Examples of the preferred aliphatic acrylates are the alkyl esters of acrylic or methacrylic acid in which the alkyl group contains from 2 to 8 carbon atoms such as n-butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, n-propyl acrylate, n-pentyl acrylate, n-hexyl acrylate, octyl acrylate and the like.