Abstract: A polymerizable material is formed by the reaction of: (A) acrylamide or methacrylamide; (B) from 1.5 to 2 moles, per mole of acrylamide or methacrylamide, of formaldehyde; and (C) an amount equivalent to the formaldehyde of a hydroxyl-group containing component comprising one or more hydroxyl or group-containing compounds containing from 1 to 4 primary or secondary hydroxyl groups per molecule, at least one of the hydroxyl groups-containing compounds being a monoacrylate or monomethacrylate of a diprimary, disecondary or primary-secondary diol, the said monoacrylate or monomethacrylate being used in an amount of from 0.1 to k mole, per mole of acrylamide or methacrylamide, when the average number of hydroxyl groups per molecule of the hydroxyl group-containing component is 1 and in an amount of from 0.