Synthesis of N-vinylcaprolactam polymers in water-containing media

Poly(N-vinylcaprolactam) (PNVCl) is a polymer possessing a lower critical solution temperature (LCST) in aqueous solutions. To the best of our knowledge, we report the first synthesis of PNVCl in water-containing media, namely in DMSO/water mixtures with as low a DMSO concentration as 10% (v/v) using a pair persulphate/tertiary amine as the redox initiator. The polymerization was carried out in three ways: (i) in homogeneous system at 20 degrees C (below LCST); (ii) as precipitation polymerization at 65 degrees C (above LCST for the given DMSO/water compositions); and (iii) cryogenically at -20 degrees C. The polymer MW distribution and tendency to segregate from solution and form a concentrated polymer phase depended on the solvent composition and polymerization temperature. PNVC1 synthesized at 65 degrees C had the largest fraction of high-molecular-weight polymer and the strongest tendency for temperature induced phase separation. Molecular-weight characteristics of the polymers obtained were evaluated with size-exclusion chromatography. Temperature-dependent solution behaviour of the samples was investigated with a thermoturbidimetric technique. Thermodynamic parameters of the temperature-induced phase separation were measured with high-sensitive differential scanning calorimetry. The synthetic methods developed are of interest for the preparation of N-vinylcaprolactam copolymers with thermally unstable co-monomers or co-monomers insoluble in organic solvents, as well as for the synthesis of chemically cross-linked PNVCl hydrogels. (C) 2000 Elsevier Science Ltd. All rights reserved.