Showing papers on "Methacrylic acid published in 2006"

Poly(methacrylic acid) Hydrogel Films and Capsules: Response to pH and Ionic Strength, and Encapsulation of Macromolecules

Abstract: Hydrogen-bonded multilayers of a neutral polymer (poly(N-vinylpyrrolidone), PVPON) with poly(methacrylic acid) (PMAA) were used as templates to introduce cross-links between PMAA layers using carbodiimide chemistry and ethylenediamine as a cross-linking agent. Upon exposure to high pH, PVPON is completely released from the hydrogel matrix, producing surface-attached PMAA hydrogels. When such hydrogels are deposited at the surface of silica particles, and the particle core is subsequently dissolved, hollow one-component hydrogel capsules are produced. PMAA hydrogel films and hollow capsules underwent reversible, large (factors of 2 or 3) changes in size in response to changes in solution pH and/or ionic strength. The capsules were used for entrapment and storage of macromolecules such as 500 kDa FITC-dextran by “locking” the capsule wall with an electrostatically associating polycation, poly-N-ethyl-4-vinylpyridinium bromide (QPVP). The release of the encapsulated macromolecules was achieved under high sal...

Thin Molecularly Imprinted Polymer Films via Reversible Addition−Fragmentation Chain Transfer Polymerization

Abstract: Mesoporous silica beads modified with an azo initiator were used for grafting of cross-linked molecularly imprinted polymers through reversible addition−fragmentation chain transfer (RAFT) mediated polymerization. The RAFT mediation allowed an efficient control of the grafting process and led to suppression of the solution propagation preventing any visible gel formation. Thus, graft copolymerization of methacrylic acid and ethylene glycol dimethacrylate using 2-phenylprop-2-yl-dithiobenzoate as the chain transfer agent and in the presence of l-phenylalanine anilide as the template led to imprinted thin film composite beads. The resulting composites were characterized by Fourier transform infrared spectroscopy, nitrogen sorption analysis, elemental analysis, fluorescence microscopy, and scanning electron microscopy and as stationary phases in chromatography. This indicated the presence of thin homogeneous films (thickness: 1−2 nm) containing imprinted sites for the template (l-phenylalanine anilide). The...

Analysis of swelling behavior of poly(methacrylamide-co-methacrylic acid) hydrogels and effect of synthesis conditions on water uptake

Abstract: An investigation of water uptake behavior of a novel pH-sensitive poly(methacrylamide-co-methacrylic acid) hydrogel system was carried out with two major objectives. First was to study the effect of various synthesis conditions like reaction temperature, initiator content and degree of dilution of feed mixture on the water absorbency of resulting hydrogels and the second was to interpret the water uptake data by various kinetic models. The 2.25 times dilution of the reaction mixture resulted in the formation of hydrogels with highest water uptake of 1423 ± 21% in the simulating intestinal fluid of pH 7.4 at 37 °C. Likewise, the optimum synthesis temperature and initiator concentration were found to be 80 °C and 11.04 × 10 −2 mM, respectively. The kinetic models proposed by Peppas and Hopfenberg were applied on the water uptake data to obtain the best fit. The enthalpy of mixing Δ H mix was also evaluated for hydrogels with varying concentrations of monomer acid in the feed mixture. Finally, the gels demonstrated sharp change in their water absorbency and mesh size of networks with pH of the swelling media, thus suggesting their strong candidature for being used as oral drug-delivery systems along the gastrointestinal tract.

Free-Radical Propagation Rate Coefficient of Nonionized Methacrylic Acid in Aqueous Solution from Low Monomer Concentrations to Bulk Polymerization

Abstract: The propagation rate coefficient, kp, for free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been studied via pulsed laser polymerization (PLP) in conjunction with aqueous-phase size-exclusion chromatography (SEC). The PLP−SEC experiments were carried out between 20 and 80 °C within the entire concentration range from dilute solution containing 1 wt % MAA up to bulk MAA polymerization. The kp values which are determined under the assumption that the relevant monomer concentration at the radical site is identical to the known overall MAA concentration decrease by about 1 order of magnitude between 1 and 100 wt % MAA. This significant lowering is almost entirely due to a reduction in the Arrhenius preexponential factor, A(kp), whereas the activation energy, EA(kp), stays essentially constant. The decrease in A(kp) is assigned to intermolecular interactions between the transition state (TS) structure for MAA propagation and an MAA environment being significantly stronger...

Microcapsules made of weak polyelectrolytes: templating and stimuli-responsive properties.

