Studies on dilute solutions of rodlike macroions. I. Light scattering, densitometry, and cryoscopy

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Abstract
Total integrated and photon correlation light scattering have been used to study two samples of poly(1,4‐phenylene‐2,6‐benzobisthiazole) (PBT) representing two methods of precipitation to recover the polymer from the polymerization solvent. Some details of the light‐scattering instrument are given. It is found that the PBT sample is rodlike, with persistence length of at least 50 nm, but that the postpolymerization processing method influences the state of interchain aggregation. The data are augmented by measurements of freezing‐point depression to estimate the degree of protonation of PBT in sulfuric acid, and by measurements of partial specific volume to provide an estimate for the geometric diameter of the chain in solution. The results show a degree of protonation of 2–4 protons per repeating unit, and partial specific volumes that are appreciably smaller than the specific volume determined for the polymers. Similar data and results are reported for poly(1,4‐phenyl‐ene‐2,6‐benzobisoxazole) and poly(1,4‐phenylene terephthalamide).