Phase transition in swollen gels XXVIII. Swelling and mechanical behavior of poly(1-vinyl-2-pyrrolidone-co-N-vinylcaprolactam) gels in water/acetone mixtures

Networks of statistical copolymers of 1-vinyl-2-pyrrolidone and N-vinylcapr olactam (molar ratios of VP/VCL=1/0, 0.8/0.2, 0.6/0.4, and 0.5/0.5) with io nic comonomer, N,N-dimethyl-N,N-diallylammonium chloride (mole fractions x( s)=0, 0.03, and 0.05) and crosslinker, 1-1 ' -divinyl-3,3 '-(ethane-1,l-diy l)di( 1-vinyl-2-pyrrolidone), were prepared by radiation polymerization in a water/ethanol mixture (H2O/EtOH = 0.5/0.5 by vol.). Swelling and mechanic al behavior was investigated in water/acetone (w/a) mixtures. For charged c opolymers, a first-order phase transition (collapse) was found. The extent of collapse (stepwise change in the gel volume), Delta, and critical aceton e concentration in the mixture at collapse, alpha (c), slightly increase wi th content of VCL and ammonium salt in gels. Shin of transition to higher a lpha (c) is caused by increasing hydrophobicity of network chains with VCL content. Decrease in swelling with increasing acetone concentration in w/a mixtures is accompanied by increase in equilibrium modulus, so that mechani cal behavior is predominantly determined by swelling. The theory of swellin g equilibria of polyelectrolyte networks, in which the effects of electrost atic interactions of the charges on the chain and finite chain extensibilit y are included, semiquantitatively describes the swelling data provided an effective concentration of charges (lower than x(s)) was introduced.