Polycondensation of boric acid (BA) with mixtures of phenyltriethoxysilane (PTEOS) and vinyltriethoxysilane (VTEOS) and with mixtures of phenyltrimethoxysilane (PTMOS) and vinyltriethoxysilane (VTEOS) in diglyme at 83–87 °C using HCl as catalyst resulted in vinyl-functionalized borosiloxane oligomers. Effect of variation of PTEOS:VTEOS and PTMOS:VTEOS ratio (keeping BA:alkoxysilanes ratio constant) and the effect of variation of BA:alkoxysilane (BA:PTEOS:VTEOS and BA:PTMOS:VTEOS) ratio on the solubility, thermal stability and ceramic residue were studied. The oligomers obtained were characterized by FTIR, GPC, pyrolysis GC and TGA. For PTEOS + VTEOS system all the oligomers were soluble in the reaction medium, but after removal of alcohol (byproduct) and diglyme (solvent), the oligomers obtained in the solid form were insoluble in common organic solvents. Unlike the PTEOS-based system, for PTMOS-based system the oligomers synthesized from monomer feed ratios (BA:PTMOS:VTEOS) 1:1:1 and 1:1.67:0.33 even after the removal of ethanol and diglyme are soluble in tetrahydrofuran, dioxane and diglyme. These two soluble oligomers show bimodal molecular weight distribution with \(\overline{{\text{M}}}_{{_{{\text{W}}} }}\) of 3,650 and \({\overline{\text{M}}}_{{\text{n}}}\) of 1860 for 1:1:1 mol ratio, and \(\overline{{\text{M}}}_{{_{{\text{W}}} }}\) of 2,540 and \({\overline{\text{M}}}_{{\text{n}}}\) of 1700 for 1:1.67:0.33 mol ratio. ²⁹Si-NMR spectra of the soluble oligomers show peaks at − 69 and − 78 ppm which are attributed to T² and T³ structures respectively. Thermogravimetric analysis of vinyl-functionalized borosiloxane oligomers from PTEOS and PTMOS indicates that the ceramic residue of the oligomers in argon atmosphere at 900 °C varies from 68 to 89% depending on the monomer feed ratio of BA to organoalkoxysilane ratio and phenyltrialkoxysilane to VTEOS ratio. With the increase in concentration of VTEOS in the monomer feed the thermal stability as well as the ceramic residue of the oligomers increase and a reverse trend is observed for variation of BA concentration. Pyrolysis of the oligomers produce C₂, C₃ hydrocarbons and benzene as the main pyrolysis products. Ceramic conversion of a typical oligomer was carried out at 900 °C, 1500 °C and 1650 °C in argon atmosphere. The ceramics obtained at 900 °C and 1500 °C are amorphous SiBOC which transform to β-SiC at 1650 °C.

硼酸 (BA) 与苯基三乙氧基硅烷 (PTEOS) 和乙烯基三乙氧基硅烷 (VTEOS) 的混合物以及苯基三甲氧基硅烷 (PTMOS) 和乙烯基三乙氧基硅烷 (VTEOS) 在二甘醇二甲醚中的混合物在 83–87 °C 下使用 HCl 作为催化剂缩聚，得到乙烯基官能化的硼硅氧烷低聚物。PTEOS:VTEOS 和 PTMOS:VTEOS 比率变化的影响（保持 BA:烷氧基硅烷比率恒定）以及 BA:烷氧基硅烷（BA:PTEOS:VTEOS 和 BA:PTMOS:VTEOS）比率变化对溶解度、热稳定性和陶瓷残渣进行了研究。获得的低聚物通过 FTIR、GPC、热解 GC 和 TGA 进行表征。对于 PTEOS + VTEOS 系统，所有低聚物都可溶于反应介质中，但在去除醇（副产物）和二甘醇二甲醚（溶剂）后，以固体形式获得的低聚物不溶于普通有机溶剂。与基于 PTEOS 的系统不同，对于基于 PTMOS 的系统，即使在去除乙醇和二甘醇二甲醚后，由单体进料比 (BA:PTMOS:VTEOS) 1:1:1 和 1:1.67:0.33 合成的低聚物仍可溶于四氢呋喃，二恶烷和二甘醇二甲醚。这两种可溶性低聚物显示出双峰分子量分布\(\overline{{\text{M}}}}_{{_{{\text{W}}} }}\)的 3,650 和\({\overline{\text{M}}}_{{\ text{n}}}\) 1860 摩尔比为 1:1:1，和\(\overline{{\text{M}}}_{{_{{\text{W}}} }}\) 2,540 和\({\overline{\text{M}}}_{{\text{n}}}\)为 1700，摩尔比为 1:1.67:0.33。可溶性低聚物的²⁹ Si-NMR 谱在 - 69 和 - 78 ppm 处出现峰，这归因于 T ²和 T ³分别构造。来自 PTEOS 和 PTMOS 的乙烯基官能化硼硅氧烷低聚物的热重分析表明，在 900 °C 的氩气气氛中，低聚物的陶瓷残留物从 68% 到 89% 不等，这取决于 BA 与有机烷氧基硅烷的单体进料比和苯基三烷氧基硅烷与 VTEOS 的比例。随着单体进料中 VTEOS 浓度的增加，低聚物的热稳定性和陶瓷残留物增加，并且观察到 BA 浓度变化的相反趋势。低聚物的热解产生 C ₂、C ₃烃类和苯为主要热解产物。典型低聚物的陶瓷转化在氩气气氛中在 900 °C、1500 °C 和 1650 °C 下进行。在 900 °C 和 1500 °C 下获得的陶瓷是无定形 SiBOC，在 1650 °C 时会转变为 β-SiC。