Synthesis of block copolymer

Prepare a solution of I-PSSNa macroinitiator (0.050 mmol), MMA (5.0 mmol), copper (I) bromide (0.050 mmol) and 2,2 -bipyridine (1.00 mmol) in a mixed solvent composed of methanol and water (80/20 ratio) and stir at 25 C for 24 h, under an argon atmosphere. The copolymer is purified by dialysis and recovered via freeze-drying. 

Prepare a solution of III-PMMA (0.0128 mmol), SSNa (1.28 mmol), copper (I) bromide (0.026 mmol) and PMDETA (0.026 mmol) in DMF in a dry flask under argon. The reaction mixture is stirred at 110 °C in an oil bath. Recovery of the product is similar to the method above. 

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Photoinitiators provide a convenient route for synthesizing vinyl polymers with a variety of different reactive end groups. Under suitable conditions, and in the presence of a vinyl monomer, a block AB or ABA copolymer can be produced which would otherwise be difficult or impossible to produce by another polymerization method. Moreover, synthesis of block copolymers by this route is much more versatile than those based on anionic polymerization, since a wider range of a monomers can be incorporated into the blocks. 

A number of techniques for the preparation of block copolymers have been developed. Living polymerization is an elegant method for the controlled synthesis of block copolymers. However, this technique requires extraordinarily high purity and is limited to ionically polymerizable monomers. The synthesis of block copolymers by a radical reaction is less sensitive toward impurities present in the reaction mixture and is applicable to a great number of monomers. 

Figure 1 Principle of synthesis of block copolymer by the use of macro-initiator. = azo or peroxy group O A = monomer B = oligomer A.

Sato, T. and Otsu, T. Formation of Living Propagating Radicals in Microspheres and Their Use in the Synthesis of Block Copolymers. Vol. 71, pp. 41 —78. 

A few studies have appeared on systems based on persistent nitrogen-centered radicals. Yamada et al.2"1 examined the synthesis of block polymers of S and MMA initiated by derivatives of the triphenylverdazyl radical 115. Klapper and coworkers243 have reported on the use of triazolinyl radicals (e.g. 116 and 117). The triazolinyl radicals have been used to control S, methacrylate and acrylate polymerization and for the synthesis of block copolymers based on these monomers [S,243 245 tBA,243 MMA,243 245 BMA,245 DMAEMA,24 5 TMSEMA,247 (DMAEMA-Wbc/fc-MMA),246 (DMAEMA-Woc -S)246 and (TMSEMA-6/ocfc-S)247]. Reaction conditions in these experiments were similar to those used for NMP. The triazolinyl radicals show no tendency to give disproportionation with methacrylate propagating radicals. Dispcrsitics reported arc typically in the range 1.4-1.8.2"43 246... 

There are additional factors that may reduce functionality which are specific to the various polymerization processes and the particular chemistries used for end group transformation. These are mentioned in the following sections. This section also details methods for removing dormant chain ends from polymers formed by NMP, ATRP and RAFT. This is sometimes necessary since the dormant chain-end often constitutes a weak link that can lead to impaired thermal or photochemical stability (Sections 8.2.1 and 8.2.2). Block copolymers, which may be considered as a form of end-functional polymer, and the use of end-functional polymers in the synthesis of block copolymers are considered in Section 9.8. The use of end functional polymers in forming star and graft polymers is dealt with in Sections 9.9.2 and 9.10.3 respectively. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

Besides their unique combination of properties, another important factor that makes organosiloxanes so attractive in the synthesis of block copolymers, is the ease of... 

Puskas, J.E. Biomacromolecular engineering Design, S3mthesis and characterization. One-pot synthesis of block copolymers of arborescent polyisobutylene and polystyrene, Polym. Adv. TechnoL, 7, 1, 2006. 

Amiduri, B Boutevin, B. and Gramain, P Synthesis of Block Copolymers by Radical Polymerization and Telomerization. VoL 127, pp. 87-142. 

Blocking aMeSt or MVE from Quasiliving Poly(IBVE) Dication. An important application of quasiliving polymerizations may be for the synthesis of block copolymers. Efforts have been made to prepare novel block polymers starting from quasiliving poly(IBVE) dication by the addition of aMeSt and/or MVE as the second monomer. Eq. 3 outlines the principle of the blocking experiments ... 

Abstract This review highlights recent (2000-2004) advances and developments regarding the synthesis of block copolymers with both linear [AB diblocks, ABA and ABC triblocks, ABCD tetrablocks, (AB)n multiblocks etc.] and non-linear structures (star-block, graft, miktoarm star, H-shaped, dendrimer-like and cyclic copolymers). Attention is given only to those synthetic methodologies which lead to well-defined and well-characterized macromolecules. 

Other more complex linear block co-, ter- and quarterpolymers, such as ABC, ABCD, ABABA can be prepared using the previously mentioned methods. An important tool in the synthesis of block copolymers involves the use of post-polymerization chemical modification reactions. These reactions must be performed under mild conditions to avoid chain scission, crosslinking, or degradation, but facile enough to give quantitative conversions. Hydrogenation, hydrolysis, hydrosilylation and quaternization reactions are among the most important post-polymerization reactions used for the preparation of block copolymers. 

Synthesis of Block Copolymers by Controlled Radical Polymerization... 

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