Comb-shaped

Anionic grafting methods (vide infra) can be applied to the synthesis of comb-shaped polymers. As an example, a polystyrene backbone is partially chloromethylated (under mild conditions) and used as an electrophilic deactivator for a living polystyrene 89). The grafting onto process yields well defined species that have been characterized accurately. The branches are distributed randomly along the backbone 90). 

Graft copolymers are comb-shaped polymers consisting of a backbone and two or more branches which differ chemically from the backbone. Branches are usually distributed randomly along the backbone, although recent advances in synthetic methods have allowed for the preparation of better-... 

Chowdhury, M.A.J., Ihara, H., Sagawa, T., and Hirayama, C., Retention versatility of silica-supported comb-shaped crystalline and non-crystalline phases in high-performance liquid chromatography, J. Chromatogr. A, 877, 71, 2000. Chowdhury, M.A., Ihara, H., Sagawa, T., and Hirayama, C., Retention behaviors of polycyclic aromatic hydrocarbons on comb-shaped polymer immobilized-silica in RPLC, J. Liq. Chromatogr. Relat. TechnoL, 23, 2289, 2000. 

Shundo, A., Nakashima, R., Fukui, M., Takafuji, M., Nagaoka, S., and Ihara, H., Enhancement of molecular-shape selectivity in high-performance liquid chromatography through multi-anchoring of comb-shaped polymer on silica, J. Chromatogr. A, 1119, 115,2006. 

N. A. Plate and V. P. Shibaev. Comb-Shaped Polymers and Liquid Crystals, Plenum, New York (1988). 

Macromers have been used to produce thermoplastic elastomers. Generally, the backbone serves as the elastomeric phase while the branches serve as the hard phases. These structures are often referred to as comb -shaped because of the similarity between the rigid part of the comb and its teeth and the structure of these graft polymers. 

Albderda van Ekenstein G, Polushkin E, Nijland H, Ikkala O, ten Brinke G. Shear alignment at two length scales comb-shaped supramolecules self-organized as cylinders-within-lamellar hierarchy. Macromolecules 2003 36 3684-3688. 

Special interest has been devoted in recent years to comb shaped polymers. This architecture consists of a backbone carrying p randomly distributed grafts of known length. 

In several cases the melt viscosity of a series of lightly-branched polymers has been determined as a function of MW, and compared with that of linear polymers, and it has been found or may be deduced from the published data that there is a cross-over molecular weight, below which the branched polymer is less viscous, but above which it more viscous, than the linear polymer of equal MW. This behaviour is observed with some comb-shaped polystyrenes (35) and poly(vinyl acetate)s (59, 89), star polybutadienes (57, 58, 123), and randomly-branched polyethylenes (56,61). Jackson has found (141) that if the ratio ZJZC of the number of chain atoms at the cross-over point, Zx, to the number at the kink in the log 0 — logM curve, Zc, [as given in Ref. (52)], is plotted against nb, the number of branches, a reasonable straight line is obtained, as in Fig. 5.1. 

Experimental data on branched polystyrenes were used to test the theory. There are some discrepancies in particular the parameter A varies from one polymer to another, especially for comb-shaped polymers y> also varies. It is suggested that the reason for the discrepancies in A may be the failure of the assumption of a Gaussian distribution of segment density. 

Decker (76) measured [17] and for a number of comb-shaped polystyrenes at 0Al, and compared the hydrodynamic volume with . The hydro-... 

Graessley s theory, though satisfactory for linear polymers, has not yet been shown to apply to branched polymers. Fujimoto and co-workers (65) attempted to apply it to comb-shaped polystyrenes, but obtained only poor agreement with experiment. They attributed this to the failure of the assumption that the state of entanglement is the same in branched polymers as in linear ones. It is not surprising that this theory fails, for (in common with earlier theories) it predicts that the zero shear-rate viscosity of all branched polymers will be lower than that of linear ones, contrary to experiment. 

It has been hypothesized by Graessley (30) and others (3, 31) that the g1/2 rule is applicable to star-shaped and slightly branched polymers whereas the g372 rule describes the behavior of highly branched "comb-shaped polymers for which [rj] B/ [y] l < 0.5. The results of this study indicate that the g1/2 rule in combination with Equation 11 adequately represents the random trifunctionally and tetrafunctionally branched... 

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