Production of submicron-sized poly(methyl methacrylate) particles by dispersion polymerization with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide

 Submicron-sized, comparatively monodisperse poly (methyl methacrylate) particles were produced by dispersion polymerization of methyl methacrylate with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide at 30 MPa for 24 h at 65 °C. The initiator operated not only as a radical initiator but also as a colloidal stabilizer, and was named an “inistab”. Received: 13 February 2001 Accepted: 20 June 2001     

Linearly polarized white fluorescence from shish-kebab type liquid crystalline poly(P-phenylenevinvlene)s with (P-phenylene)s as kebab

Liquid crystalline(LC) polymers with a shish-kebab-type moiety on their cross-conjugated(p-phenylene)s-poly(p-phenylenevinylene) s main chains were synthesized through Gilch polymerization in order to develop a kind of polymers available for linearly polarized white-light-emitting from single chain.In this system,the 2,5-bis(4’-alkoxyphenyl)benzene as the "kebabs" connects with poly(p-phenylenevinylene)(PPV) main chain backbone using its molecular gravity center and the PPV as the "shish" or "skewer"(the "shish-kebab").The polymers possess desirable properties such as excellent solubility and liquid crystalline properties.To drop the "kebabs" of the 2,5-bis(4’-alkoxyphenyl)benzene into the orientation microgroove of aligned polyimide film,not only the "shish" of polymer main chain can be aligned by the virtue of orientation of "kebabs" but also the uniform cross-conjugated structure between the "kebabs" and "shish" can be broken. Then,the alignment of the polymer main chain showed yellow light emission and was also accompanied by orientation of the LC side chains showing blue light emission,this gave rise to a notable linearly polarized white fluorescence.     

The electrophoresis of poly(N-isopropylacrylamide) microgel particles

 The electrophoretic mobility of a poly(N-isopropylacrylamide) microgel containing carboxylic groups has been measured as a function of the ionic strength, between 0.1 and 100 mM NaCl, over the temperature range 2545 ^∘C. The mobility data obtained have been evaluated using different models, including the porous-sphere, the soft-plate and the soft-sphere models as well as the hard-sphere model developed by Henry and later refined by O'Brien and White. The “porous” or “soft” behaviour is evident at lower temperatures, whereas at higher temperatures none of the models can fully explain the observed behaviour. It is suggested that the discrepancies at higher temperatures can be partly ascribed to the neglect of the relaxation effect in the “soft” models. Received: 30 June 1999/Accepted in revised form: 12 October 1999     

Competition between poly(methyl methacrylate) and poly(ethylene glycol) during their interaction with poly(silicic acid) in an organic solvent

It is shown that the interpolymer complex of poly(silicic acid) and poly(ethylene glycol) formed in the organic solvent benzene is thermodynamically more stable than the corresponding complex with PMMA. Therefore, poly(silicic acid) prepared via template polycondensation conducted in the presence of poly(ethylene glycol) contains a smaller amount of defects (branches and crosslinks) than the same polymer obtained in the presence of PMMA. To provide evidence for the interaction between poly(silicic acid) and PMMA, the dynamic light-scattering method with the use of “invisible” macromolecules has been applied for the first time.     

Anomalies and error limits in electrical-conductivity measurements in plasticized transparent poly(vinyl chloride) films

The anomalous behavior of the electrical conductivity of transparent poly(vinyl chloride) films is experimentally studied at field voltages approaching the breakdown threshold, above the threshold, and far below the threshold. The effects of strong nonlinearity, relaxation drifts, and spontaneous reversible transitions between states with high and low electrical conductivities are revealed for the first time in “thick” (20–100 μm) plasticized transparent poly(vinyl chloride) films. When a certain threshold is exceeded, relaxation oscillations in the test sample are generated and their frequency is proportional to the applied voltage. During a “mild” breakdown, the polymer film passes into the high-conductivity state (the current increases by four or more orders of magnitude), which is identical to the states observed during low-voltage transitions. A simple qualitative model explaining the anomalous character of the electrical conductivity of plasticized poly(vinyl chloride) films is advanced.     

The effects of the molecular weight and structure of poly(acrylic acid) on the formation of “blue silver”

Using UV-spectroscopy and transmittance electron microscopy it was shown that the structure of macromolecules and molecular weight of poly(acrylic acid) can significantly affect the synthesis and stabilization of so-called “blue silver.”     

