Synthesis of pH-sensitive hollow polymer microspheres and their application as drug carriers

The pH-sensitive hollow poly(N,N′-methylene bisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres were prepared by a two-stage distillation precipitation polymerization to afford a core-shell poly(methacrylic acid)/poly(N,N′-methylene bisacrylamide-co-methacrylic acid) (PMAA/(P(MBAAm-co-MAA))) microsphere with subsequent removal of poly(methacrylic acid) (PMAA) core. PMAA/P(MBAAm-co-MAA) core-shell microspheres were synthesized by the second-stage copolymerization of N,N′-methylene bisacrylamide (MBAAm) as crosslinker and the functional methacrylic acid (MAA) comonomer in acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator. The pH-responsive properties of hollow P(MBAAm-co-MAA) microspheres were investigated by dynamic laser scattering (DLS). The loading and controlled-release behavior of the drug for hollow P(MBAAm-co-MAA) microspheres was strongly dependent on the pH values with doxorubicin hydrochloride (DXR) as a model molecule. The core-shell and hollow polymer microspheres were characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), DLS and elemental analysis.     

Preparation of magnetite and tumor dual-targeting hollow polymer microspheres with pH-sensitivity for anticancer drug-carriers

The hollow poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres were prepared by the selective removal of poly(methacrylic acid) (PMAA) core from the corresponding PMAA/P(MBAAm-co-MAA) core-shell microspheres, which were synthesized via a two-stage distillation precipitation polymerization. The magnetic Fe₃O₄ nanoparticles onto the surface of hollow P(MBAAm-co-MAA) microspheres via partial oxidation of ferrous salt during the chemical deposition in the presence of potassium nitrate as oxidant with the aid of hexamethylene tetramine and the magnetic hollow microspheres were further functionalized with folic acid (FA) via the chemical linkage with amino groups of 3-aminopropyl triethoxysilane (APS)-modified P(MBAAm-co-MAA)@Fe₃O₄ microspheres to afford the magnetite and tumor dual-targeting hollow microspheres. The resultant dual-targeting hollow polymer microspheres with pH-sensitivity were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared-spectrometer (FT-IR), UV-vis absorption spectroscopy, and vibrating sample magnetometer (VSM). Finally, the drug loading capacities of the magnetite and tumor dual-targeting hollow P(MBAAm-co-MAA) microspheres and their releasing dependence on pH values were investigated with doxorubicin hydrochloride (DXR) as an anticancer drug model.     

Synthesis of hollow polymer microspheres with movable polyelectrolyte core and functional groups on the shell-layer

Hollow polymer microspheres with movable quaternary pyridinium polyelectrolyte (PE) cores and various functional groups on the shell-layers, such as hydroxyl, amide, and carboxyl, were prepared by the selectively etching of mid-silica layer with hydrofluoric acid from the corresponding poly(ethyleneglycol dimethacrylate-co-methacrylic acid)@poly(ethyleneglycol dimethacrylate- co-4-vinylpyridinium benzylchloride)/silica/polymer (P(EGDMA-co-MAA) @P(EGDMA-co-VPyBzCl)/SiO₂/polymer) tetra-layer microspheres. The tetra-layer hybrid microspheres were synthesized by a multi-stage reaction process, which included the combination of distillation precipitation polymerization for the formation of polymer-layers and the hydrolysis of tetraethyl orthosilicate (TEOS) via a modified Stöber sol-gel procedure to afford silica layer. The efficient electrostatic interaction between the cationic pyridinium species on the surface of P(EGDMA-co-MAA)@P(EGDMA-co-VPyBzCl) cores and the negative charges on the silica species was essential to get monodisperse tri-layer P(EGDMA-co-MAA)@P(EGDMA-co-VPyBzCl)/SiO₂ microspheres during the hydrolysis of TEOS. The functional polymer shell was encapsulated over 3-(methacryloxy)propyl trimethacrylate (MPS) modified tri-layer polymer/silica seeds by distillation precipitation copolymerizations of N,N′-methylenebisacrylamide (MBAAm) crosslinker and comonomers with different functional groups, including N-isopropylacrylamide (NIPAAm), 2-hydroxyethylmethacrylate (HEMA) and methacrylic acid (MAA), with 2,2′-azobisisobutyronitrile (AIBN) as an initiator in neat acetonitrile. The morphology and structure of the tetra-layer hybrid microspheres and the corresponding hollow microspheres with movable PE core and functional polymer shell-layer were characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), ξ-potential, and dynamic light scattering (DLS).     

