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A series of novel four-arm A 2 B 2 and A 2 BC and five-arm A 2 B 2 C miktoarm star polymers, where A is poly(dimethylsiloxane) (PDMS), B is polystyrene (PS), and C is polyisoprene (PI), were successfully synthesized by the combination of chlorosilane and benzyl chloride linking chemistry. This new and general methodology is based on the linking reaction of in-chain benzyl chloride functionalized poly(dimethylsiloxane) (icBnCl-PDMS) with the in-chain diphenylalkyl (icD) living centers of PS-DLi-PS, PS-DLi-PI, or (PS) 2 -DLi-PI. icBnCl-PDMS was synthesized by the selective reaction of lithium PDMS enolate (PDMSOLi) with the chlorosilane groups of dichloro[2-(chloromethylphenyl)ethyl]methylsilane, leaving the benzyl chloride group intact. The icD living polymers, characterized by the low basicity of DLi to avoid side reactions with PDMS, were prepared by the reaction of the corresponding living chains with the appropriate chloro/bromo derivatives of diphenylethylene, followed by a reaction with BuLi or the living polymer. The combined molecular characterization results of size exclusion chromatography, 1 H NMR, and right-angle laser light scattering revealed a high degree of structural and compositional homogeneity in all miktoarm stars prepared. The power of this general approach was demonstrated by the synthesis of a morphologically interesting complex miktoarm star polymer composed of two triblock terpolymer (PS-b-PI-b-PDMS) and two diblock copolymer (PS-b-PI) arms. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6587-6599, 2006 Scheme 5. Synthesis of the A 2 B 2 C five-miktoarm star polymer.Scheme 4. Synthesis of the A 2 BC four-miktoarm star polymer.

A new stepwise iterative methodology was developed for the synthesis of well-defined high-generation and high-molecular-weight dendrimer-like star-branched poly-(tert-butyl methacrylate)s (P t BMA)s and block copolymers composed of P t BMA and polystyrene (PS) segments. The methodology involves the following two reaction steps in an iterative process: (1) a linking reaction based on a 1:1 addition reaction of an α-terminal-(3-tert-butyldimethylsilyloxymethylphenyl (SMP)) 2 -functionalized living polymer with a core compound or α-terminal-(α-phenyl acrylate (PA)) 2 -functionalized polymers linked to the core and (2) a conversion of the SMP group to the PA function, to be used as the next reaction site. Repetition of the two reaction steps, (1) and ( 2), allows for the synthesis of high-generation and high-molecular-weight dendrimer-like star-branched polymers. In practice, a series of dendrimer-like star-branched (P t BMA)s up to the fifth generation (5G) were successfully synthesized. The resulting polymers, whose arm segments were four-branched at the core and two-branched at each layer, were all well-defined in branched architecture and precisely controlled in chain length, and the final 5G dendrimer-like star-branched P t BMA possessed a predictable M n value of 1.07 × 10 7 g/mol and an extremely narrow molecular weight distribution of 1.03 in M w /M n value. The synthetic possibility of similar dendrimer-like star-branched polymers composed of functional polymer segments bearing acidlabile and/or basic groups by the same methodology was also demonstrated. Furthermore, 4G dendritic architectural block copolymers with hierarchic layer structures composed of P t BMA (and poly(methacrylic acid)) and PS segments were synthesized.

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