Deuterated cyclic poly

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

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. 

The above reaction incorporating D is obviously restricted to those polycyclic hydrocarbons that react in the Co2(CO)g catalytic system but not all poly-cyclics are reactive e.g., phenanthrene reacts only very slowly under these conditions (65). Quite a few hydrocarbons have been investigated. When they react they generally seem to give only one product (62) making it possible to have specific positions labelled on specific hydrocarbons. This is obviously not a general method for preparing deuterated aromatic compounds. 

The traces obtained from the GLC analysis of the reaction (Figure 25) clearly show the production of what have been identified, through the use of GC/EI-MS, as linear phenyl terminated poly(dimethylsiloxane) oligomers (Ph-(Si(CE)j)20) -Si(CD3)2Ph). The subsequent removal of the terminal phenyl groups upon further reaction with triflic acid was seen to result in a rearrangement to small cyclic oligomers of per-deuterated dimethylsiloxane. 

The bulky t-butyl substituent Is expected also to cause more severe restriction In the possible preferred conformation of the cyclic tetramer In comparison with the corresponding linear polymer, poly((l )-t-butylox1rane). The chemical shift and coupling constant values In the NHR spectra of the cyclic tetramer in deuterated benzene and chloroform are listed In Table IV. 

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