Preparation of polymer/silica/polymer tri-layer hybrid materials and the corresponding hollow polymer microspheres with movable cores

Tri-layer poly(methacrylic acid-co-ethyleneglycol dimethacrylate)/silica/poly(ethyleneglycol dimethacrylate) (P(MAA-co-EGDMA)/SiO₂/PEGDMA) and P(MAA-co-EGDMA)/SiO₂/polydivinylbenzene hybrid microspheres were prepared by distillation precipitation polymerization of ethyleneglycol dimethacrylate (EGDMA) and divinylbenzene (DVB) in the presence of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified P(MAA-co-EGDMA)/SiO₂ microspheres as the seeds. The polymerization of EGDMA and DVB was performed in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator to coat the MPS-modified P(MAA-co-EGDMA)/SiO₂ seeds through the capture of EGDMA and DVB oligomer radicals with the aid of vinyl groups on the surface of modified seeds in the absence of any stabilizer or surfactant. Monodisperse P(MAA-co-EGDMA)/SiO₂ core-shell microspheres were synthesized by coating of a layer of silica onto P(MAA-co-EGDMA) microspheres via a sol-gel process, which were further grafted by MPS incorporating the reactive vinyl groups onto the surface to be used as the seeds for the construction of hybrid microspheres with tri-layer structure. Hollow poly(ethyleneglycol dimethacrylate) (PEGDMA) and poly(divinylbenzene) (PDVB) microspheres with movable P(MAA-co-EGDMA) core were subsequently developed after the selective etching of the silica mid-layer from the tri-layer hybrid microspheres in hydrofluoric acid. The morphology and structure of the tri-layer polymer hybrids and the corresponding hollow polymer microspheres with movable P(MAA-co-EGDMA) core were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra and X-ray photoelectron spectroscopy (XPS).     

Preparation of ellipsoidal hematite/polymer hybrid materials and the corresponding hollow polymer ellipsoids

Ellipsoidal hematite/poly(ethyleneglycol dimethacrylate) core-shell hybrid materials were prepared by distillation precipitation polymerization of ethyleneglycol dimethacrylate (EGDMA) in the presence of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified hematite (α-Fe₂O₃) particles as the seeds. The polymerization of EGDMA was performed in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator to coat MPS-modified hematite seeds through the capture of EGDMA oligomer radicals with the aid of vinyl groups on the surface of the MPS-modified hematite particles in absence of any stabilizer or surfactant. The shell-thickness of the core-shell hybrid particles was controlled by the feed of EGDMA monomer during the polymerization. Other hematite/polymer core-shell hybrid particles, such as hematite/polydivinylbenzene (α-Fe₂O₃/PDVB) and hematite/poly(divinylbenzene-co- methacrylic acid) (α-Fe₂O₃/P(DVB-co-MAA)) were also prepared by this procedure. Hematite/poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (α-Fe₂O₃/P(MBAAm-co-MAA)) were synthesized with unmodified hematite particles as the seeds. Hollow polymer ellipsoids were subsequently developed after the selective removal of the hematite core with hydrochloric acid (HCl) from hematite/polymer core-shell hybrids. The resultant core-shell hybrid particles and hollow polymer ellipsoids were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and vibrating sample magnetometer (VSM).     

Multi‐responsive polymeric microcontainers for potential biomedical applications: synthesis and functionality evaluation

Temperature and pH responsive poly(N‐isopropylacrylamide‐co‐methacrylic acid) (P(NIPAAm‐co‐MAA)) microcontainers with encapsulated magnetic nanoparticles in the shell were prepared by a two‐stage distillation precipitation polymerization. PMAA@Fe₃O₄/P(NIPAAm‐co‐MAA) core–shell nanoparticles were synthesized by the second‐stage polymerization of NIPAAm, MAA and N, N′‐methylenebisacrylamide as crosslinker in the presence of magnetic nanoparticles and PMAA as core. These novel triple‐functional microcontainers were prepared by selective removal of the PMAA core in water. Daunorubicin hydrochloride (DNR) was loaded into the microcontainers and the release profile was studied by UV–visible spectroscopy. The synthesized nanostructures were characterized with transmission and scanning electron microscopy, X‐ray diffraction and Fourier transform infrared spectroscopy. The magnetic properties were evaluated by vibrating sample magnetometry. The shrink and swelling behavior was studied by dynamic light scattering. Copyright © 2012 Society of Chemical Industry     

