Siloxane polymers poly

Synonyms Dimethyl siloxy stearoxy siloxane polymer Poly (dimethylsiloxy) stearoxysiloxane Siloxanes and silicones, dimethyl, (octadecyloxy)-terminated... 

The presence of carbon—fluorine bonds in organic polymers is known to characteristically impart polymer stabiUty and solvent resistance. The poly(fluorosibcones) are siloxane polymers with fluorinated organic substituents bonded to siUcon. Poly(fluorosibcones) have unique appHcations resulting from the combination provided by fluorine substitution into a siloxane polymer stmcture (see Silicon compounds, silicones). 

Poly(dimethyl siloxanc) with vinyl or hydrosilanc (Si-H) chain ends have been converted to ATRP initiator ends e.g. Scheme 9.62) by hydrosilylalion, Bis-functional dimethyl siloxane polymers prepared in this way were used in polymerizations of S, MA, tsobornyl acrylate and BA to form ABA triblock copolymers. 

Silaarylene and silaarylene-siloxane polymers have been reviewed [56]. Recent work of interest on such systems is that of Koide and Lenz on poly(silaarylene-siloxanes) [57] and of Ishikawa et al. [58] on poly(p-(disilanylene)phenyIenes), synthesized as shown in eq. 15. 

The preparation of poly(m-carborane-siloxane) polymers has also been successfully achieved directly from the carborane monomer.22 The reaction used is shown in scheme 9. Here, the direct salt elimination reaction between dilithiocarborane and a dichlorosiloxane (e.g., 1,5-dichlorohexamethyltrisiloxane) results in the formation of linear polymers with a molecular-weight (M ) typically of 6800 dalton. However, the reported literature detailing this approach is very limited indeed, and the reaction has not found significant use. This is most probably because only relatively low molecular-weight polymers can be produced, ultimately restricting the flexibility to produce materials of controlled mechanical properties. 

The most frequently quoted example to illustrate this behaviour is the children s toy Silly Putty , which is a poly(dimethyl siloxane) polymer. Pulled rapidly it shows brittle fracture like any solid but if pulled slowly it flows as a liquid. The relaxation time for this material is 1 s. After t = 5t the stress will have fallen to 0.7% of its initial value so the material will have effectively forgotten its original shape. That is, one could describe it as having a memory of around 5 s (about that of a mackerel ). Many other materials in common use have relaxation times within an order of magnitude or so of 1 s. Examples are thickened detergents, personal care products and latex paints. This is of course no coincidence, and this timescale is frequently deliberately chosen by formulation adjustments. The reason is that it is in the middle of our,... 

Polycondensation of Bisphenols, II, with Phosgene. Polycondensation of siloxane-linked bisphenols, II, with phosgene is the most obvious synthetic approach leading to siloxane-modified poly(arylene carbonates) since the phosgene-bisphenol polycondensation is used in the synthesis of aromatic polycarbonates (1). This method was used initially to prepare polymer (as indicated in reaction 1) as well as for the attempted synthesis of polymers 2 and 5 ... 

Heteropolycondensation of Bis-silanols, III, with Diacetoxysilanes. Heteropolycondensation of bis-silanols, III, was investigated since this approach appeared to offer a relatively rapid preparative route to a number of various siloxane-modified poly(arylene carbonates) which were required in order to obtain structure-properties correlations for such polymers. 

It was found that the reaction conditions which were optimized for the synthesis of poly(arylene siloxanylenes) (43) could be employed for the synthesis of siloxane-modified poly-(arylene carbonates). 2,4,6-Trimethylpyridine (collidine) was selected as the most suitable of all catalysts investigated (43) for the synthesis of the siloxane modified poly(arylene carbonates). Properties of polymers prepared by this method are given in Table I. In comparision to the phosgene-catalyzed homo-polycondensation of bis-silanols, III, the inherent viscosities... 

At the other end of the temperature spectrum, with high thermal stability of siloxane-modified poly(arylene carbonates) also a desired property, the onset of thermal decomposition (40) for polymers 1-12 was found to be in the range of 385-456°C (as determined from TGA curves obtained by heating polymer samples in nitrogen at a heating rate of 20°C/min.). There does not appear to be any pronounced trend in regard to variation of the thermal stability with structure in polymers 1-12. The small differences in the values of T for these polymers can be due... 

It is intriguing that even some flexible siloxane polymers form mesomorphic (liquid-crystalline) phases.34 139-166 Some illustrative data are given in Table 4.2. Both poly(diethylsiloxane) and pol y(di-n-propylsiloxane) show two crystalline modifications as well as a mesomorphic phase. (The other major class of semi-inorganic polymers, the polyphosphazenes, are also relatively flexible, and show similarly interesting behavior.)10167... 

