Dynamic Networks High Glass-Transition Temperature Polymer Networks Harnessing the Dynamic Ring Opening of Pinacol Boronates

Differential scanning calorimetry of high molar mass poly(4-vinylphenylboronic acid, pinacol ester)s evi-denced unusual reactive events above 120 8 8C, resulting in ahigh glass-transition temperature of 220 8 8C. Areversible ring-opening reactivity of pinacol boronates is proposed, involving anucleophilic attackonthe sp 2 boron and subsequent bridging between boron atoms by interconnected pinacol moieties to form adensely crosslinked network with high T g .FTIR, solid-state NMR investigations,and rheology studies on the polymer as well as double-tagging analyses on molecular model structures and theoretical calculations further support this hypothesis and indicate ar ing-opening inducing crosslinking. When diluted in an apolar solvent such as toluene,the polymer network can be resolubilized via ring closing,t hus recovering the entropically favored linear chains featuring cyclic boronate esters.