Random and alternating copolymer

Random and Alternating Copolymers a) Mechanism and Kinetics of Copolymerization... 

Propanesultone also forms random and alternating copolymers with N-substituted ethylenimines276) and similar mechanisms involving zwitter ions were suggested. The polymerization through zwitter ions was performed with cyclic phosphonite as the Mn monomer and pyruvic acid as the ME monomer250). 

A similar technique was applied to the synthesis of AB and ABA block copolymers containing random and alternating copolymer sequences [178-180]. For example poly(St-ra dora-MMA)-hZock-poly(VAc), poly(VAc-hZock-poly(St-ran-dora-MMA)-hZock-poly(VAc), poly(St)-foZoc/c-poly(DiPF-aZMBVE), poly(IBVE-aZf-MAn)-hZock-poly(St)-hZock-poly(IBVE-aZf-MAn), poly(St)-hZock-poly(EA)-random-AA), and poly(St)-hZock-poly(EA-ra dora-AA-random-MMA) were synthesized [178]. 

SCHEME 2.30 Synthesis of the Frechet-type dendrimer-substituted PFs and fluorene random and alternating copolymers. (From Marsitzky, D., Vestberg, R., Blainey, P., Tang, B.T., Hawker, C.J., and Carter, K.R., J. Am. Chem. Soc., 123, 6965, 2001.)... 

Statistical, random and alternating copolymers generally have properties which are intermediate to those of the corresponding homopolymers. Thus by preparing such copolymers it is possible to combine the desirable properties of the homopolymers into a single material. This is not normally possible by blending because most homopolymers are immiscible with each other. 

In addition to these irregularities, Winey et al. (1996) have found that in random and alternating copolymers of styrene and methyl methacrylate, the sequence distribution of monomers along the backbone of the polymer strongly affects its miscibility with polystyrene and polymethylmethacrylate homopolymers, even when the overall ratio of styrene/methyl methacrylate in the copolymer chain is held constant. A strictly alternating sequence of monomers in the copolymer was found to be more miscible with the ho-miopolymers than is a copolymer with a random sequence distribution. These results... 

The properties of statistical, random, and alternating copolymers generally are intermediate to those of the parent homopolymers. 

Random and alternating copolymers have been usually synthesized by traditional techniques (free radical, anionic, and cationic) however, in the past two decades, many copolymers have been synthesized using the relatively new... 

A comparative study of the thermal properties and of the glass transition temperatures of the (A) and (B) homopolymers and of the (AB) random and alternated copolymers and (BAB) alternated copolymers has been achieved and showed the influence of the structure of the polymer. 

Random copolymers may lead to depolymerization like (B) homopolymers. On the contrary, alternated copolymers present a much better resistance to reversion. Copolymers exhibit a lower Tg (of 10 to 20 °C) than that of the hybrid homopolymer (A) . Thermogravimetric analyses of random and alternated copolymers show that they are more stable than each homopolymer (A) or (B) . 

What is the difference between random and alternating copolymers ... 

Metallocene catalysts can produce both random and alternating copolymers of ethylene and propylene [85]. At present there does not appear to be any commercial utilization of alternating copolymers. They were reported to form in polymerizations catalyzed by bridged fluorenyl catalysts [85]. 

Theoretical models for other systems, such as star, branched, and ring polymers, random and alternating copolymers, graft and block copolymers are discussed in the book by Mattice and Suter [1]. Block copolymers are discussed in Chap. 32 of this Handbook [2]. Theories of branched and ring polymers are presented in the book by Yamakawa [3]. Liquid-crystalline polymers are discussed in the book by Grosberg and Khokhlov [4], and liquid crystalline elastomers in the recent book of Warner and Terentjev [5]. Bimodal networks are discussed by Mark and Erman [6,7]. Molecular theories of filled polymer networks are presented by Kloczkowski, Sharaf and Mark [8] and recently by Sharaf and Mark [9]. 

While the nomenclature scheme was originally derived to describe polymer blends, blocks, grafts, and IPNs, generalizing the scheme to include random and alternating copolymers and starblock copolymers made the... 

The statistical, random, and alternating copolymers above describe sequence lengths of one, two, three, or at most several mers. This section treats cases where whole polymer chains are linked together to form still larger polymer structures (ll).lTiese structures have been variously named polymer alloys, or polymer blends, but the term multicomponent polymers is used here to describe this general class of materials. 

Random and alternating copolymers typically exhibit properties that are between those of the corresponding homopolymers. Therefore, they often are developed to combine the properties of homopolymers into a single fiber. This is difficult to achieve by simply blending the homopolymers because most polymers are immiscible with each other. For example, fibers of polyaciylonitrile homopolymer have been used in hot gas filtration systems, outdoor fabrics, and precursors for carbon fibers. However, many commercial acrylic fibers actually are made... 

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