Chains: molecular siloxane, polymer

The siloxane polymer usually has a rather high molecular weight, and may have reactive ends for end-linking curing or vinyl side chains for peroxide curing. 

Rheological measurements are of central importance in the processing of siloxane polymers. Typical studies would include determination of the dependence of the bulk viscosity of the material on the average molecular weight, molecular weight distribution, and rate of shear. Characterization of the effects of any branched chains or reinforcing fillers present is also of great importance.16... 

Silicone polyethers are non-ionic in nature, and have both a hydrophilic part (low molecular weight polymer of ethylene oxide or propylene oxide or both) and a hydrophobic part (the methylated siloxane moiety). The polyether groups are either ethylene oxide or propylene oxide, and are attached to a side chain of the siloxane backbone through a hydrosilylation or condensation process. They can form a rake-like, comb structure, or linear structure. Silicone polyethers are stable up to 160-180 degrees Celsius. There is a great degree of flexibility in designing these types of polymers. A very wide variety of co-polymers is possible when the two chemistries are combined. 

The heuristic rule for solubility in liquid solvents, like dissolves like, applies similarly to polymers dissolving in SCFs. Thus, hydrocarbon polymers such as polyethylene are soluble in hydrocarbon SCFs such as the alkenes and n-alkanes, while polar polymers such as poly(methyl methacrylate) are soluble in polar SCFs such as chlorodifluoro-methane. Carbon dioxide is generally a poor solvent for most high molecular weight polymers [14], but notable exceptions exist, such as siloxane polymers and fluorinated polymers. Solubility in CO2 is also enhanced when CO2-phUic moieties are located in accessible side chains rather than in the less accessible main chain [15]. 

The newest data show that in polydime thylsiloxanes, the molecular chains possess a helical structure with three to six silicon atoms in the helix [16, 17]. Under the action of high temperatures, such a structure creates favorable conditions for the closing of rings with chain cleavage. This is also confirmed by the experimental observations. Polydimethyl-siloxane decomposes into low-molecular cyclic polymers upon heating under vacuum at high temperatures, without appreciable cleavage of the Si—C bonds ... 

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