Addition-fragmentation agents of the formula are disclosed:whereinRis hydrogen, a Cto Calkyl group,x is 1 or 2,Ris a di- or trivalent (hetero)hydrocarbyl linking group,-A*-X*- is a group formed between A and X, wherein Xcomprises an electrophilic or nucleophilic functional group and A is a functional group that is co-reactive with functional group X, andn is 0 or 1.