Abstract: The properties of water soluble or, especially water swellable polymer particles are improved by surface cross linking that is caused by providing a dispersion of gel polymer particles in an organic solvent, reacting the surfaces of these particles with dissolved cross linking agent and azeotropically distilling the dispersion.

Abstract: An exothermic gel polymerization process conducted in the presence of water is initiated at a low temperature, is held for most of the process at a higher temperature by including in the medium a particulate heat sink material, such as sodium sulphate decahydrate, that is substantially insoluble in the medium and which undergoes an endothermic phase change and is then allowed to rise to a higher temperature. Either as a result of the endothermic change, or as a result of a subsequent exothermic change, at the end of the process the heat sink material is again solid particulate material substantially insoluble in the medium and so the product is a dispersion of the material in a polymer gel. The polymer is water soluble.

Abstract: An incompletely miscible liquid mixture, e.g. a suspension polymerization mixture, is mixed by flowing through a rotating substantially horizontal tube that is incompletely filled with the mixture, so as to form pairs of vortices each with its axis transverse to the axis of the tube. The apparatus comprises the tube, that must be free of internal means for agitating the liquid within the tube, means for rotating the tube and means for feeding the liquid mixture to and through the tube.

Abstract: A compound of the formulaCH.sub.2 .dbd.CRCONHXNHCOCH.sub.2 CH.sub.2 SO.sub.3 Mwhere R is hydrogen or methyl, X is CH.sub.2 or --CH.sub.2 OCH.sub.2 -- and M is H or a water soluble cation is made by reacting N-methylolacrylamide or N-methylolmethacrylamide with sulphonated N-methylolacrylamide.