Synthesis and solution properties of linear, four‐branched, and six‐branched star polyisoprenes

A number of linear, four‐ and six‐branched regular star polyisoprenes were synthesized by anionic polymerization techniques in benzene using lithium as the counterion and polyfunctional silicon chloride compounds as the coupling agents. Light‐scattering measurements in dioxane were performed in order to establish Θ solvent conditions. Determinations of the radius of gyration of the polymers of different structure indicate that g = 〈 S 2 〉 0,br /〈 S 2 〉 0,lin agree closely with random flight calculations for the ratios. Intrinsic viscosities determined in a Θ solvent establish g ′ = [η] br /[η] lin to be 0.77 3 and 0.62 5 for the four‐ and six‐branched polyisoprenes, respectively. In a good solvent g ′ values are slightly lower. These values are compared with theoretical estimates. Viscosities of 19.29% (w/w) solutions of the polyisoprenes in n ‐decane at 25°C are correlated with the intrinsic viscosities of the polymers under Θ conditions.