. . . . . "divalent hydrocarbon groups of 1 to 20 carbon atoms, for example, alkylene groups such as methylene, dimethylmethylene, 1,2-ethylene, dimethyl-1,2-ethylene, 1,3-trimethylene, 1,4-tetramethylene, 1,2-cyclohexylene and 1,4-cyclohexylen, and arylalkylene groups such as diphenylmethylene and diphenyl-1,2-ethylene;" .