【作者】 刘群；

【导师】 翁志学； 申屠宝卿；

【作者基本信息】 浙江大学 ， 化学工程与技术， 2008， 博士

【摘要】 聚2,6-二甲基苯醚（PPO）是一种重要的耐高温热塑性工程塑料,目前工业上采用溶液聚合法合成PPO,但该方法需要溶剂回收和防爆反应器。以水代替有机溶剂作为反应介质,进行2,6-二甲基苯酚（DMP）氧化聚合制备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。本文在研究水介质中DMP氧化聚合和机理的基础上,提出水介质中制备较高分子量PPO的方法及反应器内一步法制得PPO/PS合金,有望解决水介质中DMP氧化聚合所得PPO分子量较低的弊端。采用分光光度计研究了DMP在水中溶解度,发现DMP的溶解度随SDS浓度、NaOH浓度和温度的提高而增加,在氧化聚合实验条件下,DMP溶于水。铁氰化钾（K₃Fe（CN）₆）作用下,溶于水中的DMP迅速发生氧化聚合生成低聚物,低聚物分子链端带有亲水性的苯氧阴离子,当低聚物链增长到临界聚合度时,不能溶于水而沉淀析出,形成低聚物微粒,因而水介质中DMP的氧化聚合属于沉淀聚合。低聚物微粒中含有苯环的疏水端聚集在微粒内部,而苯氧阴离子链端指向水相。随着反应的进行,聚合物分子量增加,苯氧阴离子浓度减少,粒子表面电荷密度降低,粒子间的电荷斥力降低,使粒子的稳定性下降,促使低聚物微粒发生聚并为初级粒子和初级粒子聚并成最终粒子。提出了水介质中DMP氧化聚合过程的成粒机理,即低聚物成核、一次聚并、二次聚并三个阶段。与自由基聚合不同,氧化聚合初期DMP已基本生成低聚物进入粒子相,水相中不存在DMP单体和溶解的低聚物,因此,聚合过程中粒子粒径的增长主要依靠粒子聚并,而聚合物链端苯氧阴离子浓度随聚合时间的延长而减少是促使粒子聚并的动力。采用电化学方法研究了水介质中K₃Fe（CN）₆作用下DMP氧化聚合初始动力学,确定了各反应参数对DMP氧化聚合速率的影响。发现DMP聚合初始速率随DMP和K₃Fe（CN）₆浓度的增加而增加,DMP聚合初始速率与DMP浓度的一次方成正比,与K₃Fe（CN）₆浓度的二次方成正比。DMP聚合初始速率随NaOH浓度的增加而增加,这是因为DMP的氧化电位随NaOH浓度的增加而降低,DMP聚合初始速率与NaOH浓度的二次方成正比。DMP聚合初始速率随温度的升高而增加,根据初始速率求出了不同温度下DMP聚合初始速率常数,并由Arrhenius方程求得DMP氧化聚合的表观活化能为47.7 kJ·mol^-1。最后根据Arrhenius方程和聚合初始速率与反应物浓度的关系建立了DMP聚合初始动力学模型,并验证了模型的正确性。研究了溶胀剂的种类和用量对水介质中DMP氧化聚合的影响,发现DMP聚合过程中引入一定量的溶胀剂后,可显著提高PPO的分子量。采用DSC测定了PPO/溶胀剂混合物的玻璃化温度,发现其玻璃化温度随溶胀剂用量的增加而降低,PPO/溶胀剂混合物的玻璃化温度与溶胀剂用量的关系符合Fox方程。关联了PPO分子量与PPO/溶胀剂混合物玻璃化温度的关系,结果显示玻璃化温度对PPO分子量起重要作用,这可能是由于在搅拌作用下溶胀剂使聚合物粒子溶胀,降低聚合物粒子玻璃化温度,导致粒子内低聚物分子链的活动性增加,促进低聚物的后续氧化聚合。采用透射电镜研究了水介质中合成的聚合物粒子形态,发现加入甲苯后聚合物最终粒子呈紧密的鹅卵石形,甲苯使初级粒子融合在一起,初级粒子的轮廓模糊甚至消失,而未加入甲苯时,聚合物最终粒子内可清楚地看见初级粒子的轮廓,初级粒子间存在间隙。鉴于溶液聚合的弊端,水介质中DMP氧化聚合所得的PPO分子量较低以及PPO难以加工的缺陷,提出水介质中反应器内制备PPO/PS合金的新方法。即DMP氧化聚合过程中,采用反应性的苯乙烯单体作为溶胀剂,提高PPO的分子量。待DMP氧化聚合结束后,提高反应温度,使苯乙烯在引发剂过氧化二苯甲酰（BPO）和过氧化二异丙苯（DCP）作用下原位聚合,得到热力学相容的PPO/PS合金。当苯乙烯用量为50%时,聚合得到的PPO重均分子量和得率分别为1.7×10⁵和95%,PS的重均分子量和得率分别为2.0×10⁵和93%。通过测定DMP氧化聚合过程中氧气吸收量随时间的变化,研究了DMP和催化剂浓度、N/Cu摩尔比、氧气分压、氢氧化钠浓度及温度对水介质中DMP氧化聚合初始速率的影响,发现DMP氧化聚合初始速率与氧气分压的0.1次方成正比;DMP氧化聚合初始速率随DMP和催化剂浓度及温度的增加而增加;随氢氧化钠浓度和N/Cu摩尔比的增加DMP氧化聚合初始速率先增加后降低。铜胺络合物作用下,DMP氧化聚合初始速率与其浓度的倒数成正比,说明水介质中DMP氧化聚合初始速率符合Michaelis-Menten方程,并根据不同温度下氧化聚合初始速率,计算了米氏常数（K_m）及中间体解离形成苯氧自由基和还原态铜络合物的速率常数（k₂）,发现K_m和k₂均随温度的升高而增加。研究了Cu-EDTA络合物作用下,水介质中DMP氧化聚合动力学。结果表明氧气吸收速率随DMP浓度和温度的增加而增加。根据氧气吸收量随时间的变化,计算得到PPO分子量和DMP氧化聚合速率随时间的变化,发现PPO分子量随时间逐渐增加,符合逐步聚合特性。聚合温度较低时,DMP聚合速率先随时间的延长略有增加,后随时间的延长而降低;随温度升高,DMP聚合速率增加。采用米氏方程拟合水介质中DMP聚合速率和苯氧阴离子浓度的关系,发现拟合结果偏离实验数据较远,因此米氏方程不适用于水介质中Cu-EDTA络合物催化作用下DMP氧化聚合动力学。根据DMP氧化聚合过程中催化剂随时间延长而逐渐失活,不同种类的苯氧阴离子活性不同以及非均相聚合特点,提出了水介质中DMP氧化聚合动力学模型,并采用多元非线形回归计算得到模型参数,采用模型计算得到的聚合速率与实验测定值一致,证明所提出模型的正确性。更多还原

【Abstract】 The solution polymerization of 2,6-dimethylphenol（DMP） is widely used in industrial production of poly（2,6-dimethyl-1,4-phenylene oxide）（PPO）,an important engineering plastics.However,both a solvent recovery process and an explosionproof reactor are required.The use of water as the reaction medium is environmentally friendly and PPO can be separated 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 and mechanism were studied in this paper.PPO with high molecular weight was prepared in water and a novel one-pot synthetic method for preparing PPO/PS alloy in reactor containing aqueous medium was proposed based on green chemistry.The solubility of DMP in water was studied and it was found that DMP was dissolved in water under the polymerization condition.The change of molecular weight,and particle size and distribution during the oxidative polymerization of DMP in water with time was studied.At the beginning of the oxidative polymerization of DMP,the oligomers with the hydrophilic phenoxy anion at the end of oligomer chains were formed rapidly in water.When