Synthesis of di- and triblock copolymers

In addition, Arvanitopoulos et al. [84] achieved the synthesis of di- and triblock copolymers of acrylates using cobalt oxime complexes and telechelic initiators (e.g., l,6-[di(pyridinato)cobaltoxime]hexane), respectively. 

Since there is no chain transfer involved, preparation through living polymer results in a narrow distribution of molecular weight. It is the best way to synthesize di- and triblock copolymers, star-shaped and comb-shaped polymers, and homopolymers with high molecular weight. The following is an example of the synthesis of di- and triblock copolymers ... 

Krouse and Schrock also made block copolymers with norbornene and PA, using CF3-TCDT (vide supra) as the precursor monomer to polyacetylene (Scheme XVII) [88]. Using ( BuO)2M(N(2,6- Pr)2Ph)(CHR) (M = W, Mo and R = alkyl) to ROMP both monomers allowed for the control of the molecular weight and PDI. Controlling the order of monomer addition allowed for the synthesis of di- and triblock copolymers. The polymerization reaction could be terminated with either benzaldehyde or pivaldehyde to cleave the metal cattil)%t from the propagating polymer chain. Precursor copolymers with norbomene/CF3-TCDT ratios of 1.7 1 to 5 1 could be made with Mn = 6,000-27,000 g/mol and PDI = 1.04-1.23. The elimination of hexaflu-... 

In our laboratory the motivation for the synthesis of di- and triblock copolymers was three-fold 1) synthesis of the organic blocks by a living polymerization technique such that segment length and copolymer composition could be controlled, 2) prevention of coupling of macromolecular species and 3) use of a technique that would allow for the synthesis of a plethora of copolymers based on variation of the organic monomer. Considering these qualifications, ATRP of vinyl monomers from mono- and difunctional PDMS macroinitiators was used. Scheme 3 illustrates the synthesis of ABA triblock copolymers from terminal functionalized PDMS. The method utilizes hydrosilation of attachable initiators to commercially available vinyl... 

As indicated above, conventional free-radical poljnnerization is not very well suited for the synthesis of advanced polymer architectures. Even the synthesis of di- or triblock copolymers is hardly possible using this technique. The main reason is the continuous initiation and termination of chains. This results in the early generation of dead polymer chains that no longer participate in the polymerization process. The consecutive addition of monomers as employed in living anionic polymerization for the synthesis of eg poly(styrene-6Zoc -butadiene) will only lead to the synthesis of a mixture of two homopolymers. 

Figure 7.2 Basic concept of di- and triblock copolymer synthesis.

The discovery that Ti complex (4) was an effective catalyst for living ROMP chemistry resulted in the synthesis of several new types of polymers that were inaccessible with conventional catalysts. Narrow polydispersity polymer and di- and triblock copolymers were synthesized soon after living ROMP was discovered. Because polymer chains that are formed in a living ROMP reaction are terminated with metal carbene groups, fimctionalization of the chain ends is possible. Reaction of the carbene with an aldehyde occurs in a Wittiglike fashion, making a metal oxo complex that is inert to finther metathesis chemistry and terminates the chain with the alkylidene group of the aldehyde. 

A new method for the synthesis of polyisobutylene-based block copolymers, involving living carbocationic polymerization of isobutylene and subsequent living anionic polymerization of methacrylic monomers has been demonstrated. Di- and triblock copolymers nearly free of PIB precursor and with narrow and unimodal MWD were synthesized under well-controlled conditions. 

Yamago S, lidaK, Yoshida J (2002) Synthesis of poly(meth)acrylate derivatives and their di-and triblock copolymers. J Am Chem Soc 124 13666-13667... 

Enright TE, Cunningham MF, Keoshkerian B (2010) Nitroxide-mediated bulk and miniemulsion polymerization in a continuous tubular reactor synthesis of homo-, di- and triblock copolymers. Macromol React Eng 4 186-196... 

Scheme 100 Synthesis of polyfluorene-poly(ethylene oxide) di- and triblock copolymers...

Access to the living cationic polymerization technique mentioned earlier has allowed the synthesis of a range of block copolymers, either phosphazene-phosphazene blocks, phosphazene-organic polymer blocks, or phosphazene-polyorganosiloxane blocks.Both di- and triblock copolymers have been produced, and a summary of these structures is shown in Scheme 7.7. 

The synthesis of block copolymers, mainly di- and triblock copolymers has been studied extensively and a general overview can be found in the literature [1,13,14,17]. 

Hautekeer, J.R, Varshney, S.K., Fayt, R., Jacobs, G., JerOme, R. and Teyssi, Ph. (1990) Anionic polymerization of acrylic monomers. Synthesis, characterization and modification of polystyrene-poly(tert-butylacrylate) di- and triblock copolymers. Macromolecules, 23,... 

Zhang, Z.B., Ying, S.K., and Shi, Z.Q. (1999) Synthesisof fluorine-containing block copolymers via ATRP 2. Synthesis and characterization of semifluorinated di- and triblock copolymers. Polymer, 40,5439-5444. 

Killian et demonstrated the living nature of nickel catalysts 97 and 98 (Figure 26) with the synthesis of well-defined di- and triblock copolymers of a-olefins. At -15 C, activation of 97 with MAO followed by sequential addition of monomers afforded PP-blocfe-PH with monomodal, narrow molecular weight distributions (Mw/Mn = l ll-1.13), which exhibited less branching than predicted, due to partial chain-straightening. Triblocks were prepared by aaivation of 97 or 98 with MMAO at -10 °C followed by reaction with 1-octadecene to afford a semiaystalline, chain-straightened... 

Godt and coworkers [149] reported on the synthesis of poly(p-phenyleneethynylene)-block-polyisoprene and the transformation of such rod-coils into corresponding coil-rod-coil triblock copolymers. Luminescent rod-coil or coil-rod-coil di- or triblock copolymers were synthesized by mono- or difunctional atom transfer radical polymerization from oligo(p-phenyleneethynylene) [150],... 

It was shown that high molar mass, polydisperse acrylic PnBA/PMMA diblock and triblock copolymers prepared by SGl-mediated polymerization were shown to self-assemble into various nanostmctures despite substantial molecular dis-order. ° Lamellae are observed around 55-65 vol.% PMMA, while perfectly symmetrical copolymers adopt a curved interface concave toward PMMA and form cylinders or cylindrical micelles with poor lattice order. This was assigned to unbalanced polydispersity between the two blocks arising from the lack of control over polymerization of PMMA under the synthesis conditions used. 

Controlled synthesis and detailed characterization of triblock copolymers of di-phenylsiloxane and dimethylsiloxane has been reported by Meier and co-workers147 148), who used lithium based initiators and the cyclic trimers of dimethyl and diphenyl-... 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

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