It has been found that the above objects are attained by using the compounds as described below. ##STR2## wherein R1 is hydrogen or an acyl group; R2 is an alkylene group, an oxyalkylene group; R3 is a vinylene, butadienylene, or vinylene group substituted by groups containing 6 or less carbon atoms; Ar is a divalent aromatic arylene group; X is halogen or OR4 ; and R4 is hydrogen, a metal atom or