Siloxane segments

Kinning [20] studied the bulk, surface, and interfacial structures of a series of polyureas containing polydimethylsiloxane segments. In this study, the siloxane segment molecular weight (5000) and content (25 wt%) were kept constant, while... 

Once cured, PDMS networks are essentially made of dimethylsiloxane polymeric chains crosslinked with organic linkages. The general and inherent molecular properties of the PDMS polymers are therefore conferred to the silicone network. Low surface energy and flexibility of siloxane segments are two inherent properties very useful in adhesion technology. 

Synthesis of Bisphenol-A Carbonate-Siloxane Segmented Copolymers152>... 

Poly(unsaturated ester)-siloxane segmented copolymers have been prepared by the polycondensation of epoxy-terminated polydimethylsiloxanes and carboxy-terminated poly(ethylene adipate-co-maleate) oligomers 243). Reactions have been conducted in cellosolve solvent, at 140-150 °C, in the presence of 2% by weight potassium hydroxide catalyst. The molecular weights reported were fairly low. The same group has also prepared poly(hexamethylene adipate)-polydimethylsiloxane copolymers con-... 

Dynamic mechanical analysis of siloxane-urea copolymers show a sharp loss peak around —110 °C corresponding to the Tg of the siloxane segment. The transition in... 

One of the major goals of this endeavor was to solubilize the normally intractable polyimides by the incorporation of siloxane segments, and, optionally, by solution imidization. Solubilities of a series of siloxane-modified polyimide copolymers were evaluated in a variety of solvents as indicated in Table I. Copolymer solubility was found to be a function of the siloxane oligomer concentration... 

Table I. Solubilities of Bulk (B) and Solution (S) Imidized Polydmide Siloxane) Segmented Copolymers...

Fig. 19. The XPS step profiling of imide-siloxanes segmented copolymers [119]...

In addition to the polybenzimidazole blends with imide-siloxanes, it was also demonstrated that other different polyether imide-siloxane-segmented copolymers of variable composition could be used to modify semi-crystalline polyether ketones (PEEK) by presumably an analogous mechanism. The mechanical properties and transition temperatures of those systems have been reported [124,125], and would appear to be additional suitable candidates for the harsh outer space environment (see Table 4 and Fig. 21). 

Arnold CA, Summers JD, Bott RH, Taylor L T, Ward TC, McGrath JE (1987) Structure property behavior of polyimide-siloxane segmented copolymers. SAMPE Proceedings 32 586... 

Bott RH, Summers JD, Arnold CA, Blankenship CP Jr, Taylor LT, Ward TC, McGrath JE (1988) Poly(imide siloxane) segmented copolymer structural adhesives prepared by bulk and solution thermal imidization. Int SAMPE Symp Exhibit 33 (Mater-Pathway Future pp 1177-1187... 

Yoon TH, McGrath JE (1992) Enhanced adhesive performance of thermoplastic po-ly(imide siloxane) segmented copolymer with peek-graphite composites by gas plasma treatment. High Perform Polym 4(4) 203... 

Yoon TH, Arnold-McKenna CA, McGrath JE (1992) Adhesion behavior of thermoplastic polyimides and poly(imide siloxane) segmented copolymers influence of test temperatures J Adhes 39(100) 15... 

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). 

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