First-principles calculation of particle formation in emulsion polymerization: pseudo-bulk systems

Kinetic behavior in emulsion polymerization can be conveniently assigned as either ‘zero-one’ or ‘pseudo-bulk’. Sufficiently small particles in emulsion polymerizations obey zero-one kinetics, where entry of a radical into a particle which contains a growing radical leads to instantaneous termination. Pseudo-bulk kinetics applies to particles in which more than one free radical can co-exist for a significant period; while this is commonly applicable to large particles for any monomer, it also applies to very small particles for monomers which propagate very rapidly, such as acrylates. A methodology is developed to enable particle sizes and rates to be calculated for systems in which pseudo-bulk kinetics are important during particle formation. This takes account of all significant reactions involving radical species in the water and particle phases, including the chain-length dependence of the termination rate coefficient. A ‘cross-over radius’ r_co is used to describe the particle size where termination of radicals within the particles is no longer instantaneous. The model is applied to the emulsion polymerization of butyl acrylate. All parameters are available from the literature, except for r_co and k_p¹, the rate coefficient for propagation of a monomeric radical formed from transfer. These were determined from experiments on seeded emulsion polymerizations of this monomer, involving the steady-state rate with chemical initiator and non-steady-state rate in a system initiated by γ radiolysis, after removal from the radiation source (‘relaxation’ mode). Particle sizes and rates in unseeded butyl acrylate emulsion polymerizations at 50 °C, over a range of concentrations of persulfate as initiator and sodium dodecyl sulfate as surfactant, are predicted by the model with acceptable accuracy.     

Novel approaches to developing carbon nanotube based polymer composites: fundamental studies and nanotech applications

The adsorption of several types of conducting polymers on carbon nanotubes is investigated by electrical transport measurements. We report the optoelectronic properties occurring in single-walled carbon nanotubes (SWNTs) conjugated polymer, poly(3-octylthiophene), composites. Al/polymer-nanotube composite/indium-tin oxide diodes show photovoltaic behavior proposing that the main reason for this increase is the photoinduced electron transfer at the polymer/nanotube interface. Interesting results were obtained in the case of poly(o-anisidine) (POAS)-multi-walled nanotubes (MWNTs) composites where the increment of monolayers results in a significant improvement of the specific conductivity. POAS-coated MWNTs thin films demonstrated their potentiality as a new class of materials for inorganic vapors detection for environmental applications.     

Kinetics of surface grafting on polyisoprene latexes by reaction calorimetry

The two-component redox-initiation system, cumene hydroperoxide (CHP) and tetraethylene pentamine (TEPA), was used to polymerize dimethylaminoethyl methacrylate (DMAEMA) in the presence of synthetic polyisoprene latexes. The modified latex particles are postulated to possess a ‘hairy layer’ of surface-grafted poly(DMAEMA) chains formed via an abstraction reaction between cumyloxy radicals and the isoprene moieties present in the seed polymer. The modified latexes exhibited enhanced colloidal stability to low pH, and dynamic light scattering showed that the apparent particle size was sensitive to pH. The rate of polymerization was followed by reaction calorimetry. No steady-state polymerization was observed, with a continual increase in the number of propagating chains at all initiator feed rates investigated. The data for particle size and colloidal stability, together with the calorimetric data, are consistent with radical production at the particle surface, and with abstraction near the interface being a rare event. Further, there is evidence that radical production by the redox couple is relatively slow. While this ‘topology-controlled’ reaction is responsible for the formation of the hairy layer and latex stability, the dominant polymerization process appears to be the formation of ungrafted poly(DMAEMA) in the water phase.     

