Stereoblock macromolecule

NU2 Nuopponen, M., Kalliomaeki, K., Aseyev, V., and Tenhu, H., Spontaneous and thermally induced self-organization of A-B-A stereoblock polymers of N-isopropylacrylamide in aqueous soXnAom, Macromolecules, 41, 4881, 2008. 

Fukushima, K.,Hirata, M. andKimura, Y. (2007) Synthesis and characterization of stereoblock poly(lactic acid)s with nonequivalent D/L sequence ratios. Macromolecules, 40, 3049-3055. 

Collette, J. W. Tullock, C. W. MacDonald, R. N. Buck, W. H. Su, A. C. L. Harrell, J. R. Mulhaupt, R. Anderson, B. C. Elastomeric polypropylenes from alumina-supported tetraalkyl group IVB catalysts. 1. Synthesis and properties of high molecular weight stereoblock homopolymers. Macromolecules 1989, 22, 3851-3858. 

Hauptman, E. Waymouth, R. M. ZUler, J. W. Stereoblock polypropylene Ligand effects on the stereospecificity of 2-arylindene zirconocene catalysts. J. Am. Chem. Soc. 1995,117, 11586-11587. Wihnes, G M. Lin, S. Waymouth, R. M. Propylene polymerization with stericaUy hindered unbridged 2-arylindene metallocenes. Macromolecules 2002, 35, 5382-5387. 

SCHEME 8.4 Proposed mechanism of isotactic/atactic stereoblock propylene polymerization at the active cation of 3. (Reprinted with permission from Gauthier, W. J. Corrigan, J. R Taylor, N. J. Collins, S. Macromolecules 1995, 28, 3111-311. Copyright 1995 American Chemical Society.)... 

Busico, V. Cipullo, R. Segre, A. Talarico, G VacateUo, M. Van Axel CasteUi, V. Seeing the stereoblock junctions in polypropylene made with oscillating metallocene catalysts. Macromolecules 2001,54, 8412-8415. 

De Rosa, C. Auriemma, F. CirceUi, T. Longo, R Boccia, A. C. Stereoblock polypropylene from a metallocene catalyst with a hapto-flexible naphthyl-indenyl ligand. Macromolecules 2003, 36, 3465-3474. 

Lieber, S. Brintzinger, H. H. Propene polymerization with catalyst mixtures containing different ansa-zirconocenes Chain transfer to aUcylaluminum cocatalysts and formation of stereoblock polymers. Macromolecules 2000, 33, 9192-9199. 

For a recent example of stereoblock-isotactic polypropylenes assumed to be isotactic/atactic stereoblock polypropylenes, see De Rosa, C. Auriemma, F. Circelli, T. Waymouth, R. M. Crystallization of the a and y forms of isotactic polypropylene as a tool to test the degree of segregation of defects in the polymer chains. Macromolecules 2002, 55, 3622-3629. 

Wiyatno, W. Pople, J. Gast, A. P Waymouth, R. M. Dynamic response of stereoblock elastomeric polypropylene studied by rheooptics and X-ray scattering. 1. Influence of isotacticity. Macromolecules 2002, 35, 8488-8498. 

K.L. Singfield, G.R. Brown, Optically active polyethers. 1. Studies of the crystallization in blends of the enantiomers and the stereoblock form of Poly(epichlorohydrin). Macromolecules 28, 1290-1297 (1995)... 

Instead, the more soluble fractions contain a larger number Of syndiotactic diads. It is worth remarking that the distribution of the different diads within the chains is not Bernoullian sequences of like diads are preferred over sequences of unlike diads, so that macromolecules of these fractions contain both isotactic stereoblocks and syndiotactic stereoblocks of variable length (57). The shorter the stereoblocks, the more soluble the macromolecules and the lower their melting points (6). 

The ideal structure of this polymer (Fig. 2b) consists of a head-to-tail succession of monomer units of opposite configuration (5). The syndiotactic polymers of propylene obtained so far contain variable numbers of isotactic diads (Fig. 3) moreovCT, the diad distribution is not Bernoullian and in some cases the macromolecules contain, in addition to long syndiotactic stereoblocks, short isotactic stereoblocks (57). 

The structure of real macromolecules sometimes shows deviations from ideality (true isotacticity or syndiotacticity) because (rf the presence of errors in the steric control, the possibility of catalyst isomerization, and the nonconstancy of the type insertion which leads to the presence of more or less isotactic and syndiotactic stereoblocks in the same macromolecule. 

Scheme 5. Two types of macromolecules commonly present in "partially stereoregular" polymers a) stereoblock macromoleculej b) macromolecule with randomly distributed steric irregularities ...

Cai, Z.G., Nakayama, Y, and Shiono, T. (2008b) Facile synthesis of tailor-made stereoblock polypropylenes via successive variation of monomer pressure. Macromolecules, 41,6596-6598. 

Comparison of the recorded and simulated NMR spectra and the assumption that polyester chain growth is accompanied by exchange of chiral macromolecules on alien active centers indicated that the resulting macromolecules were composed of stereoblocks with 11 repeating units derived from LA monomer of a given kind (toluene, 70 °C). Enantiomerically pure (R)- or (S)-SB02A1-0R initiators have been shown to polymerize preferentially one of the enantiomers of rac-LA, that is, (R,R)- or (S,S)-LA, respec-tively. This enantiospecific preference was indicated by the stereoselectivity ratio fep(R/RR)/fep(R/SS) (or fep(S/SS)/fep (S/RR)) equal to 28, what corresponds to Pm = 0.96 (i.e., probability of isotactic enchainment formation, equal to m diad content in the resulting polymer). 

Hietala S, Nuopponen M, KaUiomaki K, Tenhu H. Thermoassociating poly(JV-isopropylacrylamide) A—B—A stereoblock copolymers. Macromolecules. 2008 41 2627-2631. 

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