Abstract: Hollow microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are templated on silicon oxide particles using the layer-by-layer adsorption. The colloidal template is removed with a buffer system of hydrofluoric acid and ammonium fluoride. With this buffer system, the template can be dissolved in mild pH conditions, where the polymeric layers are still stable. The morphology and the thickness of the resulting capsules are investigated with atomic force microscopy. The resulting hollow capsules show pH-dependent properties. The shells are stable over a broad pH range and swell and immediately dissolve for pH values below 2.3 and above 11. If the molecular weight of the poly(methacrylic acid) is increased, the enhanced entanglement of the polymers results in a reversible swelling of the capsules at low and at high pH. The swelling degree is probed with confocal laser scanning microscopy. In addition to the pH-dependent size variations, the di...

Novel pH responsive polymethacrylic acid-chitosan-polyethylene glycol nanoparticles for oral peptide delivery.

Abstract: In present study, novel pH sensitive polymethacrylic acid-chitosan-polyethylene glycol (PCP) nanoparticles were prepared under mild aqueous conditions via polyelectrolyte complexation. Free radical polymerization of methacrylic acid (MAA) was carried out in presence of chitosan (CS) and polyethylene glycol (PEG) using a water-soluble initiator and particles were obtained spontaneously during polymerization without using organic solvents or surfactants/steric stabilizers. Dried particles were analyzed by scanning electron microscopy (SEM) and particles dispersed in phosphate buffer (pH 7.0) were visualized under transmission electron microscope (TEM). SEM studies indicated that PCP particles have an aggregated and irregular morphology, however, TEM revealed that these aggregated particles were composed of smaller fragments with size less than 1 micron. Insulin and bovine serum albumin (BSA) as model proteins were incorporated into the nanoparticles by diffusion filling method and their in vitro release characteristics were evaluated at pH 1.2 and 7.4. PCP nanoparticles exhibited good protein encapsulation efficiency and pH responsive release profile was observed under in vitro conditions. Trypsin inhibitory effect of these PCP nanoparticles was studied using casein substrate and these particles displayed lesser inhibitory effect than reference polymer carbopol. Preliminary investigation suggests that these particles can serve as good candidate for oral peptide delivery.

pH-Triggered softening of crosslinked hydrogen-bonded capsules

Abstract: We report here the first AFM single capsule mechanical measurements on hydrogen-bonded polymeric multilayer microcapsules made of poly(vinylpyrrolidone)/poly(methacrylic acid) (PVPON/PMAA) and of poly(-vinylpyrrolidone-co-NH-20)/poly(methacrylic acid) (PVPON-co-NH-20/PMAA), as well as of capsules derived from these systems chemical crosslinking. The stiffness of the non-crosslinked hydrogen-bonded capsules was found to be proportional to the square of the wall thickness which is in agreement with previous observations on other multilayer capsules and continuum mechanical theory. The found elastic modulus of 610 MPa for low pH (= 2) is typical for a highly stable, glass-like structure similar to electrostatically bound multilayers. At pH > 6, (PMAA) capsules obtained through chemical crosslinking of hydrogen-bonded (PVPON/PMAA) multilayers, or crosslinked (PVPON-co-NH-20/PMAA) capsules showed a sharp hundreds-fold stiffness decrease to ∼1 mN/m which was orders of magnitude lower than those reported earlier for polymeric multilayer systems. pH-Triggered softening was reversible and highly reproducible. Softening of both (PMAA) and (PVPON-co-NH-20/PMAA) crosslinked capsules resulted from increased PMAA ionization, and additional dissociation of intermolecular hydrogen bonds occurred in the case of (PVPON-co-NH-20/PMAA) crosslinked system.

Poly(methacrylic acid)-l-Polyisobutylene: A Novel Polyelectrolyte Amphiphilic Conetwork

Abstract: For the first time, a reliable procedure for synthesizing new acidic polyelectrolyte-containing amphiphilic conetworks (APCNs), poly(methacrylic acid)-l-polyisobutylene (PMAA-l-PIB), is described. The thorough characterization of the synthesis products is also presented through elemental analysis, differential scanning calorimetry (DSC), and basic swelling studies. Three series of APCNs were successfully synthesized in wide composition ranges by the macromonomer method using exact bifunctional methacrylate-telechelic PIB cross-linkers (MA−PIB−MA) of three different molecular weights (Mn): 2000, 5000, and 13000. The MA−PIB−MA macromolecular cross-linkers were prepared via quasiliving carbocationic polymerization. To prevent phase separation and thus insufficient network formation during synthesis, the conetworks were synthesized by thermally initiated free radical copolymerization of MA−PIB−MA and trimethylsilyl methacrylate, a hydrophobized precursor of methacrylic acid. After the next critical synthetic...

