MOLECULAR-WEIGHT DEPENDENCE OF DIBLOCK COPOLYMER SEGREGATION AT A POLYMER-POLYMER INTERFACE

Utilizing forward recoil spectrometry (FRES), we have determined the s egregation isotherm which describes the interfacial excess z(i) of di block copolymers of poly(d8-styrene-b-2-vinylpyridine) (dPS-PVP) at th e interface between the homopolymers PS and PVP as a function of phi(i nfinity) the volume fraction of diblock copolymer remaining in the hos t homopolymer. All the samples were analyzed after annealing at temper atures and times sufficient to achieve equilibrium segregation. The ef fect of the degree of polymerization of both the diblock copolymers an d the host homopolymers on the segregation isotherm is investigated. W hen the degree of polymerization of the homopolymer is much larger tha n that of the diblock copolymer, the normalized interfacial excess (z( i)/R(g)), where R(g) is the radius of gyration of an isolated block c opolymer chain, is a universal function of that portion of the block c opolymer chemical potential due to chain stretching. The existence of such a universal function is predicted by theory and its form is in go od agreement with self-consistent mean field calculations. Using these results, one can predict important aspects of the block copolymer seg regation (e.g., the saturation interfacial excess) without recourse to the time-consuming numerical calculations. (C) 1994 John Wiley & Sons , Inc.