Photo-polymerisation and study of the ice recrystallisation inhibition of hydrophobically modified poly(vinyl pyrrolidone) co-polymers

Antifreeze, ice binding and ice nucleating proteins modulate the formation and growth of ice in biological systems, enabling extremophiles to survive in sub-zero temperatures. A common feature is their rigidity, and segregated hydrophobic and hydrophilic domains. It has been demonstrated that increased hydrophobicity in rigid, facially amphipathic, synthetic polymers enhances ice recrystallisation inhibition (IRI) activity, but has not been evaluated in flexible systems. Here photochemical RAFT/MADIX polymerisation is used to obtain well-defined poly(N-vinyl pyrrolidone), PVP, copolymers to probe the impact of hydrophobicity on ice re crystallisation inhibition in a fully flexible polymer system, to increase the understanding on how to mimic antifreeze proteins. It is observed that PVP homopolymers have only very weak, molecular weight dependent, IRI and that hydrophobic co-monomers give very modest changes in IRI, demonstrating that the spacial segregation of 'philicities' is crucial, and not just the overall hydrophobic content of the polymer. These results will help design the next generation of IRI active polymers for cryopreservation applications as well as aid our understanding of how biomacromolecules can inhibit ice growth.