Single-chain scattering in heterogeneous block copolymers

• Published in: Polymer (Guilford) 1983-05, Vol.24 (5), p.519-524
• Main Authors: Bates, F.S., Berney, C.V., Cohen, R.E., Wignall, G.D.
• Format: Article
• Language: English
• Subjects: chain conformation; deuterated polymer chains; heterogeneous block copolymers; polybutadiene; Small-angle scattering
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/0032-3861(83)90097-6

Diblock copolymers consisting of polystyrene (S) attached to a polybutadiene (B) block (which is either hydrogenous or perdeuterated) have been synthesized and blended in such a way that the microphase-separated S and B domains have equal scattering-length densities, thus eliminating the component of small-angle neutron scattering (SANS) due to the domain structure. Two samples were studied: one with small spherical polybutadiene microdomains whose size was in essential agreement with calculations assuming equilibrium, and a second one of larger molecular weight in which the sphere size, while larger, was considerably smaller than predicted from equilibrium theory. The SANS spectra of these samples were analysed to give the radii of gyration R g and molecular weights M w of the labelled polybutadiene blocks from plots of I −1 versus Q 2 and least-square fits to the single-chain scattering function proposed by Debye. Results for the first sample agreed with the molecular weight obtained from chromatography and u.v. absorption and with the R g found in bulk polybutadiene of similar M w . The SANS estimates of both M w and R g for the second sample were anomallously large; these deviations may be due to (a) non-Gaussian conformations of the polybutadiene chains imposed by the nonequilibrium state of the microdomain, or (b) clustering of the deuterated polybutadiene chains within the microdomain due to small isotopic differences in chemical potential, enhanced by the larger M w . Observations on other systems suggest that the second effect is the dominant one.