Poly(hydroxyurethane‐co‐thiourethane)s cross‐linked with disulfide bonds: Synthesis via isocyanate‐free approach, thermomechanical and reprocessing properties

Abstract

Both difunctional five-membered cyclic carbonate (E5CC) and trithiocarbonate (E5CTC) were synthesized via the reactions of diglycidyl ether of bisphenol A (DGEBA) with carbon dioxide (CO 2 ) and carbon disulfide (CS 2 ), respectively. These two monomers were employed to synthesize linear poly(hydroxyurethaneco-mecaptotrithiourethane) [P(HU-co-MTU)] copolymers via the polymerization with an α,ω-diamino-terminated poly(propylene oxide). By controlling the mole ratios of E5CC to E5CTC, the P(HU-co-MTU) copolymers were synthesized with variable contents of thiol groups. It was found that the linear P(HU-co-MTU) copolymers were readily cross-linked with the disulfide bonds which were in situ generated via the radical coupling of the side thiol groups. The cross-linking exerted a profound impact on the thermomechanical properties of the materials. The glass transition temperature (T g 's), Young's moduli and tensile strengths were significantly enhanced with increasing the contents of disulfide bonds. More importantly, the networks significantly displayed the self-healing and reprocessing properties, which are attributable to the dynamic exchanges of disulfide bonds.

Biobased, Reprocessable Non-isocyanate Polythiourethane Networks with Thionourethane and Disulfide Cross-Links: Comparison with Polyhydroxyurethane Network Analogues

“…Due to their larger and more favorable ring strain, DTCs are more reactive to nucleophiles than their oxygen analogues, i.e., CCs, which enables relatively fast reactions under milder conditions. , Moreover, the amine reacts with the S–C­(S) bond in DTCs by regioselective nucleophilic addition, leading to an enhanced selectivity toward the formation of 100% primary thiol, unlike the reaction with CCs which often leads to 60–70% secondary hydroxyl groups. ,,, We note that a recent study reported polythionourethane synthesized from isothiocyanate and alcohol . The thionourethane linkage also has the sulfur atom at the thiocarbonyl position, with a linkage structure like the linkages in what the research literature has called NIPTUs since 1995. ,,,,− However, NIPTUs have additional primary thiol groups that distinguish them from polythionourethanes. Because the naming of these materials as NIPTUs is well established, ,,,,− we will refer to our materials as NIPTUs.…”

“…The thionourethane linkage also has the sulfur atom at the thiocarbonyl position, with a linkage structure like the linkages in what the research literature has called NIPTUs since 1995. ,,,,− However, NIPTUs have additional primary thiol groups that distinguish them from polythionourethanes. Because the naming of these materials as NIPTUs is well established, ,,,,− we will refer to our materials as NIPTUs. However, we acknowledge that NIPTUs contain thionourethane linkages with additional primary thiol groups.…”

“…Importantly, NIPTU networks have the potential of affording not only thionourethane cross-links but also dynamic covalent disulfide cross-links , obtained via oxidative coupling of thiol groups. , The dynamic nature of such disulfide linkages in NIPTUs has been examined recently. Zheng and co-workers , synthesized NIPTUs with linear backbones, oxidized the thiol groups into inter-chain disulfide linkages using a radical initiator, and demonstrated the reprocessability of the NIPTUs in which all cross-links were based on dynamic covalent disulfide bonds. However, no study has been published regarding the reprocessability of NIPTU networks made from multifunctional monomers and with branching thionourethane linkages as cross-links.…”

Synthesis and properties of water‐dispersible polyurethanes based on various diisocyanates and PEG as the hard segment

“…This can be influenced by the structure and length of the hard segments, which directly determine the physical properties of the polyurethane material. [9][10][11] In order to increase the mobility of the polyurethane matrix, the polyurethane main chain must be modified to ensure a higher degree of vibration and mobility in the macromolecular morphology. 12,13 Traditional polyurethanes are insoluble in water and have a hydrophobic character.…”

“…Hard domains formed by self‐organization and physical crosslinks determine the morphology of the phases. This can be influenced by the structure and length of the hard segments, which directly determine the physical properties of the polyurethane material 9–11 . In order to increase the mobility of the polyurethane matrix, the polyurethane main chain must be modified to ensure a higher degree of vibration and mobility in the macromolecular morphology 12,13 …”