Polymer encapsulation of surface-modified carbon blacks using surfactant-free emulsion polymerisation

Polymer encapsulations of two different grades of water-dispersible, surface-sulfonated carbon black, Sterling-4620 with an aggregate size of 260 nm and Black Pearls-800 (BP-800) with an aggregate size of 45.7 nm, were carried out using surfactant-free emulsion polymerisation of butyl acrylate, methyl methacrylate and allyl methacrylate. High levels of initiator were required because carbon black acts as an efficient radical trap. Although polymerisation in the presence of Sterling-4620 proceeded satisfactorily using ammonium persulfate (APS), the much larger specific surface area of BP-800 inhibited polymerisation with APS and the sodium salt of 4,4′-azobis(4-cyanopentanoic acid), a non-oxidising initiator, was necessary for effective polymerisation in the presence of BP-800. Several polymer-encapsulated Sterling-4620 and BP-800 products were prepared successfully using different amounts and compositions of polymer, and have been characterised using solvent extraction, pyrolysis, thermogravimetry, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and dynamic mechanical thermal analysis.     

In-situ polymerization of n-butyl acrylate in poly(vinyl chloride)

The in situ polymerization of n-butyl acrylate with poly(vinyl chloride) has been studied. Butyl acrylate was polymerized using a peroxydicarbonate initiator and a thiol chain transfer agent in the presence of poly (vinyl chloride) beads suspended in water. The products were examined, after pressing into sheets, for optical clarity and by dynamic mechanical analysis. It was found that if 10% butyl acrylate was peesent in the mixture homogeneous blends were formed but if 15% or more butyl acrylate was present two phase mixtures were formed. If homogeneous blends prepared as above were reswollen in butyl acrylate, and the latter then polymerized, homogeneous blends containing more poly(butyl acrylate) could be prepared. The interaction parameters between both poly(vinyl chloride' and poly(butyl acrylate) and butyl acrylate were estimated by inverse gas chromatography. Using these and an estimate of the polymer/polymer interaction parameter the three component phase diagram could be qualitatively explained.     

Atom transfer radical polymerized MR fluids

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly(butyl acrylate) by surface-initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-(4-chlorosulfonylphenyl)-ethyltrichlorosilane (CTCS) on the iron particles' surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles' surface by ATRP can significantly reduce iron particles' settling and improve stability of the MR fluid. Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of ln[M]₀/[M] against polymerization time.     

Grafting of low density poly(ethylene) with butyl acrylate: Synthesis and characterisation

Low density poly(ethylene) was grafted with butyl acrylate using benzoyl peroxide as free radical initiator in an inert atmosphere and toluene as solvent. Various parameters such as reaction time, temperature, initiator concentration and ratio of monomer to polymer were varied to study their effects on percentage of grafting and grafting efficiency of butyl acrylate on to low density poly(ethylene). The graft copolymers were characterised by IR spectroscopy. The change in the solubility behaviour of low density poly(ethylene) due to grafting was studied by turbidometric titration. Thermal stability of graft copolymers was found to be higher than that of LDPE. Intrinsic viscosity data showed an increase in viscosity with increasing grafting percentage.     

Modeling of “living” free‐radical polymerization processes. I. Batch,semibatch, and continuous tank reactors

A comprehensive mathematical model is developed for “living” free‐radical polymerization carried out in tank reactors and provides a tool for the study of process development and design issues. The model is validated using experimental data for nitroxide‐mediated styrene polymerization and atom transfer radical copolymerization of styrene and n‐butyl acrylate. Simulations show that the presence of reversible capping reactions between growing and dormant polymer chains should boost initiation efficiency when using free nitroxide in conjunction with conventional initiator and also increase the effectiveness of thermal initiation. A study shows the effects of the value of the capping equilibrium constant and capping reaction rate constants for both nitroxide‐mediated styrene polymerization (using alkoxyamine as polymer chain seeds) and atom transfer radical polymerization of n‐butyl acrylate (using methyl 2‐bromopropionate as chain extension seeds). Also the effect of introducing additional conventional initiator into atom transfer radical polymerization of n‐butyl acrylate is studied. It is found that the characteristics of long chain growth are determined by the fast exchange of radicals between growing and dormant polymer chains. Polymerization results in batch, semibatch, and a series of continuous tank reactors are analyzed. The simulations also show that a semibatch reactor is most flexible for the preparation of polymers with controlled architecture. For continuous tank reactors, the residence time distribution has a significant effect on the development of chain architecture. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1630–1662, 2002     