Synthesis and characterization of novel pH-responsive polyampholyte microgels

Abstract: We synthesized for the first time novel pH-responsive polyampholyte microgels consisting of poly(methacrylic acid) and polyl(2-(diethylamino)ethyl methacrylate) (PMAA-PDEA) that are sterically stabilized with poly-(ethylene glycol) methyl ethermethacrylate (PEGMEM). These microgcis showed enhanced hydrophilic behavior in aqueous medium at low and high pH but become hydrophobic and compact between pH 4 and 6 near the isoelectric point. Cynamic-light seattering nieasureinents sliowed that the hydrodynamic radius, R h of these mierogels is approximately 100 nm between pH 4 and h and increases to around 140 and 170 nm at pH 2 and 10, respectively. It is evident that the cross-linked MAA-DEA mierogel that is sterically stabilized with PEGMEM retains the polyampholyte properties in solution.

Molecularly imprinted polymer catalysis of a Diels-Alder reaction

Abstract: A series of synthetic polymers were designed and synthesized for enhancing the rate of the Diels-Alder cycloaddition reaction of 1,3-butadiene carbamic acid benzyl ester (1) and N,N-dimethyl acrylamide (2), to yield the corresponding endo -( 3) and exo -( 4) reaction products. Putative transition state analogues (TSAs) for the endo -( 5) and exo -( 6) reaction pathways were used as templates for the synthesis of molecularly imprinted methacrylic acid (MAA)–divinylbenzene (DVB) copolymers. The polymer system utilized was selected based upon a series of 1 H NMR studies of complex formation between template and a functional monomer analogue (Kd (app) ≈ 70 mM, d8-toluene, 293 K). Batch binding studies revealed that the imprinted polymers were selective for the TSA corresponding to the template used in the polymer synthesis. Studies on the influence of the polymers on the catalysis of the reaction of 1 and 2 demonstrated a 20-fold enhancement of the rate of the reaction relative to the solution reaction. A surprising temperature dependence of the reaction of 1 and 2 in the presence of the polymers was observed, which provides support for the role of template-functional monomer complexes in the catalysis of the Diels-Alder reaction.

Covalently crosslinked chitosan hydrogel formed at neutral pH and body temperature

Abstract: Water-soluble chitosan having double bonds (CS-MA-LA) was synthesized by sequential grafting of methacrylic acid (MA) and lactic acid (LA) via the reaction between amino groups and carboxyl groups under the catalysis of carbodiimide. Its molecular structure was verified by FTIR and (1)H NMR characterizations. Elemental analysis measured grafting ratios of 19% and 10.33% for MA and LA, respectively. CS-MA-LA was readily soluble in pure water and did not precipitate till pH 9. Gelation of the CS-MA-LA was realized by thermal treatment at body temperature under the initiation of a redox system, ammonium persulfate (APS)/N, N,N',N'-tetramethylethylenediamine (TEMED). The gelation time could be mediated in a wide range, e.g. from 6 to 20 min, by reaction temperature and/or initiator's concentration. 3T3 fibroblast culture showed that the cytotoxicity of the hydrogel extractant was dependent on the cell seeding number and the initiator's concentration. With enough number of cells (>2.5 x 10(4)) and low initiator's concentration (5 mM), the cytotoxicity introduced by the initiator is very minimal and negligible. Although the hydrogel could cause acute inflammation and foreign body reaction, no tissue necrosis and malignant infection were evidenced in vivo, demonstrating that the material has better histocompatibility. These features have endowed the chitosan with great opportunity as injectable biomaterials, which may find wide applications in the rapidly developed fields such as tissue engineering and orthopedics.

Morphological Origin of the Multistep Relaxation Behavior in Semicrystalline Ethylene/Methacrylic Acid Ionomers

Abstract: Ethylene/methacrylic acid (E/MAA) ionomers contain polyethylene crystallites, amorphous polymer segments, and ionic aggregates. While the property changes observed upon neutralization of the MAA units are often attributed to the formation of ionic aggregates, no quantitative description currently exists for how these three structural motifsalone or in combinationcontrol any of these material properties. In this paper, we define such relationships for perhaps the most basic mechanical property of interest: the small-strain modulus. At temperatures just below the melting point of the primary crystallites, the ionomers can be satisfactorily described as two-phase composites of crystallites and ionically cross-linked rubber; however, at room temperature, the modulus is far higher than such a description predicts. We trace this effect to a synergy between the ionic aggregates and secondary crystallites, which together form percolated rigid pathways through the amorphous phase at room temperature. When the sec...

