醋酸乙烯酯及丙烯酸丁酯半连续法乳液共聚合

我们曾对丙烯酸丁酯(BA)与醋酸乙烯酯(VAc)一步法乳液共聚合机理进行过研究,并对其胶膜及胶乳性能进行了表征。结果表明一步法共聚乳胶粒具有类似于“核壳结构”的形态,其内核由BA含量高的共聚物组成,外壳基本是PVAc均聚物,对此用不同的方法进行了验证。在此基础上我们以VAc-BA进行了半连续法乳液共聚合,以与一步法相比较,从而探讨反应过程与胶粒结构及材料性能的关系。     

MAA存在下VAc/BA核壳乳液聚合过程中的胶粒形态研究

用ＴＥＭ和电位滴定法对不同配方和工艺条件得到的胶粒形态结构和羧基分别进行了表征。结果表明：加入甲基丙烯酸有利于胶粒的稳定和形成规则的核壳胶粒。半连续加料不会形成完全反转的核壳结构,但是,核层在反应过程中由于聚合物簇的迁移会造成形变。由于胶粒中聚合物浓度高,粘度大,因而胶粒形态变化受动力学影响甚大,羧基分布主要是由动力学确定的。     

含丙烯酸的苯丙共聚乳液乳胶粒形态的电镜研究

采用透射电镜观测了苯乙烯-丙烯酸丁酯-丙烯酸乳液共聚体系的乳胶粒形态,讨论了组分含量、共聚物链柔性和乳液pH值等因素对乳胶粒形态、乳液粘度及成膜性的影响.结果表明:软单体的加入和体系pH值的提高将促进乳胶粒的粘连成膜和溶涨及部分聚合物的溶解.羧基主要富集于乳胶粒表面.     

种子乳液聚合法制备多孔乳胶粒

用批量乳液聚合法制备了苯乙烯（Ｓｔ）———甲基丙烯酸甲酯（ＭＭＡ）二元共聚种子乳液Ｓ１以及Ｓｔ ＭＭＡ 丙烯酸（ＡＡ）三元共聚种子乳液Ｓ２,通过连续法无皂种子乳液聚合合成了一系列不同ＡＡ或ＭＡＡ（甲基丙烯酸）含量的Ｓｔ、ＭＭＡ三元共聚乳液．将所得复合胶乳进行碱／酸分步处理,得到具有多孔结构的乳胶粒．用透射电镜对胶粒形态进行了表征,考察了不饱和酸种类和用量、碱处理初始ｐＨ值及溶胀剂对胶粒成孔的影响．     

乳液共聚反应过程与聚合物结构关系及~（13）C－NMR对聚合物结构的表征

用间歇法和半连续法进行了丙烯酸丁酯（ＢｕＡ）与醋酸乙烯酯（ＶＡｃ）乳液共聚合．１３Ｃ－ＮＭＲ对共聚产物分子结构测试表明，在间歇法共聚合中随着反应进行其组成及结构发生很大变化，而半连续法确能制得成份及结构均匀一致的Ｐ（ＢｕＡ－ＶＡｃ）共聚物．由于ＢｕＡ水溶性小于ＶＡｃ，而其竟聚率远大于ＶＡｃ，间歇法共聚合反应初期只有少量ＶＡｃ参加共聚合．通过对间歇法共聚合中不同反应时间聚合物的１３Ｃ－ＮＭＲ测试，表明反应初期聚合的ＶＡｃ以单链节或二元序列形式存在于主要由ＢｕＡ单元构成的分子链中，而并未形成较长ＶＡｃ链段．对上述试样玻璃化转变温度的测试结果与１３Ｃ－ＮＭＲ实验结果颇为一致．     

醋酸乙烯酯-丙烯酸丁酯乳液聚合成核机理

本工作研究了醋酸乙烯酯(VA)和丙烯酸丁酯(BA)乳液共聚合.通过对不同共聚单体配比下共聚合时胶乳粒径及胶粒数密度随转化率变化的分析,对VA/BA乳液共聚合成核及粒增长机理进行了探讨,指出水相成核是高VA含量时胶粒数密度较大的主要原因并解释了胶粒数密度及胶乳粒径与单体转化率的关系,同时也讨论了该共聚体系一步法聚合时反应机理与胶粒形态的关系.     

