Synthesis and functionalities of poly(N-vinylalkylamide) part XIV -: Synthesis and thermosensitive properties of poly [(N-vinylamide)-co-(vinyl acetate)]s and their hydrogels

Free radical copolymerization of water-soluble N-vinylamides such as N-vinylacetamide (NVA) and N-vinylformamide (NVF) with hydrophobic vinyl acetate (VAc) gave amphiphilic copolymers. The monomer reactivity ratios were determined as r(1) = 5.8 and r(2) = 0.68 (M-1 = NVA, M-2 = VAc) and r(1) = 6.2 and r(2) = 0.37 (M-1 = NVF, M-2 = VAc), respectively. The growing radical of the terminals of N-vinylamides propagates more favorably for N-vinylamide monomers than for VAc monomer, resulting in the possible formation of blocky copolymers. It is found that aqueous solutions of these amphiphilic copolymers exhibited a lower critical solution temperature (LCST), depending on their chemical composition, followed by coacervate formation above the LCST. Furthermore, thermosensitive hydrogels could be prepared by the free radical copolymerization of N-vinylamide and VAc in the presence of the crosslinker butylenebis(N-vinylacetamide) (Bis-NVA). The swelling ratios of these hydrogels decreased with an immediate increase in temperature from 20 to 80 degreesC, and then reversibly increased with decreasing temperature. These hydrogels showed the same thermosensitive properties as linear copolymers of NVF and VAc.