Molded cellular crosslinked vinyl lactam polymer gel and method of preparation

Claim 1

The process of producing the foamed cellular 0.1 to 10% crosslinked lactam polymer in a rigid, molded form which comprises (1) forming a uniform liquid mixture of (a) between about 10 and about 30 wt. % of a polymerizable reactant containing at least 55% N-vinyl lactam monomer; (b) between about 0.01 and about 10.0 wt. % crosslinking agent; (c) between about 60 and about 90 wt. % solvent and (d) between about 0.1 and about 5 wt. % of a free radical initiator having a decomposition temperature below the boiling point of said solvent; (2) introducing said mixture into a dish or mold; (3) in the absence of agitation and in an inert atmosphere, heating the mixture to between about 50° and about 80° C. for a period of from about 2 to about 5 hours to begin polymerization without displacement of the solvent medium, and then raising the temperature to between about 100° and about 145° C. for an additional period of from about 0.5 to about 3 hours or until a constant viscosity is reached to complete the crosslinking of the polymer; (4) recovering the crosslinked polymer in the form of a shaped rubbery intermediate and digesting said intermediate in water to swell the polymer and to extract and remove soluble monomer, linear polymer and other residuals in the aqueous phase; (5) recovering a clear, formed, crosslinked vinyl lactan polymer hydrogel from water and (6) freeze drying said hydrogel for a period of from about 2 to about 70 hours at a critical temperature of between -85° C. and -40° C. to produce a white, cellular foamed product of crosslinked N-vinyl lactam polymer.