Star copolymers radical

For the synthesis of block copolymers the reader is refered to a previous article in this series (23) and some other works describing the application of various controlled polymerization techniques for their synthesis, such as anionic polymerization (24-26), cationic polsmierization (27,28), controlled radical polymerization (29,30), as well as combinations of various techniques (31-34). Synthetic procedures for star copolymers have been reviewed (35). The first synthesis of a heteroarm star terpolymer with three immiscible blocks has been described in Reference 36. 

Guo, Y.-M., Pan, C.-Y., and Wang, J. (2001). Block and star block copolymers by mechanism transformation. VI. Synthesis and characterization of A4B4 miktoarm star copolymers consisting of polystyrene and polytetrahydrofuran prepared by cationic ring-opening polymerization and atom transfer radical polymerization. J. Polym. Sci., Part A Polym. Chem., 59(13) 2134-2142. 

Gao H, Tsarevsky NV, Matyjaszewski K (2005) Synthesis of degradable Mikloarm star copolymers via atom transfer radical polymerization. Macromolecules 38 5995-6004... 

While reverse initiation simplified setting up a miniemulsion ATRP, it limited the range of materials that could be prepared and the catalysts that could be employed in the reaction. In a reverse initiation procedure one cannot independently adjust catalyst level and DPo,ge since formation of both the lower oxidation state catalyst complex and the ATRP initiator depends on the amount of standard free radical initiator added to the reaction. Therefore, a new initiation system was developed, SR NI, that involved addition of both an ATRP initiator and a free radical initiator. SR NI allowed the preparation of block and star copolymers in a miniemulsion with low levels of an active catalyst and low levels of surfactant.The use of SR Nl provided stable latexes with high soUds content. As shown in the 2D chromatography plot in Figure 13(a), only 4.5% of linear homopolystyrene was present in the final polymer when a tri-arm poly(methyl acrylate) macroinitiator was chain extended by styrene in an SR NI it miniemulsion process. The homopolymer results from the... 

The generic features of these approaches are known from experience in anionic polymerization. However, radical polymerization brings some issues and some advantages. Combinations of strategies (a-d) are also known. Following star formation and with appropriate experimental design to ensure dormant chain end functionality is retained, the arms may be chain extended to give star block copolymers (321). In other cases the dormant functionality can be retained in the core in a manner that allows synthesis of mikto-arm stars (324). 

Figure 8.14 Schematic diagram of the interconversion between diblock copolymer and star-like nanogel throngh the radical crossover reaction of alkoxyamine units [44],...

This chapter is concerned primarily with the simultaneous polymerization of two monomers to produce statistical and alternating copolymers. The different monomers compete with each other to add to propagating centers, which can be radical or ionic. Graft and block copolymers are not synthesized by the simultaneous and competititive polymerization of two monomers. Each monomer undergoes polymerization alone. A sequence of separate, noncompetitive polymerizations is used to incorporate the different monomers into one polymer chain. The synthesis of block and graft copolymers and variations thereof (e.g., star, comb) are described in Secs. 3-15b-4, 3-15b-5, 5-4, and 9-9. 

So far, there have been only few reports about the synthesis of amphipolar polymer brushes, i.e. with amphiphilic block copolymer side chains. Gna-nou et al. [115] first reported the ROMP of norbornenoyl-endfunctionalized polystyrene-f -poly(ethylene oxide) macromonomers. Due to the low degree of polymerization, the polymacromonomer adopted a star-like rather than a cylindrical shape. Schmidt et al. [123] synthesized amphipolar cylindrical brushes with poly(2-vinylpyridine)-block-polystyrene side chains via radical polymerization of the corresponding block macromonomer. A similar polymer brush with poly(a-methylstyrene)-Wocfc-poly(2-vinylpyridine) side chains was also synthesized by Ishizu et al. via radical polymerization [124]. Using the grafting from approach, Muller et al. [121, 125] synthesized... 

Hedrick, J. L., et al. (1998), Dendrimer-like star block and amphiphilic copolymers by combination of ring-opening and atom transfer radical polymerization, Macromolecules, 31,8691-8705. 

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