NEW MATERIAL: Compounds of formula I (wherein X is an acid residue after dissolication of a proton of a strong mono- or polybasic acid or hydroxy; Y is an n-functional hydrocarbon interrupted as required by O, S, Si, ester, urea or the like and; 1R is H or hydrocarbon, 2R is a group of an alkylating agent or arylating agent; and (n) is 1-6).

USE: Useful for the production of plastics by an isocyanate plyaddition method, especially polyurethane plastics.

PROCESS: An oxetane-terminal compound of formula II (Z is n-functional hydrocarbon interrupted as required by O, S, Si, ester, N-1-substituted urethane or the like), after being reacted with an alkylating gent or an arylating agent in the presence of metal hydroxide, is reacted with a strong acid to obtain a compound of formula I.