A series of epoxy-functional telechelic oligomers containing oxetane end groups have been synthesized. The precursor monomer, extracted from outer Birch bark, was first polymerized through enzyme-catalyzed esterification to form oligomers having epoxy and/or oxetane groups in the structures. The oligoesters were subsequently crosslinked through cationic polymerization either by epoxy or oxetane homopolymerization or copolymerization when both functionalities were present. A study of the polymerizations of the resins was performed "in situ" using real-time Fourier transform infrared spectroscopy revealing a preferred copolymerization when compared with the homopolymerization. By tailoring the different structures, it was possible to control the final mechanical properties of the networks. (C) 2015 Wiley Periodicals, Inc.