纳米TiO_2粒子静电吸附引发剂及其原位锚固丙烯酸丁酯聚合

调节体系酸碱度使分散于水分散液中的纳米TiO2粒子表面带负电,进而通过静电作用高效稳定吸附上偶氮盐类引发剂2,2′-偶氮二异丁脒二氯化氢(AIBA).实验发现引发剂在TiO2粒子表面的静电吸附存在一个稳定吸附上限,其值在pH=10的体系中为0.084mmol/g(相对于TiO2的量).进一步通过原位乳液聚合在TiO2粒子表面就地引发丙烯酸丁酯(BA)的锚固聚合,制备得到了PBA/TiO2复合乳胶.对聚合动力学和聚合产物的观察发现,吸附引发剂在其中起到重大作用,只有当引发剂用量略低于稳定吸附上限时,反应过程稳定性和聚合产物分散性才较好.此时聚合反应阻聚期短、反应速率快、单体转化率高、实验重现性好.热重分析(TGA)和红外光谱分析(FTIR)结合抽提实验证实,通过原位乳液聚合可在TiO2粒子表面锚固上13.5%的不可抽提PBA聚合物.动态激光粒度分析(DLS)发现,原位锚固改性对TiO2粒子软团聚体具有稳定的解团聚作用,可有效提高纳米TiO2粒子在体系中的分散性和分散稳定性.这一化学改性作用与超声分散所带来的物理性的可逆解软团聚作用有着本质区别.     

纳米SiO_2粒子锚固偶氮引发剂及接枝聚甲基丙烯酸甲酯

对纳米SiO2 粒子锚固偶氮引发剂 ,进而引发甲基丙烯酸甲酯聚合而制备聚甲基丙烯酸甲酯(PMMA) 纳米SiO2 复合粒子进行了研究 .纳米SiO2 先用环氧型硅烷偶联剂处理 ,再与偶氮二氰基戊酸发生缩合反应而锚固上偶氮引发剂 ,通过差示扫描量热和元素分析证明了引发剂在纳米SiO2 表面的锚固 .通过改性纳米SiO2 存在下MMA的乳液聚合 ,制备得到了接枝率为 2 3 2 %、接枝效率为 36 1%的PMMA 纳米SiO2 复合粒子 .经乳液聚合后 ,纳米SiO2 粒子团聚程度减小 ,在水相中分散稳定 .     

纳米SiO_2锚固光敏基团引发MMA光接枝聚合研究

对纳米SiO2进行了锚固光引发剂的表面修饰,进而引发甲基丙烯酸甲脂(MMA)光接枝聚合制备有机/无机复合粒子.纳米SiO2粒子首先用氯化亚砜进行表面氯化,再与光引发剂2-羟基-4-(2-羟基乙氧基)-2-甲基苯丙酮(Irgacure2959)反应从而锚固上光引发剂.通过紫外光引发MMA在经过修饰过的纳米SiO2表面上进行表面光接枝聚合.采用IR、TGA和TEM等方法表征了接枝前后纳米粒子的变化,证明了表面接枝物的存在,并研究了不同反应条件对单体转化率、接枝率和接枝效率的影响.研究结果表明,搅拌对接枝过程的影响比较显著.TGA结果显示未搅拌聚合时接枝率只能达到比较小的程度,而在搅拌条件下180min内MMA的接枝率可达到110%.     

纳米SiO_2/含氟丙烯酸酯共聚物复合乳液的制备与性能及聚合动力学研究

采用原位聚合法制备纳米SiO2/含氟丙烯酸酯共聚物复合乳液,研究了其聚合反应动力学,并通过红外光谱(IR)、透射电子显微镜(TEM)、热失重(TGA)等方法表征所得产物的结构及形态、乳胶膜的耐热性能和表面性能.研究结果显示,聚合反应的表观活化能为83.15 kJ/mol,纳米SiO2/含氟丙烯酸酯共聚物复合粒子呈现出明显的核壳结构,纳米SiO2粒子的引入不仅改善了聚合物的耐热性能,也在一定程度上提高了乳胶膜的抗水性.对膜表面自由能的组成分析表明,与一般含氟乳胶膜的表面自由能的情况相反,该乳胶膜的表面能是由较大的极性部分和较小的色散部分组成.     

