采用硅酸钠有机化法制备MQ硅树脂,经过脱水缩聚降低其羟基含量,并用容量法定量分析。研究了催化剂用量、脱水缩聚时间及温度对MQ硅树脂羟基含量的影响。脱水缩聚能够明显降低MQ硅树脂的羟基含量,并可控制其质量分数为1%～2%。脱水缩聚...采用硅酸钠有机化法制备MQ硅树脂,经过脱水缩聚降低其羟基含量,并用容量法定量分析。研究了催化剂用量、脱水缩聚时间及温度对MQ硅树脂羟基含量的影响。脱水缩聚能够明显降低MQ硅树脂的羟基含量,并可控制其质量分数为1%～2%。脱水缩聚最佳工艺条件：时间为4 h,催化剂为2 g KOH配制成质量分数为50%的溶液,温度为90~100℃。展开更多
Herein the use of rare-earth compounds in catalytic reduction systems for the end-group functionalization of carboxyl-terminated low-molecularweight fluoropolymers was explored.Leveraging the high catalytic activity a...Herein the use of rare-earth compounds in catalytic reduction systems for the end-group functionalization of carboxyl-terminated low-molecularweight fluoropolymers was explored.Leveraging the high catalytic activity and selectivity of rare-earth compounds along with no residual impact on polymer product's performance,highly efficient catalytic reduction systems containing sodium borohydride(NaBH_(4))and rare-earth chloride(RECl_(3))were specifically designed for a telechelic carboxyl-terminated liquid fluoroeslastomer,aiming to facilitate the conversion of chainend carboxyl groups into hydroxyl groups and improvement in end-group reactivity.To achieve this,lanthanum chloride(LaCl_(3)),cerium chloride(CeCl_(3)),and neodymium chloride(NdCl_(3))were used separately to form catalytic reduction systems with NaBH_(4).The effects of solvent dosage,reaction temperature,reaction time length,and reductant dosage on carboxylic conversion were investigated,and the molecular chain structure,molecular weight,and functional group content of the raw materials and the products were analyzed and characterized by means of infrared spectroscopy(FTIR),proton nuclear magnetic resonance(^(1)H-NMR),fluorine-19 nuclear magnetic resonance(^(19)F-NMR),gel permeation chromatography(GPC),and chemical titration.Moreover,the catalytic activity and selectivity of the rare-earth chlorides,as well as the corresponding underlying interactions were discussed.Results indicated that the rare-earth-containing catalytic reduction systems studied in this work could efficiently convert the chain-end carboxyl groups into highly active hydroxyl groups,with a highest conversion up to 87.0%and differing catalytic reduction activities ranked as NaBH_(4)/CeCl_(3)>NaBH_(4)/LaCl_(3)>NaBH_(4)/NdCl_(3).Compared with the conventional lithium aluminum hydride(LiAIH_(4))reduction system,the NaBH_(4)/RECl_(3)systems provide multiple advantages such as mild reaction conditions,high conversion ratio with good selectivity,and environmental innocuity,and are potentially applicable as new reduction-catalysis combinations for the synthesis and functionalization of polymer materials.展开更多
文摘采用硅酸钠有机化法制备MQ硅树脂,经过脱水缩聚降低其羟基含量,并用容量法定量分析。研究了催化剂用量、脱水缩聚时间及温度对MQ硅树脂羟基含量的影响。脱水缩聚能够明显降低MQ硅树脂的羟基含量,并可控制其质量分数为1%～2%。脱水缩聚最佳工艺条件：时间为4 h,催化剂为2 g KOH配制成质量分数为50%的溶液,温度为90~100℃。
文摘Herein the use of rare-earth compounds in catalytic reduction systems for the end-group functionalization of carboxyl-terminated low-molecularweight fluoropolymers was explored.Leveraging the high catalytic activity and selectivity of rare-earth compounds along with no residual impact on polymer product's performance,highly efficient catalytic reduction systems containing sodium borohydride(NaBH_(4))and rare-earth chloride(RECl_(3))were specifically designed for a telechelic carboxyl-terminated liquid fluoroeslastomer,aiming to facilitate the conversion of chainend carboxyl groups into hydroxyl groups and improvement in end-group reactivity.To achieve this,lanthanum chloride(LaCl_(3)),cerium chloride(CeCl_(3)),and neodymium chloride(NdCl_(3))were used separately to form catalytic reduction systems with NaBH_(4).The effects of solvent dosage,reaction temperature,reaction time length,and reductant dosage on carboxylic conversion were investigated,and the molecular chain structure,molecular weight,and functional group content of the raw materials and the products were analyzed and characterized by means of infrared spectroscopy(FTIR),proton nuclear magnetic resonance(^(1)H-NMR),fluorine-19 nuclear magnetic resonance(^(19)F-NMR),gel permeation chromatography(GPC),and chemical titration.Moreover,the catalytic activity and selectivity of the rare-earth chlorides,as well as the corresponding underlying interactions were discussed.Results indicated that the rare-earth-containing catalytic reduction systems studied in this work could efficiently convert the chain-end carboxyl groups into highly active hydroxyl groups,with a highest conversion up to 87.0%and differing catalytic reduction activities ranked as NaBH_(4)/CeCl_(3)>NaBH_(4)/LaCl_(3)>NaBH_(4)/NdCl_(3).Compared with the conventional lithium aluminum hydride(LiAIH_(4))reduction system,the NaBH_(4)/RECl_(3)systems provide multiple advantages such as mild reaction conditions,high conversion ratio with good selectivity,and environmental innocuity,and are potentially applicable as new reduction-catalysis combinations for the synthesis and functionalization of polymer materials.
