Joseph J. Schwab

Structural development during deformation of polyurethane containing polyhedral oligomeric silsesquioxanes (POSS) molecules

A unique polyurethane (PU) elastomer containing inorganic polyhedral oligomeric silsesquioxane (POSS) molecules as molecular reinforcements in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques. The mechanical properties of POSS modified polyurethane (POSS-PU) were also compared to those of polyurethane without POSS. The crystal structures of two different POSS molecules were first determined by X-ray powder diffraction analysis, yielding a rhombohedral cell with aa 11.57 A ˚, aa 95.58 for octacyclohexyl-POSS (1,3,5,7,9,11,13,15octacyclohexylpentacyclo[9.5.1.13,9.15,15.17,13] octasiloxane) and aa 11.53 A ˚, aa 95.38 for hydrido-POSS (1-[hydridodimethylsiloxy]3,5,7,9,11,13,15-heptacyclohexylpentacyclo [9.5.1.13,9.15,15.17,13] octasiloxane). WAXD results showed that reflection peaks distinct to POSS crystal diffraction were seen in POSS-modified polyurethane, which suggests that POSS molecules formed nanoscale crystals in the hard domain. During deformation, the average size of POSS crystals in POSS-PU was found to decrease while elongation-induced crystallization of the soft segments was observed at strains greater than 100%. The SAXS results showed microphase structure typical of segmented

Nanoscale reinforcement of polyhedral oligomeric silsesquioxane (POSS) in polyurethane elastomer

A unique class of polyurethane (PU) elastomer containing inorganic molecules (polyhedral oligomeric silsesquioxane, POSS) as molecular reinforcement in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. WAXD results indicate that POSS molecules form nanoscale crystals showing distinct reflection peaks. The formation of POSS crystals is probably prompted by the microphase separation between solid-like hard segments and rubbery soft segments in PU. The microphase separation of hard and soft segments was observed by SAXS, which shows a long period of 111 A for 34 wt% POSS-PU and 162 A for 21 wt% POSS-PU, and hard segment domains with sizes of about 34 A for both of them. WAXD results from a series of POSS compounds with a corner substituted by a functional group of varying length were compared with POSS-PU, which also confirms the presence of nanoscale POSS crystals in the polymer matrix. © 2000 Society of Chemical Industry

Synthesis, Characterization and Reactivity of cis-cis-cis [(C6H5)4Si4O4(OH)4]

The hydrolytic condensation of PhSiCl3 (H2O/acetone, 0–5 C, 18 h) precipitates cis-cis-cis-[(C6H5)4Si4O4(OH)4] (5a) as the sole crystalline product in approximately 40% yield. The all-cis structure, which was originally assigned by J. F. Brown on the basis of IR spectroscopy and derivatization studies, was confirmed by a single-crystal X-ray diffraction study. The ether solvate of 5a crystallizes from Et2O/C6H6 as a hydrogen-bonded, dimeric structure, which kinetically stabilizes the molecule toward self-condensation reactions. In solution, particularly in the presence of weak amine bases, 5a rapidly self-condenses to form “T-resins”; self-condensation also occurs in the solid-state (25° C) over several months. Tetrasilanol 5a can be exhaustively silylated with Me3SiCl to afford excellent yields of cis-cis-cis-[(C6H5)4Si4O4(OSiMe3)4] (10), but all attempts to effect clean partial silylation produced complex mixtures of partially silylated T-resins. Attempts to effect catalytic hydrogenation of 5a to cis-c...

Polyhedral Oligomeric Silsesquioxanes (Poss): Silicon Based Monomers and their Use in the Preparation of Hybrid Polyurethanes

Abstract : A series of Polyhedral Oligomeric Silsesquioxane (POSS) monomers bearing reactive hydroxyl functionalities, suitable for incorporation into step-growth polymers, is described. These monomers are difunctional in nature and are particularly well suited for use as chain extenders in the synthesis of polyurethanes. This work describes the synthesis of these POSS and their incorporation into a series of polyurethanes. Preliminary thermal, mechanical and rheological data for the POSS containing polyurethanes will also be discussed.

STRUCTURAL ASSIGNMENT OF A MOLYBDENUM-CONTAINING SILSESQUIOXANE WHICH CATALYZES THE METATHESIS OF OLEFINS : DPFGSE-NOE AND X-RAY DIFFRACTION STUDIES

The reaction of [(c‐C6H11)7Si7O9(OSiMe3)(OTl)2] with [Mo(CHCMe2Ph)(NAr)(OSO2CF3)2(dme)] (Ar=2,6‐diisopropylphenyl) affords 4a as the predominant (>99%) molybdenum‐containing product. Assignment of 4a as the syn‐isomer with juxtaposed arylimido and Me3Si groups was made on the basis of double pulsed field gradient spin echo (DPFGSE) NOE experiments and confirmed by a single‐crystal x‐ray diffraction study.

A General Strategy for Synthesizing Cubeoctameric Silsesquioxanes Containing Polymerizable Functional Groups

A general method has been developed for the preparation of silsesquioxanes with potentially polymerizable p,p′-disubstituted diphenylmethyl groups attached to one vertex of the “T” framework, including [Cy7−Si8O12(CH2)4CH(C6H4OH)2] ( 9a ), [Cy7Si8O12(CH2)10CH-(C6H4OH)2] ( 9b ), [Cy7Si8O12(CH2)4CH(C6H4NH2)2] ( 10a ), [CY7Si8O12(CH2)10CH(C6H4NH2)2] ( 10b ), Cy7Si8O12(CH2)4CH(C6H4NH2)2] ( 14 ). The reaction of [Cy7Si8O12CH2CH2CH2CO2CH3] ( 2 ) with BrMgC6H4OCH2Ph ( 6a ) affords an interesting disilanol derived from the hydrolytic cleavage of one Si-O-Si linkage in a completely condensed Ts framework.