the critical molecular weight was reached,the oligomers precipitated from the water and original particles with a size of 20-50 nm were formed,in which the hydrophobic parts with benzene ring aggregated inside of the particles and the hydrophilic groups with phenoxy anion pointed to the aqueous phase.With the development of the oxidative polymerization,the molecular weight increased,while the concentration of the phenoxy anion and density of electric charge on the surface of the original particles decreased,and the repulsion force between particles weakened.Therefore,the stability of particles in water decreased,and the original particles coagulated and the stable primary particles with a size of 0.1μm formed at the same time.With the further development of the polymerization,the density of electric charge on the surface of the primary particles decreased gradually, resulting in the further coagulation of the primary particles and the formation of the final particles with a size of 10μm.The number of the primary particles gradually decreased with the polymerization time,while that of the particles with a size of 10μm increased and finally the particle size was mainly about 10μm at the end of the polymerization.A three-stage mechanism of the particle formation mechanism during the oxidative polymerization of DMP in water was proposed,that is,the particle nucleation,the first coagulation,and the second coagulation.During the oxidative polymerization of DMP the increase of particle size mainly depended on the particle coagulation,and the driving force of the particle coagulation was the decrease of the concentration of the hydrophilic phenoxy anion with the polymerization time.The initial oxidative polymerization kinetics of DMP in water with K₃Fe（CN）₆ was investigated by the electrochemical method.It was found that the initial polymerization rate of DMP increased with the increase of DMP and K₃Fe（CN）₆ concentration,and the reaction orders with respect to the concentration of DMP and K₃Fe（CN）₆ were 1 and 2,respectively.The initial polymerization rate of DMP increased with the increase of NaOH concentration due to the decrease of the oxidative potential of DMP,and the reaction order with respect to NaOH concentration was 2.The initial polymerization rate of DMP increased with the increase of temperature.The initial polymerization rate constant of DMP was calculated and the apparent activation energy of the oxidative polymerization of DMP was calculated to be 47.7 kJ·mol^-1 according to Arrhenius equation.The initial polymerization kinetics of DMP under the action of K₃Fe（CN）₆ was proposed according to the reaction order and Arrhenius equation.The effects of the species and content of swelling agent on the molecular weight of PPO synthesized in water were studied.It was found that the molecular weight of PPO increased significantly after introducing a certain amount of swelling agent during the oxidative polymerization of DMP.T_g of PPO/swelling agent mixture decreased with the increase of the content of swelling agent and the relation between T_g of PPO/swelling agent mixture and the content of swelling agent obeyed Fox equation.The relation between the molecular weight of PPO and T_g of PPO/swelling agent mixture was correlated and it was revealed that T_g played an important role in the molecular weight of PPO synthesized in water,which was probably because swelling agent could swell polymer particles under the action of agitation and lower its T_g,resulting in the increase of the mobility of oligomer