Reaction kinetics of the incorporation of 2,2-bis [4-(2-hydroxyethoxy)phenyl]propane in poly(butylene terephthalate) via solid-state polymerization

The kinetics of the incorporation of an aromatic diol in poly(butylene terephthalate) (PBT) via solid-state polymerization (SSP) was studied. The selected diol was 2,2-bis[4-(2-hydroxyethoxy)phenyl]-propane (Dianol 220). Mixtures consisting of 85 mol % PBT and 15 mol % Dianol were isothermally polymerized in the solid-state at 180 degrees C while the polymerization time was varied. Combining HPLC and H-1 NMR spectroscopy results showed that Dianol monomer reacts with PBT via two consecutive first-order reactions, the Dianol monoester being an intermediate and fully incorporated Dianol as the final product. The two corresponding reaction rate constants were determined by fitting the first-order equations with experimental data, revealing that free Dianol monomer is more reactive toward transesterification with PBT than its monoester. Dianol was fully incorporated in PBT after a reaction time of 4 h. This result was confirmed by C-13 NMR sequence distribution analysis. SEC measurements showed that the molecular weight and polydispersity first decrease during the SSP reaction due to chain scission of PBT. The subsequent recombination of polymer chains after complete incorporation of all Dianol monomer leads to a buildup of the molecular weight resulting in high molecular weight copolymers.