Hybrid Inorganic/Organic Diblock Copolymers. Nanostructure in Polyhedral Oligomeric Silsesquioxane Polynorbornenes.
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Hybrid Inorganic/Organic Diblock Copolymers. Nanostructure in Polyhedral Oligomeric Silsesquioxane Polynorbornenes. Timothy S. Haddad*, Patrick T. Mather§, Hong G. Jeon‡, Seung B. Chun§, Shawn H. Phillips† *ERC Corp., and †Air Force Research Lab, Edwards Air Force Base, CA 93524 §Institute of Materials Science, University of Connecticut, CT 06269 ‡Systran Corp., Air Force Research Lab, Wright Patterson Air Force Base, OH 45433 ABSTRACT Our main approach to the synthesis and study of hybrid organic/inorganic materials involves incorporating nano-size inorganic polyhedral oligomeric silsesquioxane (POSS) clusters into various polymeric resins. A typical POSS cluster is a discrete silicon and oxygen framework solubilized with organic groups and contains a single reactive site. This lone site of reactivity is used to covalently attach the inorganic macromers pendent to a polymer backbone without causing any crosslinking. This strategy permits the synthesis of melt processable, linear hybrid polymers containing pendent inorganic clusters, and allows us to study the effect these clusters have on chain motion, polymer properties and morphology. The synthesis of norbornenyl-based (POSS) macromers, their ring opening metathesis copolymerizations with varying amounts of norbornene, and analysis of the effect of the pendent POSS group is presented. Ring opening metathesis polymerization permits the easy synthesis of both random and diblock copolymers. Transmission electron microscopy (TEM) clearly images POSS-rich domains against the POSSfree regions. Major differences in polymer morphology are observed as the amount of inorganic POSS is varied, between random and diblock copolymers, as well as between polymers that differ only in the solubilizing cycloalkyl groups on the POSS cluster. INTRODUCTION The design of new materials with enhanced properties continues to be a driver for the investigation of hybrid materials. As hybrid materials are copolymers based on inorganic and organic comonomers, they display enhanced properties by bridging the property space between two dissimilar types of materials [1]. A typical hybrid material will contain a crosslinked inorganic phase bound (often covalently) with an organic phase. An alternative approach, that several groups have pursued, is to append well-defined monodisperse silica-like clusters into thermoplastic resins [2-7]. The resulting hybrid polymers are easily processed, yet their physical properties are modified by the effect of the nano-sized inorganic component. Our research has focused on using well-defined POSS (polyhedral oligomeric silsesquioxane) molecules for the inorganic component. Thermoplastics modified with POSS tend to show an increase in glass transition and modulus, a large increase in heat distortion temperature and a reduction in flammability. Changes to the rheological properties appear to
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