The proton signals at 2.6-3.0 ppm are assigned to the methylene groups adjacent to the disulfide and ester-carbonyl in 1 H NMR and can be used as a first proof of the integration of DTDPA in the polymer structure. The decrease in the intensity of the ester-carbonyl stretches when decreasing the amount of initiator in the feed enforces the participation of DTDPA in the polymerization (Figure ). In FTIR, the absorbance of the ester-carbonyl stretch was present at 1729.6 cm -1 (Figure ). By comparison, the value for the carboxylic acid-carbonyl stretch of DTDPA was 1630.2 cm -1 (Figure ). Figure also shows the inverse-gated 13 C NMR spectrum of the resulting polymer. We identified the different structural units and calculated their relative abundance as well the degree of branching of AB2 type monomers (Table ), as reported by Hölter and Frey. The molecular weight of the resulting polymers is also reported in Table , as calculated from 1 H NMR (Equation S1). For chain growth polymerizations, including cationic polymerization, the degree of polymerization can be related to the kinetic chain length, which is the result of the number of consumed monomers per initiated chain. Therefore, increasing the initiator concentration will lead to a decrease in the degree of polymerization, and hence a decrease of the average molecular weight of the polymer. hPG5-DTDPA, with its 5:1 ratio of monomer to initiator, has a lower molecular weight than hPG20-DTDPA with its 20:1 ratio. On the other hand, the degree of branching is inversely proportional to the ratio of DTDPA present in the feed. This may be related to the availability of many glycidol monomers that can be activated in the presence of a larger amount of DTDPA -and therefore the increased possibility of reaction between the secondary hydroxyl groups and other monomers.