MALDI-TOF MS stability study of model poly(p-phenylene terephthalamide)s

In the present study, we address the possibility of matrix-assisted laser desorption/ionization (MALDI)–time-of-flight MS analysis-induced chain fragmentation in poly(p-phenylene terephthalamide) (PPD-T) by considering two possible sources: (1) grinding-induced fragmentation resulting from the evaporation–grinding MALDI sample preparation method (E-G method) and (2) in-source/metastable fragmentation induced by the MALDI laser. An analysis of variance (ANOVA) statistical study found, with a high probability, that obtaining MALDI spectra with the effective laser area as large as possible (the “fanned-out” setting) did not cause any chain fragmentation due to the E-G MALDI sample preparation method, even when three additional grinding steps were used. However, the effect of laser fluence was less clear. A significant effect of laser fluence was observed for lower mass oligomers (<1,400 Da), but there was essentially no effect for higher mass species up to our limit of ANOVA measurement (∼2,300 Da). Plausible explanations are presented to explain these observations. The most likely scenario is that “unexpected” end-group modifications occur during PPD-T synthesis, producing small quantities of low mass species, which are amplified by the MALDI-EG extraction procedure.     

Spectrochemical investigations in molecularly organized solvent media: evaluation of pyridinium chloride as a selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in aqueous carboxylate-terminated poly(amido) amine dendrimers and anionic micelles

The ability of pyridinium chloride (PC) to selectively quench alternant as opposed to nonalternant polycyclic aromatic hydrocarbons (PAHs) in organized media is examined. PC was previously shown to be a selective quenching agent of alternant PAHs in neat polar solvents. Carboxylate-terminated poly(amido) amine (PAMAM-CT) dendrimers and anionic surfactants – sodium dodecanoate (SD), sodium octanoate (SO), and sodium dodecylsulfate (SDS) – were chosen as the solubilizing media for this study. Selective quenching of alternant PAHs is observed in the presence of the SDS and SO micelles. However, the extent of PAH quenching in SO is significantly reduced compared to PAHs dissolved in either water or SDS micelles. In the case of the smaller generation 4.5 (G4.5) PAMAM-CT dendrimers, PC was prevented from quenching both alternant and nonalternant PAHs to any appreciable extent. The dendrimer is able to “protect” the PAHs from the PC quencher that resides at the dendrimer surface. Both, SD and G5.5 PAMAM-CT precipitated out of solution with the addition of PC. Differences between traditional micelles and “unimolecular micelle” dendrimers were also examined. These studies further confirm that the PAHs did not reside in the “analogous” palisade region of the dendrimers as they do in micelles. The PAHs must reside in the outermost branches of the dendrimer, but sufficiently far enough away from the charged surface groups, where PC associated, to prevent fluorescence quenching. This work further illustrates the differences between “unimolecular micelle” dendrimers and traditional micelles. Received: 27 July 2000 / Revised: 25 September 2000 / Accepted: 27 September 2000     

Miscibility and transesterification in ternary blends of poly(ethylene naphthalate)/poly(trimethylene terephthalate)/poly(ether imide)

Miscibility and morphology of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate)/poly(ether imide) (PEN/PTT/PEI) blends were investigated by using a differential scanning calorimeter (DSC), optical microscopy (OM), wide-angle X-ray diffraction (WAXD), and proton nuclear magnetic resonance (¹H-NMR). In the ternary blends, OM and DSC results indicated immiscible properties for polyester-rich compositions of PEN/PTT/PEI blends, but all compositions of the ternary blends were phase homogeneous after heat treatment at 300 °C for more than 30 min. An amorphous blend with a single T _g was obtained in the final state, when samples were annealed at 300 °C. Experimental results from ¹H-NMR identified the production of PEN/PTT copolymers by so-called “transesterification”. The influence of transesterification on the behaviors of glass transition and crystallization was discussed in detail. Study results identified that a random copolymer promoted the miscibility of the ternary blends. The critical block lengths for both PEN and PTT hindered the formation of crystals in the ternary blends. Finally, the transesterification product of PEN/PTT blends, ENTT, was blended with PEI. The results for DSC and OM demonstrated the miscibility of the ENTT/PEI blends.     

Origin of “cold” water molecules in the composition of low-molecular-mass products of the mechanical fracture of poly(methyl methacrylate)

A hypothesis on the correlation between the origin of “cold” (∼53 K) water molecules released by a growing crack and a low (∼123 K) temperature of stretched and then thermoelastically cooled polymer chains that ruptured at the crack top is advanced. A mechanism behind the formation of “cold” water molecules is suggested. It includes their “soft” desorption due to mechanical action onto thermoelastically cooled side groups with adsorbed cooled water molecules from an unloading wave that is induced by the rupture of the main chain and that travels along it.     

