Herstellung,charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren

An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 10⁵ < M < 3 · 10⁶), poly(α-methylstyrene)s (7 · 10⁴ < M < 4 · 10⁶), and block copolymers (2 · 10⁵ < M < 2,5 · 10⁶). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = M_w/M_n–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the two segment types yield light scattering measurements which give molecular weights M_w, radii of gyration 〈r²〉^1/2 and second virial coefficients A₂ with almost the same accuracy as in the case of homopolymers. The radii of gyration and the intrinsic viscosities of the block copolymers give no evidence for any “intramolecular phase separation” in the good solvent toluene. The coil conformation corresponds closely to that of the homopolymers.