Synthesis and properties of eighteen‐arm polybutadienes

A series of eighteen‐arm regular star polybutadienes with molecular weights between 9.9 × 104 and 1.9 × 106 were prepared and characterized. Evidence is presented for the expanded configuration of the large eighteen‐arm stars in a θ solvent. The intrinsic viscosities of the eighteen‐arm stars gave g′ = [η]/[η]l = 0.284 in dioxane at 27°C (θ solvent) and 0.225 in toluene at 35°C (good solvent). The linear viscoelastic properties of the melts were also determined. The plateau modulus, GN°, is the same as for linear polybutadiene. The zero‐shear viscosities (η0) and the longest relaxation times (Tmax) increase exponentially with the arm molecular weight Ma and are identical to those of four‐arm polybutadienes with the same Ma. The zero‐shear recoverable compliance (Je°) increases linearly with molecular weight. v′ in Je°GN° = v′Na, where Na is the number of entanglements per arm, is 0.95 slightly larger than 0.66 for four‐arm polybutadienes. Similarly, g2 is higher than calculated from the Rouse–Ham theory.