POLY 543 |
| Polyhedral Oligomeric Silsesquioxanes (POSS) are nanoparticles that are used to enhance the thermal and mechanical properties of many polymeric systems. Starting in 1993 there has been extensive research in understanding how POSS affects these properties. Certain POSS macromers can be copolymerized with organic monomers to form nanocomposite type materials. A model is emerging for how addition polymerized POSS copolymers can undergo a type of self assembly to form a nanocomposite. The R-group on the POSS moiety plays a critical role in determining the properties of the nanocomposite, as it determines the level of compatibility of the POSS with the comonomer and how strongly the POSS cages associate. A common (but not always observed) phenomenon with POSS in glassy polymers, is that cyclohexylPOSS often increases thermal transitions while isobutylPOSS frequently plasticizes. It is possible that this is due to the length scale of the POSS-cage domains and/or their level of compatibility with the polymer matrix. To help define the microstructure of addition copolymers, the POSS macromer and organic monomer reactivity ratios need to be known. Previously, we reported that the reactivity ratios of styrene and isobutylPOSS-styrene, (C4H9)7(C8H7)([Si8O12], r(styrene) = 0.84 and r(iBuPOSS-styrene) = 0.38) to be indicative of random copolymerization. We now report similar reactivity ratio data for a cyclohexylPOSS-styrene copolymerized with styrene: r(styrene) = 0.80 and r(CyPOSS-styrene) = 0.14. Therefore, one expects a free radical polymerization to yield fairly random copolymers. The consequences of this observation are that the POSS aggregation phenomena observed for many different copolymers is a self assembly process and not simply caused by block copolymerization. |
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Silicones and Silicone-Modified Materials
6:00 PM-8:00 PM, Tuesday, 12 September 2006 Moscone Center -- Hall D, Poster
Division of Polymer Chemistry |