Tuning Reprocessing Temperature of Aliphatic Polyurethane Networks by Alkoxyamine Selection.

Recent studies have shown that the largest employed thermoset family, polyurethanes (PUs), has great potential to be reprocessed due to the dynamic behavior of carbamate linkage. However, it requires high temperatures, especially in the case of aliphatic PUs, which causes side reactions besides the desired exchange reaction. To facilitate the reprocessing of aliphatic PUs, in this work, we have explored the dynamic potential of alkoxyamine bonds in PU networks to facilitate the reprocessing under mild conditions considering their fast recombination ability. Taking advantage of the structural effect of the nitroxide and alkyl radicals on the dissociation energy, two different alkoxyamine-based diols have been designed and synthesized to generate PU networks. Our study shows that replacing 50 mol % of a nondynamic diol chain extender with these dynamic blocks boosts the relaxation times of the networks, enabling reprocessing at temperatures as low as 80 °C.

Oxime metathesis: tuneable and versatile chemistry for dynamic networks.

Oxime chemistry has emerged as a versatile tool for use in a wide range of applications. In particular, the combination of oximes with esters and urethanes has enabled the realisation of Covalent Adaptable Networks (CANs) with improved and tunable dynamic properties. Nevertheless, an exclusively oxime-based chemistry has not yet been explored in the fabrication of CANs. In this work, we investigate the mechanism of the acid-catalysed dynamic exchange of oximes. We propose a metathesis mechanism that is well supported by both experimental and computational studies, which highlight the importance of the substituent effect on the exchange reaction kinetics. Then, as a proof of concept, we incorporate oxime groups into a cross-linked polymeric material and demonstrate the ability of oxime-based polymers to be reprocessed under acid catalysis while maintaining their structural integrity.

Thermally Reversible Organocatalyst for the Accelerated Reprocessing of Dynamic Networks with Creep Resistance.

The industrial implementation of covalent adaptable networks hinges on the delicate task of achieving rapid bond exchange activation at specific temperatures while ensuring a sufficiently slow exchange at working temperatures to avoid irreversible deformation. In this pursuit, latent catalysts offer a potential solution, allowing for spatiotemporal control of dynamic exchange in vitrimer networks. However, the irreversible nature of their activation has led to undesired creep deformation after multiple cycles of reprocessing. In this work, we demonstrate that a tetraphenylborate tetramethyl guanidinium salt (TPB:TMG) undergoes a reversible thermal dissociation, releasing free TMG. This thermally reversible organocatalyst can be readily introduced as an additive in industrially relevant materials such as disulfide-containing polyurethane networks (PU) that undergo disulfide exchange in the presence of a base catalyst. In contrast with a free-base-catalyzed process, we demonstrate the dual benefit of adding the thermally reversible TPB:TMG in preventing creep at lower temperatures and also enabling reprocessability of disulfide-containing PU networks at elevated temperatures. The remarkable reversibility of this thermally activated catalyst allows for multiple reprocessing cycles while effectively maintaining a creep-free state at service temperature.

Zein as a versatile biopolymer: different shapes for different biomedical applications.

In recent years, the interest regarding the use of proteins as renewable resources has deeply intensified. The strongest impact of these biomaterials is clear in the field of smart medicines and biomedical engineering. Zein, a vegetal protein extracted from corn, is a suitable biomaterial for all the above-mentioned purposes due to its biodegradability and biocompatibility. The controlled drug delivery of small molecules, fabrication of bioactive membranes, and 3D assembly of scaffold for tissue regeneration are just some of the topics now being extensively investigated and reported in the literature. Herein, we review the recent literature on zein as a biopolymer and its applications in the biomedical world, focusing on the different shapes and sizes through which it can be manipulated.