Block copolymers of n‐propyl p‐styrene sulfonate with isoprene and styrene: Synthesis, characterization, and phase separation behavior

Abstract A series of ABA block copolymers based on n ‐propyl p ‐styrene sulfonate (A block) and isoprene or styrene (B block) were synthesized and characterized. The synthesis was based on methods developed previously for the anionic polymerization of n ‐propyl p ‐styrene sulfonate [S. J. Whicher and J. L. Brash, J. Polym. Sci., Polym. Chem. Ed. , 19 , 1995 (1981)], and consisted of forming a polyisopryl dianion by initiation with sodium naphthalene in THF at 0°C. n ‐Propyl p ‐styrene sulfonate was then added and propagated at −94°C. As was the case for n ‐propyl p ‐styrene sulfonate alone, it was found that only limited chain growth of this monomer initiated by living polyisoprene was possible, resulting in maximum A block molecular weights of about 10,000. The phase separation behavior of copolymers having a range of composition, as well as that of a blend of polyisoprene and poly( n ‐propyl p ‐styrene sulfonate) was investigated by examining thin films in the electron microscope. In the copolymers, phase separation was observed with transmission EM when THF was used as the solvent for film casting. Domain morphology was as expected for the various copolymer compositions. When films were cast from chloroform, phase separation was minimal, although it could be improved by annealing. Annealing produced relatively diffuse intermixed domains which occasionally formed unusual triangular patterns. Phase separation of the blend of homopolymers gave domains that were large enough to be mapped with SEM using both secondary electron and EDXA detectors.