团聚纳米SiO_2在苯乙烯乳液聚合过程中的再分散过程及机理

用二氧化硅 (SiO2 )存在下的乳液聚合法制备了聚苯乙烯 (PSt) 纳米SiO2 复合材料 ,研究了苯乙烯(St)乳液聚合过程中团聚纳米SiO2 的解离与再分散过程及分散的机理 .发现商品纳米SiO2 粒子以团聚体形式存在 ,团聚体大小远超出纳米级范围 .随聚合时间的延长 ,St的转化率逐渐增加 ,而PSt SiO2 复合微胶囊的粒径逐渐减小 ,反应 12 0min后 ,转化率和复合微胶囊粒子的粒径趋于稳定 .透射电镜 (TEM)也显示PSt SiO2 复合微胶囊粒子具有海岛结构 ,而SiO2 粒子的粒径在纳米范围内 ,表明在乳液聚合过程中SiO2 团聚体被逐渐解离 ,并重新分散到纳米尺度 .红外光谱研究发现 ,在乳液聚合过程中 ,除生成PSt均聚物外 ,还在纳米SiO2 表面生成了PSt接枝共聚物 ,改善了无机纳米粒子与聚合物之间的界面相容性 .聚合过程中的反应热和剪切搅拌是团聚体被解离和重新分散的主要原因 ,而生成的聚合物起到隔离作用     

超声辐照乳液聚合制备聚丙烯酸正丁酯空心微球

利用超声辐照引发包覆乳液聚合制备了聚丙烯酸正丁酯(PBA)空心微球.TEM和DLS结果显示,空心微球粒径均一,壳层厚度均匀.FTIR结果显示,壳-核物质间以物理吸附相结合,没有形成化学键.同时,利用TEM和DLS研究了空心微球的形成机理,阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)在CMC浓度以下首先吸附在纳米SiO2粒子表面形成双层结构,然后丙烯酸正丁酯(BA)单体增溶进入CTAB层间,在超声辐照引发、分散作用下包覆聚合形成均一的PBA-SiO2壳-核粒子,再利用HF溶液去除无机核,得到PBA空心微球.     

甲基丙烯酸甲酯/纳米SiO_2粒子分散液的细乳化和细乳液聚合

对包含纳米SiO2粒子的甲基丙烯酸甲酯(MMA)的细乳化和细乳液聚合行为进行了研究.发现在超声细乳化过程中,90%以上的分散于MMA相的纳米SiO2粒子将从油相逃逸到水相.采用甲基丙烯酸3-(三甲氧基甲硅烷基)丙酯(MPS)偶联剂处理SiO2粒子,可以增加其表面亲油性,抑止这种逃逸,经测定几乎全部SiO2粒子在超声细乳化后仍稳定停留在细乳化亚微液滴中.通过进一步细乳液聚合,得到了分散稳定、界面清晰的包裹有纳米SiO2粒子的聚甲基丙烯酸甲酯复合粒子乳液.     

微波聚合制备单分散、超细聚甲基丙烯酸甲酯微球

在微波辐照下,通过甲基丙烯酸甲酯(MMA)的无乳化剂乳液聚合,制备出粒径单分散、超细聚甲基丙烯酸甲酯(PMMA)微球。微波显著缩短聚合诱导期,加快聚合反应,其部分原因是微波加快引发剂过硫酸钾(KPS)的分解。实验证明微波辐照下KPS的表观分解活化能(ED)由128.3kJ/mol降低到106.0kJ/mol。单体浓度是影响PMMA乳液粒子尺寸的主要因素,在[MMA]小于0.3mol/L时,平均粒径随单体浓度提高而线形增加;[MMA]为0.3～1.0mol/L时,平均粒径稳定在约200nm;之后随单体浓度进一步增加,乳液稳定性变差。引发剂浓度增加对平均粒径影响较小,但增大引发剂浓度可显著降低粒径分散度。选取[MMA]为0.23～0.3mol/L、[KPS]为3×10-3～6×10-3mol/L可以得到粒径200nm的单分散微球。以丙酮/水(体积比1/3)为反应介质,可制备出数均粒径45nm的PMMA纳米粒子。在体系中加入3.5×10-3mol/L的Cu2+,可制备出数均粒径67nm、单分散的PMMA纳米粒子。     