Synthesis and cross-linking of polyisoprene latexes

Seeded and ab initio emulsion polymerizations of isoprene using redox initiation systems were investigated and suitable reaction conditions determined to prepare polyisoprene latexes with minimal cross-linking. Polymerizations initiated with the potassium persulfate/sodium bisulfite (KPS/SBS) redox couple had a significant inhibition period and low yield. Polymerizations initiated with the tert-butyl hydroperoxide/tetraethylene-pentamine redox couple showed reasonable yields and no apparent inhibition. It is postulated that the lipophilic nature of the t-butyl group plays a favorable role in the entry of hydroperoxide-initiated oligomeric radicals, while persulfate-initiated radicals are more likely to undergo aqueous phase termination before entry. The cross-linking reaction by benzoyl peroxide (BPO) at 70 °C was investigated using this lightly cross-linked polyisoprene latex. ¹H NMR and gel permeation chromatography results were consistent with a reaction mechanism in which the radicals formed by the decomposition of BPO react exclusively with polyisoprene to abstract a hydrogen atom, and the resulting radicals react by termination to form cross-links. No loss of double bonds was found, suggesting that radical formation is overwhelmingly achieved by hydrogen abstraction and cross-linking occurs by termination between two radicals. Cross-linking was accompanied by chain scission, which was observed only at the beginning of the reaction. At low weight-fractions of polymer, the rate of cross-linking was dependent on the concentrations of BPO and abstractable hydrogens in a manner consistent with the postulated mechanism.     

Purple red and luminescent polyiminoarylenes containing the 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) chromophore

New DPP-containing polyiminoarylenes were prepared from 1,4-diketo-2,5-dihexyl-3,6-di(4′-bromophenyl)pyrrolo[3,4-c]pyrrole and various arylamine derivatives using palladium-catalyzed amination reactions. The arylamine comonomers were aniline (ANI), t-butylaniline (TBA), 2-aminoanthracene (AAN), 1-aminopyrene (APY) and N,N′-diphenyl-p-phenylenediamine (PDA). Purple red polymers with good solubility in common organic solvents and molecular weights between 4.4 and 35.8 kDa were obtained. Polymer solutions were readily fluorescent with quantum yields between 19 and 62%, while solution-cast films only showed a weak fluorescence. All polymers exhibit low band gaps of approximately 1.9 eV. Cyclovoltammetric studies indicate quasireversible oxidation for polymers with TBA, APY and PDA as comonomer units, and quasireversible reduction for the polymer with AAN comonomer unit. Polymers with APY and PDA comonomer units are electrochromic and can be switched between red in the neutral and greenish grey in the oxidized state.     

Incorporation of magnetic nanoparticles into lamellar polystyrene-b-poly(n-butyl methacrylate) diblock copolymer films: Influence of the chain end-groups on nanostructuration

In this article, we present new samples of lamellar magnetic nanocomposites based on the self-assembly of a polystyrene-b-poly(n-butyl methacrylate) diblock copolymer synthesized by atom transfer radical polymerization. The polymer films were loaded with magnetic iron oxide nanoparticles covered with polystyrene chains grown by surface initiated-ATRP. The nanostructuration of the pure and magnetically loaded copolymer films on silicon was studied by atomic force microscopy, ellipsometry, neutron reflectivity and contact angle measurement. The present study highlights the strong influence of the copolymer extremity - driven itself by the choice of the ATRP chemical route - on the order of the repetition sequences of the blocks in the multi-lamellar films. In addition, a narrower distribution of the nanoparticles’ sizes was examined as a control parameter of the SI-ATRP reaction.     

Induction of chirality into a fully sulfonated poly(methoxyaniline) via acid-base interactions with chiral amines

A wide range of chiral amines and amino alcohols associate with poly(2-methoxyaniline-5-sulfonic acid) (PMAS) in aqueous solution, from which optically active PMAS·(amine) films can be cast. The chiral induction is believed to be initiated by acid-base interactions with “free” sulfonic acid groups on the PMAS chains. Chiral amine:PMAS dimer molar ratios as low as 1:4 give PMAS·(amine) films with similar optical activity to those cast from 1:1 molar mixtures, indicating that only one in four of the “free” sulfonate groups on the PMAS chains need to be electrostatically bound by chiral ammonium ions to achieve optimal chiral induction. Circular dichroism studies show that the enantiomeric amines (R)-(+)- and (S)-(−)-1-phenylethylamine induce the opposite helical hands for the supermolecular assemblies of PMAS chains. However, there is no clear correlation between the sign of the CD signals for the PMAS·(amine) films and the configuration of structurally diverse amines.     

