Polydimethylsiloxane sequences

So far in this chapter on sequencing, two techniques have predominated NMR spectroscopy and Py-GC. An exception is the work of Zhuang and co-workers [67] who used ToF-SIMS in their study of the distribution of polydimethylsiloxane (PDMS) segment lengths at the surface of PDMS-urethane-segmented copolymers. Their aim was to establish whether, at the copolymer surface, the distribution of segment or chain lengths is different from that in the bulk of the polymer. 

Silanol-terminated linear polydimethylsiloxane pol3miers can be crosslinked to elastomers by a variety of reactions. Among these is the reaction with acetoxysilanes, shown schematically in reaction sequence A. The first reaction takes place upon... 

Fig. 23a-c. Relative amplitude of the slowly decaying tail of the transverse relaxation curve measured in a linear polyethylene (PE), b polydimethylsiloxane (PDMS), and c polytetrahydrofuran (PTHF) as a function of the molecular mass [36], The data have been recorded with standard Hahn echo and Carr/Purcell/Meiboom/Gill pulse sequences. The values of the critical molecular weight are indicated on the abscissa axes. Extrapolating the data for M - Mc suggests q l as predicted by the whip model (Eq, 167)... 

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