The invention provides solid supported anionic catalysts, suitable for gas phase anionic polymerization of conjugated diene monomers, that are useful for anionically producing very high molecular weight branched diene polymers, such as styrene butadiene rubber, polybutadiene rubber, polyisoprene rubber, and the like. The catalysts comprise a metalatable particle, such as a bound rubber, a thermoplastic polymer or a cured elastomer, that is multiply metalated with Group IA alkali metal atoms. The multi-branched diene polymers obtained by gas phase anionic polymerization employing the catalysts exhibit desirable properties, such as an extremely high molecular weight, a controlled molecular weight distribution, Tg and vinyl content, and the ability to readily absorb hydrocarbon solvents and oils. The polymers are easily compounded to form vulcanizable elastomeric compounds and articles, such as tires, that have excellent resistance to wear and tear and exhibit reduced hysteresis properties.