Glucose Sensors. Siloxane polymers are known to be extremely flexible. This flexibility will, of course, be sensitive to the amount of side-chain substitution present along the polymer backbone. For instance, in the homopolymer used in these studies (polymer A), the presence of a ferrocenylethyl moiety bound to each silicon subunit should provide an additional degree of steric hindrance, and thus a barrier to rotation about the siloxane backbone, in comparison with the copolymers, which have ferrocene relays attached to only a fraction of the Si atoms. Because these siloxane polymers are insoluble in water, their flexibility is an important factor in their ability to facilitate electron transfer from the reduced enzyme. Relays contained within more rigid redox polymers, such as poly(vinylferrocene), cannot achieve close contact with the enzyme s redox centers and are thus less effective as electron transfer mediators (25,34). The importance of this feature can be seen quite clearly by comparing the mediating ability of the homopolymer A with that of copolymers B-D, as shown in Figures 4 and 5. 

It is clear from these results that the ability of the redox polymers to mediate electron transfer from reduced choline oxidase is dependent upon the structure of the polymer backbone. The trend in mediating efficiency is qualitatively the same as that found for the glucose sensors siloxane-ethylene oxide branch polymer > poly(ethylene oxide) > poly(siloxane). 

Keohan FL, Hallgren JE (1990) Novel poly(imide-siloxane) polymers and copolymers. Adv Chem Ser 224 (Silicon-Based Polym Sci) 165... 

According to the statistical-mechanical theory of rubber elasticity, it is possible to obtain the temperature coefficient of the unperturbed dimensions, d InsjdT, from measurements of elastic moduli as a function of temperature for lightly cross-linked amorphous networks [Volken-stein and Ptitsyn (258 ) Flory, Hoeve and Ciferri (103a)]. This possibility, which rests on the reasonable assumption that the chains in undiluted amorphous polymer have essentially their unperturbed mean dimensions [see Flory (5)j, has been realized experimentally for polyethylene, polyisobutylene, natural rubber and poly(dimethylsiloxane) [Ciferri, Hoeve and Flory (66") and Ciferri (66 )] and the results have been confirmed by observations of intrinsic viscosities in athermal (but not theta ) solvents for polyethylene and poly(dimethylsiloxane). In all these cases, the derivative d In sjdT is no greater than about 10-3 per degree, and is actually positive for natural rubber and for the siloxane polymer. 

In synthesized cyclolinear siloxane polymers (CLSP) the dimethylsiloxane unit was taken as a flexible spacer [74], Table 10 shows temperatures and heat transitions in relation to the flexible spacers lengths. These polymers were found in the crystalline and thermotropic states, like trans-tactic poly-(decaorganocyclohexasiloxanes), but temperature range of the... 

We would like to report the synthesis of a star-shape poly(vinylmethyl-c6>-dimethyl)siloxane polymers functionalized in their exterior, which makes them especially suitable for application as catalytic supports. Similarly to catalysts bound to periphery-functionalized dendrimers [3] they offer regularly distributed and available catalytic sites. 

In this chapter we want to discuss the correlation of the mesophase behavior of a cyanobiphenyl-based SCLCP with its backbone structure. As shown before, the backbone structure, the spacer lengths, and the mesogen density per repeat unit have great influence on the LC mesophase evolved. Ligure 8 shows some examples of backbone structures bearing the cyanobiphenyl-moiety that have been reported in literature. The above-mentioned ROMP-derived polymers poly-(II-n) [39],poly-(IV-n) [42,47],poly-(VI-n) [41],andpoly-(VII-n) [53] will be compared with each other and with acrylate-based [56-59], siloxane-based [60] and vinylcyclopropane-based systems [61]. The detected mesophases and their transition temperatures are summarized in Table 6. 

The monomers XXIV-m-n were polymerized with initiator 4 in a monomer to initiator ratio of about 50. Table 16 summarizes the physico-chemical data for these polymers. Poly-(XXIV-m-n) exhibited smectic C mesophases, but these phases were only observed over a small temperature range and isotropization occurred shortly after the glass transition. It was not possible to identify the mesophase by polarized optical microscopy, but the smectic phase was confirmed by X-ray scattering experiments. Transition temperatures increased with the length of the carbon segments (n) but decreased with increasing siloxane segment (m). 

D) polybutadiene, (E) polytetramethyl - sulp henyl siloxane, (F) poly(methyl methacrylate), (G) poly(ethylene glycol), (H) poly(vinyl acetate) and (I) polystyrene [redrawn from G. C. Berry and T. G. Fox, Adv. Polym. ScL, 5,261 (1968)]. 

Homopolymers. Flexibility. The most important siloxane polymer is poly(dimethylsiloxane) (PDMS), [-Si(CH3)20-] (3). PDMS is also one of... 

---