Influence of temperature and composition on the small-angle neutron scattering from polydiene star diblock copolymers and mixtures with homopolymers

The small-angle scattering from star diblock copolymers (SDCs) has been cal culated using the incompressible random phase approximation (RPA) and metho dologies recently developed. The influence of the interaction parameter and incorporation of homopolymer has been explored theoretically for SDCs of d euteriopolybutadiene and polymethylpentadiene with four arms. For the copol ymer where the polybutadiene was the outer block of the arm, the scattering over a temperature range from 298 to 418 K has been explored. Fits to the data have been obtained using the random phase expressions providing values of the interaction parameter and radius of gyration of the inner block. Th e dimensions of the inner block are unaltered from the unperturbed dimensio ns of the linear polymer of the same degree of polymerisation. The temperat ure variation of scattered intensity suggests a spinodal temperature for mi crophase separation of 196 K. Although the scattering of the mixtures of th e SDC with either of the homopolymer exhibited features predicted by the ra ndom phase approximation theory, data could only be fitted by using unreali stic values of intermolecular and intramolecular interaction parameters or using radius of gyration values of the homopolymer that indicated phase sep aration between SDC and homopolymer. SDC data provide support for phase sep aration being the pertinent explanation for these phenomena. (C) 1999 Elsev ier Science Ltd, All rights reserved.