Interfacial ring-opening polymerizations (iROP) of α-amino-acid derived N-thiocarboxyanhydrides (NTAs) in hexanes or heptane suspension using soluble primary amine initiators have been demonstrated to produce polypeptides with controlled molecular weight and low-tomoderate molecular weight distribution under mild conditions. The NTA monomers were shown to have significantly enhanced moisture and thermal stability relative to Ncarboxyanhydrides (NCAs), resulting in long shelf life and allowing the polymerization to occur quantitatively in open air.

Linear polypeptoid macromonomers with controlled chain length and composition were prepared by norbornene methylamine-initiated copolymerization of N-ethyl N-carboxyanhydride (Et-NCA) and Nbutyl N-carboxyanhydride (Bu-NCA). Polypeptoid bottlebrush copolymers with varying backbone length and side chain composition were subsequently synthesized using the grafting-through method via the ring-opening metathesis polymerization (ROMP) of norbornenyl-terminated poly(N-ethyl glycine)-ranpoly(N-butyl glycine) macromonomers. The bottlebrush copolypeptoids are thermally responsive with a cloud point transition in aqueous solution similar to the linear macromonomers. In contrast to the linear macromonomers, the cloud point transition of the bottlebrush copolypeptoids is strongly dependent on the thermal history of the solution. Freshly prepared aqueous solutions of the bottlebrush copolypeptoids do not exhibit any notable cloud point transition, whereas the solutions that have been thermally annealed at high temperature exhibit sharp and reversible cloud point transition. Intriguingly, upon inorganic salt addition, the aqueous solutions of the bottlebrush copolypeptoids exhibit normal cloud point transition which is independent of the solution thermal history. It was suggested that the thermal annealing and the presence of a salt facilitated the conformational reorganization of the bottlebrush copolypeptoids to favor hydrophobic collapse and intermolecular aggregation, resulting in a cloud point transition.

Polymers with reversible elongation upon cooling (EUC) and contraction upon heating (CUH) enabled applications in actuators, fasteners, dampers, grippers, swimmers, sealants, etc. With the current working temperature being limited to mainly above zero Celsius, applications for subzero Celsius environments are obstructed. In addition, current reversible actuation needs a constant tensile load, or for the best case, under zero tensile load. Reversible EUC and CUH under compressive load is almost impossible and has not been explored. In this work, a cis poly(1,4-butadiene) based system has been developed. Actuated below zero Celsius, 69% EUC occurred under a tensile load; and 6.2% EUC and 17.9% CUH occurred under 0.05 MPa compressive load. The reversible actuation was driven by both entropy and enthalpy, which was validated by a series of characterization tools.

Non-ionic water-soluble helical polypeptides bearing reactive side chains can be efficiently modified with hydrophobic or hydrophilic moieties to produce water-soluble conjugates.