纳米SiO_2表面基团在MMA原位本体聚合中的阻缓聚作用

分别以3-(甲基丙烯酰氧)丙基三甲氧基硅烷(MPS)和辛基三甲氧基硅烷(OTMS)为活性和惰性硅烷的代表,对SiO2进行不同锚固密度的表面修饰,并以改性SiO2的甲基丙烯酸甲酯(MMA)单体分散液为原料,通过原位本体聚合制得一系列SiO2含量不同的高分散性SiO2/PMMA复合材料.考察SiO2表面基团活性程度和SiO2含量对聚合反应动力学、基体聚合物分子量以及复合材料硬度的影响,探究修饰状态不同SiO2在本体自由基聚合中的作用机制.发现SiO2表面硅羟基及其锚固MPS的活性双键会对聚合反应起阻缓聚作用,进而会显著降低基体聚合物的分子量及复合材料的硬度.而惰性硅烷OTMS对SiO2表面的锚固则会消耗SiO2表面硅羟基、并屏蔽其影响,因而随着OTMS锚固密度的提高,基体分子量和复合材料硬度均会随之提高,特别是当表面修饰达到饱和状态时,SiO2的阻缓聚作用已可忽略.     

原位聚合法制备具有温敏PNIPAM壳的核-壳结构聚合物纳米微球的研究

结合大分子自组装和原位自由基聚合方法,采用油溶性引发剂偶氮二异丁腈(AIBN),在聚(ε-已内酯)(PCL)纳米粒子表面引发聚合单体N-异丙基丙烯酰胺(NIPAM)和交联剂亚甲基双(丙烯酰胺)(MBA),制备得到了核-壳结构的PCL/PNIPAM聚合物纳米微球.系统研究了单体和交联剂用量、壳层目标交联度、初始PCL/DMF溶液的浓度及引发剂AIBN含量4个反应参数对核-壳结构PCL/PNIPAM纳米微球的PNIPAM壳层得率、微球尺寸、温敏性能及电镜形貌的影响.结果表明,在制备核-壳结构PCL/PNIPAM纳米微球的反应过程中,PCL粒子表面的聚合和水中的聚合二者之间相互竞争.适当增加引发剂AIBN的添加量,有利于制备得到核/壳比例可控的PCL/PNIPAM纳米微球;交联剂MBA较高的反应活性导致形成了非均匀交联的PNIPAM壳层.     

The role of initiation in the synthesis of silica/poly(methyl methacrylate) nanocomposite latex particles through emulsion polymerization

Silica/poly(methyl methacrylate) nanocomposite latex particles have been synthesized by emulsion polymerization of methyl methacrylate using a nonionic surfactant: nonylphenol poly(oxyethylene) and three different initiators, namely: 2,2′-azobis(2-amidinopropane) dihydrochloride (AIBA), potassium persulfate (KPS) and azobis(isobutyronitrile) (AIBN), being cationic, anionic and nonionic, respectively. A silica sol with an average diameter of 68 nm was used as the seed. The polymerization reaction was conducted under alkaline conditions in order to evaluate the role of the surface charge of the hydrophilic silica on the coating reaction. AIBA was found to be adsorbed on the silica surface owing to electrostatic interactions of the amidine function of the cationic initiator with the silanolate groups of the oxide surface, while the anionic and the nonionic initiators did not adsorb on silica under the same conditions. Nonetheless, whatever the nature of the initiator, polymerization took place on the silica particles as evidenced by transmission electron microscopy. The extent of interaction between the inorganic surface and the polymer particles was quantified by means of ultracentrifugation and a material balance. As much as 65% by weight of the total polymer formed was found to be present at the silica surface using AIBA, while only 40% for KPS and 25% for AIBN was found to cover the silica particles under alkaline conditions. We demonstrate that by using a cationic initiator and by controlling the pH of the suspension it is possible to significantly decrease the amount of free polymer. Coating of the silica particles took place through a kind of in situ heterocoagulation mechanism. Received: 8 December 2000 Accepted: 22 February 2001     

