Deuterated cyclic

Blends of protonated and deuterated cyclic PDMS and also blends of protonated and deuterated linear PDMS were studied. It was found that the radius of gyration Rg of the linear and cyclic chains varies with molar mass according to different power laws. The exponent 0.53 for linears is dose to the value of 0.50 predicted for flexible chains, obeying a Gaussian statistics in solution. A lower value of 0.42 forcydic indicates a more compact conformation in the melt. Another consequence of these data concerns the ratio of the mean square radii of gyration (Rg) /(Rg)i, which is a constant in solution (0.5), but decreases with the molar mass for PDMS in the molten state. 

Dagger, A. C. Semiyen, J. A., Hydrogenated and Deuterated Cyclic Poly(dimethylsiloxanes). In Silicones and Silicone-Modified Materials, Clarson, S. 

In this chapter we show how hydrogenated cyclic PDMS is prepared, characterised and investigated. These studies form the basis of our preparation and characterisation of the first deuterated cyclic polymers [12] [13] [14]. These are per-deuterated PDMS [(CD3)2SiO], and they were obtained by a modification of the method described by Beltzimg and coworkers [15]. Preparative GPC was used to prepare sharp fractions in a similar way to the hydrogenated materials. 

Fxperimental. The first range of per-deuterated cyclics have been achieved in improved yield via the route shown in Figure 24 fix)m per-deuterated methyl iodide [12]. 

The per-deuterated cyclic dimethylsiloxanes produced in these reactions were to be fijrther polymerised in various ways to yield mixtures of larger cyclic and linear polymers which could be separated and fractionated using preparative GPC in a recognised fashion. 

Table II Peak assignments for the GC/EI-MS spectra of the small per-deuterated cyclic dimethylsiloxanes.

The successfiil preparation of foe small per-deuterated cyclic dimethylsiloxanes now meant that larger cyclics and linears could in theory be prepared in a recognised fashion from the small rings via either foe Brown and Sluzarczuk [4] or foe Chojnowski [30] [31] [32] [33] methods. Die investigations in to foe triflic acid reaction with dimethyldiphenylsilane, however, showed the possibility that foe reaction might be catalytic and so this was attempted with deuterated materials and is described below. 

The polydisperse per-deuterated cyclic PDMS recovered from the catalytic reaction was fractionated in to twelve sharp fractions using the preparative GPC instrument detailed earlier [5]. A section of the preparative trace is shown in Figure 35. The fractions were an ysed using analytical GPC calibrated with cyclic PDMS standards and the results of the analysis are shown in Table IV. 

The purity of the deuterated cyclic PDMS fractions were verified using infrared absorption, mass spectrometry and and Si nuclear magnetic resonance spectroscopies. 

Figure 35 Preparative GPC chromatogram recorded during the fractionation of the deuterated cyclic PDMS.

The toher work carried out investigating die effects of dilution and triflic acid concentration on the reaction with bis(trideuteomcthyl)diphenylsilane has optimised a catalytic route to both linear and cyclic po -deuterated PDMS of high purity in good yields enabling the first narrow fractions of deuterated cyclic polymers to be prepared. 

The identification of a viable route which yields sufficient quantities of per-deuterated cyclic polymers to allow 15 actionation in to very sharp fractions, now enables us for the first time to carry out neutron scattering experiments investigating the conformations and properties of cyclic and linear pol3miers in chemically identical blends. 

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. 

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