Copolymers tetrablock

The living character of the ROMP promoted by the initiator Ru(CHPh)(Cl)2 (PCy3)2 (Cy = cyclohexane) was tested with the synthesis of diblock, triblock, and tetrablock copolymers of norbornene derivatives carrying acetyl-protected glucose, [2,3,4,6-tetra-O-acetyl-glucos-l-O-yl 5-norbornene-2-carboxylate], A or maltose groups, [2,3,6,2/,3/,4/,6/-hepta-0-acetyl-maltos-1-O-yl 5-norbornene-2-carboxylate], B, shown in Scheme 41 [102]. The AB, ABA, and ABAB structures were prepared by sequential addition of monomers with narrow molecular weight distributions to quantitative conversions. 

The synthesis of some multiblock copolymers was attempted by successive polymerization using this iniferter technique. However, pure tri- or tetrablock copolymers free from homopolymers were not isolated by solvent extraction because no suitable solvent was found for the separation. In 1963, Merrifield reported a brilliant solid-phase peptide synthesis using a reagent attached to the polymer support. If a similar idea can be applied to the iniferter technique, pure block copolymer could be synthesized by radical polymerization. The DC group attached to a polystyrene gel (PSG) through a hydrolyzable ester spacer was prepared and used as a PSG photoiniferter (Eq. 53) [186] ... 

Fig. 11a,b. Bright field TEM micrographs of a a linear tetrablock copolymer b a topologically asymmetric miktoarm starblock copolymer of the same composition and molecular weight (see text) (reproduced with permission from [62])... 

Brannan AK, Bates FS (2004) ABCA tetrablock copolymer vesicles. Macromolecules 37 8816-8819... 

Fig. 15. Phase diagram of block copolymers and random copolymers. Circles are results for homopolymers squares are results for diblock copolymers diamonds are results for triblock copolymers up triangles are results for a mixture of A-B-A and B-A-B triblock copolymers left triangles are results for tetrablock copolymers X s are results for random copolymers with average sequence length 1 = 55 crosses are results for random copolymers with / = 20 asterisks are results for a completely random copolymer.

It is possible to measure the order-order (To o) or order-disorder (Tq-d) temperatures by using thermomechanical analysis [29, 31-33]. The thermomechanical analysis data (2°C min and 1 rad s ) reported in Fig. 16.7 shows that the two temperatures (To o=140°C and To d = 175°C) are similar for the pure diblock and the [SIS-SI] blend with SI=85%. This point shows that the behavior of the diblock copolymer is really a key parameter for the [SlS-Sl] blends with high diblock content, by controlling their behavior at low frequencies. As far as the tetrablock copolymers are concerned, it seems on the contrary that there is no lower limit to the level of the secondary plateau. As Fig. 16.5 indeed demonstrates, the level of the secondary plateau for tetrablock materials follows the same power law variation even at high diblock contents. 

Doxastakis, M., K. Chrissopoulou, A. Aouadi, B. Frick, T. P. Lodge, and G. Fytas. 2002, Segmental dynamics of disordered styrene-isoprene tetrablock copolymers. /. Chem. Phys. 116 4707-4714. 

Figure 35 Bright-field TEM micrographs of linear tetrablock copolymers (left) and topologically asymmetric miktoarm star-block copolymers (right) of the same composition and molecular weight. Reprinted from Tselikas, Y. Hadjichristidis, N. Lescanec, R. L. etal. Macromolecules 996,29,3390. ...

Bazan reported on the synthesis of pseudo-tetrablock copolymers comprised of ethene and 5-norbomen-2-yl acetate, using the initiator system (LiPr2)Ni(q -CH2Ph) (PMes) [(LiPr2) = 77-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino) propanamide] and 2.5 equivalents of Ni(cod)2 [bis(l,5-cyclooctadiene)nickel [121, 130, 131]. Square-planar nickel complexes with anionic P,0-chelate ligands were used by Goodall and coworkers for the co- and terpolymerization of norbomene and 5-norbomene-2-carboxylic acid ethyl ester with ethene [126]. 

Coffin, R.C., Diamanti, S.J., Hotta, A. et al. (2007) Pseudo-tetrablock copolymers with ethylene and a functionaUzed comonomer. Chemical Communications, 3550-3552. 

Li, Z. and Liu, G.J. (2003) Water-dispersible tetrablock copolymer synthesis, aggregation, nanotube preparation, and impregnation. Langmuir, 19,10480-10486. 

Figure 3 shows the right-hand side of Eq. 1 versus (Q Rg) for branched polymer 1 as compared with the triblock copolymer and branched polymer 2. Branched polymer 1 is the only one of the calculated polymers that is not composed strictly of triblock copolymers. Branched polymer 1 may be considered as an infinite polymer made up of tetrablock copolymers or of triblock copolymers in the backbone with diblock copolymers as branches. The maximum in the scattering curve for branched polymer 1 is at larger values of (Q Rgn than that of the other polymers, partly because the Rg of this polymer pertains to the tetrablock copolymer subunit. Branched polymer 1 was included in the calculation because synthetic methods for this polymer are easier to find than for the other branched polymers. 

There have been few reports to date on quasicrystaUine structure foimatimi from BCPs. Hayashida et al. obtained a 2D quasicrystaUine structure, a tUing pattern with 12-fold symmetry, from an ABC star BCP and homopolymer blend (see Fig. 3) [34]. The Bates group at the University of Minnesota generated a 3D dodecagonal quasicrystal from diblock and tetrablock copolymers [33]. These unique structures are mediated by macromolecular packing frustration. However, a substantial number of unanswered questions about the stmcture formation await further in-depth studies of these interesting morphologies. 

A block copolymer contains two or more separate blocks of monomers to form a polymer with the structure poly(A-f -B) [9], where A and B are monomers and b denotes that it is a block. Copolymers can be classified according to how the monomers are arranged in the polymer structure. Linear copolymers consist of a single main chain, whereas branched copolymers consist of a single main chain with one or more polymeric side chains. Examples of branched copolymers are graft copolymers, brush copolymers and comb copolymers [10]. Block copolymers with two, three or four distinct blocks are called diblock copolymers, triblock copolymers and tetrablock copolymers, respectively, (Figure 2.4) [10]. 

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)... 

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