有机硅改性丙烯酸酯共聚乳液合成方法及胶膜性能的研究

用一次投料法、单体乳液滴加法和引发剂滴加法有机硅改性丙烯酸酯共聚乳液，聚合过程、胶粒形态及乳液稳定性的观测结果表明：单体乳液滴加法是合成该类乳液的最佳方法，研究了单体乳液滴加法中有机硅含量与聚合反及胶膜性能的关系，结果表明：有机硅含量在１５％以下时，聚合反应可以顺利进行，胶膜性能不仅依赖于聚合时有机硅单体的总量，而且还依赖于有机硅单体中活性硅氧烷所占的比例。     

乳液共聚反应过程与聚合物结构关系及13C－NMR对聚合物结构的表征

 用间歇法和半连续法进行了丙烯酸丁酯（ＢｕＡ）与醋酸乙烯酯（ＶＡｃ）乳液共聚合．^１３Ｃ－ＮＭＲ对共聚产物分子结构测试表明，在间歇法共聚合中随着反应进行其组成及结构发生很大变化，而半连续法确能制得成份及结构均匀一致的Ｐ（ＢｕＡ－ＶＡｃ）共聚物．由于ＢｕＡ水溶性小于ＶＡｃ，而其竟聚率远大于ＶＡｃ，间歇法共聚合反应初期只有少量ＶＡｃ参加共聚合．通过对间歇法共聚合中不同反应时间聚合物的^１３Ｃ－ＮＭＲ测试，表明反应初期聚合的ＶＡｃ以单链节或二元序列形式存在于主要由ＢｕＡ单元构成的分子链中，而并未形成较长ＶＡｃ链段．对上述试样玻璃化转变温度的测试结果与^１３Ｃ－ＮＭＲ实验结果颇为一致．     

离子型共聚单体用于高固含量无皂乳液聚合的研究：甲基丙烯酸异丁 …

该文采用自行合成的一种带亲水性磺酸离子基团及羟基的可共聚单体３－烯丙氧基－２－羟基丙磺酸钠（ＡＨＰＳ）用于甲基丙烯酸异丁酯／甲基丙烯酸甲酯／丙烯酸丁酯（ＩＢＭＡ／ＭＭＡ／ＢＡ）无皂乳液聚合体系。对乳胶粒粒径大小、乳液流体力学行为、共聚物的动态力学性质、拉伸行为及耐水性进行了研究,并对乳胶粒的成核机理进行了探讨。实验结果表明,带亲水性离子基团可共聚单体ＡＨＰＳ的加入可获得０．６μｍ左右的乳胶粒,乳液     

聚合物Ⅱ链的生成及相分离对复合乳胶粒形态的影响

复合乳胶粒的特殊结构使其比均相乳胶粒具有更好的综合性能和更广泛的应用领域。本文综述了分步种子乳液聚合第二步反应中,聚合物Ⅱ链的生成以及由此引起的相分离对复合乳胶粒形态的影响。在聚合物Ⅱ链的生成过程中,种子乳胶粒中引发剂的类型和浓度、单体M2的浓度及其在乳胶粒中的分布等会影响聚合物Ⅱ链的生成位置和生成速率,进而影响复合乳胶粒的形态;在相分离中,新生成的聚合物Ⅱ链在界面张力的驱动下扩散迁移,缠结成簇,与种子聚合物Ⅰ相分离,通过成核-增长(NG)的相分离影响复合乳胶粒的形成过程。     

半连续和间歇式丙烯酸酯三元乳液共聚产物的形态及分子结构研究

研究了半连续和间歇式丙烯酸酯三元乳液共聚产物的形态和分子结构。结果表明,半连续式胶乳粒子呈“多核核壳结构”,其粒径和粒径分布随单体滴加速度减慢而变小。间歇式胶乳粒径较大,粒径分布亦更宽,呈硬相在外的“单核核壳结构”;共聚物分子链中VAc结构单元的序列较长。两种方法所获无规共聚物均存在微相分离结构,分离程度随单体滴加速度的加快而变大。     

VAc/BA核壳乳液聚合乳胶粒形态演化

由两种单体分阶段种子乳液聚合制得的核壳型乳胶粒 ,可能存在着多种多样的形态 .由于不同的形态在使用中具有不同的性能 ,因此 ,核壳型乳胶粒的结构形态的研究一直受到人们的十分重视 .近年来 ,Ｓｕｎｄｂｅｒｇ[1] 等指出 ,正向、反向、两半球、两种孤立粒子等四种形态是热力学平衡形态 ,其他形态则是未达平衡的过渡形态 .并且提出用界面自由能最小的方法判别其中哪一种是最终平衡形态 .显然 ,自不平衡形态到平衡形态需要链迁移 ,Ｃｈｅｎ[2 ] 、Ｊｏｎｓｓｅｎ[3 ] 、Ｇｏｎｚａｌｅｚ[4] 等指出 ,链迁移的阻力是粘性力 .对于聚醋酸乙烯酯…     

