J. T. Gruver

Molecular Weight Effects in Adsorption of Rubbers on Carbon Black

Abstract The molecular weight dependence of the adsorption of polybutadiene on carbon black from a poor solvent, n-heptane, and bulk, i.e., the phenomenon of “bound rubber”, was investigated. For narrow distribution polymers the adsorption is proportional to Mn, where n = 0.14 for adsorption from n-heptane solution; n = 0.5 for adsorption from bulk. Anomalously low solution adsorption was observed for polymers of very high molecular weight (> 500,000). This is ascribed to a sieve effect by aggregates of carbon black particles which cannot be penetrated by the large molecular coils. In high structure blacks, which pack more loosely, and in large particle blacks, which form larger interstices between particles, onset of anomalous adsorption is shifted toward higher molecular weights.

Melt Viscosity of Random Copolymers of Butadiene and Styrene Prepared by Anionic Polymerization

The melt viscosity of narrow distribution, linear, random copolymers of butadiene (75%) and styrene (25%) prepared by anionic polymerization was investigated in both the Newtonian and non‐Newtonian regimes of flow. The Newtonian viscosity is shown to obey the usual 3.4th power dependence on Mw The temperature dependence is represented satisfactorily by the Vogel equation, as modified by Berry and Fox. Non‐Newtonian viscosities are reduced to a single master curve for all polymers, temperatures, and shear rates, using the Newtonian viscosity as the sole shift factor (η/η0 vs. η0γ). Comparison of this master curve with those of two narrow distribution polybutadienes of different microstructure produces agreement within 0.2 of a logarithmic unit on the η0γ‐scale. All three master curves lie one to two decades toward higher reduced shear rates than various “universal” curves reported in the literature for polymers of broader molecular weight distribution.

The Viscosity of Carboxy-Terminated Polybutadienes

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. Theor...

THE EFFECT OF CARBON BLACKS ON THE FREE RADICAL THERMAL POLYMERIZATION OF STYRENE

Carbon blacks inhibit the free radical thermal polymerization of styrene. On completion of an induction period the same carbons accelerate the polymerization. There is strong evidence that the inhibition reaction is due to surface quinone groups. No entirely satisfactory mechanism has been found for the accelerating action. Calcination or graphitization destroy both initiator and inhibitor activity, but catalytic reduction at room temperature only eliminates the inhibiting effect, presumably by reducing the quinones to hydroquinones which are not inhibitors per se.