Surface patterning of micron-sized aluminum flakes by seeded dispersion polymerization: Towards waterborne colored pigments by gold nanoparticles adsorption

The concomitant polymer embedding and surface patterning of micron-sized aluminum flakes by dispersion polymerization of styrene is reported. The aluminum pigments coated by a thin silica layer were modified by trimethoxysilylpropyl acrylate grafting (TMSPA-grafted Al@silica). Dispersion polymerization of styrene was further performed in alcoholic or hydro-alcoholic media in the presence of the organically modified TMSPA-grafted Al@silica pigments as a seed and poly(N-vinylpyrrolidone) (PVP) as a steric stabilizer to lead to hybrid aluminum flakes. The weight fraction of polymer onto the aluminum pigment surface was tuned from 14 to 29 wt.% by the hydro-alcoholic continuous phase composition and from 19 to 38 wt.% by the initiator content. The chemical nature of the initiator plays an important role in the surface patterning of the hybrid aluminum flakes as 2,2′-azobis(isobutyronitrile) initiator provided polymer nodules, i.e. due to a pattern of polymer protrusions with nodules shape at the surface of the inorganic substrate, while a flat and continuous polymer layer was obtained with 2,2′-azobis(2-amidinopropane) dihydrochloride initiator. Moreover, the introduction of ammonium groups at the surface of the polymer particles was possible by the delayed addition of a cationic acrylate co-monomer ([2-(acryloyloxy)ethyl]-trimethylammonium chloride) rendering the pigments dispersible in water. Finally, gold nanoparticles were successfully deposited onto the micro-patterned aluminum flakes to open the way towards new colored aluminum pigments. Both location of cationic ammonium function in the polymer nodule and nature of gold nanoparticles ligands were investigated with the aim to evaluate the amount of adsorbed gold nanoparticles. The final hierarchically patterned aluminum pigments dispersed in water exhibited an intense purple color.     

Poly(lauryl acrylate) and poly(stearyl acrylate) grafted multiwalled carbon nanotubes for polypropylene composites

Two new polymer grafts on an industrial grade multiwalled carbon nanotube (MWCNT) were prepared through a non-oxidative pathway employing controlled free radical polymerization for surface initiated polymer grafting. After photochemical introduction of an ATRP initiator onto the MWCNT, polymerizations of lauryl or stearyl acrylate were performed, resulting in two novel polymer modifications on the MWCNT (poly(lauryl acrylate) or poly(stearyl acrylate)). The method was found to give time dependent loading of polymers as a function of time (up to 38 wt% for both acrylates), and showed a plateau in loading after 12 h of polymerization. The modified nanomaterials were melt mixed into polypropylene composites with very low filler loading (0.3 wt%), whereafter both the thermal and electrical properties were investigated by DSC and dielectric resonance spectroscopy. The electrical properties were found to be substantially improved, where poly(lauryl acrylate) was found to be the superior surface modification, resulting in a conductive composite.     

乳液聚合法丙烯酸酯类聚合物的合成及抗静电性能考察

通过种子预乳化半连续乳液聚合技术,以苯乙烯（St）、丙烯酸丁酯（BA）和丙烯酸羟乙酯（HEA）为共聚单体,合成一类新型的两亲聚合物。考察了引发剂用量、乳化剂用量、反应温度等因素对乳液聚合工艺及聚合物的影响,优化了反应条件,同时对合成聚合物的结构、表面电阻率及亲水性进行了考察。结果表明：当乳化剂质量分数为0.75%、引发剂质量分数为0.5%、HEA质量分数为40%时,合成的乳液稳定性能最佳,转化率高达98.42%;聚合物的表面电阻率低达4.93×105Ω,且其亲水性好。     

