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Acrylate
Kinds of Acrylate Terms modified by Acrylate Selected AbstractsNovel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) DispersantJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Kuttan Prabhakaran Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time-delayed in situ generation of Mg2+ ions from the sparingly soluble MgO forms Mg,poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°,30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa. [source] Temperature-Responsive Water-Soluble Copolymers Based on 2-Hydroxyethyl Acrylate and Butyl AcrylateMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2007Grigoriy A. Mun Abstract Amphiphilic copolymers have been synthesised by free radical copolymerisation of 2-hydroxyethyl acrylate with butyl acrylate, the reactivity ratios of which indicate practically equal reactivity. The copolymers containing less than 30 mol-% of BA were soluble in water and exhibited a LCST in aqueous solutions. It was found that the interaction between these copolymers and poly(acrylic acid) in aqueous solutions resulted in the formation of interpolymer complexes stabilised by hydrogen bonds and hydrophobic interactions. This interaction was significantly affected by solution pH and led to modification of the temperature-responsive behaviour of the copolymers. [source] Polymerization of Methyl Acrylate by a 2,6-Bis(2-benzimidazyl)pyridine Zirconium Dichloride/MAO Catalyst SystemMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2006Hyun Yong Cho Abstract Summary: A novel non-metallocene Zr(IV) complex bearing a bianionic form of the ligand 2,6-bis(2-benzimidazolyl)pyridine is synthesized. This Zr complex is an active catalyst for the polymerization of MA via coordination polymerization in the presence of methylaluminoxane MAO. The activity and MWD are increased as the polymerization temperature increases. The maximum activity is observed at Al/Zr molar ratio of 100 and the deactivation is shown above 100, resulting from an inactive bimetallic complex between catalyst and free TMA presented in MAO. Decrease in MWD is observed with higher MAO concentration due to its role in chain transfer during the chain propagation. The reaction of the ligand and catalyst synthesis. [source] Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n -Butyl AcrylateMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2009Nasir M. Ahmad Abstract Chain transfer to polymer (CTP) in conventional free-radical polymerizations (FRPs) and controlled radical polymerizations (ATRP, RAFT and NMP) of n -butyl acrylate (BA) has been investigated using 13C NMR measurements of branching in the poly(n -butyl acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymerizations as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concentration of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-molecular CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concentrations is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymerizations, the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irrespective of the type of control, controlled radical polymerizations give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymerization. [source] Hybrid Miniemulsion Polymerization of Acrylate/Oil and Acrylate/Fatty Acid SystemsMACROMOLECULAR REACTION ENGINEERING, Issue 3 2008Juchen Guo Abstract Acrylate,alkyd hybrid latex via miniemulsion polymerizations show promise as water-borne coating systems. However, poor homogeneity of the particles caused by the immiscibility of the alkyd in polyacrylate limits monomer conversion and film formation. To resolve this problem, the hybrid miniemulsion polymerization of acrylate in the presence of linoleic acid and sunflower seed oil was carried out. Products were characterized by solvent extraction, dynamic light scattering, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and transmission electron microscopy (TEM). The results provide clear evidence that substituting a fatty acid or natural oil with smaller molecular size (weight) for a conventional alkyd improves the grafting efficiency, and enhances the homogeneity of the hybrid polymer particles in water-borne latex systems. [source] Synthesis and Properties of a Superabsorbent Polymer Prepared by Copolymerization of Sodium Acrylate with Sodium 1-(Acryloyloxy)propan-2-yl PhosphateMACROMOLECULAR REACTION ENGINEERING, Issue 2 2007Zhenbin Chen Abstract A novel monomer, 1-(acryloyloxy)propan-2-yl phosphoryl dichloride, was synthesized and characterized in this work. Thereafter, the monomer was neutralized with sodium hydroxide and copolymerized