摘要
聚苯醚(PPO)是一种重要的耐高温热塑性工程塑料,溶液聚合是目前工业上合成PPO的方法,但过程后期体系粘度高,传热/传质困难,溶剂回收/高温脱挥等后处理复杂,易污染环境。以水代替有机溶剂作为反应介质,进行2,6-二甲基苯酚(DMP)氧化聚合以合成PPO,不仅对环境友好,而且由于PPO不溶于水,在产物分离等方面都具有明显优势。本文研究水介质中铁氰化钾作用下DMP的氧化聚合行为,并合成得到PPO。
通过研究反应工艺参数对PPO和副产物3,3',5,5'-四甲基-4,4'-联苯醌(DPQ)得率的影响,探讨了DMP氧化聚合选择性的影响因素,阐明了温度、NaOH及SDS浓度等对DMP氧化聚合选择性的影响。研究发现,PPO和DPO得率随铁氰化钾浓度增加而增加;只有在碱性条件下,DMP才能发生聚合反应,随着氢氧化钠浓度的增大,PPO的得率和分子量先增加后降低,DPQ得率随着氢氧化钠浓度的增大而逐渐降低;体系中加入SDS后,可得到较高分子量的PPO,而不加入SDS时,PPO分子量较低;反应温度为50℃时,可得到DPO含量低、分子量高的PPO。
采用电位分析法研究了水介质中铁氰化钾作用下DMP氧化聚合反应动力学。研究发现,DMP的聚合速率主要受氢氧化钠浓度、铁氰化钾浓度以及温度等的影响。随着氢氧化钠浓度的增加,DMP的氧化聚合速率增加。采用循环伏安法研究了氢氧化钠浓度对DMP氧化电位的影响,发现DMP的氧化电位随着NaOH浓度的增加而降低,表明氢氧化钠浓度的增加有利于DMP的氧化聚合。随着铁氰化钾浓度的增加,DMP氧化聚合反应初始速率增加,原因在于随铁氰化钾浓度增加,苯氧阴离子与之碰撞的几率增加。随着亚铁氰化钾浓度的增加,DMP的氧化聚合速率降低。实验范围内,DMP氧化聚合初始速率随着温度的升高而增加。根据氧化聚合初始速率与DMP和铁氰化钾的初始浓度,计算得到DMP聚合反应初始速率常数k_0,lnk_0与ln1/T呈线性关系,根据Arrhenius方程计算得到DMP氧化聚合的表观活化能为45.7kJ.mol~(-1)。
DMP聚合过程中铁氰化钾只为氧化剂,其用量较大。采用铜胺络合物为DMP氧化聚合的催化剂,可降低其用量,初步研究了水介质中铜胺络合物催化作用下DMP的氧化聚合。采用分光光度法研究了铜胺络合物的稳定性以及用氧气吸收法测定了NaOH浓度及配体种类对DMP氧化聚合速率的影响。
The solution polymerization of 2,6-dimethyl phenol(DMP)is widely used in industrial production of poly(2,6-dimethyl-1,4-phenylene oxide)(PPO),an important engineering plastics,however,the heat and mass transfer is hindered at the later period because of the high viscosity of the reaction system.Furthermore,both a solvent recovery process and an explosion proof reactor are required.The use of water as the reaction medium is environmentally friendly and PPO can be separated from water easily due to its insolubility in water.Therefore,the oxidative polymerization of DMP to form PPO using water as the reaction medium would be of significance.The oxidative polymerization of DMP in water at the action of potassium ferricyanide was studied and PPO was synthesized.
The influences of temperature,sodium hydroxide and SDS concentration on yields of PPO and the by-product,4-(3,5-dimethyl-4-oxo-2,5-cyclohexadientlidene)-2,6-dimethyl-2,5-cyclohexadienone(DPQ),were studied and the factors that affected the selectivity of oxidative polymerization were elucidated.It was found that both PPO and DPQ yield increased with potassium ferricyanide concentration.The alkaline concentration in water influenced the yield and the molecular weight of PPO. The oxidative polymerization of DMP can occur only under the alkaline solution. Both the yield and the molecular weight of PPO increased with sodium hydroxide concentration firstly and then decreased.PPO with the high molecular weight was obtained after the addition of SDS,while the molecular weight of PPO was low without SDS in water.The yield of DPQ was low and the molecular weight of PPO was high at the temperature of 50℃.
The kinetics of oxidative polymerization of DMP at the action of potassium ferricyanide was studied by potentiometric measurements.It was found that the temperature,potassium ferricyanide and sodium hydroxide concentration influenced the reaction rate of DMP.The reaction rate of DMP increased with the sodium hydroxide concentration.The influence of sodium hydroxide concentration on the oxidative potential of DMP was studied by cyclic voltammertry.It was found that with the increase of sodium hydroxide concentration,the oxidative potential of DMP decreased,indicating that the increase of sodium hydroxide concentration was beneficial to the oxidative polymerization of DMP.The reaction rate of DMP increased with increasing potassium ferricyanide concentration,while the reaction rate of DMP decreased with increasing potassium ferrocyanide concentration,with The initial oxidative polymerization rate of DMP increased with the increase of temperature.According to the initial oxidative polymerization rate and initial concentrations of DMP and potassium ferricyanide,the initial reaction rate constant (k_0)was calculated.An apparent activation energy was calculated to be 40.7 kJ·mol~(-1) according to Arrhenius equation.
Potassium ferricyanide was only an oxidant and its concentration was high during the oxidative polymerization of DMP.In the presence of a copper-amine complex the oxidative polymerization of DMP was also studied.The Stability of the copper-amine complex was studied by UV-Vis,and the influence of sodium hydroxide concentration and amine ligands on the reaction rate of DMP was determined by the oxygen-uptake measurement.
引文
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