Tuning the Viscosity Profiles of High-T_g Poly(1,2,3-triazolium) Covalent Adaptable Networks by the Chemical Structure of the N-Substituents

Abstract

Tuning the viscosity profiles of high Tg poly(1,2,3-triazolium) covalent adaptable networks by the chemical structure of the N-substituents

Suppressing Creep and Promoting Fast Reprocessing of Vitrimers with Reversibly Trapped Amines

“…[1,[4][5][6] As such, processability is mainly controlled by the rate of dynamic rearrangements of the network architecture itself. [7,8] Therefore, an important design constraint to consider for vitrimers, is the fact that every reactive crosslinking moiety also requires the ready availability of a second reactive moiety. [9][10][11] Without exception, the rate determining step in vitrimer cross-link exchanges relies on the availability of two distinct reactive species, with at the one hand the reactive cross-link itself, and on the other hand a reactive side chain or chain-end that will receive the new cross-link after exchange.…”

Reprocessing of Covalent Adaptable Polyamide Networks through Internal Catalysis and Ring-Size Effects

“…For this purpose, an ever-increasing amount of dynamic chemistries have been considered, yielding polymer materials with significant differences in mechanical behavior with temperature. ,− For example, an important distinction can be made between dissociative and associative dynamic networks based on how cross-linking points are (dis)­connected as a function of time, resulting in different viscosity profiles. Dissociative CANs will show a temporary decrease in network connectivity due to a bond-breaking prior to the formation of a new bond leading to net depolymerization when applying heat. , In contrast, associative CANs or vitrimers are characterized by a constant connectivity due to the formation of new cross-linking points before breaking previous ones. , Despite their differences, both CAN types have been considered to meet current processing challenges and are dependent on the underlying dynamic covalent chemistry which can be influenced by additives, , sterical hindrance, and electron density changes. − Moreover, it is important to note that the exact molecular exchange mechanism in several cases may be ambiguous or condition-dependent, making a distinction between associative and dissociative less obvious. , …”

Reversible crosslinking and fast stress relaxation in dynamic polymer networks via transalkylation using 1,4-diazabicyclo[2.2.2] octane

“…The polymer networks with excess of amine and excess of bromine both showed efficient stress relaxation in rheological step-strain stress relaxation experiments. At 140 °C, relaxation times for both stoichiometries are faster than observed in many reported systems, e.g., triazolium and trialkylsulfonium based transalkylation networks, 42,45,63 and several orders of magnitude faster than observed in a range of systems based on transesterification reactions. [65][66][67][68] Since the networks are made from easily accessible chemicals and the exchange reaction is efficient at relatively low temperatures, this system offers a simple route towards moldable, recyclable network polymers.…”

“…42 For other systems the activation energy is even lower and relaxation times are longer. It is worth noting here that in a very recent publication 63 on the triazolium system the use of benzylic N-substituents resulted in relaxation times that were about two orders of magnitude lower than those in the systems with only aliphatic N-substituents, but all of the investigated systems had activation energies between 126 and 155 kJ/mol. These results may suggest that part of the fast relaxations that are observed in the current studies may be caused by the fact we used a benzyl bromide substituent and not an alkyl bromide substituent.…”