Block copolymers obtained by free radical mechanism. II. Butyl acrylate and methyl methacrylate

Block copolymers were synthesized using methyl methacrylate and butyl acrylate as the monomers and a multifunctional initiator, di-t-butyl 4,4'-azobis(4-cyanoperoxyvalerate). The polymerizations for the formation of the block copolymers were carried out in two stages. First the poly(methyl methacrylate) polymeric initiator was synthesized and isolated. In the second stage, the thermallyactivated azo group in the polymer backbone initiated the polymerization of butyl acrylate. Upon termination by combination a tri-block results. Selective solvent fractionation was used to separate the block from the homopolymers.     

Nanoparticle formation by highly diffusion-controlled emulsion polymerisation

Emulsion polymerisations of several monomers with different water solubilities including styrene, butyl acrylate, methyl methacrylate, vinyl acetate, and methyl acrylate were carried out under highly diffusion-controlled conditions. The monomer was placed on top of an aqueous solution of an emulsifier and an initiator, while being gently stirred. Polymerisation occurred by diffusion of monomer from the monomer phase via the interface to the micellar solution. Nanoparticles as small as 25 nm were produced as a result of reduced particle growth and delayed depletion of emulsifier micelles. Nanolatexes with relatively high solids content (20%) but with a low surfactant/monomer ratio (1/50) were obtained. The monomers with the highest solubility, with the exception of methyl acrylate, produced the smallest particles. The rate of diffusion-controlled polymerisation was found to be almost proportional to the saturation monomer concentration in the water phase . The results were compared with those obtained with a high rate of agitation which allowed kinetics of polymerisation to become the rate determinant. While particles obtained by kinetics-controlled emulsion polymerisation of the monomers were large, as well as similar in size, particles obtained from diffusion-controlled runs were small, but different in size. On the other hand, particles made by kinetics-controlled emulsion polymerisation had increasing surface coverage (by emulsifier) with monomer solubility in water. Whereas, nanoparticles made by diffusion-controlled emulsion polymerisation reached almost a constant surfactant coverage independent of the monomer type (except for methyl acrylate), a surface coverage as low as 0.20 was found to be sufficient for stabilisation of nanoparticles.     

Particle morphology development in hybrid miniemulsion polymerization

Incompatibility between polymer phases resulting from hybrid minienulsion polymerization of acrylic monomers in the presence of alkyd resin leads to interesting particle morphologies. In this paper, morphology was deduced through crosscomparison of results from several forms of microscopy. For the combination of methyl methacrylate and alkyd, a derivative of core/shell morphology was observed through the combination of transmission electron microscopy, scanning electron microscopy, and spin diffusion NMR. A raspherry-like shell was found to form on the hybrid particle surface consisting of a full coverage of small (roughly 25 nm) polymethyl methacrylate spheres anchored to the particle surface through grafting with the alkyd core. Migration of the spheres to tha surface is thought to be induced by phase separation, and the size of the spheres precludes their origin from homoparticles from homogeneous nucleation. Homopolymethyl methacrylate particles were also detected in the particle distribution, resulting from the aqueous-phase initiator and hydrophilicity of methyl methacrylate monomer. For copolymer/alkyd systems (either methyl methacrylate/butyl acrylate/acrylic acid/alkyd or methyl methacrylate/butyl acrylate/alkyd), more traditional core/shell morphologies were observed with a lesser degree of homonucleated particles. A significantly different result was found in the combination of butyl acrylate and alkyd, resulting in a continuous particle-phase of polylbutyl acrylate and small internally dispersed island domains of alkyd. This is likely due to the lesser incompatibility between polybutyl acrylate and alkyd along with their similar hydrophobicity and glass transition temperatures. A higher degree of grafting between the alkyd and polybutyl acrylate also contributed to the compatibility between the two components, when compared to hybrid methyl methyl methacrylate/alkyd systems.     

