Structural effects on the reprocessability and stress relaxation of crosslinked polyhydroxyurethanes

Abstract

Crosslinked polyhydroxyurethane (PHU) networks synthesized from difunctional six‐membered cyclic carbonates and triamines are reprocessable at elevated temperatures through transcarbamoylation reactions. Here we study the structural effects on reprocessability and stress relaxation in crosslinked PHUs. Crosslinked PHUs derived from bis(five‐membered cyclic carbonates) are shown to decompose at temperatures needed for reprocessing, likely via initial reversion of the PHU linkage and subsequent side reactions of the liberated amine and cyclic carbonate. Therefore, several six‐membered cyclic carbonate‐based PHUs with varying polymer backbones and crosslink densities were synthesized. These networks show large differences in the Arrhenius activation energy of stress relaxation (from 99 to 136 kJ/mol) that depend on the network structure, suggesting that transcarbamoylation reactions may be highly affected by both chemical and mechanical effects. Furthermore, all crosslinked PHUs derived from six‐membered cyclic carbonates show mechanical properties typical of thermoset polymers, but recovered as much as 80% of their as‐synthesized tensile properties after elevated temperature compression molding. These studies provide significant insight into factors affecting the reprocessability of PHUs and inform design criteria for the future synthesis of sustainable and repairable crosslinked PHUs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44984.

Unexpected Synthesis of Segmented Poly(hydroxyurea–urethane)s from Dicyclic Carbonates and Diamines by Organocatalysis

“…16 Recent studies have reported the dissociative reversible aminolysis reaction in PHU reprocessability process; however, no detailed mechanism has been discussed. 50,52 Our study suggests that urea formation occurred in presence of basic catalysts. A mechanism has been proposed, as illustrated in Scheme 2.…”

Vitrimers: directing chemical reactivity to control material properties

“…52 Dichtel, Hillmyer and coworkers also reported a comparable effect in hydroxyurethane vitrimers, in which an ether based-vitrimer displayed an E a of about 100 kJ mol À1 while a corresponding aliphatic-based material generated a higher energy barrier of 136 kJ mol À1 . 53 A similar comparison was done by Torkelson and co-workers in hydroxyurethane vitrimers. 55 Three different vitrimers, constituted of polybutadiene (PB), poly(tetramethylene oxide) (PTMO), and polydimethylsiloxane (PDMS), have been evaluated and compared with regard to their recycling efficiency.…”

Tough and Multi‐Recyclable Cross‐Linked Supramolecular Polyureas via Incorporating Noncovalent Bonds into Main‐Chains

“…Moreover, the toughness of cross-linked polyurea could be significantly improved from 0.63 to 74.17 MJ m −3 and 124.17 MJ m −3 through incorporating 9.7% and 14.6% noncovalently bonded monomers, respectively, which is very prominent among the reported recyclable cross-linked thermosets. [7,11,12,[14][15][16]27,44,46,[48][49][50][51][52][53][54][55][56][57] Therefore, CSPU with superior toughness, remarkable solvent resistance, high transparency, and excellent multiple recyclability was achieved through the strategy of incorporating noncovalent bonds into main-chains.…”