Polymers and oligomers of formula (I), based on unsatd. 2-10C hydrocarbons and with one or two 2-oxazolinyl terminal gps., in which A = polymer or oligomer residue derived from the unsatd. hydrocarbon (A'), and R = H, 1-10C alkyl, 6-10C aryl or 3-6C cycloalkyl. Also claimed are (i) comb polymers (II) obtd. by cationic ring-opening homo- or co-polymerisation of (I); (ii) comb polymers (III) obtd. by reacting (I) with base polymers contg. reactive gps.; (iii) thermoplastic moulding materials or thermosets contg. (I), (II) or (III) or mixts. thereof; (iv) a process for the prodn. of (I) by polymerisation or oligomerisation of (A'), modification with one or two terminal ester gps., and Lewis acid-catalysed ring closure with 2-amino-1- alcohols; (v) processes for the prodn. of (II) and (III) under the above conditions; (vi) films, fibres and mouldings obtd. from the materials claimed in (iii).