【作者】 吕挺；

【导师】 单国荣；

【作者基本信息】 浙江大学 ， 化学工艺， 2010， 博士

【摘要】 以偶氮二异丁咪唑啉盐酸盐(AIBI)或过硫酸铵(APS)为引发剂,在聚乙二醇(PEG)水溶液中进行丙烯酰胺(AM)的双水相聚合,制备了稳定的聚丙烯酰胺(PAM)水分散液。该水分散液不含任何有机溶剂,可直接使用,具有无二次污染、快溶水的特点,可广泛应用于污水处理、造纸及印染等行业。本论文研究了PAM与PEG间的相互作用及AM在该双水相(聚合)体系中的分配；研究了AM在PEG水溶液双水相聚合中PAM液滴演变及各因素对其的影响,提出了液滴形成、生长、稳定机理；分别建立了AIBI与APS引发AM在PEG水溶液中双水相聚合动力学模型,成功地对其聚合动力学进行了预测。表征了PAM与PEG分别在固体共混物与水溶液中的相互作用,发现PEG链上的部分-O-与PAM链上的部分-NH2发生了氢键缔合。考察了聚合物分子量、温度及小分子物质的加入对PAM与PEG相互作用的影响。分子量较大的PAM易自身卷曲成线团,PEG通过氢键缠结在PAM线团周围。升高温度可削弱其氢键缔合。研究了聚合物浓度、分子量、温度对AM在PAM-PEG-H20双水相体系中分配的影响,发现水是影响其分配的重要因素。AM分配系数随PEG浓度或分子量的增加而减小,随PAM浓度或分子量的增加而增大。随温度的升高,分配系数先减小后升高,最低值在50℃附近。研究了AM在PEG水溶液双水相聚合过程中的单体分配系数。采用动态光散射(DLS)在线检测了双水相聚合初期液滴形成、生长规律,发现液滴在经历初期短暂的稳定后进入了聚并期,其滴径分布先变宽后变窄。采用透射电镜(TEM)及激光粒度仪观察了反应各阶段液滴形态与尺寸,发现PAM液滴不断从连续相析出,在聚合中前期液滴聚并明显,而在聚合中后期由于体系粘度较大,液滴聚并受限,最终得到了大小液滴、球状与条状液滴共存的多分散体系。提出了AM在PEG水溶液中双水相聚合的液滴形成、生长机理。详细研究了各聚合因素对最终双水相聚合产品PAM液滴形态与尺寸的影响,发现其液滴形态及尺寸与聚合速率与单体分配有关。随引发剂、单体浓度的增加,成滴速率加快,液滴聚并增多,使液滴形态趋于条状。而聚合温度同时影响聚合速率与单体分配,对液滴形态与尺寸的影响较为复杂。PEG浓度的增加,使液滴尺寸变大,液滴形态先由条状变为球状,然后变为爆米花状,说明PEG不仅有稳定液滴的作用,还有促进液滴形成,加剧液滴聚并的作用。特丁醇的加入使液滴聚并增多,而乙二醇的加入使液滴变得更加稳定。考察了聚合速率以及体系粘度对AM在PEG水溶液中双水相聚合过程稳定性影响。发现当聚合速率过快时,在聚合初期液滴聚并过度,容易产生絮凝物(Coagulum)。在线检测了聚合过程中的体系粘度演变,发现其粘度演变与相分离有关。当体系粘度较大时,PAM从连续相析出的速率减慢,容易形成凝胶块状产品。控制适当的聚合速率与体系粘度是制备稳定产品的关键。采用Flory-Huggins理论预测了AM在PEG水溶液双水相聚合过程中各相物质组成及各相体积的变化,发现其与实验值能很好地吻合。分别建立了AIBI与APS引发AM在PEG水溶液中双水相聚合的聚合动力学模型,准确地预测了双水相聚合动力学；同时,计算结果显示,引发剂在两相的分配、自由基吸附与脱吸对聚合动力学的影响很小。更多还原

