Disclosed is a compound of the formula ##STR00001## wherein R.sub.1 and R.sub.1' each, independently of the other, is an alkyl group having at least one ethylenic unsaturation, an arylalkyl group having at least one ethylenic unsaturation, or an alkylaryl group having at least one ethylene unsaturation, R.sub.2, R.sub.2', and R.sub.3 each, independently of the others, are alkylene groups, arylene groups, arylalkylene groups, or alkylarylene groups, and n is an integer representing the number of repeat amide units and is at least 1.