Phase Behavior of cis–trans Mixtures of Double-Decker Shaped Silsesquioxanes for Processability Enhancement

Abstract

Closed double-decker shaped silsesquioxanes (DDSQ-(Ph)8-2­((Me)­(R))) with R as phenyl, para-phenylamine, and para-phenylethynyl phenyl were synthesized. Isolation of nearly pure trans and cis isomers was obtained by fractional recrystallization. Crystallographic and thermal characteristics of these isolated isomers were obtained by X-ray diffraction of a single crystal and differential scanning calorimetry (DSC). It was observed that melting temperature increases as the size of the R group decreases from para-phenylethynyl phenyl to phenyl and the magnitude of the entropy difference at melting increases as the size of the R group increases. Isolated isomers were then mixed to different cis-to-trans ratios, and their thermal characteristics investigated by DSC. The upper portion of the phase diagram was constructed for these DDSQ compounds using results from DSC traces. Interestingly, cis and trans isomers of these DDSQ compounds form a binary eutectic. Experimentally observed eutectic composition and temperature were found to be close to the calculated values based on the ideal eutectic mixing rule. These data allow users to broaden the thermal processability window by reducing the system melting temperature without affecting the reaction onset temperature of the functional groups.

Phase Behavior of Selected Condensed Double-Decker Shaped Silsesquioxane Compounds

“…Once separated, it was demonstrated that cis DDSQ-2(RR') has a different crystallographic structure than trans DDSQ-2(RR') as well as different thermal and physical properties [4,5,19].…”

“…Recently, the phase behavior of cis and trans DDSQ-2(RR') binary mixtures where R was methyl and R' was phenyl, aniline, or 1,4-phenylethynyl(phenyl) was reported [19]. From the study, it was determined that the bulkier moiety has a reductive effect on the melting temperature of isolated cis and trans isomers.…”

“…Synthesis of (C 6 H 5 ) 8 Si 10 O 14 (CH 3 ) 4 7,7,17,17-tetramethyl-1,3,5,9,11,13,15,1octaphenylhexacyclo[9.13.1 1,9 .1 3,15 .1 5,13 .1 11,19 ]decasiloxane -DDSQ-2Me 2 (2) Compound 2 was synthesized using the general procedure with (CH 3 ) 2 SiCl 2 (7.85 mmol, 0.96 mL). This provided 4.01 g (91% yield) of compound 2 as a white powder.…”

“…These hybrid polymers exhibit lower contact angles, lower dielectric constant, and improved flammability, with a minimal impact on the mechanical and optical properties with respect to control polymers [6,[11][12][13][14][15][16][17]. It was recognized for R different than R', the as-synthesized product is a mixture of cis and trans isomers about the double-decker shaped silsesquioxane core [1,2,4,5,[18][19][20]. Isolation of these isomers can be achieved by selective solvent fractional crystallization, liquid chromatography, or a combination of both depending on the chemical moiety of R and R' [2,5,9,[18][19][20].…”

“…It was recognized for R different than R', the as-synthesized product is a mixture of cis and trans isomers about the double-decker shaped silsesquioxane core [1,2,4,5,[18][19][20]. Isolation of these isomers can be achieved by selective solvent fractional crystallization, liquid chromatography, or a combination of both depending on the chemical moiety of R and R' [2,5,9,[18][19][20].…”