An-Type Star Homopolymers

Three arm star polymers of IBVE were synthesized by living cationic polymerization using trifunctional initiators 8 and 9 with the same trifluoroacetate initiating functions but different cores [19, 20]. The experimental conditions were selected to obtain living polymerization. A series of acetic acid derivatives including trifluoroacetic acid and the IBVE-acid adduct were found to be efficient 

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An-type star corresponds to a star with n similar homopolymer branches (n>2)... 

Asymmetric PS stars of the type (PSA)n(PSB)n were also prepared by the divinyl-benzene (DVB) method [9]. Living PS chains, prepared by sec-BuLi initiation, were reacted with a small amount of DVB producing star homopolymers. The DVB core of the stars contains active anions which, if no accidental deactivation occurs, are equal to the number of the arms that have been linked to this core. These active sites are available for the polymerization of an additional quantity of monomer. Consequently further addition of styrene produced asymmetric star polymers... 

In analogy to linear-block copolymers different cases can be distinguished when blending asymmetric miktoarm (PS-PI)n-PS and H-shaped (PS-PI)3-PS-(PI-PS)3 copolymers with homopolymer PS [122]. If the latter s molecular weight is lower than the respective PS block, a transition from the L structure to hexagonally packed cylinders without observation of an intervening cubic morphology is observed in the case of the (PS-PI)n-PS types. If the H-shaped (PS-PI)3-PS-(PI-PS)3 star-block copolymer is blended with 30% to... 

Hadjichristidis and coworkers [230] studied the hydrodynamic behavior, in dilute solution, of miktoarm stars of the types A2B and A2B2 where A, B = PS, PI, and PBD in solvents good for both segments or theta for one of the arms and good for the others. Analysis of the results suggests that the experimentally determined values of intrinsic viscosity, [q], viscometric radius, Rv, and Rh for the copolymers are higher than the ones calculated from homopolymer star data. The phenomenon was perceived as an indication of repulsive interactions between A and B chains, which tend to increase the sizes of the individual chains and of the star molecule as a whole [230]. A similar conclusion was reached from SEC experiments on polystyrene-poly-f-butylacrylate miktoarm stars with equal number of branches of the two components [243]. The phenomenon, in this case, was more pronounced as the molecular weight of the branches increased. 

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