Light‐scattering characterization of poly(ethylene terephthalate)

By 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 R g , the weight‐average molecular weight M w , and the second virial coefficient A 2 and such dynamic properties as the translational diffusion coefficient D , or its equivalent hydrodynamic radius R h , and the second (diffusion) virial coefficient k d were determined for several PET samples of different molecular weights by using light‐scattering intensity and linewidth measurements. An empirical relation between D o (or R h ) and M w was established: R h = (1.77±0.15)X10 −2 M with R h and M w expressed in units of nanometers and grams per mole, respectively. The empirical exponent α D (ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent α η (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.