Limonene 1,2-oxide (LMO) and a-pinene oxide (a-PO) are two high reactivity biorenewable monomers that undergo facile photoinitiated cationic ring-opening polymerizations using both diaryliodonium salt and triarylsufonium salt photoinitiators. Comparative studies showed that a-PO is more reactive than LMO, and this is because it undergoes a simultaneous double ring-opening reaction involving both the epoxide group and the cyclobutane ring. It was also observed that a-PO also undergoes more undesirable side reactions than LMO. The greatest utility of these two monomers is projected to be as reactive diluents in crosslinking photocopolymerizations with multifunctional epoxide and oxetane monomers. Prototype copolymerization studies with several difunctional monomers showed that LMO and a-PO were effective in increasing the reaction rates and shortening the induction periods of photopolymerizations of these monomers. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013