ISSN:
0887-624X
Keywords:
hydrosilylation
;
silsesquioxane
;
oxysilylation
;
allyloxyaromatic
;
hydridosilane
;
hydridosiloxane
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Pt-and Pd-catalyzed reactions of a set of allyloxyaromatic mono-and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum-1,3-divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4-allyloxy methylbenzoate gave relative reactivities (HSiO1.5)8 ≫ Et3SiH 〉 HMe2Si—O—SiMe2H 〉 Ph2SiH2. The cubic silsesquioxane, (HSiO1.5)8, is so reactive hydrosilylation is over in 1-3 h at 0°C. All other reactions required 〉 40°C and longer reaction times. Initial efforts to form high polymers by Pt-catalyzed reactions of bis-allyloxy aromatics with Ph2SiH2 provide polymers with bimodal MW distributions (polystyrene), Mws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of Si—O bonds, “oxysilylation.” The same products appear (10-15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph3P[Pd(dba)2/Ph3P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph2SiH2 〉 HMe2SiOSiMe2H 〉 Et3SiH. Polymerization with Pd catalysts provides polymers with Mws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO1.5)8 with 4 equiv. of 4-(4-allyloxy-benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [Mn ≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC transitions is presented. © 1994 John Wiley & Sons, Inc.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pola.1994.080321608
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