The Viscosity of Carboxy-Terminated Polybutadienes

Abstract

Abstract Newtonian viscosities have been determined for carboxy-terminated polybutadienes varying in microstructure, molecular weight and degree of carboxy-functionality. The latter was varied by total or partial methylation of initially di- or mono-functional polymers. The viscosity of non-functional (methylated) polybutadienes is shown to be proportional to the 3.4 power of the weight average chain length, irrespective of microstructure, provided the comparison is made at equal (T−Tg). The temperature dependence of viscosity is well represented by the Vogel equation, with constants given by Berry and Fox for polybutadiene of 8% vinyl unsaturation, again independent of microstructure. The presence of carboxy end groups increases the viscosity as a result of an association equilibrium with raises the effective molecular weight of the polymer. The absolute magnitude of the temperature coefficient of viscosity increases with carboxy-functionality, as required by the postulated association equilibrium. Theoretical calculations show that the viscosities of mono-carboxy polybutadiene and α,ω-dicarboxypolybutadiene cannot be reconciled unless some of the carboxy-associations in the latter are intramolecular. In the molecular weight range considered the glass temperature is substantially independent of carboxy-functionality.