Benzil-di-(.beta.-succinimidoethyl)ketal of the following structural formula ##STR1## and novel benzil ketal derivatives thereof. The novel benzil ketal derivatives are characterized by having a structure in which a 5- or 6-membered cyclic imidecontaining group is bonded to each of the two oxygen atoms of ketal. Because these compounds have a high decomposition or sublimation temperature and the ability to initiate photopolymerization, they are useful as photopolymerization initiators in the production of photopolymerizable shaped articles from a molten blend of a photopolymerizable thermoplastic polymer composition.