Ferritin immobilization on patterned poly(2-hydroxyethyl methacrylate) brushes on silicon surfaces from colloid system

In this paper, we describe a graft polymerization/solvent immersion method for generating poly(2-hydroxyethyl methacrylate) (PHEMA) brushes in various patterns. We used a novel fabrication process, involving very-large-scale integration and oxygen plasma treatment, to generate well-defined patterns of polymerized PHEMA on patterned Si(100) surfaces. We observed brush- and mushroom-like regions for the PHEMA brushes, with various pattern resolutions, after immersing wafers presenting lines of these polymers in MeOH and n-hexane, respectively. The interaction between PHEMA and ferritin protein sheaths in MeOH and n-hexane (good and poor solvent for PHEMA, respectively) was used to capture and release ferritins from fluidic system. The “tentacles” behaver for PHEMA brushes was found through various solvents in fluidic system. Using high-resolution scanning electron microscopy, we observed patterned ferritin Fe cores on the Si surface after pyrolysis of the patterned PHEMA brushes and ferritin protein sheaths, which verify the “tentacles” behaver for PHEMA brushes.     

Preparation of electrospun chitosan/poly(vinyl alcohol) membranes

Electrospinning of chitosan from its solutions in 2% aqueous acetic acid was studied by adding poly(vinyl alcohol) (PVA) as a “guest” polymer. Properties of the chitosan/PVA solutions including viscosity, conductivity, and surface tension were measured, and effects of the polymer concentration, chitosan/PVA mass ratio and processing parameters (applied voltage, flow rate, capillary-to-collector distance) on the electrospinnability of chitosan/PVA were investigated. Analyses of scanning electron micrographs and transmission electron micrographs suggested that the chitosan/PVA ultrafine fibers were often obtained along with beads, and chitosan was located in the elctrospun fibers as well as in the beads. Uniform chitosan/PVA fibers with an average diameter of 99 ± 21 nm could be prepared from a 7% chitosan/PVA solution in 40:60 mass ratio. Results of Fourier transform infrared spectroscopy and X-ray diffraction demonstrated that there were possible hydrogen bonds between chitosan and PVA molecules, which could weaken the strong interaction in chitosan itself and facilitate chitosan/PVA electrospinnability. The electrospun chitosan/PVA membranes showed higher water uptake and would have potential applications in wound dressings.     

Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the “extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”, “arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.     

Electrocatalytic activity of poly(3-methylthiophene) electrodes

Poly 3-methylthiophene (P3MT) modified electrodes have shown an improvement for detecting catecholamines when compared to classical ones. Past work with this polymer electrode suggested the possible presence of “active sites,” which are believed to be the polymer’s center of electrocatalytic activity. The interaction of 1,5-anthroquinone-disolfonic acid (1,5-AQDS) at the P3MT electrode showed a nonreversible behavior resulting in the blocking of “the active sites,” suggesting the specific electcatalytical activity of this polymer is limited to catechol and similar compounds. In order to improve catecholamine detection, two methods of electropolymerization for P3MT were compared under similar conditions; (1) a constant potential for a specific length of time, and (2) potential cycling. It was found that cycling provided a more sensitive CV, i.e. increased number of active sites. Under a controlled pH study (pH range 2–9), the polymer electrode maintained its superior performance, manifested as lower ΔE and higher i, toward catechol over the traditional electrodes. Two different supporting electrolytes were used, sulfate and phosphate, and it was found that in neutral or basic solutions containing phosphate, the oxidation and reduction potentials of catechol shifted to lower values. Solutions containing sulfate exhibited no shift in the oxidation potential at any pH value.     

Effect of amines on the controlled synthesis of poly(methyl methacrylate) catalyzed by ruthenacarboranes

The effects of amines on the activity of ruthenium catalysts in the controlled synthesis of poly(methyl methacrylate) are reported at 80°C. The introduction of tert-butylamine or triethylamine into the polymerization system raises the polymerization rate by 1–2 orders of magnitude without reducing the high degree of control over the chain propagation step. The “living” character of methyl methacrylate polymerization in the presence of ruthenacarboranes and amines is proved by the fact that, as the monomer conversion increases, the molecular weight of the resulting polymer increases linearly and the polydispersity index decreases. The polymer can serve as a macroinitiator for postpolymerization and block copolymer synthesis.     