with sodium acrylate to obtain a superabsorbent polymer. The superabsorbent polymer was then modified to improve its swelling properties (i.e., the water absorbency under load, the hydrogel strength, the resilience and the dispersion). Both single factor and orthogonal design experiments were adopted to obtain optimal conditions. The superabsorbent polymer prepared under the optimal conditions showed improved water absorbency in physiological saline [17 g,·,g,1 under load (P,=,2,×,103 Pa) and 65 g,·,g,1 at atmospheric pressure] and other swelling properties, such as hydrogel strength, resilience and dispersion, also improved. [source] Photoinduced Racemization of an Optically Active Helical Polymer Formed by the Asymmetric Polymerization of 2,7-Bis(4- tert -butylphenyl)fluoren-9-yl Acrylate,ANGEWANDTE CHEMIE, Issue 49 2009Takeshi Sakamoto Dr. Ein Lichttrick: Ein durch asymmetrische anionische Polymerisation hergestelltes optisch aktives helicales Polymer mit Vorzugshändigkeit ging bei Photobestrahlung eine Stereomutation ein. Dagegen blieb die Helix beim Erhitzen stabil (siehe Bild). Diese photoinduzierte Racemisierung eines synthetischen helicalen Polymers verlief ohne Änderung der chemischen Bindung wie Bindungsbildung, Bindungsspaltung oder Isomerisierung einer Doppelbindung. [source] ChemInform Abstract: Lewis Acid Mediated Reactions of 1-Cyclopropyl-2-arylethanone Derivatives with Allenic Ester, Ethyl Acetoacetate, and Methyl Acrylate.CHEMINFORM, Issue 49 2008Min Shi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] An Imidazolium-Based Phosphinite Ionic Liquid (IL-OPPh2) as a Reusable Reaction Medium and PdII Ligand in Heck Reactions of Aryl Halides with Styrene and n-Butyl Acrylate.CHEMINFORM, Issue 32 2007Nasser Iranpoor Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Highly Diastereo- and Enantioselective Copper-Catalyzed Domino Reduction/Aldol Reaction of Ketones with Methyl Acrylate.CHEMINFORM, Issue 24 2006Julia Deschamp Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Baylis,Hillman Reactions of N-Arylidenediphenylphosphinamides with Methyl Vinyl Ketone, Methyl Acrylate, and Acrylonitrile.CHEMINFORM, Issue 39 2002Min Shi Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Palladium-Catalyzed Arylation of Butyl Acrylate and Acrylamide with Aryl Iodides in Water.CHEMINFORM, Issue 28 2002Hong Zhao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Copolymerization of Divinylsilyl-11-silicotungstic Acid with Butyl Acrylate and Hexanediol Diacrylate: Synthesis of a Highly Proton-Conductive Membrane for Fuel-Cell ApplicationsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 3 2009James Abstract Highly conducive to high conductivity: Polyoxometalates were incorporated in the backbone of a hydrocarbon polymer to produce proton-conducting films. These first-generation materials contain large, dispersed clusters of polyoxometalates. Although the morphology of these films is not yet optimal, they already demonstrate practical proton conductivities and proton diffusion within the clusters appears to be very high. [source] Using the Aggregation of Latex Polymers in the Fabrication of Reproducible Enzyme ElectrodesELECTROANALYSIS, Issue 17 2003Wibowo Rahmat Abstract An enzyme electrode for glucose is described as a model system to demonstrate a fabrication method using latex aggregation and entrapment of enzyme. Electrosterically-stabilized latex particles synthesized by emulsion polymerization in batch from acrylic acid, methyl methacrylate and butyl acrylate, and glucose oxidase were coagulated together at pH,5.5 with ethanol. A platinum disk electrode dipped in the solution becomes coated with latex/enzyme. The relative thickness of the film and relative amount of enzyme may be controlled by the time the electrode is in contact with the solution. The enzyme was then immobilized by covalent attachment of amine groups to carboxylic moieties in the polymer using 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide hydrochloride and N -hydroxysuccinimide. Five minutes contact with the latex/enzyme solution and subsequent amide coupling, gave electrodes with a reproducibility of 5.7% RSD, a wide dynamic range (0,100,mM) and good storage properties. [source] An accessible micro-capillary electrophoresis device using surface-tension-driven flowELECTROPHORESIS, Issue 9 2009Swomitra K. Mohanty Abstract We present a rapidly fabricated micro-capillary electrophoresis chip that utilizes surface-tension-driven flow for sample injection and extraction of DNA. Surface-tension-driven flow (i.e. passive pumping) [G. M. Walker et al., Lab. Chip. 2002, 2, 131,134] injects a fixed volume of sample that can be predicted mathematically. Passive pumping eliminates the need for tubing, valves, syringe pumps, and other equipment typically needed for interfacing with microelectrophoresis chips. This method requires a standard micropipette to load samples before separation, and remove the resulting bands after analysis. The device was made using liquid phase photopolymerization to rapidly fabricate the chip without the need of special equipment typically associated with the construction of microelectrophoresis chips (e.g. cleanroom) [A. K. Agarwal et al., J. Micromech. Microeng. 