Monodisperse temperature-responsive hollow polymer microspheres: Synthesis, characterization and biological application

Temperature-responsive hollow poly(N-isopropylacrylamide) (PNIPAAm) microspheres were prepared by a two-stage distillation precipitation polymerization to afford a core-shell microspheres with subsequent removal of poly(methacrylic acid) (PMAA) core. PMAA@PNIPAAm core-shell microspheres were synthesized by the second-stage polymerization of NIPAAm in the presence of PMAA as core with N,N′-methylenebisacrylamide as crosslinker in acetonitrile, in which the hydrogen-bonding interaction between the carboxylic acid group of PMAA core and the amide group of NIPAAm as well as MBAAm played a key role to form the core-shell microspheres. The hollow PNIPAAm microspheres with different thicknesses, which were controlled by the monomer loading level and the crosslinking degree, were developed after the removal of PMAA core. The loading and controlled-release behavior of the drug on the hollow PNIPAAm microspheres was investigated with doxorubicin hydrochloride. The core-shell and hollow microspheres were characterized with transmission electron microscopy, scanning electron microscopy, dynamic light scattering, static light scattering, X-ray photoelectron spectroscopy, elemental analysis, and FT-IR spectra.     

Preparation and characterization of titanium dioxide core and polymer shell hybrid composite particles prepared by two-step dispersion polymerization

Titanium dioxide core and polymer shell composite poly (styrene-co-divinylbenzene)-methacrylic acid [P (St-co-DVB)-MAA]] particles were prepared by two-step dispersion polymerization. Fourier transform IR spectroscopy and elemental analysis were used to measure the content of methacrylic acid in composites particles. X-ray measurement photoelectron spectroscopy (XPS) measurements indicated the presence of an MAA unit on the surface of the composite particles. The combined results of the elemental analysis and the XPS measurements showed that the copolymer on the surface of poly (St-co-DVB)-MAA composite particles was rich in MAA compared with that in the interior of the composite particles. Field-emission scanning electron microscopy (FE-SEM) was used to study the morphology characterization. The composite particles produced showing good spectral reflectance compare with bare TiO₂. TGA results indicated that the encapsulation efficiency and estimated density of composite particles. Encapsulation of TiO₂ was up to 87.4% and the density was ranged from 1.78 to 2.06 g/cm³. Estimated density of the composite particles is suitable to 1.73 g/cm³, due to density matching with suspending fluid.     

Facile synthesis of high-magnetization Fe3O4@polydivinylbenzene core–shell submicrospheres

Fe₃O₄@polydivinylbenzene (PDVB) submicrospheres were prepared via distillation–precipitation polymerization of DVB in the presence of submicron magnetite colloid nanocrystal clusters (MCNCs) as seeds. The surface of the MCNCs was modified with vinyl groups before PDVB encapsulation. The resulting Fe₃O₄@PDVB particles showed a well-defined core–shell structure, and the shell thickness could be readily controlled by the DVB dosage. A lowly cross-linked poly(methacrylic acid) (PMAA) layer could be further coated onto the highly cross-linked PDVB shell via a second-stage DPP process, suggesting the presence of residual vinyl groups on the surface of the Fe₃O₄@PDVB particles. The hybrid particles showed rather high magnetization and near superparamagnetism, hence capable of easy magnetic separation.     

Designing and preparing of quercetin surface‐imprinted material and its molecular recognition characteristics

