Two-block copolymers

Bravo, 1984). Hybrids of these systems, where chromatography and electrophoresis are used in each spatial dimension, were reported nearly 40 years ago (Efron, 1959). Belenkii and coworkers reported on the analysis of block copolymers by TLC (Gankina et al., 1991 Litvinova et al., 1991). Two-block copolymers of styrene and f-butyl methacrylate were separated first with regard to chemical composition by TLC at critical conditions, followed by a SEC-type separation to determine the molar masses of the components. 

Court and Hashimoto [186] investigated morphological transitions triggered by blending two block copolymers with different volume fractions. 

E4 polystyrene-Z)/ocA -[l,4-polybutadiene-grq/Z -poly(styrene-co-acrylonitrile)] (copolymer from styrene and acrylonitrile grafted to a 1,4-polybutadiene-polystyrene two-block copolymer at unspecified sites of some of the but-2-ene-... 

Well developed is the anionic polymerization for the preparation of olefin/di-olefin - block copolymers using the techniques of living polymerization (see Sect. 3.2.1.2). One route makes use of the different reactivities of the two monomers in anionic polymerization with butyllithium as initiator. Thus, when butyl-lithium is added to a mixture of butadiene and styrene, the butadiene is first polymerized almost completely. After its consumption stryrene adds on to the living chain ends, which can be recognized by a color change from almost colorless to yellow to brown (depending on the initiator concentration). Thus, after the styrene has been used up and the chains are finally terminated, one obtains a two-block copolymer of butadiene and styrene ... 

Another way of synthesizing B-A-B triblock copolymers is to use a coupling reaction.2 Monocarbanionic poly-B precursor is used to initiate the polymerization of A. The living two block copolymer is then reacted stoichiometrically with an efficient bifunctional coupling agent, such as dibromo-p-xylene or dimethyldichlorosilane, or even phosgene. This coupling reaction yields the triblock copolymers. 

Polyether polyols are high molecular weight polymers that range from viscous liquids to waxy solids, depending on structure and molecular weight. Most commercial polyether polyols are based on the less expensive ethylene or propylene oxide oi on a combination of the two. Block copolymers are manufactured first by the reaction of propylene glycol with propylene oxide to form a homopolymer. 

Exercise 29-29 Suppose one were to synthesize two block copolymers with the following structures ... 

A number of classes of polymer blends containing block copolymers have been studied. Namely, binary blends of a block copolymer with a homopolymer, ternary mixtures of a block copolymer with two homopolymers and blends of two block copolymers. Experimental and theoretical studies of all these mixtures are the subject of Chapter 6. 

Thin films of blends containing two block copolymers... 

The role of surface-active agents may, with a pair of polymers A and B, also be played by a two-block copolymer AB. It has been observed that a small addition of AB results in a considerably finer dispersion in the blend. This can be explained in two ways ... 

This section reports on the physicochemical characteristics of water-soluble complexes formed between PEO-PLL block copolymers and retinoic acid. Two block copolymers were used. The lengths of the PEO blocks in both are identical, the molecular weight was 5000 g/mol (Mw/Mn=l.l). This corresponds to a degree of polymerization of 114. The length of the PLL block varies PEO-PLL18 has 18 L-lysine monomer units and PEO-PLL30 has 30. A sketch of the molecular structures is given in Fig. 17. 

An interesting synthesis of block copolymers by cationic polymerization of vinyl compounds was described by Kennedy and Melby [277] who used 2-chloro-6-bromo-2,6-dimethylheptane as coinitiator. Br- is eliminated by triethylaluminium, and styrene can be polymerized, without transfer, on the generated carbocation. After all the styrene has reacted, diethylaluminium chloride is added to eliminate Cl- from the coinitiator and thus produce new carbocations on the polymer chain. In the presence of 2-methylpropene, the two-block copolymer poly(styrene)-6/ock-poly(2-methylpropene) is formed. 

Two block copolymers of trimethylcellulose-b-polyoxyethylene have been reported (139). The trimethylcellulose blocks containing one a-chloro ether end were treated with silver hexafluoroantimonate, AgSbF, in THF solution between — 10 C and + 23 C to facilitate a living cationic THF polymerization of polyoxytetramethylene blocks, as shown in Fig. 8. 

We first compare the 7-V-characteristics of the two block copolymers with PvTPA and PvDMTPA as donor, whose bulk morphologies are quite similar, as shown in Fig. 7a,b. The /sc in the device made of PvDMTPA 28 l8-ft-PPcrAcr7235 squares) amounts to 1.14 m A cm 2 which is a fivefold increase compared to 0.23mAcm-2 in PvTPAi416-fe-PPerAcr8626 (diamonds). This indicates that D-A... 

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