Fluorine‐containing polymers. V. Light scattering and viscosity study of poly‐1,1‐dihydroperfluorobutyl acrylate

Light scattering measurements in benzotrifluoride indicate that poly‐1,1‐dihydroperfluorobutyl acrylate (poly‐FBA) has been polymerized in emulsion and solution to molecular weights up to 40 million. If the polymerization is carried to high conversion, long chain branching results, presumably by chain transfer to the polymer. Intrinsic viscosities near 1.0 in benzotrifluoride for molecular weights of 10 million are explained largely on the basis of the high monomer molecular weight using Flory's equation relating molecular weight, intrinsic viscosity, and molecular dimensions. From the equation the intrinsic viscosity of a polymer should be expected to decrease roughly as the 3/2 power of the monomer molecular weight, if the increased bulk does not alter the chain flexibility. Long chain branching and the fact that benzotrifluoride is a poor solvent exaggerate the effect. Light scattering and intrinsic viscosity data indicate that the θ temperature for benzotrifluoride (that temperature at which solvent polymer interactions vanish) is only a few degrees below room temperature. Precipitation of poly‐FBA from dilute solutions near 15°C. confirms this fact. Methyl perfluorobutyrate is found to be a better solvent, but the value of the second virial coefficient and the exponent in the equation relating intrinsic viscosity to molecular weight are lower than predicted from swelling data. The freely jointed segment length has been calculated to be 15 carbon atoms, which is larger than reported for other rubbery materials. Short range interactions of the large side chains apparently result in a fair degree of chain stiffness which may be related to the high transition temperature of poly‐FBA relative to its hydrocarbon analog.