Some Organic-Inorganic Composites, Illustrative Simulations on Elastomer Reinforcement, and an Overview of Symposium Con
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Some Organic-Inorganic Composites, Illustrative Simulations on Elastomer Reinforcement, and an Overview of Symposium Contributions
J. E. Mark Department of Chemistry and the Polymer Research Center, The University of Cincinnati, Cincinnati, OH 45221-0172 ABSTRACT This review first describes organic-inorganic composites which have been prepared using techniques similar to those employed in the new sol-gel approach to ceramics. Organometallics such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyamides) that typically contain hydroxyl groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming novel organic-inorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic-type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer-modified ceramic. Under some conditions, bicontinuous systems are obtained. The second part addresses one of the major unsolved problems in the area of rubberlike elasticity, specifically a molecular understanding of the mechanisms by which the mechanical properties of elastomers are improved by the incorporation of particulate fillers such as carbon black or silica. Theoretical work on the reinforcement thus obtained is illustrated by some Monte Carlo calculations on one aspect of the problem, namely excluded volume effects of the filler particles on the network chain configurations. The resulting end-to-end distributions are then used in standard molecular models to generate stress-strain isotherms, which document the nature of the reinforcement obtained. The final part provides an overview of the specific papers presented at this symposium, and attempts to place them into the broad general context of "Filled and Nanocomposite Polymer Materials". ORGANIC-INORGANIC COMPOSITES Ceramic-Reinforced Polymers Introduction. Many elastomers are generally compounded with a permanent reinforcing filler, particularly those which cannot undergo strain-induced crystallization [1, 2]. In fact, the reinforcement of natural rubber and related elastomeric materials by carbon black is one of the most important processes in elastomer technology. Recently, however, a variety of other polymers such as poly(dimethylsiloxane), partially crystalline polymers, glassy polymers, and even rigid-rod polymers have become of interest in this regard [3-11]. Similarly, there is also interest in other fillers, such as precipitated silica, titania, clays, and metalic particles, and some of these can now be generated in-situ. The preparation and characterization of such organicinorganic composites is the main subject of the present review.
KK1.1.1
The polymer which has been used most extensively in studies of such precipated fillers is poly(dimethylsiloxane) (PDMS) [-Si(CH3)2O-]x. It has been chosen in part
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