【作者】 张芬；

【导师】 杨万泰；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 博士

【摘要】 分散聚合可以一步制备出粒径范围在1-15μm之间的单分散聚合物微球而得到广泛关注。在传统分散聚合中,微球一般通过高分子量聚合物稳定剂吸附或接枝在微球上,靠聚合物的空间或静电空间作用稳定微球,且稳定剂用量一般要高于5 wt%,而对于较传统的静电稳定作用研究较少。本论文详细研究了电荷稳定分散聚合体系的反应特点及反应机理,找到了一种制备单分散洁净聚合物微球的方法。主要研究内容如下：1.研究了一种简单高效的原位自稳定分散聚合体系,在甲醇／水混合溶剂中,采用可聚合的、带正电荷的小分子单体甲基丙烯酰氧乙基三甲基氯化铵(DMC)与苯乙烯原位共聚形成稳定剂,可制备出粒径范围在200-1600 nm之间的单分散的、表面带正电荷的聚苯乙烯(PS)微球；聚合速度快,DMC稳定效率高,0.025 wt%便可制备出稳定单分散的PS微球；介质组成、稳定剂含量、单体及引发剂浓度对微球粒径及其分布的影响与传统分散聚合类似；通过X射线光电子能谱、核磁、离子交换电导滴定对微球组成和表面基团的分析,以及合成模型单体丙基酰氧乙基三甲基氯化氨代替DMC进行聚合反应,表明此分散聚合体系中DMC共聚到微球表面起到稳定作用,反应过程中真正的稳定剂为St和DMC原位聚合形成的PS-PDMC共聚物。2.在St/DMC/甲醇／水聚合体系中,通过跟踪聚合反应过程,首次直接观察到粒子的成核-聚并过程,发现沉淀出来的聚合物链的分子量对形成球形粒子有重要作用,并且水含量对微球的成核增长模式有很大影响,得到三种成核／增长模型：水／甲醇(20／80)反应体系：典型的分散聚合体系,在溶液相成核,粒子相增长；纯甲醇反应体系：首先在溶液相成核,并通过吸附溶液相中形成的聚合物及不稳定小粒子进行增长,当溶液中聚合物分子量长到一定值时发生二次成核,新形成的粒子进行粒子相增长；水／甲醇(5／95)反应体系：前90 min反应与传统分散聚合类似,之后粒子的增长模式变为外延增长,即在粒子表面增长。此研究对于丰富分散聚合过程、理解微球成核增长机理有重要的意义。3.在甲醇／水混合溶剂中,研究了可聚合的、带负电荷的小分子单体苯乙烯磺酸钠(NaSS)做稳定剂来制备PS微球,可制备出粒径范围在470-1600 nm之间的单分散的、表面带负电荷的PS微球；NaSS稳定效率非常高,0.05 wt%便可制备出稳定单分散的PS微球；介质组成、稳定剂含量、单体及引发剂浓度对微球粒径及其分布的影响与DMC稳定体系类似；通过X射线光电子能谱分析验证了NaSS共聚在PS微球表面。4.传统分散聚合体系中,较难制备出高度交联的PS微球,在St／DMC／甲醇／水聚合体系中,采用一步加料法,随着交联剂二乙烯基苯(DVB)加入量的增加,所制备的微球的凝胶含量及玻璃化转变温度均增加；跟踪微球的生长过程发现交联PS微球的生长机理与非交联类似,包括溶液相成核和粒子相增长,到反应后期由于粒子内部交联使得聚合过程中在微球表面产生相分离,且溶液聚合形成的聚合物链粘附在粒子表面,得到表面粗糙的微球；通过调节稳定剂DMC的加入量,可制备出凝胶含量高达85%的交联PS微球。采用两步加料法,在微球增长最快的反应时间内加入交联剂,可进一步提高PS微球的交联度,制备出经四氢呋喃浸泡后可保持形状的高度交联的PS微球；通过调节DVB的补加量,得到形状非对称的交联PS微球；通过延迟DVB的补加时间到反应开始2.5h后,可制备出PS／交联PS核壳微球。5.在St/NaSS/甲醇／水聚合体系中,采用两步加料法,在反应后期将功能性单体甲基丙烯酸缩水甘油酯(GMA)、丙烯酸(AA)、异丙基丙烯酰胺(NIPAm)、4-烯丙氧基-2-羟基苯甲酮(BP-OH)滴加到反应体系中,可制备出表面带有环氧基团、羧基、温敏性聚合物及光活性基团的PS微球,通过实验发现亲水性单体不易共聚到微球表面,亲油单体较容易。6.丙烯酸酯类单体的分散聚合,当甲醇／水≤70／30时可制备出稳定的聚甲基丙烯酸甲酯(PMMA)微球；当丙烯酸丁酯(BA)/St≥1/1时,所制备的微球在室温下成膜,微球的玻璃化转变温度(Tg)随BA含量的增加呈减小趋势；通过两步加料法,在反应后期将单体St补加到反应体系中,可以制备出PBA/PS核壳聚合物微球。更多还原