Investigation of complex formation between poly(N-vinyl imidazole) and various metal ions using the molar ratio method

The complex formation of poly(N-vinyl imidazole) (PVIm) with various metal ions was studied. UV-vis spectroscopy was employed to study the interaction of PVIm and metal ions in aqueous solution. Formation constants of PVIm-metal complexes were calculated by applying a “mole ratio” method. The stoichiometric ratios between polymer and metal ions were found to be␣4. The stability constants for the complexes of PVIm with bivalent transition metal ions were in agreement with the Irving-William series. The biggest formation constant was found for the PVIm-Cu²⁺ complex system. Received: 4 January 1999 Accepted in revised form: 1 February 1999     

Preparation of micrometer-sized, monodisperse, hollow polystyrene/poly(ethylene glycol dimethacrylate) particles with a single hole in the shell

Micrometer-sized, monodisperse, hollow polystyrene (PS)/poly(ethylene glycol dimethacrylate) (PEGDM) composite particles with a single hole in the shell were prepared by seeded polymerization using (ethylene glycol dimethacrylate/xylene)-swollen PS particles in the presence of sodium dodecyl sulfate (SDS). Single holes were observed at SDS concentrations above 3 mM, much lower than in the PS/polydivinylbenzene (PDVB) system previously reported (above 45 mM). Phase separation inside droplets occurred at lower conversion in the PEGDM system than the PDVB system. Phase separation in the droplet at the early stage of the polymerization is an important factor for the formation of the single hole in the shell. Part CCCXIII of the series “Studies on Suspension and Emulsion.”     

Ternary upper-critical-solution-temperature behavior in a blend system comprising poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene

 Upper-critical-solution-temperature (UCST) behavior in a ternary blend of poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene is reported. The as-cast ternary blend is immiscible at ambient conditions and comprises two different phases, and, however, turns into a miscible system above the “clarity point” ranging from 160 to 300 °C for different ternary compositions. The maximum clarity point is labeled as the UCST for the ternary system, which is about 295 °C. Above the clarity point, the originally immiscible ternary blend turned into one miscible phase. Owing to the thermodynamic UCST behavior and kinetic hindrance, the immiscible ternary polymer blend can be locked into a pseudo-miscible state if it is heated to a temperature above the clarity point followed by a rapid-cooling processing scheme. The quenched ternary blend can remain in a pseudo-miscible state as long as the service temperature does not exceed the glass-transition temperature of the blend. Received: 17 July 2001 Accepted: 3 October 2001     

Grafting from ramie fiber with poly(MMA) or poly(MA) via reversible addition-fragmentation chain transfer polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to control the grafting of methyl methacrylate (MMA) and methyl acrylate (MA) from natural ramie fibers substrate. The hydroxyl groups of ramie fibers were first converted to 2-dithiobenzoyl isobutyrate as a RAFT chain transfer agent (CTA), which was further grafted with MMA or MA mediated by the RAFT polymerization in a presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as a free chain transfer agent. Hydrophobic poly(MMA) or poly(MA) modified ramie fibers with contact angles greater than 130° were obtained. The modified ramie fibers were analyzed by gravimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetry and contact angle measurements. The results indicate that the polymer chains had indeed been grafted from the surface of the ramie fibers with an average 33% of the hydroxyl groups in the raw ramie fiber substituted by 2-bromoisobutyryl bromide and an average grafting ratio of 25% poly(MMA) or poly(MA) related to ramie fiber. The homopolymers formed in the copolymerization were also analyzed to estimate molecular weights and polydispersity indices of grafting chains from the surface of ramie fibers by size exclusion chromatography, which showed narrow polydispersity with the PDIs to be <1.32. This study provides a novel and feasible approach to the preparation of functional composite materials for utilizing the abundant natural ramie fiber cellulose resource.     

Long-lived polymer radicals. IV. Reactions of poly(N-methylacrylamide) and poly(N-methylmethacrylamide) radicals with binary mixtures of vinyl monomers

N-methylacrylamide (NMAAm) and N-methylmethacrylamide (NMMAm) were polymerized to give polymer microspheres containing living propagating radicals. The microsphere polymer radicals were allowed to react with some binary mixtures of vinyl monomers including alternating copolymerization combinations. The reaction processes were investigated by ESR spectroscopy. In the poly(NMMAm) radical/methyl methacrylate (MMA)/styrene (St) system, the propagating radical from MMA was mainly observed at the higher MMA concentration, while polySt radical prevailed at the lower MMA concentration. In the poly(NMMAm) radical/α-methylstyrene (α-MeSt)/diethyl fumarate system, the α-MeSt radical was exclusively observed, while the maleic anhydride (MAn) radical was predominantly observed in the α-MeSt/MAn system. In the MAn/diphenylethylene system, the propagating radicals from both monomers were observed at comparable concentrations. The poly(NMAAm) microsphere radical behaved differently in the reaction with the MMA/St mixture. The poly(NMAAm) microsphere was found to incorporate preferentially St, leading to formation of the St radical. The St preference was enhanced in the St/cyclohexyl methacrylate (CHMA) system. These results were in agreement with those of block copolymerization via the reaction of poly(NMAAm) radical with the MMA/St or CHMA/St mixture, where the compositions of the resulting polymers were analyzed by pyrolysis gas chromatography.