Quercetin is an important compound of flavonoids. In this work, quercetin molecule surface‐imprinted material with high performance was prepared using a novel surface‐imprinting technique of “synchronously graft‐polymerizing and imprinting.” The modified micron‐sized silica gel particles containing amino groups were used as matrix, methacrylic acid (MAA) was used as functional monomer, and N,N′‐Methylenebisacrylamide (MBA) was used as crosslinker. In dimethyl formamide solution of quercetin, MAA molecules arranged automatically around the template quercetin molecule by right of hydrogen bonding interactions of two type, ordinary hydrogen bond and π‐type hydrogen bond. By initiating the surface‐initiating system of – , the graft/cross‐linking polymerization of MAA on SiO₂ particles and the quercetin molecule surface‐imprinting were simultaneously carried out, forming quercetin molecule surface‐imprinted material MIP‐PMAA/SiO₂. With another two flavonoids, rutin and genistein, as contrasting substances, the molecule recognition character of the quercetin molecule surface‐imprinted material MIP‐PMAA/SiO₂ was investigated with batch and column methods. The experimental results show that the imprinted material MIP‐PMAA/SiO₂ possesses special recognition selectivity and excellent binding affinity for quercetin molecule. The binding capacity of MIP‐PMAA/SiO₂ for quercetin is 0.325 mmol/g, and its selectivity coefficients for quercetin relative to rutin and genistein are 7.69 and 4.40, respectively. The main conditions of imprinting process affect the property of MIP‐PMAA/SiO₂ greatly, and the optimal molar ratio of monomer MAA to crosslinker MBA is 7 : 1 and appropriate molar ratio of monomer MAA to template quercetin is equal to 6 : 1. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41112.     

Role of nanoclay in determining microfibrillar morphology development in PP/PBT blend nanocomposite fibers

In this work, a new and highly efficient method of surface-initiated free radical graft-polymerizations on the surfaces of silica gel particles was put forward, and the graft-polymerization of methacrylic acid (MAA) was conducted. This method was convenient, feasible and highly effective. Coupling agent ??-mercaptopropyltrimethoxysilane(MPTS) was first bonded onto the surfaces of silica gel particles, obtaining the modified particles MPTS-SiO₂, onto which mercapto groups were chemically attached, so a redox initiation system of graft-polymerization was constituted by the mercapto group on the surfaces of MPTS-SiO₂ particles and the cerium (IV) salt in the solution. And then the surface-initiated free radical graft-polymerization of MAA on the surfaces of silica gel particles was carried out, resulting in the grafted particles PMAA/SiO₂ with a very high grafting density (35?g/100?g) of PMAA. The grafted particles PMAA/SiO₂ were characterized by infrared spectrum (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The effects of the main factors on the new surface-initiated graft polymerization were emphatically examined, and the corresponding mechanism of the graft-polymerization was investigated in depth. The experimental results show that the mercapto group-cerium salt system analogous to the hydroxyl group-cerium salt system, can also effectively initiate vinyl monomers to be graft-polymerized on the surfaces of solid particles, and furthermore, it is a highly effective surface-initiated graft-polymerization method. In this graft-polymerization system, several factors such as sulfuric acid concentration, the used amount of cerium salt and the reaction temperature affect the grafting density greatly. For the graft-polymerization of MAA, the appropriate reaction conditions are as follows: reaction time of 3?h, reaction temperature of 50?°C, cerium concentration of 5.0?×?10^?3?M, acid (H⁺ ion) concentration of 0.15?M and MAA concentration of 0.5?M.     

Superparamagnetic thermoresponsive composite latex via W/O miniemulsion polymerization

In this research, the thermoresponsive composite latex particles were prepared via W/O miniemulsion polymerization. Fe₃O₄ nanoparticles were homogeneously dispersed inside the poly(NIPAAm‐co‐MAA) latex particles. In the first step, PAA oligomers were used as stabilizers to produce a stable water‐based Fe₃O₄ ferrofluid, which could mix well with the water‐soluble monomers. In the second step, the Fe₃O₄/poly(NIPAAm‐co‐MAA) composite latex particles were synthesized via W/O miniemulsion polymerization. This polymerization proceeded in cyclohexane at room temperature, with Span80 as the emulsifier, NIPAAm as the thermoresponsive monomer, MAA as a comonomer with ? COOH functional groups, and APS/SMBS as the redox initiator system. The distribution of Fe₃O₄ nanoparticles inside the composite latex particles was expected to be homogeneous. The nucleation and morphology of the composite latex particles were mainly controlled by the concentration of the surfactant, Span80, in cyclohexane. The properties of the composite latex were examined with several instruments such as DSC and TGA. Finally, the superparamagnetic and thermoresponsive characteristics of this functional composite latex were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3987–3996, 2006     

Release behavior of freeze‐dried alginate beads containing poly(N‐isopropylacrylamide) copolymers

