The empirical form for the dependence, Tg(n) ≅ Tg(∞)·(1 + α/n), of the glass transition temperature Tg on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, Tg(n) ≅ Tg(∞) · [1 + c/(n·Nrot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent Nrot and composition-independent c terms. Nrot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers.
No takes yet. Share an insight, caveat, or question.
Bicerano et al. (1996) studied this question.