Poly(trimethylene terephthalate) − solid state polycondensation and the formation of monodisperse Extended-Ring crystals

• The course of solid-state polymerization was monitored using MALDI-TOF mass spectrometry, GPC, DSC, SAXS, and WAXS. • Even-numbered cycles are preferentially formed as the thermodynamically most stable reaction products. • The cycles form monodisperse, extended-ring crystallites, and the molecular weight distribution depends on the reaction conditions. • The size of the cycles was found to be determined by the thickness of the crystallites. Linear, low-molar-mass poly(trimethylene terephthalate) (PTT) was synthesized via the polycondensation of 1,3-propanediol and dimethyl terephthalate and investigated by matrix-assisted laser desorption/ionization time of flight (MALDI TOF) mass spectrometry, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and x-ray scattering. The obtained PTT was used in crystalline plaque or powder form for studies of its solid-state polycondensation (SSP). The combination of powder and vacuum increased the number-average molecular weight (M n ) by a factor of three. Interestingly, even-numbered cycles with degrees of polymerization (DPs) between six and 16 were preferentially formed. Annealing after doping with tin catalysts produced three cyclic main reaction products (C10, C12 and C14), which suggest that thermodynamic control of transesterification processes favors the formation of three types of monodisperse extended-ring crystallites (ERC) with thicknesses of 5, 6 of 7 repeat units. Additionally, a predominantly cyclic PTT was prepared, once again demonstrating the formation of even-numbered ERC upon annealing. Crystallinities calculated from WAXS measurements showed satisfactory agreement with those determined by DSC. SAXS measurements confirmed that the crystal thickness defined by ERC is also valid for long chains and large cycles that crystallize with chain folding.