Light‐scattering characterization of poly(ethylene terephthalate)

Abstract

AbstractBy using a closed‐circuit filtration system, we have succeeded in clarifying poly(ethylene terephthalate) (PET) dissolved in hexafluoroisopropanol (HFIP). Such static properties as the radius of gyration Rg, the weight‐average molecular weight Mw, and the second virial coefficient A2 and such dynamic properties as the translational diffusion coefficient D, or its equivalent hydrodynamic radius Rh, and the second (diffusion) virial coefficient kd were determined for several PET samples of different molecular weights by using light‐scattering intensity and linewidth measurements. An empirical relation between Do (or Rh) and Mw was established: Rh = (1.77±0.15)X10−2 M with Rh and Mw expressed in units of nanometers and grams per mole, respectively. The empirical exponent αD(ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent αη (ca. 0.71±0.02). Several intensity correlation functions were measured very precisely using long accumulation times. A Laplace inversion was performed using the singular‐value decomposition technique. The approximate molecular weight distribution (MWD) determined by light‐scattering spectroscopy was in reasonable agreement with a completely independent determination of MWD using gel permeation chromatography (GPC). It was interesting to note, though not surprising, that GPC showed emphasis on lower‐molecular‐weight fractions, while light‐scattering emphasized higher‐molecular‐weight fractions. The agreement further strengthens some complementary aspects of the two techniques.