2006, 16, 332,340; S. K. Mohanty et al., Electrophoresis 2006, 27, 3772,3778]. Batch fabrication time for the device presented here was 1.5,h including channel coating time to suppress electroosmotic flow. Devices were constructed out of poly-isobornyl acrylate and glass. A standard microscope with a UV source was used for sample detection. Separations were demonstrated using Promega BenchTop 100,bp ladder in hydroxyl ethyl cellulose (HEC) and oligonucleotides of 91 and 118,bp were used to characterize sample injection and extraction of DNA bands. The end result was an inexpensive micro-capillary electrophoresis device that uses tools (e.g. micropipette, electrophoretic power supplies, and microscopes) already present in most labs for sample manipulation and detection, making it more accessible for potential end users. [source] Integrated microdevice for preconcentration and separation of a wide variety of compounds by electrochromatographyELECTROPHORESIS, Issue 3 2009Gaelle Proczek Abstract An integrated microdevice was developed to couple on-chip SPE to separation by channel electrochromatography. An acrylate-based monolith was synthesized within a glass microdevice by photoinitiated polymerization. It was used for both separation and preconcentration by direct injection on the head of the stationary phase or by confining the preconcentration step in a given zone of the stationary phase. The composition of the polymerization mixture was chosen to achieve a monolithic material containing both hydrophobic and charged moieties to ensure an electroosmotic flow for separation. As a consequence the extraction procedure occurs via hydrophobic and ionic interactions. Neutral, ionizable and charged compounds were successfully preconcentrated and separated within the microdevice through electrochromatographic mechanisms, highlighting the versatility of this device. The performance of the integrated microdevice was demonstrated with the preconcentration and separation of a mixture of PAHs for which a signal enhancement factor (SEF) of 270 was achieved within 120,s of preconcentration. In the case of charged and ionizable compounds, according to the electrolyte composition, contributions of both reverse-phase and ion-exchange mechanisms were used to perform effective electrochromatographic preconcentration. A SEF of 250 was obtained for the model-charged compound within 20,s of preconcentration. Finally, the potentials of on-chip preconcentrate and separate both neutral and ionized compounds have been demonstrated using a mixture of model compounds. [source] CEC separation of heterocyclic amines using methacrylate monolithic columnsELECTROPHORESIS, Issue 11 2007Elena Barceló-Barrachina Abstract Two methacrylate-based monolithic columns, one with a negatively charged group (sulfonic group) and another with a new monomer N,N -dimethylamino ethyl acrylate (DMAEA), were prepared and tested for the separation of basic compounds by CEC. This new monolithic stationary phase was prepared by the in situ polymerization of DMAEA with butyl methacrylate and ethylene dimethacrylate, using a ternary porogenic solvent consisting of water, 1-propanol and 1,4-butanediol. The performance of this column was evaluated by means of the analysis of a family of heterocyclic amines. Separation conditions such as pH, amount of organic modifier, ionic strength and elution mode (normal or counterdirectional flow) were studied. At the optimal running electrolyte composition, and using the counterdirectional mode, symmetrical electrochromatographic peaks were obtained, with the number of theoretical plates up to 30,000 and a good resolution between closely related peaks. The 2-acrylamido-2-methyl-1-propane-sulfonic acid column was used for CEC-MS, taking advantage of the compatibility of its elution mode (normal flow) with the MS coupling. [source] Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using ,,,-Unsaturated Carbonyl Ligands,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2008Rocío A. Arteaga-Müller Abstract Reduction of mono(cyclopentadienyl)niobium