Differential scanning calorimetry (DSC) and NMR analysis of the isolated polymer were consistent with a statistical copolymer in all cases, and inconsistent with a block copolymer or a mixture of homopolymers (Figure .18). DSC analysis of the l-lactide/e-caprolactone from Table , entry 3 resulted in a single glass transition at -8.5°C very close to the theoretical value (-8.1°C) predicted by the Fox equation, as has been reported for statistical l-lactide/e-caprolactone copolymers. To quantify sequence selectivity, we calculated the R-value following the statistical model outlined by Kasperczyk and the 1 H NMR assay used by Bonnet and Visseaux (Section S7.6). As defined, the R-value would be 0 for a block copolymer, 1 for a statistical copolymer, and 2 for a precisely alternating copolymer with a 1:1 lactyl to caprolactyl unit ratio (1:2 lactide to e-caprolactone ratio). Our dizinc catalysts all gave R-values greater than 1, consistent with a predominantly alternating copolymer, with PD 4- tBu Zn2I3 (1) giving the highest R-value (1.36, entry 3). For accuracy and for a fair comparison to literature values, we also evaluated the R-value by quantitative C NMR for this sample. We obtained an R-value of 1.35 by quantitative C NMR, compared with a theoretical maximum of 1.5 at this e-caprolactone loading. This alternating selectivity exceeds that reported by any main group catalyst for this reaction, and we compare those values in Section S7.11. By contrast, the monometallic P 4-tBu HZnI2 (11) and ZnI2 gave significantly lower R-values of 1.24 and 1.08 respectively (entries 9 and 10).