Polymer of formula (1) bearing an alkoxysilane end group: in which: is a double or single bond; each of R1, R2, R3, R4, R5 and R6 is H, a halo, an alkoxycarbonyl or an alkyl, m and p are each from 0 to 5, each of R and R′ is an alkyl, Z is an alkylene, optionally interrupted with COO, q is 0 or 1, r is 0, 1 or 2, and n is such that the number-average molar mass of the polymer (1) is from 400 to 50 000 g/mol, and the polydispersity index of the polymer (1) is from 1.0 to 2.0. Preparation by ring-opening metathesis polymerization.Use as an adhesion promoter or a reactive plasticizer.