complexes [NbCpRCl4] [CpR = C5Me4H (1), C5H4SiMe2Cl (2), C5H4SiMe3 (3)] with Na/Hg in the presence of methyl methacrylate [MMA, CH2=C(Me)C(O)OMe (a)], methyl acrylate [MA, CH2=CHC(O)OMe (b)] and mesityl oxide [MO, CMe2=CHC(O)Me (c)] afforded the corresponding derivatives [NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA (1a); CpR = C5H4SiMe2Cl, LL = MMA (2a), MA (2b), MO (2c); CpR = C5H4SiMe3, LL = MMA (3a), MA (3b)] in variable yields depending on both the cyclopentadienyl and the ,,,-unsaturated carbonyl compounds. The reactivity of these complexes was studied toward protic and Lewis acids. Addition of triflic acid TfOH (Tf = CF3SO2) to 3b gave the triflate complex [NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 (4)]. The Lewis acids E(C6F5)3 (E = B, Al) reacted with complexes 2b and 3b to give the three-membered metallacyclic (or ,2 -enone) compounds [NbCpRCl2{,2 -CH2=CHC(OMe){O·E(C6F5)3}}] [CpR = C5H4SiMe2Cl, E = B (5), Al (6); CpR = C5H4SiMe3, E = B (7), Al (8)], which decomposed to the corresponding adducts MA·E(C6F5)3. The same reaction with the 2a and 3a derivatives only allowed the observation of the corresponding adducts MMA·E(C6F5)3. Complexes 2a,b and 3a,b reacted with CO with elimination of the acrylate compounds, MA and MMA, respectively, to give the carbonylniobium(III) compounds [NbCpRCl2(CO)2]2 [CpR = C5H4SiMe2Cl (9), C5H4SiMe3 (10)]. Analogous reactions with CNAr showed the elimination of the free MA and MMA compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Photochemical Reactivity of 2-Azido-1,3-thiazole and 2-Azido-1,3-benzothiazole: A Procedure for the Aziridination of Enol EthersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2009Maurizio D'Auria Abstract Direct irradiation of a mixture of the azido,tetrazole tautomers of 2-azido-1,3-thiazole and 2-azido-1,3-benzothiazole in toluene solution gives products arising from the intermediate nitrene, which in turn undergoes ring opening in the case of 2-azido-1,3-thiazole to give a polymer, and dimerization in the case of 2-azido-1,3-benzothiazole to give [1,3]benzothiazolo[2,,3,:3,4][1,2,4,5]tetraazino[6,1b][1,3]benzothiazolein low yields. When irradiation is performed in the presence of methyl acrylate or various enol ethers, aziridination of the double bond is observed, with good yields in the case of enol ethers. Among these, 1-(6-methyl-3,4-dihydro-2H -pyran-2-yl)ethanone undergoes aziridination with complete diastereoselectivity to give the (1RS,3RS,6SR) diastereomer.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Straightforward Strategy for the Stereoselective Synthesis of Spiro-Fused (C-5)Isoxazolino- or (C-3)Pyrazolino-(C-3)quinolin-2-ones from Baylis,Hillman Adducts by 1,3-Dipolar Cycloaddition and Reductive Cyclization,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 32 2008Virender Singh Abstract A straightforward and general approach for the stereoselective synthesis of spiro-fused (C-5)isoxazolino- or (C-3)pyrazolino-(C-3)quinolin-2-ones from the adducts offorded from the Baylis,Hillman reaction of 2-nitrobenzaldehyde and ethyl acrylate by sequential 1,3-dipolar cycloaddition and reductive cyclization is presented. It was found that the reductive cyclization of the isoxazoline derivatives proceeded efficiently in the presence of In/HCl, whereas similar reductions of pyrazolines gave better yields when carried out in the presence of an Fe/AcOH mixture. However, similar attempts employing the Baylis,Hillman adduct of 2-nitrobenzaldehyde and methyl vinyl ketone did not yield the desired compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis and Use of New Substituted 1,3,5-Hexatrienes in Studying Thermally Induced 6, -Electrocyclizations,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2007Hans Wolf Sünnemann Abstract An acyclic, two heterocyclic, and two bicyclic alkenylstannanes, 3, 4a, 4b, 8 and 11, respectively, were synthesized in yields ranging from 43 to 97,%, and each was subjected to a sequence of Stille and Heck couplings with 2-bromocyclohexenyl triflate (13) and alkyl (tert -butyl and methyl) acrylate to furnish seven new 1,3,5-hexatrienes 19, 20, 21, 22 - tBu, 22 -Me, 23 and 43, respectively, in 58,84,% yields. For the alkenylstannanes 4a,b, 8 and 11, customized combinations of catalysts had to be used. The Stille,Heck sequence involving 13, 3 and tert -butyl acrylate could be performed in a one-pot mode and proceeded in 75,% yield. The hexatrienes were heated in decalin solutions so as to effect 6,-electrocyclization. Temperatures and reaction times were optimized individually. The hexatrienes 29, 31 and 36 gave the bi- and tricyclic cyclohexadienes 28, 30 and 