【Abstract】 A stable poly(acrylamide) (PAM) aqueous dispersion has been prepared via the aqueous two-phase polymerization of acrylamide (AM) in aqueous poly(ethylene glycol) (PEG) solution with 2,2’-azobis[2-(2-imidazolin-2-yl)propane]-dihydrochloride (AIBI) or ammonium persulfate (APS) as the initiator. This kind of product without containing any organic solvent has rapid dissolution rate in water, and can be used directly without any pollution, and therefore, it can be applied in many fields such as waste water treatment, paper making, spinning and printing industries. In this thesis, the interaction between PAM and PEG blend and in water, the partition of AM in the aqueous two-phase (polymerization) system, the evolution of droplet size and morphology during polymerization and the effects of various factors on the final droplet size and morphology were investigated systemically, as well as the droplet formation mechanism, and polymerization system stability for the aqueous two-phase polymerization of AM in aqueous PEG solution. Based on these studies, a kinetic model was proposed which could well predict the aqueous two-phase polymerization kinetics.IR,1H NMR and viscosity experiments were carried out to analyze the interaction between PAM and PEG in their solid blends and aqueous solution. It was confirmed that part of-O-groups of PEG molecular chain interacted with part of-NH2 groups of PAM molecular chain through hydrogen bonding in their relatively concentrated aqueous solution. The effects of the polymer molecular weight, temperature, and the addition of some compound with low molecular weight on the interaction between PAM and PEG in water were studied. The PAM molecular chains, especially having high molecular weights, preferred to form spherical clews in aqueous PEG solution, and these clews are surrounded with the PEG molecular chains through hydrogen bonding. Moreover, this kind of hydrogen bonding could be broken by raising the temperature.The effects of polymer concentration and molecular weight as well as the temperature on the AM partition in the aqueous two phase system of PAM-PEG-H2O were investigated. It was shown that the water content in each phase is vital to determine the AM partition. The AM partition coefficient decreased with the increase of PEG concentration or molecular weight, and with the decrease of PAM concentration or molecular weight. With temperature rising, the partition coefficient decreased until the temperature reached about 50℃, and then increased again while raising the temperature sequentially. Thereafter, the monomer partitioning behaviors during the aqueous two-phase polymerization process were investigated systemically.The droplet appearance and growth in the initial stage of the aqueous two-phase polymerization was followed by dynamic light scattering (DLS). Results show that the PAM droplet aggregates with each other significantly after a temporary period in which the droplet can exist stably. Therefore, the droplet size distribution become wide at first, and then become narrow again with the polymerization proceeding. The size and morphology of aqueous PAM droplet at every stage were observed by laser particle size analyzer and transmission electron microscopy (TEM). It was found that the small droplets are separated continuously from the continuous phase in the whole polymerization. At the relatively low conversion stage of polymerization, the droplet aggregation is significant. However, the droplet coalescence was restrained at high conversion stage because of the high viscosity. Finally, polydisperse droplets with both spherical and stripe shape were obtained. Based on these results, a mechanism of droplet formation and growth was proposed for the aqueous two-phase polymerization of AM in aqueous PEG solution.The influences of various polymerization conditions on the droplet size and morphology were studied systemically. It was found that the size and morphology of the droplets are closely dependent on the polymerization rate and monomer partition. The morphology of the droplets inclined to become stripe shape because of more droplet aggregation with increasing initiator or monomer concentration. Besides the polymerization rate, the polymerization temperature could also affect the droplet size and morphology in the hand of monomer partition. The increase of PEG concentration leads to generate bigger and round droplets at first, and then inclined to form popcorn droplets. This result strongly indicates that increasing the PEG concentration not only restrained the aggregation of the droplets, but also shortened the critical length of PAM radical chain to accelerate the droplet formation which does not favor the droplet stabilization. The addition of TBA and glycol to the polymerization system both decreased the droplet size; the former caused lots of aggregation to form many stripe shape droplets; however, the latter made the droplets become more stable. The effects of polymerization rate and system viscosity on the process stability of the aqueous two-phase polymerization were explored. A droplet aggregation period was found in the initial stage, in which the PAM coagulum is easy to be generated due to the high polymerization rate. Moreover, the viscosity evolution during the polymerization under various reaction conditions was determined on line. It was found that the viscosity was relevant to the phase separation. When the system viscosity is too high, the phase separation is very slow. If the polymerization rate is too rapid at this time, massive gel would be produced. All these results demonstrate that controlling appropriate polymerization rate is a key factor to keep the stability of the aqueous two-phase polymerization system.Flory-Huggins (FH) theory was applied to predict the composition of each phase during the whole polymerization. The prediction of monomer concentration, PAM and PEG mass fraction in each phase under various polymerization conditions agreed well with the experimental data. Based on FH theory, a model was established for simulating the polymerization kinetics of the aqueous two phase polymerization of AM in aqueous PEG solution. The theoretical calculation by the kinetic model showed that the partition of initiator, radical absorption from continuous phase and radical desorption from the dispersion phase have neglectable effect on the polymerization kinetics. The effects of initiator, monomer and PEG concentration on the polymerization kinetics were also studied systemically. It was found that the proposed kinetic model can predict well the polymerization kinetics over a wide range of various polymerization conditions.更多还原