Polymer hydration and microphase decomposition in poly(N-vinylcaprolactam)–water complex

Abstract

Poly(N-vinylcaprolactam) (PVCL) is a synthetic analogue of biomolecules (enzymes, proteins). It demonstrates a specific hydration and undergoes a coil–globule transition. The PVCL–D2O system (PVCL massM= 106) has been investigated by small-angle neutron scattering (SANS) atT= 296–316 K to identify the structural features of the collapse at concentrationC= 0.5 wt% near the threshold of the coil overlap. (The collapse leads to the segregation of the phase enriched with polymer atT> 305 K). The SANS experiments atq= 0.1–5 nm−1(scales from monomer unit to globule gyration radiusRG≃ 16 nm) have revealed a stretched coil–globule transformation in the range 305–309 K. Using high-resolution SANS (q= 0.002–0.02 nm−1) the globule association to form fractal structures (sponge-like) of surface dimensionDF≃ 2.4–2.6 was examined. The coexistence of globules and disordered chains (regions ∼5–10 nm) was found. The growth of the content of globular phase was induced by the conformational transition in disordered molecular fragments from coiled (dimensionD≃ 1.8) to stretched chains (D≃ 1.2).