34, incorporating allylic alcohol and allyl ether termini, by 6,-electrocyclization and subsequent [1,5]-hydrogen shift, as single products in good yields (85,93,%). In contrast, the hexatrienes 19, 20, 21 and 39 furnished mixtures of the initial electrocyclization products 26, 32, 37 and 40 as well as the products of a subsequent [1,5]-hydrogen shift 27, 33, 38 and 41, respectively. The tricyclic hexatrienes 22 - tBu, 22 -Me and 23 bearing alkyl (tert -butyl, methyl) acrylate termini also selectively gave the tetracyclic dienes 48 - tBu, 48 -Me and 50 in 71,77,% yields by electrocyclizations and subsequent hydrogen shifts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Lewis Acid Induced [2+2] Cycloadditions of Silyl Enol Ethers with ,,,-Unsaturated Esters: A DFT AnalysisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2005Manuel Arnó Abstract The Lewis acid (LA) induced cycloaddition of trimethysilyl vinyl ether with methyl acrylate has been studied by DFT methods at the B3LYP/6-31G* level. In the absence of an LA, a [4+2] cycloaddition between the silyl enol ether and methyl acrylate in the s-cis conformation takes place through an asynchronous, concerted bond-formation process. This cycloaddition presents a large activation enthalpy of 21.1 kcal,mol,1. Coordination of the LA AlCl3 to the carbonyl oxygen atom of methyl acrylate yields a change of molecular mechanism from a concerted to a two-step mechanism and produces a drastic reduction of the activation energy. This stepwise mechanism is initialized by the nucleophilic attack of the enol ether at the ,-position of methyl acrylate in a Michael-type addition. The very low activation energy (7.1 kcal,mol,1)associated with this nucleophilic attack can be related to the increase of the electrophilicity of the LA-coordinated ,,,-unsaturated ester, which favors the cycloaddition through a polar process. The subsequent ring-closure allows the formation of the corresponding [2+2] and [4+2] cycloadducts. While the [4+2] cycloadduct is formed by kinetic control, the [2+2] cycloadducts are formed by thermodynamic control. The energetic results provide an explanation for the conversion of [4+2] cycloadducts into the thermodynamically more stable [2+2] ones. The cis/trans ratio found for the catalytic [2+2] process is in agreement with the experimental outcome. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Colloidal Films That Mimic CiliaADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Fang Liu Abstract Cilia are wavy hair-like structures that extend outward from surfaces of various organisms. They are classified into two general categories, primary cilia, which exhibit sensing attributes, and motile cilia, which exert mechanical forces. A new poly(2-(N,N -dimethylamino)ethyl methacrylate- co -n-butyl acrylate- co - N,N -(dimethylamino) azobenzene acrylamide) (p(DMAEMA/nBA/DMAAZOAm) copolymer is prepared using colloidal synthesis, which, upon coalescence, form films capable of generating surfaces with cilia-like features. While film morphological features allow the formation of wavy whiskers, the chemical composition of the copolymer facilitates chemical, thermal, and electromagnetic responses manifested by simultaneous shape and color changes as well as excitation wavelength dependent fluorescence. These studies demonstrate that synthetically produced polymeric films can exhibit combined thermal, chemical, and electromagnetic sensing leading to locomotive and color responses, which may find numerous applications in sensing devices, intelligent actuators, defensive mechanisms, and others. [source] Quantification of Grafting Densities Achieved via Modular "Grafting-to" Approaches onto Divinylbenzene MicrospheresADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Leena Nebhani Abstract The surface modification of divinylbenzene (DVB)-based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero-Diels,Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this "grafting-to" method. Two variants of the RAFT-HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number-averaged molecular weight, Mn,=,4200,g,mol,1; polydispersity index, PDI,=,1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2,×,1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn,=,6000,g,mol,1, PDI,=,1.25; Mn,=,26,000,g,mol,1, PDI,=,1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T,=,60,°C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7,chains,nm,2 for Mn,=,6000,g,mol,1 and 4,chains,nm,2 for Mn,=,26,000,g,mol,1, or 2.82,×,1019 and 1.38,×,1019,chains g,1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry. [source] A Versatile Solvent-Free "One-Pot" Route