Isocyanate-free chemistry and the introduction of dynamic bonds are a promising combination toward the development of more sustainable polyurethane (PU) networks. Here, we present the synthesis of reprocessable, isocyanate-free PU networks through atom-economical reactions for both monomers and polymers, valorizing CO 2 as a building block. The monomers employed were five-membered cyclic carbonates prepared through an efficient (>99% conversion) reaction between CO 2 and epoxides with high yield (up to 97% at a 100 gram scale), catalyzed by the moisture-tolerant and easily prepared DBU•I 2 complex. The structural diversity of the monomers and the utilization of cystamine bearing the dynamic S−S motif realized PU networks with a finely tuned profile of thermal (T g from −9 to 44 °C), mechanical (E from 0.2 to 1700 MPa), and viscoelastic properties (E′ from 0.03 to 5.5 MPa at 1 Hz). Facile recycling (100 °C, 20 min) of the networks was enabled thanks to the rapidly exchanging disulfide bonds and the modulated cross-link density. Moistureinduced plasticization of the networks was identified, and its effect on the properties of the networks was elucidated. The atom economy and energy-efficiency methodology, avoiding toxic reagents and preventing waste generation, make this approach an attractive and greener pathway to PU networks taking a step toward a circular plastic economy.
Polyhydroxyurethane-graft-poly(ε-caprolactone) copolymers were prepared in bulk by designing a polyhydroxyurethane system with polymer-in-monomer solubility.
Long-chain polyamide covalent adaptable networks with high strength and short relaxation times were prepared based on a renewable ethylene brassylate and disulfide exchange.
Biobased
polyamide (PA) thermosets composed of renewable ethylene
brassylate were synthesized through a one-step reaction under solvent-free
conditions, at 100 °C in the presence of an organocatalyst. Under
these conditions, thermoset formation times as low as 10 min were
achieved. The thermosets were easily prepared as thin, transparent
films with high strength, flexibility, and high thermal stability.
The ester-to-amine content and formation of ethylene glycol in situ
as a byproduct of the reaction were studied and correlated with the
final properties of the materials. Crystalline oligoester segments
were identified as a result of ring-opening polymerization and were
shown to have a beneficial effect on the mechanical properties of
the thermosets and endowed shape-memory behavior. In contrast to other
routes, employing multistep monomer preparation, harsh conditions,
and chlorinated reagents, this procedure contributed to the development
of sustainable, functional PA thermosets.
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