chains and facilitation of the oxidative polymerization at the later period.The morphology of the polymer particle synthesized in water was observed by transmission electron microscope and it was found that after the introduction of toluene the final polymer particle showed compact cobblestone morphology.Toluene made primary particles fuse together and the profile of primary particles was so ambiguous that could not be seen.Considering the defect of solution polymerization of DMP,the low molecular weight of PPO synthesized in water and difficulty in processing of PPO,a novel one-pot synthetic method for preparing PPO/PS alloy in reactor was proposed based on green chemistry.During the oxidative polymerization of DMP,the reactive styrene was used as swelling agent to improve the molecular weight of PPO.After the oxidative polymerization of DMP,styrene was in-situ polymerized under the initiation of dibenzoyl peroxide（BPO） and dicumyl peroxide（DCP）,finally thermodynamically compatible PPO/PS alloy was prepared.When styrene content was 50 wt%,for the synthesized PPO/PS alloy the yield and the weight-average molecular weight were determined to be 95%and 1.7×10⁵ for PPO,93%and 2.0×10⁵ for PS,respectively.The influence of the concentration of DMP and catalyst,molar ratio of N/Cu, oxygen partial pressure,NaOH concentration and temperature on the initial polymerization rate（R₀） of DMP was studied.It was found that the initial polymerization rate of DMP increased with the concentration of DMP and catalyst. The initial polymerization rate increased with the molar ratio of N/Cu at first and then decreased.The reaction order with respect to the oxygen partial pressure was 0.1, therefore the oxygen partial pressure had litle influence on the initial polymerization rate.The initial polymerization rate increased with NaOH concentration and reached its maximum value at a concentration of 0.50 mol/L.1/R₀ was in direct proportion to 1/[DMP]₀,which indicated that the initial polymerization kinetics of DMP obeyed Michaelis-Menten model.The dissociation rate constant of the intermediate complex （k₂） and Michaelis-Menten constant（K_m） at various temperatures were calculated,and both k₂ and K_m increased with temperature.The heterogeneous oxidative polymerization kinetics of DMP with copper-EDTA in water was studied.It was found that the oxygen-uptake rate increased with the increase of DMP concentration and temperature.The change of oxidative polymerization rate and molecular weight of PPO with time was calculated, and it was found that the molecular weight of PPO increased gradually at the earlier stage and rapidly at the later stage,which was in accordance with the traditional stepwise polymerization.The polymerization rate increased with time at the initial stage of polymerization and then decreased under low temperature.The polymerization rate calculated based on the oxygen-uptake disagreed with the result estimated by Michaelis-Menten kinetic model,indicating that Michaelis-Menten kinetic model applied to the polymerization of DMP in organic solvents was not appropriate to describe the full course of the polymerization of DMP in water.In order to reflect the catalyst deactivation during the oxidative polymerization and difference of the reactivity between monomer,the oligomer soluble in water,and the oligomer unsoluble in water,a new heterogeneous kinetic model was proposed according to Flory statistical theory.It was found that the polymerization rate estimated by the new model was consistent with the calculated data.更多还原