142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

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Asymmetric Star Polymers Synthesis and Properties 85 Scheme 10 2.2.1.3 Synthesis of A 3 B Miktoarm Star Copolymers The work on the A 2 B stars was expanded to the synthesis of miktoarm stars of the type A 3 B, where A is PI and B is PS [28]. SiCl 4 was used as the linking agent. Living PS chains were reacted with an excess of the linking agent for the preparation of the trichlorosilane end-capped PS. After the evaporation of excess SiCl 4 the macromolecular linking agent was added to a slight excess of the living PI chains to obtain the A 3 B star. The reaction sequence, given in Scheme 10, was monitored by SEC. The products after extensive characterization were found to have high degree of molecular and compositional homogeneity. A similar procedure was followed for the synthesis of miktoarm stars of the type B(A-b-B) 3 , A being PI and B PS [27]. A different approach but still in the frame of the chlorosilane method was adopted by Tsiang for the synthesis of (A-b-B)B 3 miktoarm star copolymers, where A is PS and B is PB [29]. Living PB chains were reacted with SiCl 4 in a molar ratio 3:1, followed by the addition of the living diblock PS-b-PBLi. The key step of the method is the succesfull synthesis of the (PB) 3SiCl intermediate product. The reduced steric hindrance of the PBLi chain end poses questions about the purity of this polymer, since several byproducts, such as (PB) 2SiCl 2, (PB) 4Si, PBSiCl 3 can be formed in the first step of the synthesis. SEC analysis was performed to monitor the reaction sequence. It is obvious that the method developed by Tsiang is very demanding with regard to the stoichiometry of the reagents. The byproducts are almost impossible to separate. 2.2.1.4 Synthesis of A n B (n‡‡‡‡ 5) Miktoarm Star Copolymers Miktoarm star copolymers of the type A 5 B were prepared [30] in a similar manner to the A 2 B and A 3 B type stars. The reaction sequence is outlined in Scheme 11. Living PS chains were reacted with 1,2-bis(trichlorosilyl)ethane in a ratio Li:Cl=1:6. Dropwise addition of the living polymer solution into the vigorously stirred solution of the linking agent was performed to minimize the coupling product. Under these conditions 15% of the coupled product was formed. The
86 N. Hadjichristidis, S. Pispas, M. Pitsikalis, H. Iatrou, C. Vlahos Scheme 11 Scheme 12 pentachlorosilane-capped PS was then reacted with excess PILi for the preparation of the A 5 B copolymer. Fractionation techniques were employed to isolate the desired polymer. The stoichiometric addition of the living PS to the silane was chosen in this case instead of using excess silane, since this hexafunctional silane is solid and consequently its excess cannot easily be removed. The progress of the reaction was monitored by SEC. The combined characterization results proved the narrow distribution in molecular weight and composition of the final products. Star polymers having several PS branches and only one poly(2-vinyl naphthalene), PVN branch were prepared by Takano et al. using anionic polymerization techniques [31]. Sequential anionic block copolymerization of (4-vinyl-phenyl) dimethylvinylsilane (VS) and VN was employed. The double bonds attached to silicon have to remain unaffected during the polymerization of VS. This was ac-
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142 Advances in Polymer Science Edi
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Branched Polymers I Volume Editor:
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Volume Editor Dr. Jacques Roovers I
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Preface While books have been writt
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Contents Synthesis of Branched Poly
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Synthesis of Branched Polymers by C
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Dendrimers and Dendrimer-Polymer Hy
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Author Index Volumes 101-142 Author
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Author IndexVolumes 101-142 231 Dun
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Author Index Volumes 101-142 233 Ka
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Author Index Volumes 101-142 235 Og
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Author Index Volumes 101-142 237 Su
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Subject Index Addition-fragmentatio
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Subject Index 241 Microphases 11z,
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142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

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