Novel covalent adaptable networks (CANs) of ethylene/1-octene copolymers (EOCs) made by free-radical processing: comparison of structure–property relationships of EOC CANs with EOC thermosets

Abstract

Ethylene-based copolymers such as ethylene/1-octene copolymers (EOCs) are commonly used in blends for thermoplastic elastomers, foams, and consumer articles. These blends may be permanently cross-linked to enhance elasticity at the...

Covalent Adaptable Networks Made by Reactive Processing of Highly Entangled Polymer: Synthesis-Structure-Thermomechanical Property-Reprocessing Relationship in Covalent Adaptable Networks

“…This implies a commonality in the underlying core mechanism governing the viscoelastic responses of creep in these PHMA CANs, which is largely independent of cross-link density. Notably, these activation energies are markedly lower than most of those previously reported for BiTEMPS-based CANs (∼100–130 kJ/mol) − which align with the bond dissociation energy of dynamic sulfur–sulfur bonds in BiTEMPS-containing molecules (∼110 kJ/mol) . This result suggests that the dissociative dynamic chemistry of the BTMA cross-linker is not the dominant contributor to the creep behavior of these PHMA CANs.…”

“…The results of the SAOS study are presented in Figure S6. We chose 5.0 wt % BTMA as the cross-linker loading for this experiment, as 5.0 wt % BTMA loadings have been used in previous work to synthesize robust PE and random EOC CANs. , The extent of curing in the PHMA CAN was assessed by monitoring its increase in normalized shear storage modulus ( G ′) as a function of time while subjected to a 0.1% oscillatory strain at a 1.0 Hz frequency. The PHMA CAN exhibited a t 0.95 value, the time when normalized G ′ reaches 0.95, of 20 min.…”

“…When fitted to the KWW function, the stress relaxation profiles show substantial breadth (with β ranging from 0.66 to 0.68 for the 5–2 PHMA CAN in tension and from 0.48 to 0.59 and 0.18 to 0.19 for the 15–1.5 PHMA CAN in tension and shear, respectively). Yet, it is evident not only from the R 2 values of the fits (which range from 0.958 to 0.988 and are generally lower than those of other CAN stress relaxation fittings reported by our group) ,, but also from the shapes of the fits superimposed onto the relaxation profiles that this function does not strongly account for each of the relaxation modes, particularly the relaxation at short times. Figure a makes this disparity between relaxation profile and fit particularly evident.…”

“…Beyond the cross-linking process itself, the extent of the dynamic covalent character of the generated cross-links greatly impacts the properties of the resulting network. − Dynamic covalent bonds undergo associative exchange or reversible dissociative reactions that reconfigure their chemical arrangements upon sufficient exposure to a stimulus such as heat or light. , Cross-linked networks that contain dynamic covalent bonds are known as covalent adaptable networks (CANs) or dynamic covalent polymer networks (DCPNs). − These materials have gained attention as recyclable or degradable alternatives to conventional thermosets; the presence of permanent cross-links in thermosets prevents the flow of polymer chains at high temperature and, thus, disallows their remolding or remelt processing. In contrast, dynamic covalent bonds confer local chain mobility on CANs due to their ability to rearrange, allowing for reprocessability. − CANs have been synthesized with associative dynamic chemistries such as transesterification, − transamination, ,− boronic ester exchange, − and disulfide exchange − as well as dissociative dynamic chemistries such as the Diels–Alder reaction, − alkoxyamine chemistry, − hindered urea exchange, − and dialkylamino disulfide chemistry. − CANs synthesized exclusively with associative dynamic chemistries are sometimes called vitrimers. , CANs may also exhibit several concurrent dynamic chemistries, as in the case of polyurethanes, polyhydroxyurethanes, polythiourethanes, , and others. − …”

“…Furthermore, no study has investigated structure-property relationships of thermomechanical and viscoelastic properties based on the cross-link density of CANs that were cross-linked through their side chains by radical-based methods. Using our radical-based reactive process for upcycling PE and random EOCs into CANs, , we aim to fill these voids in the field by making CANs from PHMA, a suitable polymer with alkyl side chains amenable to free-radical grafting.…”