The synthesis of a physically crosslinked NVP based hydrogel

Complexes of polyvinyl pyrrolidinone–polyacrylic acid (PVP–PAA) were prepared by photopolymerisation from a mixture of the monomers NVP and AA. The complexes were characterised by means of differential scanning calorimetry, Fourier transform infrared spectroscopy (Ftir), potentiometric titration, swelling studies and gel permeation chromatography. The Ftir spectra of PVP–PAA copolymer complexes indicates hydrogen bonding between the carbonyl group in the PVP and the carboxylic acid group in the PAA moiety. As the percentage of AA increases in the copolymer there is evidence of increased intermolecular hydrogen bonding between the carboxylic acid groups of the AA segments. Swelling of the PVP–PAA complex in a higher pH medium is significantly different from results in low pH solutions. The critical pH range was found to be between 4.07 and 4.49. Above a pH of 4.49, there is a progressive break up of the polymer chain due to a reduction in the amount of intermolecular hydrogen bonding. There is also a significant increase in the solubility of the copolymer complex at higher pHs. The low solubility of the copolymer at low pH may make the complex suitable for gastric drug delivery systems.     

Benzo[1,2-b:4,5-b′]dithiophene-based copolymers applied in bottom-contact field-effect transistors

Three copolymers of benzo[1,2-b:4,5-b′]dithiophene and 3,3′-bis(alkyl)-5,5′-bithiophene (dodecyl, tetradecyl and hexadecyl side chains) have been synthesized through Stille copolymerization. The polymers have number-average molecular weights over 20 kg/mol, are well-packed in the bulk and thin film, and possess an ionization potential of −5.1 eV in thin film, which offers stability versus oxidation in environmental conditions. The thin film packing of the polymer with dodecyl side chains leads to an excimeric emission upon excitation, which is not observed for longer side chain lengths. The presence of the dimers responsible for this excimer formation results in a device performance improvement as well. Field-effect transistors fabricated from these copolymers have On/Off ratios >10⁷, equal saturation and linear hole mobilities above 10⁻² cm²/Vs, almost no hysteresis and turn-on voltages around 0 V in bottom-contact devices.     

Copolymerization of 1-vinylpyrrolidone with N-substituted methacrylamides: monomer reactivity ratios and copolymer sequence distribution

In order to enhance their resistance to polar solvents and their film forming ability compared to these of neat polyvinylpyrrolidone (PVP), water soluble copolymers which combined rather large PVP sequences with ammonium groups were obtained. Free radical copolymerization of 1-Vinyl-2-Pyrrolidone (NVP) with 3-(dimethylamino)propyl-methacrylamide (DMA) and 3-(methacrylamido)propyltrimethyl-ammonium, methylsulfate (TMA) was investigated in water at 68 °C using a water soluble initiator (4,4′-azobis(4-cyanovaleric acid ACVA)). The copolymer samples obtained at low conversion levels (<10%) could not be recovered quantitatively for these particular copolymers. Therefore, a numerical integration modeling, accounting for change in copolymer composition with conversion, was preferred to determine the optimal reactivity ratios from experimental data obtained at moderate conversions. The reactivity ratios (system TMA-NVP: r_TMA 4.47, r_NVP 0.038, system DMA-NVP: r_DMA 5.67, r_NVP 0.37) proved a strong preferential incorporation of the methacrylamide monomers. The reactivity ratios were then used to estimate the copolymer sequence distributions. It is shown that rather large NVP sequences can be obtained with low TMA or DMA initial contents at moderate conversion. Moreover, these copolymers easily formed films which withstood polar solvents and could be readily cross-linked by thermal curing, opening interesting prospects for membrane separation systems.     

Polymeric monolithic materials: Syntheses, properties, functionalization and applications

The synthetic particularities for the synthesis of polymer-based monolithic materials are summarized. In this context, monoliths prepared via thermal-, UV- or electron-beam triggered free radical polymerization, controlled TEMPO-mediated radical polymerization, polyaddition, polycondensation as well as living ring-opening metathesis polymerization (ROMP) will be covered. Particular attention is devoted to the aspects of controlling pore sizes, pore volumes and pore size distributions as well as functionalization of these supports. Finally, selected, recent applications in separation science, (bio-) catalysis and chip technology will be summarized.     

