Copolymerizability of ${gamma}$-valerolactone (${gamma}$VL), a five-membered cyclic ester with other monomers, such as ethylene glycol (EG), L-lactide (LL), propylene oxide (PO) and $eta$-butyrolactone ($eta$BL) has been investigated. The copolymerization was carried out in bulk state in the presence of various ionic initiators. It was found that cationic initiators are effective, and BF$_3$Et$_2$O is the most effective. On the contrary, anionic initiators including coordinated anionic initiators, are generally inactive.