AbstractCrosslinked xerogels in the form of rods have been prepared to>99.9 conversion by the γ‐ray initiated copolymerization in vacuo obn‐butyl acrylate (BA) withN‐vinyl‐2‐pyrrolidone (VP) in the presence and absence of a crosslinking agent. Thin (about 0.5 mm) disks were swollen in water at 21°C, the final equilibrium swelling being the true water content only for copolymers of high BA content. At low‐medium BA content, swelling was accompanied by the release of a small water‐soluble fraction, leading to a slightly reduced apparent value for the water content. True water contents could be obtained more rapidly by prior Soxhlet extraction with boiling water. For xerogels containing>about 75 VP by weight, the resultant hydrogels had water contents>about 80. The influences of dose, dose rate copolymer composition, and concentration of crosslinker on the water content, sol fraction, and extension ratio were investigated. A high level of reproducibility in properties of the hydrogels was obtained by numerous replicate experiments. The feasibility of scaling up the preparation to produce long (60 cm) xerogel rods of uniform properties has been demonstrated. For these copolymers, swelling in several common organic solvents generally exceed
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