Siloxane-Organic Copolymers

For decades I avoided mixtures or copolymers of organic resins with silicones, even abhorred them, because I did not want the pristine properties of my silicone brain children to be degraded or ruined by adulteration. Now, all manner of siloxane-organic copolymers (such as the polyimide block copolymers) with disciplined structures and admirable properties have been developed. 

Scheme S. Synthesis of a block semigraft siloxane-organic copolymer.

Cazacu, M. Racles, C. Alexandru, M. Ignat, M. loanid. A. Vlad, A., Morphology and Surface Properties of Some Siloxane-Organic Copolymers. Polym. Int. 2008, 58, 697-702. 

This section is dedicated to all-siloxane copolymers. Siloxane-organic copolymers constitute a separate, very broad class of maaomolecular stmctures, and the reader is referred to more specialized reviews. 

Biomedical Applications Due to their excellent blood compatibility (low interaction with plasma proteins) and high oxygen and moisture permeabilities, siloxane containing copolymers and networks have been extensively evaluated and used in the construction of blood contacting devices and contact lenses 376). Depending on the actual use, the desired mechanical properties of these materials are usually achieved by careful design and selection of the organic component in the copolymers. 

Poly(imide-siloxane)s copolymers have been prepared by the reaction of 4,4 -(4,4 -isopropylidene-diphenoxy)bis(phthalic anhydride), 4,4 -oxydiani-line, and an amino-propyl terminated poly(dimethyl-siloxane) [12]. The polymers exhibit a good solubility in various organic solvents. In addition, 4,4 -(hexafluoroisopropylidene)diphthalic anhydride was used as hard block segment [84]. 

Chapter 5 is a review of polyhedral oligomeric silsesquioxanes (POSS), hybrid POSS-organic copolymers, and POSS resin nanocomposites. Although silsesquioxanes have been known since tiie 1960s, only recently, through controlled synthesis and purification, have their structure and unique properties been determined and their useful applications been explored. This chapter is complemented by a discussion of the synthesis and properties of silica- and silsesquioxanes-containing polymer nanohybrids in Chapter 6. Chapter 7 involves a review of the preparation and characterization of siloxane-based polyviologens, polyurethanes, and divinylben-zene elastomers. 

Gaines [13] has reported on dimethylsiloxane-containing block copolymers. Interestingly, if the organic block would not in itself spread, the area of the block polymer was simply proportional to the siloxane content, indicating that the organic blocks did not occupy any surface area. If the organic block was separately spreadable, then it contributed, but nonadditively, to the surface area of the block copolymer. 

The most commonly used siloxane modifiers are those having phenyl, trifluoro-propyl and cyanopropyl substituents. Introduction of phenyl units into the polydimethylsiloxane backbone either in the form of methylphenylsiloxane or diphenyl-siloxane increases the thermal and oxidative stability, glass transition temperature and the organic solubility characteristics of the resulting copolymers. At low levels (5-10 percent by weight) of incorporation, bulky phenyl groups also break up the regularity of polydimethylsiloxane chains and inhibit the crystallization (Tc... 

Drake, R. MacKinnon, I Taylor, R. Recent Advances in the Chemistry of Siloxane Polymers and Copolymers. In The Chemistry of Organic Silicon Compounds Rappoport, Z., Apeloig, Y., Eds. Wiley Chichester, 1998 Vol. 2, Part 3, Chapter 38, pp 2217-2244. 

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