Dimethylsiloxane cyclic polymers

When dimethyldichlorosilanc Is hydrolyzed simply by stirring with a large excess of water, there is formed a colorless oil containing a large variety of molecular species. About one half of the oil consists of cyclic polymers of dimethylsiloxane of the type... 

The hydrolysis of, for example, dimethyl dichlorosilane to cyclic dimethylsiloxanes and linear diols can be regarded as following a similar pattern, if OHs+Cl" is taken as the analogue of NH4+C1". Increase of acid concentration, or the use of a mutual solvent, increases the proportion of cyclic polymers their proportion is decreased by the use of insufficient, alkaline or scarce water in the foi-m of hydrated salts (see pp. 80 ff. in ref. 65). 

Orrah DJ, Semiyen JA, Rossmurphy SB (1988) Studies of cyclic and linear poly(dimethyl-siloxanes). 28. Viscosities and densities of ring and chain poly(dimethylsiloxane) blends. Polymer 29 1455-1458... 

INTRODUCTION Polymer molecules may have a variety of architectural structures such as linear, ring, star, branched, and ladder chains as well as three-dimensional network structures. The first synthetic cyclic polymers to be prepared and characterized were the poly(dimethylsiloxanes) (PDMS), which were reported in ] 977 (1) Since that time a number of other cyclic polymers have been synthesized including cyclic polystyrene, cyclic poly(phenylmethylsiloxane), cyclic poly(2-vinylpyridine), cyclic polybutadiene, and cyclic poly(vinylmethylsiloxane). ... 

Assistant Dean of the College of Engineering, and Director of the Polymer Research Center, University of Cincinnati, Ohio Poly(dimethylsiloxanes), cyclic Polymeric selenium Polymeric sulfur... 

Considerable information on polysiloxane cyclics is available in reviews of cyclic polymers in general. Considerable attention has been paid to cyclics of poly(dimethylsiloxane), poly(phenylmethylsiloxane), and... 

Scales, L. E. Semiyen, J. A., Equilibrium Ring Concentrations and the Statistical Conformations of Polymer Chains Part 14. Calculation of the Concentrations of Medium Sized Cyclics in Poly(dimethylsiloxane) Equilibrates. Polymer 1976,17, 601-604. 

Clarson, S. J., Cyclic Poly(dimethylsiloxane). In Polymer Data Handbook, 2nd ed. Mark, J. E., Ed. Oxford University Press New York, 2009 pp 113-115. 

Clarson, S. J. Mark, J. E. Semiyen, J. A., Studies of Cyclic and Linear Poly(dimethylsiloxanes) 24. Topological Trapping of Cyclic Polymers into Unimodal and Bimodal Model Network Structures. Polym. Comm. 1987,28, 151-153. 

The base polymers are mainly high-molecular-weight linear polydimethyl-siloxanes prepared by the base- or acid-catalyzed polymerization of cyclic dimethylsiloxanes [(CH3)2SiO—] (see Section 2,A). The copolymerization of methylvinylcyclosiloxanes with dimethylsiloxanes afford polymers with methylvinylsiloxy groups that can be rapidly cross-linked by peroxides such as 2,4-dichlorobenzoyl peroxide or other systems as described in Preparation 2-7. 

Narrow fractions of hydrogenate cyclic poly(dimethylsiloxanes) have b n prepare in good yield. A comprehensive series of analytical techniques have displaye the purity of the products and demonstrated the isolation of cyclic polymers. 

The conformational and dynamic properties of cyclic polymers have been the subject of considerable interest over a number of years [73] [74]. The new synthetic procedure developed for the preparation of per-deuterated cyclic and linear poly(dimethylsiloxane) (PDMS) polymers [12] [13] [14] now offers unique possibilities for neutron scattering studies. For the first time, it has allowed sufficient deuterated materials to be available for fractionation using our preparative GPC instrument. The resulting narrow fractions are ideally suited for both static and dynamic studies of cyclic and linear polymers. This range incorporates the critical molar mass for entanglement in PDMS. 

Clarson, S.J.,Mark, J.E., and Semiyen, J.A. (1986) Studies of cyclic and linear poly(dimethylsiloxanes) Effect of ring size on the trapping of cyclic polymers into network structures. Polymer Communications, 27,244-245. 

Kirst, K.U., Kremer, R, Pakula, T., and Hollingshurst, J. (1994) Molecular dynamics of cyclic and linear poly (dimethylsiloxanes). Colloid Polymer Science, 272,1420-1429. 

Other attempts made by Rempp et al. [48, 49] and VoUmert et al. [50] used a similar method but changed the solvent conditions using, for example, a mixture of benzene and tetrahydrofuran (THF). This allowed good coupling for the synthesis of cyclic polymers with different building blocks such as poly(2-vinyl pyridine), polybutadiene, poly(dimethylsiloxane), poly(propylene oxide), poly(ethylene oxide), and a variety of other polymers (Scheme 4). 

In Section 3 of this chapter it was mentioned that polymers obtained by intermolecular condensation of bifunctional monomers may often be prepared alternatively by an addition polymerization of a cyclic compound having the same composition as the structural unit. Typical examples are shown in Table III. The processes indicated are appropriately regarded as addition polymerizations. Each of these polymers may also be prepared through the condensation of suitable bifunctional monomers. The dimethylsiloxane polymer, for example, may be prepared, as indicated in Table I (p. 45), through the condensation of dimethyl dihydroxysilane formed by hydrolysis of the di-chlorosilane... 

A rare exception to the dominance of enthalpic driving force is provided by the unstrained eight-membered ring (Me2SiO)4, which undergoes ROP to give poly(dimethylsiloxane). For this process, A//rop is approximately zero but the remarkable skeletal flexibility of the polysiloxane backbone makes the TAArop term favourable and entropy provides the driving force for ROP. Exceptional behaviour occurs in the extremely rare cases of monomers where the polymerisation is driven by entropy and A7/rop is unfavourable. In these cases, the formation of polymer is favoured at elevated temperatures. For example, cyclo-Sg will polymerise above 150 °C (where the favourable TAArop term dominates), but slowly depolymerises back to the cyclic Sg monomer at room temperature. ... 

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