Synthesis of hollow spherical calcium phosphate nanoparticles using polymeric nanotemplates

Abstract: Poly(methylmethacrylate)-block-poly(methacrylic acid) (PMMA-b-PMAA) copolymer was synthesized by an atom transfer radical polymerization (ATRP) technique. The block copolymer was employed as a template for the controlled precipitation of calcium phosphate from aqueous solution at different pH values. A Ca2+ ion selective electrode was used to study the interactions between Ca2+ ions and the polymer, which indicated a possible weak interaction between Ca2+ and un-ionized MAA segments at pH~4.0 in addition to electrostatic interaction between Ca2+ and ionized MAA segments at higher pH. An interesting structure representing that of a superstructure consisting of hybrid nano-filaments was observed by the transmission electron microscope at pH~4.0. The filaments originated from a core of similar size to primary polymer aggregates, suggesting that cooperative interactions at a local level between dissolving calcium phosphate clusters and disassembling polymer segments are responsible for the secondary growth process. A hollow spherical morphology was obtained at pH~7.0 and 9.0. Such calcium phosphate/polymer monohybrids with complex morphologies are interesting and might be useful as novel drug delivery carriers, ceramics precursors, reinforcing fillers or biomedical implants.

Composition-tunable properties of amphiphilic comb copolymers containing protected methacrylic acid groups for multicomponent protein patterning.

Abstract: Methods to micropattern multiple protein components on surfaces under mild conditions are of interest for biosensing, proteomics, and fundamental studies in cell biology. Here, we report on the composition-dependent thin-film solubility behavior of o-nitrobenzyl methacrylate (oNBMA, a protected form of methacrylic acid)/methyl methacrylate (MMA)/poly(ethylene glycol) methacrylate (PEGMA) random terpolymers, materials which are promising as aqueous-processible photoresists. Over a broad range of terpolymer compositions, these materials formed initially water-insoluble films, which, upon UV irradiation, rapidly dissolved in aqueous solutions above a critical pH. This threshold pH ranged from approximately 5-7 depending upon the copolymer composition and decreased as the relative ratio of MMA to PEGMA in the copolymers decreased. In addition, in a narrow window of compositions near 35:0:65 oNBMA/MMA/PEGMA (wt ratio), an inverse behavior was observed: thin films that were initially water soluble became kinetically stable in aqueous solutions after UV exposure. The time for these films to completely dissolve was hours rather than seconds, and the rate of dissolution was both temperature- and pH-dependent. This behavior is consistent with a transient stability imparted by inter- and intramolecular hydrogen bonding in the film. Using copolymers of this composition as negative tone photoresists, we demonstrated patterning of two proteins into two discrete regions of a surface. The selective solubility of the resist copolymer allows the entire patterning process to be completed using only biological buffers as solvents and across a temperature range between 4 and 37 degrees C without subjecting either protein to ultraviolet irradiation or dehydration. These materials are thus of interest for complex surface photopatterning under mild aqueous conditions.

Polyether-containing copolymer

Abstract: Copolymers are disclosed, comprising two monomer components (A) and (B), component (A) representing an olefinically-unsaturated monocarboxylic acid or an ester or salt thereof, or an olefinically-unsaturated sulphuric acid comonomer or a salt thereof and the component (B) is an ether comonomer of formula (I). According to the invention, the copolymer shall contain the components (A) and (B) in the proportions 30 to 99 Mol. % and 70 to 1 Mol. %, comonomer component (A) being of the group acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, allylsulphonic acid, vinylsulphonic acid and suitable salts and alkyl or hydroxyalkyl esters thereof. The invention further relates to a composition, containing the claimed copolymer in addition to a hydraulic binder such as for example, cement, gypsum, lime and anhydrite. Said copolymers are of application as flow-improvers or dispersants for non-set compositions containing a hydraulic binder.

Self-assembly of mixtures of block copolymers of poly(styrene-b-acrylic acid) with random copolymers of poly(styrene-co-methacrylic acid).

Abstract: The effects of the addition of random copolymers of poly(styrene-co-methacrylic acid) [P(S-co-MAA)] on the self-assembly of block copolymers of poly(styrene-b-acrylic acid) (PS-b-PAA) are described...