Anchoring of polyacrylate onto silica and formation of polyacrylate/silica nanocomposite particles via in situ emulsion polymerization

Polyacrylate/silica nanocomposite latex particles were prepared by in situ emulsion polymerization of acrylate monomers initiated by 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) adsorbed by silica nanoparticles. The anchoring of polyacrylate (ACR) onto silica nanoparticles was achieved through the physical absorption and chemical grafting reaction. The elution and HF etching experiments showed that most silica nanoparticles were encapsulated by ACR to form the raspberry-like ACR/silica nanocomposite latex particles. The silica nanoparticles with a greater grafting degree of ACR tended to locate in the bulk of the polymer, and the silica particle with a lower grafting degree would not be combined with polymer latex particles and always remained in water phase. The formation of the final ACR/silica nanocomposite latex particles included the anchoring of ACR onto silica primary particles, aggregation of silica primary particles to form the silica-containing latex particles, and the growth of latex particles.     

Synthesis and characterization of silica/poly (methyl methacrylate) nanocomposite latex particles through emulsion polymerization using a cationic azo initiator

Following a previous work (J. L. Luna-Xavier et al., Colloid Polym. Sci.279, 947 (2001)), silica-poly (methyl methacrylate) (PMMA) nanocomposite latex particles have been synthesized in emulsion polymerization using a cationic initiator, 2,2'-azobis (isobutyramidine) dihydrochloride (AIBA), and a nonionic polyoxyethylenic surfactant (NP30). Silica beads with diameters of 68, 230, and 340 nm, respectively, were used as the seed. Coating of the silica particles with PMMA was taking place in situ during polymerization, resulting in the formation of colloidal nanocomposites with a raspberry-like or a core-shell morphology, depending on the size and nature of the silica beads. The amount of surface polymer was quantified by means of ultracentrifugation and thermogravimetric analysis as extensively described in the first article of the series (see above reference). The influence of some determinant parameters such as the pH of the suspension, the initiator, silica, monomer, or surfactant concentration on the amount of coating polymer and on the efficiency of the coating reaction was investigated in details and discussed in light of the physicochemical properties of the seed mineral. Electrostatic attraction between the positive end groups of the macromolecules and the inorganic surface proved to be the driving force of the polymer assembly on the seed surface at high pH, while polymerization in adsorbed surfactant bilayers (so-called admicellar polymerization) appeared to be the predominant mechanism of coating at lower pH. Optimal conditions have been found to reach high encapsulation efficiencies and to obtain a regular polymer layer around silica.     

Efficient synthesis of poly(2-vinylpyridine)-silica colloidal nanocomposite particles using a cationic azo initiator

Colloidal poly(2-vinylpyridine)-silica nanocomposite particles can be efficiently prepared by emulsion polymerization at 60 degrees C using a commercial 20 nm aqueous silica sol as the sole stabilizing agent. Unlike previously reported colloidal nanocomposite syntheses, transmission electron microscopy studies indicate very high silica aggregation efficiencies (88-99%). The key to success is simply the selection of a suitable cationic azo initiator. In contrast, the use of an anionic persulfate initiator leads to substantial contamination of the nanocomposite particles with excess silica sol. The cationic azo initiator is electrostatically adsorbed onto the anionic silica sol at submonolayer coverage, which suggests that surface polymerization may be important for successful nanocomposite formation. Moreover, the 2-vinylpyridine can be partially replaced with either styrene or methacrylic comonomers to produce a range of copolymer-silica nanocomposite particles. The poly(2-vinylpyridine)-silica nanocomposite particles have a well-defined core-shell morphology, with poly(2-vinylpyridine) cores and silica shells; mean diameters typically vary from 180 to 220 nm, and mean silica contents range from 27 to 35% by mass.     