Synthesis and characterization of film-forming poly(urethaneimide) cationomers containing quaternary ammonium groups

In a recent work, we have described an original family of poly(urethaneimides) containing tertiary amine groups from a polytetramethylene oxide diol (PTMO1000), N-methyldiethanolamine (MDEA), 4,4′-methylene-bis-phenylisocyanate (MDI) and 4,4′-hexafluoroisopropylidene-bis-phthalic anhydride (6FDA). This paper reports their quaternization with various alkylating agents to give the cationic quaternary ammonium groups. An optimization of the experimental conditions led to three new families of PUI cationomers with a good structural control and high quaternization degrees. These polymers differed in the number of their cationic groups (0 < x ≤ 0.7 equiv.), the type of their counter-ions X⁻ (methyl sulfate, tosylate, triflate, chloride, bromide, iodide) and their steric hindrance by the length of their n-alkyl side chain (C₁-C₆). Complementary NMR techniques, including HSQC and COSY two-dimensional NMR, enabled to characterize the control of the polymer structure and to determine quantitatively the quaternization degree of the PUI cationomers. Properties in solution (solubility and viscosity) and in the solid state (film-forming ability and density) were then examined in relation with the membrane separation application targeted for these new PUI cationomers.     

A promising environmentally-friendly manganese-based catalyst for alkyd emulsion coatings

A manganese(IV) complex (MnMeTACN) containing 1,4,7-trimethyl-1,4,7-triazacyclononane (MeTACN), in the presence of polyamines, significantly accelerated the oxidation of ethyl linoleate (EL) emulsions, and appeared to be a potential environmentally-friendly alternative for Co-based driers that are currently widely used for alkyd emulsion coatings. The polyamines greatly enhanced the catalytic activity of MnMeTACN in decomposing the formed hydroperoxides during the oxidation of EL.     

Polymerization of olefins with bulky substituents. 1. Homo- and copolymerization of 3-(1-adamantyl)propene

The use of bulky substituents like adamantane has been shown in the past to influence the glass transition temperatures of polymers significantly. In this paper the synthesis and homopolymerization of the monomer 3-(1-adamantyl) propene is described, as well as the copolymerization of this monomer with ethene, propene, 1-pentene, 4-methyl-1-pentene, 1-hexene and 1-octene. The resultant copolymers proved to be largely insoluble in organic solvents. It was also demonstrated that the presence of the bulky methyladamantyl side group influenced the glass transition temperatures of the copolymers in comparison with the corresponding homopolymers.     

Preferential solvation of the eutectic mixture of liquid crystals E7 in a polysiloxane

Blends of the nematic liquid crystal E7 and poly(methylphenylsiloxane) (PMPS) with molecular weight 120,000 g/mol are investigated by high performance liquid chromatography (HPLC) measurements. This study was prompted by observations made recently while analyzing the phase behavior of poly(siloxane)/E7 and poly(acrylate)/E7 systems. A remarkable increase of the nematic to isotropic transition temperature T_NI was found when polymer was added to the liquid crystal. Surprisingly, the increase of T_NI was enhanced with the polymer concentration up to 80 wt%, where it reached its highest value. This behavior could be interpreted by invoking a preferential solvation of the constituents of E7 towards the polymer. The present investigation provides an evidence of this phenomenon using HPLC data.     

Radical crossover reactions of a dynamic covalent polymer brush for reversible hydrophilicity control

Reversible hydrophilicity control of a radically exchangeable polymer brush with dynamic covalent linkages was successfully demonstrated. A polymer brush with alkoxyamine units was prepared via surface-initiated atom transfer radical polymerization, and reversible surface hydrophilicity control was achieved via dynamic covalent exchange reactions of alkoxyamines. Exchange reactions between alkoxyamine units in the side chains of the polymer brush and the terminal of poly(4-vinylpyridine) (P4VP) were carried out in order to prepare a side-chain functionalized polymer brush. Subsequent quaternization of P4VP chains with iodomethane was carried out to prepare a more hydrophilic surface. In addition, a de-grafting reaction of the quaternized P4VP side chains was performed to confirm reversibility of the alkoxyamine via radical exchange reactions on the surface. All the composition and wettability changes were investigated via X-ray photoelectron spectroscopy and contact angle measurements.     