ATRP poly(acrylate) star formation: A comparative study between MALDI and ESI mass spectrometry

Optimised matrix-assisted laser desorption/ionisation (MALDI) and electrospray ionisation (ESI) mass spectrometry (MS) methodologies were systematically compared in terms of their relative abilities to identify distinct chemical species present in samples associated with a polymer mechanistic study. In order to perform the investigation, formation processes involved in atom transfer radical polymerisation (ATRP) mediated methyl acrylate (MA) star polymerisations were studied. In addition to the 4-armed ATRP initiator employed in the polymerisations, initiator side-products were found to generate oligomeric chains. At a relatively high monomer to polymer conversion, terminal Br loss was observed in these oligomers; this Br loss was hypothesised to occur via degradative transfer reactions involving the radicals (CH₃)₂?OH, ?H₃ and ?H₂COCH₃, which were derived from the acetone used as a solvent in the polymerisations, as well as hydrogen radicals donated by the ligand N,N′,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA). In performing these studies, ESI was found to identify a greater number of distinct chemical species in the samples under investigation when compared to the employed MALDI technique, suggesting that the utilisation of ESI must be strongly considered in polymer mechanistic investigations if the maximum number of end-group functionalities within a given polymer sample are to be identified.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.     

丙烯酸丁酯改性C_9石油树脂的研究

利用丙烯酸丁酯改性C9石油树脂,以AIBN为引发剂,以正庚烷为溶剂,采用自由基溶液聚合法合成了C9石油树脂/丙烯酸丁酯接枝共聚物。采用单因素实验和正交实验,考察了反应中单体的选择、单体用量、引发剂用量、反应温度、反应时间对接枝率以及单体转化率的影响。最佳反应条件为:反应温度为80℃,反应时间为4 h,引发剂用量为0.75 g,丙烯酸丁酯的用量为12%,在此条件下,产物的接枝率为27.03%。红外光谱分析证实了接枝产物的生成。     

A kinetic investigation of butyl acrylate polymerization

An experimental investigation of the kinetics of the bulk free radical polymerization of butyl acrylate initiated with 2,2′-azobisisobutyronitrile (AIBN) was conducted at 50° and 60°C using two initiator concentrations. Conversion levels were measured by gravimetry and were independently confirmed using replicate runs. The experiments, conducted in glass ampoules, were performed over the full conversion range. A mathematical model for process simulation purposes was developed. The model was able to predict conversion at the two temperatures and initiator concentrations, thus providing a better understanding of the butyl acrylate homopolymerization kinetics.     

PVA作用下含氟丙烯酸酯共聚乳液的制备与表征

以聚乙烯醇(PVA)为乳化剂,采用Fe2+-H2O2引发体系,以全氟烷基乙基甲基丙烯酸酯(FM)、丙烯酸丁酯(BA)、苯乙烯(St)、甲基丙烯酰氧乙基三甲基氯化铵(DMC)、丙烯酸羟乙酯(HEA)为主要单体进行乳液聚合,制得了阳离子含氟丙烯酸酯多元共聚物乳液。通过FTIR、1HNMR、透射电镜(TEM)、示差扫描量热(DSC)及接触角测试对共聚物结构、乳胶粒径及形态、乳胶膜表面性能进行了研究。结果表明,该乳液的粒子形态呈球形,单分散性良好,平均粒径为90～100nm;随着共聚物中含氟单体质量分数的增加,乳胶膜的表面自由能显著降低;退火处理有助于含氟基团迁移到乳胶膜表面,乳胶膜表面自由能进一步降低。     

单电子转移-蜕化链转移活性自由基细乳液聚合制备PS-b-PBA-b-PS共聚物

以碘仿为引发剂、连二亚硫酸钠/碳酸氢钠为催化体系、十二烷基硫酸钠/十六烷为乳化体系,通过单电子转移-蜕化链转移（SET-DT）活性自由基细乳液聚合合成碘端基化聚丙烯酸丁酯（I-PBA-I）,进而以其为大分子引发剂引发苯乙烯聚合,制备聚苯乙烯-b-聚丙烯酸丁酯-b-聚苯乙烯（PS-b-PBA-b-PS）三嵌段共聚物,并进行共聚物结构和性能表征。发现两个阶段的SET-DT细乳液聚合均具有大的反应速率,碘仿引发剂用量少,可获得高分子量PBA和PS-b-PBA-b-PS共聚物。PS-b-PBA-b-PS共聚物具有微相分离和热塑性弹性体特征,PS质量分数为50%的嵌段共聚物的拉伸强度达9.8 MPa,断裂伸长率为660%。     

