Facile synthesis of phenyl‐rich functional siloxanes from simple silanes. Issue 21 (16th September 2020)

• Record Type: Journal Article
• Authors: Schneider, Alyssa F.; Lu, Emily K.; Lu, Guanhua; Brook, Michael A.
• Is Part Of: Journal of polymer science. Volume 58:Issue 21(2020)
• Page Start: 3095
• Page End: 3106
• Publication Date: 2020-09-16
• Subjects: phenylhydrosiloxanes -- phenylsilicone synthesis -- Piers‐Rubinsztajn reaction -- redistribution free process -- structured copolymers; Polymers -- Periodicals; Polymerization -- Periodicals; Polymerization; Polymers; Periodicals; 547.7
• DOI: 10.1002/pol.20200527
• Languages: English
• ISSNs: 2642-4150

Abstract

Abstract: Phenyl‐rich silicone polymers are used for their excellent thermal properties and high refractive indices. Traditional syntheses of these polymers utilize cationic or anionic equilibration, which limits the molecular weights that can be achieved due, in part, to the coproduction of cyclic monomers that must be removed. Kinetically controlled processes may reduce the impact of these limitations, but require high temperatures, alkyllithium initiators and an inert atmosphere; precise structures are difficult to access. The Piers‐Rubinsztajn reaction, combined with hydrolysis, allows the synthesis of highly ordered, Si‐H terminated, phenyl‐rich silicone homo‐ and copolymers comprised of phenylmethyl, diphenyl and, dimethylsilicone monomers. The processes are mild and permit a high level of structural control, including alternating copolymers with different levels of phenyl content (Ph/Si = 0.3–1.5) with molecular weights up to ~100 kDa. Yet higher molecular weights could be achieved—Mn up to 300 kDa—when phenyl‐rich siloxanes were incorporated into block copolymers with dimethylsilicones (Ph/Si = 0.4). Unlike kinetic processes in which cyclic byproducts are formed by redistribution or backbiting (particularly at high conversion), in this process cyclics form near the onset of the reaction and only with low molecular weight starting materials (< 4 siloxane units). Abstract : High molecular weight, high aryl content, HSi‐terminated phenyl and diphenylsilicones are readily prepared from alkoxy‐ and hydrosilane monomers and oligomers. Without backbiting or redistribution, in the presence of B(C6 F5 )3 as catalyst, the process combining hydrolysis and condensation is mild and permits a high level of structural control.