Facile synthesis of phenyl‐rich functional siloxanes from simple silanes

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-M n 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).

High Refractive Index, Enantiopure Silicones Based on BINOL

“…The PR reaction superficially appears to be a typical condensation reaction. However, previous work has shown that the process more closely mimics the kinetics of a chain growth process, one consequence of which are very narrow dispersities, often Đ M < 1.5; [ 11 ] purely step growth polymerization would normally lead to dispersities of 2 in the best case. [ 45 ] Nevertheless, the same challenges of producing high molecular weight polymers obtain in these processes as with AA + BB condensation reactions; a slight mismatch of the [HSi]/[OH] reduces the final molecular weight and will affect the nature of the terminating groups.…”

“…Various other strategies have been employed to increase RI, including the use of “in line” aromatic compounds such as silphenylene, [ 12 ] phenylacetylene derivatives, [ 13 ] and compounds that include polycyclic aromatic hydrocarbons. [ 14 ] Phenylsilicones may achieve an RI near 1.55–1.58 [ 11 ] and, for the polycyclic aromatic compounds described by Kickelbick et al., up to 1.63. [ 15 ] Note that the inclusion of high RI constituents such as titania [ 16 ] or the use of densely reticulated materials can also lead to materials/composites with higher RI, up to about 1.6.…”

“…[4][5][6][7][8] Phenyl compounds are widely available commercially and may contain phenylmethyl-and/or diphenylsilicone monomers, typically in addition to Me 2 SiO monomers as random copolymers or blocks. [9][10][11] Their preparation has been optimized in industry, but using challenging chemistry: arylboranes, Grignard processes etc. Various other strategies have DOI: 10.1002/marc.202200022 been employed to increase RI, including the use of "in line" aromatic compounds such as silphenylene, [12] phenylacetylene derivatives, [13] and compounds that include polycyclic aromatic hydrocarbons.…”

When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D3

“…One simply chooses the number of alkoxysilane or silanol substituents, or water, required for the synthesis of a given linear or branched monomer, and then adds the appropriate mono-, di- or oligofunctional HSi-containing molecules in the presence of BCF [ 25 ]. It is thus possible to create linear polymers, including block-copolymers, simply by combining telechelic HSi + HOSi silicones or HSi silicones + water [ 26 , 27 , 28 ]. We have previously exploited this method to reliably introduce branches along linear silicone backbones [ 29 ] including, in the limit, highly branched dendron-like structures [ 30 ], including MDTQ resins (D = Me 2 SiO 2/2 ) [ 31 ] ( Figure 2 ).…”

Polysiloxanes Grafted with Mono(alkenyl)Silsesquioxanes—Particular Concept for Their Connection

“…The significant perspectives for polysiloxanes concern modification of their structure. It may be performed at the stage of polysiloxanes chain formation, i.a., anionic ring-opening polymerization of cyclic siloxanes, or hydrolytic polycondensation of two chloro/alkoxysilanes varying in functional groups [23,[31][32][33]. On the other hand, it may be achieved by modification of functional group present on the existing polysiloxane chain, mostly via catalytic reactions [34][35][36][37][38][39][40][41][42][43][44], to gain co-polymers with precise and tailored properties [45][46][47][48][49][50][51][52][53][54][55].…”