Beads composed of alginate, poly(N‐isopropylacrylamide) (PNIPAM), the copolymers of N‐isopropylacrylamide and methacrylic acid (P(NIPAM‐co‐MAA)), and the copolymers of N‐isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM‐co‐MAA‐co‐ODA)), were prepared by dropping the polymer solutions into CaCl₂ solution. The beads were freeze‐dried and the release of blue dextran entrapped in the beads was observed in distilled water with time and pH. The degree of release was in the order of alginate bead < alginate/PNIPAM bead ≈ alginate/P(NIPAM‐co‐MAA) bead < alginate/P(NIPAM‐co‐MAA‐co‐ODA) bead. On the other hand, swelling ratios reached steady state within 20 min, and the values were 200–800 depending on the bead composition. The degree of swelling showed the same order as that of release. Among the beads, only alginate/P(NIPAM‐co‐MAA‐co‐ODA) bead exhibited pH‐dependent release. At acidic condition, inter‐ and intraelectrostatic repulsion is weak and P(NIPAM‐co‐MAA‐co‐ODA) could readily be assembled into an aggregate due to the prevailing hydrophobic interaction of ODA. Thus, it could block the pore of bead matrix, leading to a suppressed release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced toughness for polyamide 6 with a core-shell structured polyacrylic modifier

Polyamide 6 (PA 6) is an important thermoplastic with excellent strength, stiffness, and good chemical resistance. The notch sensitivity and low notch impact toughness of PA 6, however, limit its application. A core-shell structured polyacrylic modifier, poly(n-butyl acrylate)/poly(methyl methacrylate-co-methacrylic acid) modifier (PBM-co-MAA), was used to toughen PA 6. To study the effect of PBM-co-MAA particles on the toughness of PA 6, various contents of poly(BA) in PBM-co-MAA latexes of 300 nm were synthesized by seed emulsion polymerization. The results showed that polymerization had an instantaneous conversion higher than 95 wt% and an overall conversion higher than 97 wt%. The PBM-co-MAA particles had a clear core–shell structure confirmed by transmission electron microscope (TEM). The mechanical properties of PA 6/PBM-co-MAA blends showed that the notch impact strength of PA 6/PBM-co-MAA blends with 85 wt% poly(BA) and 0.5 wt% MAA in PBM-co-MAA was nearly six times greater than that of pure PA 6, being consistent with the scanning electron microscope (SEM) observations on the fractured surfaces. The notch impact strengths of PA 6/PBM-co-MAA blends were also better than that of PA 6/PBM blend, which did not contain MAA functional group in the modifier. Dynamic mechanical analysis (DMA) results showed improved compatibility between PA 6 matrix and core-shell toughening modifier, which should contain a functional group in the shell layer and a suitable core rubbery content to toughen PA 6 effectively.     

Preparation of Novel Poly(hydroxyethyl methacrylate-coglycidyl methacrylate)-Grafted Core-Shell Magnetic Chitosan Microspheres and Immobilization of Lactase

Poly(hydroxyethyl methacrylate-co-glycidyl methacrylate)-grafted magnetic chitosan microspheres (HG-MCM) were prepared using reversed-phase suspension polymerization method. The HG-MCM presented a core-shell structure and regular spherical shape with poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) grafted onto the chitosan layer coating the Fe₃O₄ cores. The average diameter of the magnetic microspheres was 10.67 μm, within a narrow size distribution of 6.6–17.4 μm. The saturation magnetization and retentivity of the magnetic microspheres were 7.0033 emu/g and 0.6273 emu/g, respectively. The application of HG-MCM in immobilization of lactase showed that the immobilized enzyme presented higher storage, pH and thermal stability compared to the free enzyme. This indicates that HG-MCM have potential applications in bio-macromolecule immobilization.     

Degradable inorganic/polymer core-shell microspheres for pH-triggered release of indole-3-acetic acid

Abstract

The narrowly dispersed functional silica/poly(di(metacryloylooxy-1-ethoxy) methane-co-acryl amide) (SiO₂/P(DMOEM-co-AAm)) core-shell microspheres were synthesized by distillation precipitation polymerization of DMOEM as a degradable crosslinker and AAm as a functional monomer with the presence of 3-(methacryloxy)propyltrimethoxysilane (MPS) modified silica microspheres as seeds. Indole-3-acetic acid (IAA) can be efficiently loaded into the microspheres with a loading capacity of 37.5% via hydrogen-bonding interaction between the carboxylic acid group of IAA and the amide groups on the surface of SiO₂/P(DMOEM-co-AAm). The loaded IAA can be triggered released by pH due to the presence of pH-responsive crosslinker (DMOEM).     

