Molecular weight control for alfin catalyzed 1,3-diene polymers by 1,4-diene straight chain or cyclic hydrocarbons (and their derivatives) has been demonstrated. The microstructure of these moderated polymers is identical to the polymers obtained without molecular weight control. From the wide series of copolymers preparable with this improved polymerization method four were chosen for their evaluation after laboratory testing for processability, physicals, and economics. Copolymers of butadiene—isoprene (90/10 and 97/3) and butadiene—styrene (85/15 and 95/5) virgin or oil extended have been shown to be economically attractive and to give superior wear, traction, and adequate heat build up.
Control of molecular weight of alfin catalyzed diene polymers has been demonstrated for polymers of butadiene, isoprene, styrene, piperylene and combinations of these. The 1,4-dihydro derivatives of benzene and naphthalene are effective molecular weight moderators. The known microstructure of alfin polymers remains unchanged with the use of these agents. Molecular weight controlled alfin gums process readily on standard rubber machinery. Oil extenders or softeners, although not necessary, are easily incorporated. The feasibility of continuous processing has been demonstrated for the production of catalyst, moderators and polymers on pilot plant scale. A wide series of polymers and copolymers at predetermined molecular weights and compositions have been produced in the same pilot plant. Alfin polybutadiene with limited amounts of styrene is essentially a solution type SBR. Alfin copolymers with styrene and/or isoprene have undergone preliminary road tests in tires. Wear and heat build-up data indicate performance to be intermediate between SBR and polybutadiene.
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