Correlation of swelling and crosslinking density with the composition of the reacting mixture employed in radical crosslinking copolymerization

This article reports the scaling laws relating the synthesis conditions with the crosslinking density (ν e ) and swelling degree ( S ) of poly( N ‐vinylimidazole) hydrogels (PVI) prepared by radical crosslinking copolymerization in aqueous solution, with N,N ′‐methylene bisacrylamide (BA) as crosslinker. Multiple linear regression of ν e versus BA concentration ([BA]) and total comonomers concentration ( C T ) in double log scale render the scaling law ν e ∼ C   T 0.81× [BA] 1.04 as comparable to that predicted by the model of polymer network with pendant vinyl groups (ν e ∼ C T × [BA]), and showing inverse dependence on C T to that expected, following from stoichiometry, for an ideal network (ν e ∼ 2[BA]/ C T ). S scales with ν e through a solvent‐dependent exponent ranging from −0.46 to −0.54, only slightly over the value predicted by the Flory–Rehner theory (−0.6) or the blob's model by de Gennes (−0.5 to −0.8). Finally, the scaling law of S with the composition of the reacting mixture is also solvent‐dependent and it seems to result not only from the dependence of ν e on C T and [BA] but also from that of v 2r , the polymer volume fraction in the reference state, and χ, the polymer–solvent interaction parameter. Models used seem to overestimate the contribution of entanglements to the effective crosslinking density of PVI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 263–269, 2007