight, K is a constant and M is the molecular weight. This relation is understandable if one considers that the fractional free volume due to the chain ends decreases as the molecular weight increases. Assuming that molecular motion of a chain end is greater than for an internal part of the chain, a low molecular weight polymer will have a T g lower than a corresponding high molecular weight polymer. The constant K is the contribution of the end-groups $$ K = \frac{{2\rho {N_A}\theta }}{{{\alpha _f}}} $$ where p is the polymer density, N A is Avogadro’s number, θ is the contribution of a chain end to the free volume and αf is the thermal expansion coefficient of the free volume.