Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms

Abstract

A series of comb-type polycarbosilanes of the type [Si(CH 3 )(OR)CH 2 ] n {where R ϭ (CH 2 ) m RЈ, RЈ ϭ OO-p-biphenylOX [X ϭ H (m ϭ 3, 6, 8, or 11) or CN (m ϭ 11)], and RЈ ϭ (CF 2 ) 7 CF 3 (m ϭ 4)} were prepared from poly(chloromethylsilylenemethylene) by reactions with the respective hydroxy-terminated side chains in the presence of triethylamine. The product side-chain polymers were typically greater than 90% substituted and, for RЈ ϭ OO-p-biphenylOX derivatives, they exhibited phase transitions between 27 and 150°C involving both crystalline and liquid-crystalline phases. The introduction of the polar p-CN substituent to the biphenyl mesogen resulted in a substantial increase in both the isotropization temperature and the liquid-crystalline phase range with respect to the corresponding unsubstituted biphenyl derivative. For R ϭ (CH 2 ) 11 OO-biphenyl side chains, an analogous side-chain liquid-crystalline (SCLC) polysiloxane derivative of the type [Si(CH 3 )(O(CH 2 ) 11 OObiphenyl)O] n was prepared by means of a catalytic dehydrogenation reaction. In contrast to the polycarbosilane bearing the same side chain, this polymer did not exhibit any liquid-crystalline phases but melted directly from a crystalline phase to an isotropic liquid at 94°C. Similar behavior was observed for the polycarbosilane with a fluorocarbon chain, for which a single transition from a crystalline phase to an isotropic liquid was observed at Ϫ0.7°C. The molecular structures of these polymers were characterized by means of gel permeation chromatography and high-resolution NMR studies, and the crystalline and liquid-crystalline phases of the SCLC polymers were identified by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction.

Molecular‐Level Processing of Si‐(B)‐C Materials with Tailored Nano/Microstructures

“…The absorption band at 1251 cm −1 corresponds to the Si−CH 3 rocking. The Si−CH 3 bond is not mentioned in the admitted structure of AHPCS, but is usually reported in the literature …”

“…The 1 H NMR spectra are compared to that of AHPCS in Figure b. 1 H signals are detected at 0.05 (−Si−C H 3 ), 0.4 (−Si−C H 2 ), 1.56–1.9 (Si−C H 2 −CH=CH 2 ), 3.40–3.8 (−Si H 3 C≡), 3.80–4.10 (−Si H 2 CH 2 ), 4.85–5.05 (−Si−CH 2 −CH=C H 2 ), and 5.71–5.93 ppm (−Si−CH 2 −CH=CH 2 ) in the spectrum of AHPCS, as reported in the literature . The 1 H NMR spectra of PBCS 200 , PBCS 100 , and PBCS 60 , in comparison with the AHPCS spectrum, show a decrease in the intensity ratio of the allyl proton to the Si−H peak (at 4.2 and 3.8 ppm, respectively).…”

Dynamic Anti-Icing Coatings: Complex, Amphiphilic Hyperbranched Fluoropolymer Poly(ethylene glycol) Cross-Linked Networks with an Integrated Liquid Crystalline Comonomer

“…To impart liquid crystalline character to the polymer matrix, a mesogenic unit was incorporated in the form of a comonomer during polymerization. In order to determine the types of mesophases and the temperatures at which these mesophases formed, a combination of differential scanning calorimetry (DSC), ,,− polarized optical microscopy (POM), and X-ray diffraction (XRD) were used to characterize and identify the types of liquid crystalline phases of the mesogenic unit and its corresponding monomer. From DSC, two melting transitions were observed for the mesogenic unit upon heating, at 84 and 100 °C (Figure S1A).…”

Packing Studies on Poly(di‐n‐alkylsilylenemethylene)s

“…The poly(silylenemethylene)s (PSMs, [SiRR′CH 2 ] n ),1–15 and their hyperbranched analogues,1,2,15 have attracted considerable interest in recent years as a novel class of hybrid inorganic/organic polymers, as well as for use as precursors to silicon carbide. Among the potential advantages that this class of polymers may offer compared with other inorganic/organic hybrid polymers are a combination of low glass transition temperature ( T g ), high synthetic versatility (similar to that of polyphosphazenes and polysiloxanes), and good chemical stability similar to that of the polyolefins 1,2.…”