Tailoring mechanical properties of highly porous polymer foams: Silica particle reinforced polymer foams via emulsion templating

The aim of this work was to synthesise highly open porous low-density polymer foams with superior mechanical properties by the polymerisation of the organic phase of concentrated emulsions. The continuous organic phase of the concentrated emulsion template occupying up to 40 vol% was polymerised leading to polymer foams with much improved mechanical properties. The Young's modulus as well as the crush strength of the foams was further increased dramatically by reinforcing the polymer phase with nanosized silica particles. To ensure that the silica particles were covalently incorporated into the polymer network, methacryloxypropyltrimethoxysilane (MPS) was added to the formulation, which reacts with the silica via hydrolysis reactions. The Young's modulus of silica reinforced foams increased by 280% and the crush strength by 218% in comparison to foams without reinforcement.     

Polymorphism of syndiotactic poly(p-fluoro-styrene)

Syndiotactic poly(p-fluoro-styrene) (s-PPFS) has been prepared with a polymerization procedure which allows reaching high average molecular masses and satisfactory yields. The polymorphic behavior of the polymer has been mainly studied by X-ray diffraction, calorimetric and infrared analyses. The main crystalline phase of s-PPFS, obtained by melt processing or cold-crystallization, exhibits trans-planar chains, is orthorhombic (a = 9.5 Å, b = 28.7 Å, c = 5.1 Å) and melts at nearly 320 °C. The X-ray analysis shows a strict analogy of this orthorhombic phase with the β phase of s-PS, also as for the occurrence of two limit ordered (β″) and disordered (β′) modifications, which differ for the intensity of reflections characterized by h + k = 2n + 1. A metastable crystalline phase, also exhibiting trans-planar chains, has been observed for as-polymerized samples as well as for amorphous samples crystallized by sorption of toluene or 1,4-difluoro-benzene. Mainly on the basis of solvent sorption and desorption experiments, it is suggested that this metastable phase is a co-crystalline phase with the low-molecular-mass guest molecules.     

Morphology, hydration, and proton transport in novel sulfonated polyimide-silica nanocomposites

A series of inorganic-organic nanocomposites containing sulfonated polyimides and silica particles were synthesized. Anhydride-terminated pre-polymers were prepared, followed by introduction of reactive silanes. Casting, curing, and acidification routines lead to nanocomposites with significantly different properties compared to parent sulfonated polyimides. The presence of silica was qualitatively confirmed using energy dispersive X-ray spectrometry and studied using solid-state ²⁹Si NMR. Thermogravimetric analysis provided a more quantitative assessment of the inorganic fraction. Electron microscopy, water vapor sorption, and impedance studies were conducted to understand how silica and ion content influences morphology and proton conductivity. Ion clusters were visible following Ag⁺ staining, and silica nanoparticles were imaged in unstained samples. Silica nanoparticles significantly reduce the solubility of prepared membranes, and promote membrane hydration. For nanocomposites prepared from high molecular weight pre-polymers, silica incorporation promotes conductivity at low relative humidity. However, for nanocomposites made from low molecular weight or high ionic content pre-polymers, silica dilutes the ion concentration and lowers proton conductivity.     

Synthesis and luminescence properties of three novel polyfluorene copolymers

We report on the synthesis and characterization (including structural, optical, electrochemical and electroluminescence properties) of three alternating F-alt-X copolymers, where F is 9,9-bis(2′-ethylhexyl)fluorene unit and the X comonomer varies from a phenylene, to a thiophene and to a thiophene-S,S-dioxide unit. Among these X comonomers, the phenylene group is at the origin of a blue-emitting copolymer with unitary luminescence efficiency in solution, while thiophene-S,S-dioxide promotes the highest electron affinity. These copolymers are also used in the fabrication of light-emitting diodes.