Colloidal microgels as transdermal delivery systems

This paper presents a report of the synthesis of temperature-sensitive microgels based on a copolymer of butyl acrylate (10%) co-polyNIPAM (90%), in the presence of and in the absence of ibuprofen (IBU), methyl paraben (MP) and propyl paraben (PP), by a surfactant-free emulsion polymerisation in water. N^′,N^′-methylenebisacrylamide was used as a cross-linking agent and potassium persulphate as an initiator. Physicochemical properties of the microgels were determined using different techniques including dynamic light scattering and transmission electron microscopy. It is speculated that the microgel appearance is similar to a core-shell microgel, having in the core the complex IBU or MP or PP-butyl acrylate and in the shell poly(NIPAM). Permeation across a model silicone membrane and human skin was investigated over a range of temperatures (292–313 K). The transport rate of IBU and, PP from these poly(NIPAM) microgels is significantly reduced by two and one orders of magnitude, respectively, compared with the transport rate from saturated solutions. Such a reduction in flux was not however observed for MP.     

Preparation and performance in paper coating of silicone‐modified styrene–butyl acrylate copolymer latex

Silicone‐modified styrene–butyl acrylate copolymer latex was synthesized by emulsion copolymerization by using octamethylcyclotetrasiloxane (D₄), styrene, and butyl acrylate as raw materials, potassium persulfate as initiator and propylmethacrylate triethoxysilane (KH‐570) as crosslinking agent. The infrared spectra studies showed that the vinyl monomers were completely copolymerized with D₄. The prepared silicone‐modified copolymer latex with the interpenetrating polymer networks tended to have higher stability, and better toluene and water resistance than styrene–butyl acrylate latex. The glossiness of coated paper was improved with silicone‐modified copolymer latex, and it was at a maximum when D₄ was about 3% of total monomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 333–336, 2001     

Emulsion Semi-Batch Terpolymerization Process Using Hybrid Emulsifiers for Synthesizing New Emulsion Pressure Sensitive Adhesives (EPSAs)

In order to obtain a suitable formulation of designing direct synthesis of acrylic latexes to be used as emulsion pressure sensitive adhesives (EPSA), having high shear resistance together with high peel strength and tack, free radical emulsion polymerization of hard monomers, such as styrene (St), vinyl acetate monomer (VAM), methyl methacrylate (MMA) and butyl methacrylate (BMA), and soft monomers, butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA) along with multifunctional monomers, namely acrylic acid (AA), were carried out. The effect of the type of hard and soft acrylic monomers, the type and level of emulsifiers, and the initiator concentration on the emulsion polymer stability and final properties of the EPSA were investigated. The results obtained showed an optimized composition. This composition led to a significant increase in shear strength and peel strength to 909 kPa and 0.45 N/mm, respectively, while the synthesized PSA was still too tacky, 5.5 cm, according to adhesion performance testing. For making this successful balance of the conflicting adhesion properties of PSA, a series of anionic and nonionic emulsifiers were investigated. It was interestingly found out that the hybrid emulsifiers (anionic coupling with nonionic) with the optimized compositions could enhance the stability of the emulsion system and improve the properties of PSA compared with the mono-emulsifier. We also tried to adjust the initiator concentration with the level of the optimized hybrid emulsifier, polyoxyethylene alkyl phenyl ether (K30), dioctyl sulfosuccinate (DOSS), and sodium vinyl sulfonate (SVS) with the ratio 2:1:1, resulting in a highly preferred proportion of the 0.5 part of the initiator versus 1.25 parts of the hybrid emulsifier in terms of the total weight of the monomers.