Poly well-defined block copolymers

Ion coupling of anionic and cationic living polymers is an interesting procedure for the synthesis of a well-defined block copolymer. Attempted coupling of the polystyrene anion with the poly-THF cation initiated by triethyloxonium tetrafluoro-borate yielded a block copolymer mixed with homopolymers394. The block ef-... 

The reverse strategy, polymerization of the acrylate block followed by styrene, has been successful and has allowed the preparation of well-defined block copolymers with levels of control comparable to ATRP procedures. In this strategy, an alkoxyamine functionalized poly(n-butyl acrylate) block, 70, is initially grown and then used to polymerize styrene at 123 °C under argon for 8 h. This results in 92% conver-... 

The synthesis of a well defined block copolymer, containing a poly(N-vinylimidazole) block (PVim), has been demonstrated by Ge et al. [23]. The polymerization was realized via a RAFT procedure employing xanthates as chain transfer agents. Initially, the polymerization of NIPAM monomer, affording PNIPAM macro-CTA, was realized followed by the polymerization of Vim, Figure 4. The obtained block copolymers had controllable molecular characteristics with a Mw/M value ca. 1.2. The living nature of the Vim polymerization has been confirmed by kinetic experiments, for the first 150 min of the polymerization reaction. It has to be noted that the above procedure was the first example of the synthesis of PVim containing block copolymers. 

Many combinations of various acrylate and methacrylate block copolymers were obtained by ATRP and the knowledge gathered by these approaches has led to the synthesis of even more complex AB copolymers consisting of PMMA and poly (vinylacetylene), or PEO and poly(acrylonitrile) by incorporating various types of halide-based reagents leading to well-defined block copolymers. The synthetic route of the latter combination is given in Scheme 17. 

Dai, CA., Yen, W.C., Lee, Y.H., Ho, C. C., and Su, W.F. (2007) Facile synthesis of well defined block copolymers containing regioregular poly(3-hexyl thiophene) via anionic macroinitiation melhod and their self-assembly behavior. J. Am. Chem. Soc., 129, 11036-11038. 

Despite the fact that initiation of ONDCA does not proceed stoichiometrically with this type of initiator, a living polymerization within the limits of the classical definitions (no chain termination, no chain transfer)[2, 3] may be performed. In case polymerizations were started with NBE, well defined block-copolymers with regard to block-size and molecular weight, one block consisting of poly(ONDCA) and another of poly-NBE, may be prepared. 

Ito, M. and Ishizone, T. (2004) Synthesis of well-defined block copolymers containing poly(N-isopropylacrylamide) segment by anionic block copolymerization of N-aietbo ymethyl-N-isopropylacrylamide. Designed Monomers and... 

The Uving nature of the CROP of 2-oxazolines allows the preparation of well-defined block copolymers by the sequential monomer addition method that is, after full conversion of the first monomer, a second monomer can be introduced resulting in the formation of diblock copolymers (Scheme 6.15) [88, 89]. When this procedure is repeated several times, triblock [90,91] and tetrablock copolymers [92] are readily accessible. By using a similar sequential procedure, diblock and triblock copolymers consisting of both poly(tetrahydrofuran) and poly(2-oxazoline)... 

Thus, N-pyrimidine phthalimide reacted with hexylamine at room temperature to form an amide-amide. The initial amide-amide formation proceeded more rapidly in chloroform as compared to dimethylsulfoxide (DM SO). However, the ring closure reaction to the imide was favored by the more polar, aprotic DMSO solvent, yielding the imide in nearly quantitative yield after 3 hours at 75 °C. The authors were able to utilize this synthetic approach to prepare well-defined segmented poly(imide-siloxane) block copolymers. It appears that transimidi-zation reactions are a viable approach to preparing polyimides, given that the final polyimide has a Tg sufficiently low to allow extended excursions above the Tg to facilitate reaction without thermal decomposition. Additionally, soluble polyimides can be readily prepared by this approach. Ultimately, high Tg, insoluble polyimides are still only accessable via traditional soluble precursor routes. 

The same methodology was applied to construct side chain polymers containing the beta-sheet forming tetrapeptide Ala - Gly - Ala - Gly (AGAG) [42]. This side chain polymer was subsequently used as a macroinitiator for ATRP to prepare flanking blocks of amorphous poly methyl methacrylate. Infra-red spectroscopy clearly showed that the resulting well-defined triblock copolymer possessed a beta-sheet secondary structure. 

The samarocene complexes SmMe(C5Me5)2(THF) and Smn(( 5Mc5)212 were employed as initiators for the synthesis of the well-defined block and triblock copolymers poly(trimethylsilyl methacrylate)-fc-PMMA, PTMSMA-fo-PMMA, PMMA-fo-PTMSMA, PTMSMA-fo-P BuA, PMMA-fo-P BuA, and PMMA-fo-P BuA-fo-PMMA [115]. When the procedure started with MMA polymerization, followed by the addition of TMSMA, block copolymers with low polydispersity and stoichiometric molecular weights in very good agreement with the experimental values were obtained. The reverse mode of add-... 

A similar synthetic strategy was used to attempt the preparation of block copolymers of poly(styrene-co-t-butyl acrylate). In an endeavor to prepare a poly(t-butyl acrylate) macroinitiator (11), t-butyl acrylate was polymerized using 1-phenyl-l-(2, 2, 6 ,6-tetramethyl-l -piperidinyloxy)-ethane (4) at a temperature of 130°C (Scheme 4). However, in stark contrast to the TEMPO mediated polymerization of styrene, the polymerization of t-butyl acrylate resulted in polymers with broad polydispersities (e.g. M = 9415 PD = 2.2). As a result these poly (t-butyl acrylate) macroinitiators were too ill-defined for the preparation of well-defined block... 

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