【Abstract】 Dispersion polymerization is a unique method to prepare monodisperse polymer particles with diameters in the 1-15μm size range in a single polymerization step. While the stability of the particles or latex, both during polymerization and as end-products, is normally achieved via a steric/electrosteric stabilization mechanism from chemically grafted or physically adsorbed polymers with an applied amount of at least 5 wt%, and the commonly used electrostatic stabilization mechanism was studied less. In this thesis, the polymerization characters and mechanism of charge-stabilized dispersion polymerization system was studied in detail, which enriched the dispersion polymerization, and developed new methods to fabricate clean polymer particles. The main contents were listed as followed:1. A simple and highly efficient in-situ self-stabilized dispersion polymerization system by copolymerization of cation-charged monomer 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC) with styrene (St) in a methanol/water (MeOH/H2O) mixture was studied. Monodisperse cation-charged polystyrene (PS) particles with average diameters of approximately 200-1600 nm could be directly obtained. The polymerization rate was very fast and a much lower amount of DMC (0.025 wt% based on styrene) was required to prepare monodisperse and stable PS particles. The reaction parameters:solvent composition, stabilizer content, monomer and initiator concentration had similar effect on particle size and size distribution with the conventional dispersion polymerization. By using X-ray photoelectron spectrometry (XPS), NMR and ion-exchange/conductometric titration to characterize the composition of the particles and the surface charge density, and by synthesizing model monomer to replace DMC to proceed the polymerization, it was found that DMC was copolymerized on the particle surface to stabilize the particles, and the true stabilizer was the PS-PDMC copolymer formed in-situ.2. In St/DMC/MeOH/H2O polymerization system, by following the polymerization process, the metastable state of the nucleation stage, their aggregates and the aggregating process, was first observed experimentally; the molecular weight of the deposited polymer played a very important role on the formation of spherical particles; and water content had great effect on the particle nucleation/growth process. Three polymerization modes were obtained:1) A water/methanol (20/80) system, corresponding to a typical dispersion polymerization mode where the particle nucleation occurred in the solution phase and growth in the particle phase; 2) a pure methanol system, including a first nucleation in the solution phase with growth by absorption of the small particles formed in this phase, and a secondary nucleation when high molecular weight copolymers appeared in the solution phase with growth in the particle phase; and 3) a water/methanol (5/95) system, similar to the conventional dispersion polymerization mode during the first 90 min, with subsequent epitaxial growth. It was very important to enrich the dispersion polymerization process and understand the particle nucleation/growth mechanism.3. Using a polymerizable sodium styrene sulfonate (NaSS) as the stabilizer, methanol/water mixture as the reaction medium to produce clean PS particles was investigated. Surface-charged and monodisperse PS particles with average diameters of approximately 470-1600 nm could be obtained. NaSS was quite efficient as the stabilizer, and as little as 0.05 wt% was enough to prepare stable latex with monodisperse particles. The reaction parameters:solvent composition, stabilizer content, monomer and initiator concentration had similar effect on particle size and size distribution with the DMC stabilized polymerization system. XPS result indicated that NaSS had copolymerized on the particle surface.4. It was difficult to produce highly cross-linked PS particles in the conventional dispersion polymerization. In St/DMC/MeOH/H2O polymerization system, using one-step polymerization method, as the increasing of the divinylbenzene (DVB) content, the gel content:and the glass transition temperature (Tg) of the produced particles both increased. By following the polymerization process of the cross-linked particles, it was found that the polymerization mechanism was similar with that of uncorss-linked particles:including the nucleation in the solution phase and growth in the particle phase, and phase separation occurred and polymer chains formed in the solution attached on the particle surface at the later polymerization time because the interior of the particles were cross-linked, and thus particles with coarse surface were obtained. By tuning DMC concentration, cross-linked PS particles with 85% gel content were produced by one-step polymerization method. Using two-step method, by adding cross-linker during the fastest polymerization stage, highly cross-linked PS particles which could maintain their shape in THF were obtained; changing the adding amount of DVB at the second step, unsymmetrical cross-linked PS particles could be produced; PS/cross-linked PS core-shell particles were produced by adding DVB 2.5h after the reaction began.5. In St/NaSS/MeOH/H2O polymerization system, using two-step polymerization method, PS particles with epoxy groups, carboxylic groups, temperature response polymer and photoreactive groups on the surface were produced by adding glycidyl methacrylate (GMA), acrylic acid (AA), N-isopropylacrylamide (NIPAm) and 4-allyloxy-2-hydroxybenzophenone (BP-OH) into the reaction system at the later stage of the polymerization. According to the results, it was found that hydrophobic monomers were likely to copolymerize on the particle surface by the two-step polymerization method, while hydrophilic monomers were not. 6. In DMC/MeOH/H2O polymerization system, when the ratio of MeOH/H2O was less than 70/30, stable polymethylmethacrylate (PMMA) particles were produced; when the ratio of butyl acrylate (BA)/St was greater or equal to 1/1, the Tg of the obtained PS/PBA particles were less than room temperature, and the Tg of the particles decreased with the increasing of BA content. Using two-step polymerization method, by adding St into the polymerization system at the later stage, PBA/PS core-shell polymer particles could be obtained.更多还原