Characterization of particle surface and morphology in vinyl acetate-butyl acrylate emulsion copolymers — Influence of the copolymerization pathway

Surface characterization was investigated in vinyl acetate (VAc) butyl acrylate (BuA) copolymer latexes of various compositions and prepared with four different emulsion polymerization processes: conventionnal batch, composition-controlled batch, core-shell, emulsifier-free semi-continuous. Surface end-groups (sulfate or carboxylic) titration results were first compared and discussed according to the type of process and as a function of conversion. As previously shown [1], it was confirmed that batch latex particles present a heterogeneous structure with a rich VAc outlayer, as in core-shell particles. As expected, semi-continuous and composition-controlled batch particles exhibit surface end-group characteristics revealing a more homogeneous distribution of both monomers within the particles. These differences in particle morphology were corroborated by analyzing water-polymer interface in these latexes using the soap titration method, with the sodium dodecyl sulfate (SDS) or sodium hexadecyl sulfate (SHS) as emulsifier probes. When the BuA was batch-polymerized onto PVAc seed particles, the estimated surface composition seemed to show that probably phase rearrangement occurs in the particle during the synthesis or upon aging. It was also confirmed that SDS displays an abnormal adsorption due to complexation and solubilization in the rich-VAc shell of the particles.     

聚硅氧烷/丙烯酸酯核/壳复合胶乳的粒径分布与成核机理

通过种子乳液法合成出具有高有机硅含量核 壳结构的聚硅氧烷 丙烯酸酯复合粒子 .研究了聚合方法、乳化剂浓度、引发剂浓度、单体滴加速度等工艺条件对复合乳液粒径尺寸、分布与形态的影响 ,并对复合乳液的成核机理进行了探讨 .研究表明 ,乳化剂浓度对乳液粒子的粒径分布和形态、结构有显著影响 ,引发剂浓度增加将使粒子粒径减小 ;相对一次投料法 ,种子乳液法生成的粒子分布窄 ,具有明显核壳结构 ,通过壳层单体滴加速度可以控制粒子的粒径尺寸和分布 ;而壳层丙烯酸酯聚合物主要是在聚硅氧烷种子表面的“过渡层”聚合、富集而成 .     

Modification of Adhesive and Latex Properties for Starch Nanoparticle‐Based Pressure Sensitive Adhesives

Starch nanoparticle (SNP)‐based pressure sensitive adhesives (PSAs) with core‐shell particle morphology (starch nanoparticle core/acrylic polymer shell) are produced via seeded, semi‐batch emulsion polymerization at 15 wt% SNP loading (relative to total polymer weight) and 40 wt% latex solids. Crosslinker and chain transfer agent (CTA) are introduced to the acrylic shell polymer formulation at a range of concentrations according to a 3² factorial design to tailor the latex and adhesive properties of SNP‐based latexes. The crosslinker and CTA show no significant effect on polymerization kinetics, particle size, and viscosity. Latex gel content is predicted using an empirical model, which is a function of crosslinker and CTA concentration. Both the gel content and glass transition temperature strongly affect the adhesive properties (tack, peel strength, and shear strength) of the SNP‐based latex films. 3D response surfaces for the adhesive properties are constructed to facilitate the design of SNP‐based PSAs with desired properties.     

PS/SiO2纳米复合粒子的制备及反应机理研究

采用一步法合成出PS/SiO₂纳米复合粒子,得到产物的产率和接枝效率均在95以上.与传统的预处理方法相比,一步法在工艺上简单易行,重复性好;复合粒子粒径、形态及分散状况与预处理方法无明显差别.对一步法制备中硅烷偶联剂的作用机理进行了探讨,通过调节偶联剂添加量可以使偶联剂在复合粒子中起到偶联剂或交联剂或二者兼有的作用.动力学研究表明,在实验配方条件下,反应遵循与前人类似工作截然不同的机理模型.此外,对复合粒子的形态与结构进行计算表明,在实验条件下,产物中平均每个复合粒子内含有5～6个初始的SiO₂纳米粒子,这些粒子团聚在一起形成核,PS接枝并包覆于团聚体外形成壳.     

Surfactant templating effects on the encapsulation of iron oxide nanoparticles within silica microspheres

Hollow silica microspheres encapsulating ferromagnetic iron oxide nanoparticles were synthesized by a surfactant-aided aerosol process and subsequent treatment. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB) played an essential role in directing the structure of the composite. Translation from mesoporous silica particles to hollow particles was a consequence of increased loading of ferric species in the precursor solution and the competitive partitioning of CTAB between silicate and ferric colloids. The hypothesis was that CTAB preferentially adsorbed onto more positively charged ferric colloids under acidic conditions. At a critical Fe/Si ratio, most of the CTAB was adsorbed onto ferric colloids and coagulated the colloids to form larger clusters. During the aerosol process, a silica shell was first formed due to the preferred silicate condensation on the gas-liquid interface of the aerosol droplet. Subsequent drying concentrated the ferric clusters inside the silica shell and resulted in a silica shell/ferric core particle. Thermal treatment of the core shell particle led to encapsulation of a single iron oxide nanoparticle inside each silica hollow microsphere.     

