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

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.