Segmented Thermoplastic Polymers Synthesized by Thiol–Ene Click Chemistry: Examples of Thiol–Norbornene and Thiol–Maleimide Click Reactions

Abstract

Thiol–ene click reactions are used to synthesize segmented thermoplastic materials for the first time via a soft segment + hard segment + chain extender approach that is commonly used to synthesize thermoplastic polyurethane elastomer (TPU). We employ a relatively long chain difunctional thiol (2500 g/mol) as soft segment, a small-molecule thiol as chain extender, and rigid cyclic-ene monomers, including norbornene (containing either urethane or urea linkages in the backbone) and maleimide, as hard segments to achieve thiol–norbornene and thiol–maleimide thermoplastics. The majority of the thiol–norbornene polymers synthesized with 45% or 55% urethane-based norbornene hard segments exhibit phase separation with broad interfaces as indicated by dynamic mechanical analysis (DMA) and hold promise as both thermoplastic elastomers competitive with TPUs and broad-temperature-range damping materials. Thiol–norbornene polymers synthesized with 50% urea-based norbornene hard segments are nanophase separated with sharp interfaces (as indicated by DMA and small-angle X-ray scattering) due to the stronger interurea hydrogen bonding as compared with interurethane interactions. The low strain at break (∼30%) and high Young’s modulus (200–300 MPa) suggest that the 50% hard segment forms the matrix in these polymers, disallowing elastomeric response. Segmented thiol–maleimide thermoplastics, synthesized without isocyanates at 45% and 50% hard-segment content, exhibit highly effective nanophase separation and properties indicating potential to be competitive with some thermoplastic non-isocyanate polyurethane (NIPU) elastomers and TPUs.

Solvent- and Catalyst-free Synthesis, Hybridization and Characterization of Biobased Nonisocyanate Polyurethane (NIPU)

“…The vibration peaks at 1684 cm −1 and 1649 cm −1 were attributed to the urethane groups and ester groups, respectively. Compared with Figure 4, the C=O vibration peak at 1691 cm −1 shifted to lower wavenumbers of 1684 cm −1 , which indicated that the epoxy group provided additional hydrogen bonding for HNIPU [42,43]. Further, Scheme 4 showed the additional hydroxyl groups because of the ring opening of epoxy groups, which could lead to more hydrogen bonding.…”

Reaction Environment Effect on the Kinetics of Radical Thiol–Ene Polymerizations in the Presence of Amines and Thiolate Anions

“…TEC reactions for polymer synthesis and functionalization are commonly deemed as “click” reactions due to their high chemical- and regio-selectivity, insensitivity to solvent and water, full atom economy, and typically rapid kinetics that afford quantitative conversions. This behavior has led to the use of the TEC reactions and the similar radical-mediated thiol–yne reaction, which possess the same click-like characteristics, ,,,− for the synthesis of advanced functional materials, particularly linear step-growth polymers, − covalent adaptable networks (CANs), − and functionalized surfaces or macromolecules. − Further, because TEC reactions do not require toxic metal catalysts and are generally orthogonal to many organic functional groups present in biomolecules, TEC is widely used for bioconjugation strategies as well as for the formation and modification of cell-encapsulating hydrogels. ,− …”

Polythioethers with Controlled α,ω‐End Groups Prepared by Visible Light Induced Thiol–Ene Click Polymerization of Dithiol and Divinyl Ether with 4‐(N,N‐diphenylamino)benzaldehyde as Organocatalyst

“…NPM is intensively used to detect sulfhydryl groups. [ 64–66 ] In the present work, the polythioletheroligomer was prepared at a molar ratio of [BDMT]:[DEGVE] = 1.5:1 and the reaction time was 4 h. Then, the obtained polythiolether was purified and mixed with 0.5 g of NPM with anisole as the solvent. After 12 h of reaction, the product was purified for characterization.…”