Structure, Microscopic Ordering, and Viscous Properties of Amorphous Poly(n‐alkylsilsesquioxane) Liquids and Solids Synthesized by Cosolvent‐Free Hydrolytic Polycondensation of n‐Alkyltrimethoxysilanes

Abstract

Poly(n‐alkylsilsesquioxane) [poly(R‐SQ)] liquids with R = Et, Pr, or Bu are prepared from acid‐catalyzed n‐alkyltrimethoxysilane – water binary systems through hydrolytic polycondensation followed by aging. The resultant liquids contain a lot of SiOH groups whereas the viscosities remain almost constant during storage at room temperature over a month. Heat treatment for 1 day at 200 °C in N2 yields poly(Et‐SQ) and poly(Pr‐SQ) solids whereas poly(Bu‐SQ) remains viscous. High‐energy X‐ray diffraction measurements confirm that all samples are amorphous and nonporous. The total structure factor S(Q) of poly(R‐SQ)s and amorphous silica are similar, apart from the prominent prepeak observed for poly(R‐SQ)s at Q ≈ 0.5 − 0.7 Å−1. This prepeak undergoes a distinct shift to lower Q with an increase in the alkyl chain length. These observations indicate the presence of microscopic inhomogeneity consisting of silica‐rich and alkyl‐rich domains and their ordering with a periodicity of ≈9 − 12 Å both in liquid and solid forms of poly(R‐SQ). Thermal curing modifies S(Q) of poly(Et‐SQ) only slightly. The overall shapes of the total correlation function T(r) are similar between poly(R‐SQ)s and a‐SiO2, suggesting the similarity of short‐range order of Si−O network between these materials.

Poly(cyclohexylsilsesquioxane)-Based Hydrophilic Thermoset-Resistant Deep-Ultraviolet-Transparent Glasses with Low Melting Temperatures

“…Silsesquioxane (SQ; RSiO 3/2 ) units, where R represents an organic functional group, are important building blocks of organosilicates. − Their states of matter from solid to liquid and thermal response vary widely depending on the composition, topology, molar mass, and type of R groups. Polysilsesquioxanes [poly­(R-SQ)­s] with small alkyl groups (e.g., methyl and ethyl groups) typically form solids that irreversibly cure and do not melt upon heating. − Poly­(R-SQ)­s with longer alkyl groups, such as n -propyl ( n -Pr) and n -butyl ( n -Bu) groups, are viscous or soft at room temperature and difficult to solidify. ,− In contrast, poly­(R-SQ)­s containing aryl groups (e.g., phenyl and benzyl groups) often exhibit thermoplasticity and form stiff clear glasses after melting at ca. 100–200 °C ,,,− because the weak π bonds between the aryl groups readily dissociate upon heating and are reversibly restored after cooling.…”

Synthesis of poly(methylsilsesquioxane-co-dimethylsiloxane) liquids and deep-ultraviolet transparent elastic resins through co-solvent-free water-rich hydrolytic polycondensation of organoalkoxysilanes

“…alcohols), other organic solvents, or other additives. 10,[21][22][23][24][25] This co-solvent-free method facilitates the formation of poly(RT) liquids including those with ethyl (R = Et), n-propyl (Pr), and n-butyl (Bu) groups. 10,24 In contrast, poly(MeT) becomes a gel and its liquid was not obtained.…”

“…10,[21][22][23][24][25] This co-solvent-free method facilitates the formation of poly(RT) liquids including those with ethyl (R = Et), n-propyl (Pr), and n-butyl (Bu) groups. 10,24 In contrast, poly(MeT) becomes a gel and its liquid was not obtained. 10 Heat treatment at 200 °C turns poly(EtT) into a resin and poly(PrT) into a rubbery solid, whereas poly(BuT) remains viscous.…”

“…10 Heat treatment at 200 °C turns poly(EtT) into a resin and poly(PrT) into a rubbery solid, whereas poly(BuT) remains viscous. 21,24 The average molar mass of poly(RT) liquids (R = Et, Pr, Bu) decreases with increasing alkyl chain length. 10,24 In this article, we present a facile method for synthesizing liquid precursors of poly(MeT-co-Me 2 D) with f T = 0.8, using only alkoxysilanes, water, and a catalytic amount of acid (H + to Si molar ratio of 2 × 10 −4 ).…”

“…21,24 The average molar mass of poly(RT) liquids (R = Et, Pr, Bu) decreases with increasing alkyl chain length. 10,24 In this article, we present a facile method for synthesizing liquid precursors of poly(MeT-co-Me 2 D) with f T = 0.8, using only alkoxysilanes, water, and a catalytic amount of acid (H + to Si molar ratio of 2 × 10 −4 ). These liquid precursors enabled the formation of monolithic dense stiff poly(MeT-co-Me 2 D) thermosetting resins that exhibit excellent deep-ultraviolet (DUV, λ ≲ 300 nm) transparency and complete elastic recovery.…”