Synthesis and thermal studies of aliphatic polyurethane dendrimers: a geometric approach to the Flory–Fox equation for dendrimer glass transition temperature

Abstract

A new convergent synthesis for polyurethane dendrons to generation 4, and dendrimers to generation 3, is presented with control of surface functionality. The systematic synthesis of twenty-six new dendritic materials has led to a study of the factors affecting T_g using widely accepted approaches. The established understanding of dendritic polymerT_g behaviour is that the Flory–Fox models, used for linear polymers, are unsuitable as the high number of chain ends and globular nature of dendrimers requires special consideration. In our review of the accepted understanding we have shown that the conventional Flory–Fox models predict T_g∞ accurately and generate identical values to the established modifications of the Flory–Fox equation that consider ‘dendrimer-relevant’ aspects such as the non-zero values of n_e/M at infinite molecular weight. We also present a new approach using the geometric parameters of dendrimer mass evolution suggesting that the Flory–Fox equation is indeed appropriate for determination of dendrimerT_g∞.