Micellization Behaviour of Linear and Nonlinear Block Copolymers Based on Poly(n-hexyl isocyanate) in Selective Solvents.

Block copolymers have attracted significant scientific and economic interest over the last decades due to their ability to self-assemble into ordered structures both in bulk and in selective solvents. In this work, the self-assembly behaviour of both linear (diblocks, triblocks and pentablocks) and nonlinear (miktoarm stars and a block-graft) copolymers based on poly(n-hexyl isocyanate), PHIC, were studied in selective solvents such as n-heptane and n-dodecane. A variety of experimental techniques, namely static and dynamic light scattering, dilute solution viscometry and atomic force microscopy, were employed to study the micellar structural parameters (e.g., aggregation number, overall micellar size and shape, and core and shell dimensions). The effect of the macromolecular architecture, the molecular weight and the copolymer composition on the self-assembly behaviour was studied. Spherical micelles in equilibrium with clusters were obtained from the block copolymers. Thermally stable, uniform and spherical aggregates were found from the triblock copolymers. The poly(n-hexyl isocyanate)-b-polyisoprene-b-poly(n-hexyl isocyanate),-HIH copolymers tend to adopt closed loop conformation, leading to more elongated cylindrical-type structures upon increasing the concentration. Clustering effects were also reported in the case of the pentablock terpolymers. The topology of the blocks plays an important role, since the poly(n-hexyl isocyanate)-b-polystyrene-b-polyisoprene-b-polystyrene-b-poly(n-hexyl isocyanate), HSISH terpolymer shows intermicellar fusion of spherical micelles, leading to the formation of extended networks. The formation of spherical micelles in equilibrium with clusters was obvious in the case of the miktoarm stars, whereas the block-graft copolymer shows the existence of mainly unimolecular micelles.

Synthesis of Tri- and Multiblock Polymers with Asymmetric Poly(ethylene oxide) End Blocks.

We report the anionic synthesis of poly(ethylene oxide-b-isoprene-b-ethylene oxide) (OIO') triblock copolymers and poly(ethylene oxide-b-styrene-b-butadiene-b-ethylene oxide) (OSBO') tetrablock terpolymers with asymmetrically sized poly(ethylene oxide) (PEO) end blocks using triisopropylsilyloxy-1-propyllithium (TIPSOPrLi) as a protected initiator and diphenylmethyl potassium (DPMK) as the base activator for EO polymerization. All final products and precursors were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) techniques confirming monomodal and narrow molecular weight distributions and controlled molar masses. The growth of independently controlled PEO blocks was additionally demonstrated by the characterization of residual PEO blocks obtained from the ozonolysis of OIO'.