Preparation of ASA (acrylonitrile-styrene-acrylate) structural latexes via seeded emulsion polymerization

Acrylonitrile-styrene-acrylate (ASA) structural latexes were synthesized in a two-stage seeded emulsion polymerization. In the first-stage, partially cross-linked poly (n-butyl acrylate) (PnBA) and poly (n-butyl acrylate-stat-2-ethyl hexyl acrylate) P (nBA-stat-2EHA) (75/25 by wt) rubber cores were synthesized, and then in the second-stage, a hard poly (styrene-stat-acrylonitrile) (SAN) (70/30 by wt) shell was grafted on to the rubber seeds. The effects of surfactant type and second-stage monomer addition mode have been investigated on the final morphology of two-stage emulsion particles. The results indicated that an application of anionic surfactant, that is, sodium dodecyl sulfonate (SDS), along with sodium persulfate (KPS) initiator for both stages, and with first-stage tert-butyl hydroperoxide (t-BHP) and second-stage KPS initiators led to a hemisphere particle morphology. On the other hand, raspberry and core-shell structures were observed for the structural latexes, which were prepared using a non-ionic surfactant, that is, nonylphenol ethoxylated polyethylene glycol (Igepal CO-850), accompanying KPS initiator for both stages. It is clear, however, that the relative surface hydrophilicity of the core phase, altered by the surfactant type considerably affected the type of morphology formed. For obtained structural latexes, the gradual addition of the second-stage monomers to the core latexes resulted in a fairly real core-shell structure with a higher shell thickness. On the contrary, a raspberry structure in which the rubber phase was enlarged by the second-stage polymer microdomains was observed for the second-stage monomer addition batch. In fact, the shell semi-batch polymerization conditions lower the shell plasticizing effect, and increase the kinetic barrier to prevent from further second-stage monomer diffusion and microdomain formation within the rubbery phase.     

Compositional and structural characterization of alloyed carbide by 3D atom probe and high‐resolution TEM

During tempering of solute supersaturated ferrous martensite, the face‐centered cubic MC‐type carbides (M is alloy elements) such as VC and NbC phases usually co‐precipitate on crystal defects such as dislocation and take on plate‐like morphology. Over‐tempering makes the plate‐like shape change to spherical shape because of Ostwald coarsening. The coarsening process strongly correlates to the diffusion behaviors of the carbon and carbide‐forming elements, and consequently inhomogeneous compositional and structural distribution in the carbides is formed. Three‐dimensional atom probe and high‐resolution transmission electron microscopy have been proved useful methods to characterize the composition, morphology and nanostructure of the carbides that precipitate in a quench‐tempered micro‐alloyed steel. Depending on the actual affinity with C and the diffusion behavior, Si and Al are rejected from the alloy carbide, whereas Mn, V and Nb are inhomogeneously enriched in it. The morphology and structure change with the compositional redistribution. During the coarsening process of the pre‐existing plate‐like carbide, transition carbide that is semi‐coherent with ferritic matrix is formed because of the disparity in diffusion ratio of different solutes. A core–shell complex nanostructure is consequently formed in the coarsening carbide, and the core and shell are identified as V₈C₇ enriched in Mn, Mo and Mo₂C, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Production of micron-sized monodispersed core/shell composite polymer particles by seeded dispersion polymerization

 The effect of the weight ratio of seed polymer/monomer on the morphology of the poly(methyl methacrylate) (PMMA)/polystyrene (PS) monodispersed composite particles produced by batch seeded dispersion polymerization of styrene with 1.64-μm-sized monodispersed PMMA seed particles in a methanol/water medium (4/1 w/w) was examined. In the PMMA/PS weight ratios of 3/1 and 2/1, the composite particles had a clear morphology consisting of a PMMA core and a PS shell. In the ratio of 1/1, a lot of small PS domains were observed in the PMMA core though the PS shell was still formed. By stepwise addition of styrene monomer, the formation of the small PS domain was depressed and complete core/shell morphology was formed. Absorption/release treatments of toluene into/from the PMMA/PS (1/1 w/w) composite particles resulted in a drastic morphological change from the core/shell structure to a multi- layered one. Received: 2 February 1999 Accepted in revised form: 7 April