Next, we compared the homopolymerization reactivity of PD 4-tBu Zn2I3 (1) toward lactones and glycolide under the conditions optimal for lactide polymerization (Section S7.3). Of these monomers only e-caprolactone gave a homopolymer under these conditions, but with lower activity and molecular weight control than lactide homopolymerization (Table .2, entry 1). We did not obtain a homopolymer from b-butyrolactone, g-butyrolactone, wpentadecalactone, d-valerolactone, or glycolide (entries 2-6).