Synthesis of model polycyclohexylene/polyethylene miktoarm star copolymers with three and four arms

The synthesis of well-defined 3- and 4-miktoarm star copolymers of the A(2)B and A(3)B types is described, where A is 1,4-polybutadiene and B is poly(1,3-cyclohexadiene). The synthetic approach involves the reaction of poly(1,3-cyclohexadienyl)lithium with an excess of methyltrichlorosilane or tetrachlorosilane followed, after the removal of excess silane, by a small excess of polybutadienyllithium. Characterization was carried out by size exclusion chromatography, low-angle laser light scattering, laser differential refractometry, and NMR spectroscopy. The complete heterogeneous catalytic hydrogenation of the A(2)B and A(3)B miktoarm stars, with a calcium carbonate-supported palladium catalyst, leads to the formation of A(2)B and A(3)B miktoarm stars with one amorphous polycyclohexylene arm with an extremely high glass-transition temperature and two or three crystalline polyethylene arms. Differential scanning calorimetry was used to determine the glass-transition temperature of the amorphous blocks of the starting and hydrogenated stars and the melting temperature of polyethylene. Solid-state C-13 NMR spectroscopy was performed to ensure the complete saturation of the polycyclohexadiene and polybutadiene arms. (C) 2002 Wiley Periodicals, Inc.