Synthesis of Latex Particles with Surface Functional Groups and Their Applications for the Fabrication of Porous Materials

In this study, monodisperse latex particles with specific surface functional groups were synthesized by emulsifier-free emulsion polymerization. Amidine or carboxylated polystyrene nanospheres with narrow size distribution were prepared by emulsion polymerization using AIBA (α,α′-zodiisobutyramidine dihydrochloride) as amine-containing initiator or acrylic acid as carboxyl-containing comonomer, respectively. Factors affecting the particle size and distribution were systemically studied by changing the amount of initiator or monomer, the polymerization temperature, and the stirring speed of emulsion polymerization reactor. Monodisperse polymethylmethacrylate beads were also synthesized by soapless emulsion polymerization using methacrylic acid or aminoethylmethacrylate hydrogen hydrochloride as comonomer for the surface functionalization of the particles. As applications of the latex beads, the polymeric particles were adopted as templating materials for the fabrication of macroporous titania film and meso-macroporous silica particles by colloidal templating method.     

Size control of polystyrene nodules formed on silica particles in soap-free emulsion polymerization with amphoteric initiator

An amphoteric initiator of 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was applied to fabrication of raspberry-shaped composite particles in soap-free emulsion polymerization of styrene in the presence of silica particles surface-modified with 3-methacryoxypropyltrimethoxysilane. In the polymerizations, pH of the solution was ranged from 7.9 to 9.9 to alter dissociation degree of ionizable groups in the initiator. Raspberry-shaped particles were obtained in a pH range of 8.0 to 9.3 followed by a tendency in which average size of polystyrene (PSt) nodules adsorbed onto the silica particles decreased with pH. This tendency was similar to that of polymer particles formed in conventional soap-free emulsion polymerization in the absence of the silica particles. An increase in silica particle concentration led to a decrease in the final size in PSt nodules. The decrease was caused by the stabilization of polymer particles fixed to the silica surface against polymer particle aggregation in water phase.     

Polystyrene-coated micro-sized particles by "in situ" surface initiated polymerization in accord with Langmuir model adsorption

This study describes the mechanism of adsorption of polystyrene chains PS "in situ" growth from micro-sized commercial silicate particles, i.e. Feldspar. The main aim is to derive adsorption isotherms from thermal gravimetric analysis (TGA) and size exclusion chromatography (SEC) data obtained during the direct polymerization of PS initiated by a pre-adsorbed radical initiator onto the inorganic surface. The adsorption isotherm plot indicates that the PS adsorption is in accord with the Langmuir Model. The amount of PS monolayer coverage increases with polymerization time, and it is highly dependent on the monomer diffusion to the surface during the hybrid inorganic/organic synthesis. Such behavior depends on the concentration gradient between monomer concentration in solution and that adsorbed by polymerization onto the micro-sized particles surface of Feldspar.     

Synthesis of poly(chitosan‐N‐isopropylacrylamide) complex particles with the method of soapless dispersion polymerization

Crosslinked poly(chitosan‐N‐isopropylacrylamide) [poly(NIPAAM‐chitosan)] complex particles were successfully synthesized with the method of soapless dispersion polymerization. The anionic initiator ammonium persulfate (APS) and the cationic initiator 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (AIBA) were used to initiate the copolymerization. The poly(NIPAAM‐chitosan) copolymer particles synthesized with APS as the initiator had a homogeneous morphology, whereas the copolymer particles synthesized with AIBA as the initiator showed a core–shell morphology. In addition, various variables such as the particle size, reaction rate, and ζ potential were taken into account. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2053–2063, 2003     

聚合物模板微球表面电性对中空二氧化硅微球形貌的影响

分别以过硫酸钾和偶氮二异丁基脒盐酸盐为引发剂,以聚乙烯吡咯烷酮(PVP)为分散剂,在水中引发苯乙烯聚合制备了2种表面分别带负电性和正电性基团的聚苯乙烯(PS)模板微球.在氨水催化下,利用正硅酸乙酯的水解缩合,形成PS/SiO_2复合微球,去除模板后得到中空SiO_2微球,并对其进行FTIR、电子显微镜、TGA以及氮气吸附等分析表征.结果表明,PS模板微球表面的电性决定了OH-的分布,从而导致PS模板微球表面SiO_2壳层不同的形成机制.当以表面带负电的PS微球为模板时,可得到树莓状的中空SiO_2微球;而以表面带正电的PS微球为模板时,得到是表面光滑的,具有介孔结构的中空SiO_2微球.