Polymer–metal composite particles: Metal particles on poly(St‐co‐MAA) microspheres

Poly(styrene‐co‐methacrylic acid) P(St‐co‐MAA) microspheres with a monodisperse size distribution were prepared by emulsifier‐free emulsion copolymerization of St and MAA. The effects of MAA content on the polymerization rate and the content of MAA in the copolymer were investigated by gravimetrical and IR methods, respectively. The results of XPS measurement indicated the presence of a carboxyl functional group. By chemical metal deposition, nickel or palladium particles were formed and deposited on the surface of P(St‐co‐MAA) microspheres to form P(St‐co‐MAA)Ni or P(St‐co‐MAA)Pd composite particles. XRD measurement and TEM observation confirmed that nickel and palladium metal particles in a small size (20–40 nm) were distributed on surface of the copolymer microspheres. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1693–1698, 2000     

Dispersion properties of BaTi4O9/Ba2Ti9O20 colloids with amphoteric polyelectrolytes

An amphoteric water-soluble copolymer, i.e., polyacrylamide/(α-N,N-dimethyl-N-(3-(β-carboxylate)acrylamino)propyl) ammonium ethanate (PAM/DAE) was synthesized and used as a dispersion agent for BaTi₄O₉/Ba₂Ti₉O₂₀ (BT₄/B₂T₉) particles. PAM/DAE was prepared from acrylamide and (α-N,N-dimethyl-N-(3-(β-carboxylate)acrylamino)propyl) ammonium ethanate in a basic condition through a free radical polymerization. The dispersing property of this copolymer was examined by means of rheology, particle size, and leached Ba²⁺ concentration measurements. The results indicate that PAM/DAE could reduce the viscosity of slurries greatly, and cause BT₄/B₂T₉ particle sizes a shift to smaller values. Compared with a commercial dispersant, ammonium salt of poly(methacrylic acid) (PMAA–NH₄), PAM/DAE is as effective in preparing dispersed suspensions. More importantly, PAM/DAE could lessen the leached Ba²⁺ concentration.     

Hydrogels based on N-isopropylacrylamide and methacrylic acid: thermal stability and glass transition behaviour

Summary The thermal stability and glass transition behaviour of crosslinked poly(N-isopropylacrylamide) [P(N-iPAAm)], poly(methacrylic acid) [P(MAA)], their random copolymers and sequential interpenetrating polymer networks (IPNs) have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). P(MAA) shows a two-step process of degradation. P(N-iPAAm) shows an unique process of degradation at higher temperature. Copolymers having higher content in N-iPAAm units have a lower thermal stability than their component homopolymers and show an unique degradation process at high temperature. On the contrary, enriched MAA copolymers show better stability but they exhibit two degradation steps at the main degradation region. Sequential IPN samples exhibit a better stability than their component homopolymers and copolymers. The high temperature backbone degradation occurs in only one step, which indicates the formation of a true interpenetrating network. The T _g of the same series of materials has been also measured. A T _g vs composition plot of P(N-iPAAm-co-MAA) copolymers presents a S-shaped curve indicating that structural units interact among them through strong specific interactions. For interpenetrating polymer networks, it seems that only one T _g occurs indicating a good compatibility and interpenetration. Received: 1 December 2001 /Revised version: 12 February 2002/ Accepted: 12 February 2002     

Electrospinning of poly(MMA-co-MAA) copolymers and their layered silicate nanocomposites for improved thermal properties

Copolymers consisting of methyl methacrylate (MMA) and methacrylic acid (MAA) and their layered silicate nanocomposites were electrospun to form fibers with diameters in the sub-micron range. The presence of MAA increased the T_g and thermal stability of the copolymers through formation of anhydrides upon heating. Fibers of uniform diameters were obtained for the poly(MMA-co-MAA) copolymers and nanocomposites containing montmorillonite (MMT), while protrusions were observed on the electrospun fibers from nanocomposites containing fluorohectorite (FH). The electrospinnability of copolymer solutions and nanocomposite dispersions predicted based on both rheological analyses and conductivity measurements correlates well with the experimental electrospinning observations. Dispersion of clays within the nanocomposites improved the electrospinnability of the nanocomposite dispersions. MMT is predominantly exfoliated and well distributed within the fiber and oriented along the fiber axis. Char formation was observed when the MMT-containing fibers were heated above the decomposition temperature, indicating a potential for reduced flammability and increased self-extinguishing properties, whereas the FH-containing materials disintegrated into either film or powder form.