Synthesis of Functionalized Polycarbosilanes via One-Pot ADMET Polymerization−Macromolecular Substitution

Abstract

Three substituted unsaturated polycarbosilanes were prepared from the same parent using a two-step, one-pot ADMET polycondensation-nucleophilic substitution route. Condensation metathesis of di(4-pentenyl)dichlorosilane using Schrock's [Mo] catalyst produces a polymer backbone containing two reactive silicon-chlorine bonds per unit. Replacement of these bonds with stable alkyl moieties was performed using an excess of alkyllithium reagent without undesirable main chain alkylation or crosslinking. Upon functionalization, moisture-stable polymers were synthesized, indicating quantitative substitution was achieved. All of the resulting polymers are amorphous, elastomeric materials. Variation of the two pendant groups from phenyl to methyl resulted in a T g change of over 85°C.

ADMET Polymerization as a Route to Functionalized Polycarbosilanes

“…Quantitative 13 C NMR spectra of each polymer indicated approximately 80% trans olefin content, which is typically observed in metathesis polymerization. [3,22] Differential scanning calorimetry showed a T g range between À83 and À66 8C, and no discernable T m , indicating the polymers are completely amorphous, which is comparable to other silicon-containing polymers with similar backbones. [9,22,23] In contrast, when di(4-pentenyl)diphenoxysilane (6) was polymerized, noticeable differences in chemical reactivity and thermal behavior were observed compared to the other polycarbosilanes.…”

“…[3,22] Differential scanning calorimetry showed a T g range between À83 and À66 8C, and no discernable T m , indicating the polymers are completely amorphous, which is comparable to other silicon-containing polymers with similar backbones. [9,22,23] In contrast, when di(4-pentenyl)diphenoxysilane (6) was polymerized, noticeable differences in chemical reactivity and thermal behavior were observed compared to the other polycarbosilanes. The resulting polymer is significantly more resistant to hydrolytic crosslinking, so GPC analysis could be performed.…”

“…Typical for step-growth polymers prepared via ADMET, polymer 10 exhibited a unimodal distribution with a number average molecular weight of 18 000 g/mol and M w /M n of 1.8. [3,22] DSC analysis reveals the dramatic effect that placing two bulkier and more rigid moieties such as phenoxy groups pendant to a carbosilane backbone has on its thermal behavior. The T g of polymer 10 was À29 8C, a shift of 34 to 54 degrees when compared to polymers 7-9, which have the same backbone and similar degree of polymerization.…”

The chemistry of the carbon–transition metal double and triple bond: annual survey covering the year 2002

“…24) [168]; (2) silicon-containing dienes (e.g. 25) [169]; (3) co-ADMET polymerization of 1,9-decadiene and (divinyl)(tetraethoxy)disiloxane [CH 2 =CHSi(OEt) 2 OSi(OEt) 2 CH=CH 2 ] [170]; and (4) co-ADMET polymerization of 1,9-decadiene and epoxy-containing monoolefins [171]. A combination ROMP-ADMET polymer was prepared by exposure of strained alkenes and bis(␣,␤-unsaturated carbonyl) compounds (e.g.…”

Chain‐End and Chain‐Internal Crosslinking in “Latent Reactive” Silicon Elastomers

“…A few research groups have used this methodology to synthesize carbosilane/carbosiloxane copolymers bearing alkoxy or halide groups as well as the incorporation of disilacyclobutanes. [65,[70][71][72][73][74][75] For example, we have demonstrated the presence and significance of introducing ''chain-internal'' latent reactive silicon-methoxy bonds permitting the synthesis of a linear elastomer which can be easily shape processed. [65] Recently, Interrante and co-workers have synthesized carbosilane copolymers where the disilacyclobutane rings were imbedded into the copolymer's backbone.…”