Synthesis, characterization and self-assembly of linear and miktoarm star copolymers of exclusively immiscible polydienes

Linear and non-linear copolymers of the PB-b-PI sequence [PB: polybutadiene of high 1,4-microstructure (∼92%) and PI: polyisoprene of high 3,4-microstructure (∼55–60%)] and their corresponding miktoarm star copolymers of the PB(PI3,4)2 and PB(PI3,4)3 type were synthesized by combining anionic polymerization and selective chlorosilane chemistry. Molecular characteristics, thermal properties and structure/properties relationship are reported for the specific copolymers and especially the self-assembly is of major importance and interest due to the nature of the blocks. The identical electron densities between the two polydienes led to impossible morphological characterization through small angle X-ray scattering (SAXS) and only transmission electron microscopy results verify the adopted morphology for each copolymer, justifying the assumption that the segment–segment interaction parameter between the two polydienes of high 1,4-microstructure (∼92%) for the PB and ∼55–60% 3,4-microstructure for the PI is well above zero. The consistency of the bulk morphology results of this study compared with those of the extensively studied system of the PS(PI)n=1,2,3 type (PS: polystyrene), were unexpectedly coherent. High chain flexibility provided by the two polydiene segments, leads to promising properties unattainable from corresponding thermoplastic triblock copolymers of these polydienes with PS (PS-b-PI-b-PS, PS-b-PB-b-PS), especially for rheological studies.