to Polymer Nanocomposites and the in situ Formation of Calcium Phosphate/Layered Silicate Hybrid NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Hans Weickmann Abstract Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyurethane (PU) nanocomposites containing well-dispersed calcium phosphate/layered silicate hybrid nanoparticles were prepared in a versatile solvent-free "one-pot" process without requiring separate steps, such as organophilic modification, purification, drying, dispersing, and compounding, typical for many conventional organoclay nanocomposites. In this "one-pot" process, alkyl ammonium phosphates were added as swelling agents to a suspension of calcium/layered silicate in styrene, methyl methacrylate, or polyols prior to polymerization. Alkyl ammonium phosphates were prepared in situ by reacting phosphoric acid with an equivalent amount of alkyl amines such as stearyl amine (SA) or the corresponding ester- and methacrylate-functionalized tertiary alkyl amines, obtained via Michael Addition of SA with methyl acrylate or ethylene 2-methacryloxyethyl acrylate. Upon contact with the calcium bentonite suspension, the cation exchange of Ca2+ in the silicate interlayers for alkyl ammonium cations rendered the bentonite organophilic and enabled effective swelling in the monomer accompanied by intercalation and in situ precipitation of calcium phosphates. According to energy dispersive X-ray analysis, the calcium phosphate precipitated exclusively onto the surfaces of the bentonite nanoplatelets, thus forming easy-to-disperse calcium phosphate/layered silicate hybrid nanoparticles. Incorporation of 5,15,wt% of such hybrid nanoparticles into PMMA, PS, and PU afforded improved stiffness/toughness balances of the polymer nanocomposites. Functionalized alkyl ammonium phosphate addition enabled polymer attachment to the nanoparticle surfaces. Transmission electron microscopy (TEM) analyses of PU and PU-foam nanocomposites, prepared by dispersing hybrid nanoparticles in the polyols prior to isocyanate cure, revealed the formation of fully exfoliated hybrid nanoparticles. [source] Reactive Imprint Lithography: Combined Topographical Patterning and Chemical Surface Functionalization of Polystyrene- block -poly(tert -butyl acrylate) FilmsADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Joost Duvigneau Abstract Here, reactive imprint lithography (RIL) is introduced as a new, one-step lithographic tool for the fabrication of large-area topographically patterned, chemically activated polymer platforms. Films of polystyrene- block -poly(tert -butyl acrylate) (PS- b -PtBA) are imprinted with PDMS master stamps at temperatures above the corresponding glass transition and chemical deprotection temperatures to yield structured films with exposed carboxylic acid and anhydride groups. Faithful pattern transfer is confirmed by AFM analyses. Transmission-mode FTIR spectra shows a conversion of over 95% of the tert -butyl ester groups after RIL at 230,°C for 5 minutes and a significantly reduced conversion to anhydride compared to thermolysis of neat films with free surfaces in air or nitrogen. An enrichment of the surface layer in PS is detected by angle-resolved X-ray photoelectron spectroscopy (XPS). In order to demonstrate application potentials of the activated platforms, a 7,nm,±,1,nm thick NH2 -terminated PEG layer (grafting density of 0.9 chains nm,2) is covalently grafted to RIL-activated substrates. This layer reduces the non-specific adsorption (NSA) of bovine serum albumin by 95% to a residual mass coverage of 9.1,±,2.9,ng cm,2. As shown by these examples, RIL comprises an attractive complementary approach to produce bio-reactive polymer surfaces with topographic patterns in a one-step process. [source] High-Strain Shape-Memory PolymersADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Walter Voit Abstract Shape-memory polymers (SMPs) are self-adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures. In this study, the glass transition temperature (Tg) is adjusted between 28 and 55,°C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA). Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a Tg of 28,°C, at 663% for a Tg of 37,°C, and at 553% for a Tg of 55,°C. A new compound, 4,4,-di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape-memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%. The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape-memory cycle caused large-scale disfiguration. The materials in this study are intended to enable future applications where both recoverable high-strain capacity and the ability to accurately and independently position Tg are required. [source] Dual-Tone Patterned Mesoporous Silicate Films Templated From Chemically Amplified Block CopolymersADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Sivakumar Nagarajan Abstract Directly patterned mesoporous silicate films are prepared using positive- and negative-tone strategies by performing phase selective silica condensation within lithographically exposed poly(styrene- b - tert -butyl acrylate) (PS- b -PtbA) templates containing photoacid generators. The use of supercritical fluid as a process medium enables rapid diffusion of the silicate precursor within the prepatterned block copolymer template film without disrupting its morphology. Template exposure through the mask triggers area selective generation of acid, which in turn both deprotects the poly(tert -butyl acrylate) block to yield a poly(acrylic acid) block and provides a catalyst for silica precursor condensation yielding pattern formation at the device level. Because the acid generated in the UV exposed field preferentially segregates into hydrophilic poly(acrylic acid) domains of the phase segregated, deprotected block copolymer, precursor condensation is simultaneously controlled at nanoscopic length scales via templating by the underlying block copolymer morphology. The ability of PS- b -PtbA to undergo chemical transformation in two stages, deprotection followed by crosslinking, enables precise replications of the photomask in positive and negative tones. Detemplating via calcination yields patterned mesoporous silicate films without etching. Template formulations are optimized using infrared spectroscopic studies and the silicate films are characterized using electron microscopy and scanning force microscopy. [source] Guided Cell Migration on Microtextured Substrates with Variable Local Density and AnisotropyADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Deok-Ho Kim Abstract This work reports the design of and experimentation with a topographically patterned cell culture substrate of variable local density and anisotropy as a facile and efficient platform to guide the organization and migration of cells in spatially desirable patterns. Using UV-assisted capillary force lithography, an optically transparent microstructured layer of a UV curable poly(urethane acrylate) resin is fabricated and employed as a cell-culture substrate after coating with fibronectin. With variable local pattern density and anisotropy present in a single cell-culture substrate, the differential polarization of cell morphology and movement in a single experiment is quantitatively characterized. It is found that cell shape and velocity are exquisitely sensitive to variation in the local anisotropy of the two-dimensional rectangular lattice arrays, with cell elongation and speed decreasing on symmetric lattice patterns. It is also found that cells could integrate orthogonal spatial cues when determining the direction of cell orientation and movement. Furthermore, cells preferentially migrate toward the topographically denser areas from sparser ones. Consistent with these results, it is demonstrated that systematic variation of local densities of rectangular lattice arrays enable a planar assembly of cells into a specified location. It is envisioned that lithographically defined substrates of variable local density and anisotropy not only provide a new route to tailoring the cell-material interface but could serve as a template for advanced tissue engineering. [source] A General Strategy to Disperse and Functionalize Carbon Nanotubes Using Conjugated Block CopolymersADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Jianhua Zou Abstract A general strategy to disperse and functionalize pristine carbon nanotubes in a single-step process is developed using conjugated block copolymers. The conjugated block copolymer contains two blocks: a conjugated polymer block of poly(3-hexylthiophene), and a functional non-conjugated block with tunable composition. When the pristine carbon nanotubes are sonicated with the conjugated block copolymers, the poly(3-hexylthiophene) blocks bind to the surface of de-bundled carbon nanotubes through non-covalent ,,, interactions, stabilizing the carbon nanotube dispersion, while the functional blocks locate at the outer surface of carbon nanotubes, rendering the carbon nanotubes with desired functionality. In this paper, conjugated block copolymers of poly(3-hexylthiophene)- b -poly(methyl methacrylate), poly(3-hexylthiophene)- b -poly(acrylic acid), and poly(3-hexylthiophene)- b -poly(poly(ethylene glycol) acrylate) are used to demonstrate this general strategy. [source] | |||||||||||||||||||||||||||||||