Cationic polymerization Research Papers - Academia.edu (original) (raw)

Macromonomers were obtained by cationic polymerization of propylene oxide and epichlorohydrin proceeding by theactivated monomer mechanism with hydroxyethyl acrylate as initiator. Up to DP, -15 for propylene oxide and DP, -20 for... more

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- Materials Engineering, Chemical Engineering, Analytical Chemistry, Polymer

Hybrid materials derived from a thiol-ene and cationic polymerization were obtained from concomitant polymerization. The hybrid materials were cured by both photopolymerization and thermally induced polymerization. The kinetics of the photopolymerization were measured using time resolved-IR and optical pyrometry. The nucleophilic character of the polysulfide obtained initially in the thiol-ene polymerization inhibited the development of the cationic photoinitiated polymerization of epoxy monomers. Besides, the epoxide groups underwent a proton catalyzed addition reaction with the thiols to form new sulfides groups in the reaction mixture. It is proposed that the formed sulfides can terminate the growing polyether chains forming dormant species like trialkylsulfonium salts. These salts promote the thermal polymerization of the epoxy monomer in a post treatment, producing hard and transparent materials. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4829-4843, 2007

- by Ricardo Ortíz
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- Materials Engineering, Kinetics, Morphology, Photopolymerization
- by Giulio Malucelli
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- Engineering, Adhesion, Photopolymerization, Cationic polymerization

Cotton fabrics were water-repellent-finished by radical ultraviolet curing of silicone and urethane acrylates with different formulations. The fabrics were impregnated with undiluted resins and with toluene solutions or water emulsions. Moreover, cationic ultraviolet-curable systems were also investigated, such as an epoxy-functional polysiloxane and mixtures of an epoxy resin with hydroxyl-containing silicone additives. The gel content and polymerization yield were considered for the ultraviolet-curing process evaluation. Water-resistance properties were determined in terms of the contact angle, wettability, moisture adsorption, and water vapor permeability measurements, whereas the morphology and surface composition of treated fabrics were examined with scanning electron microscopy and energy-dispersive X-ray analysis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

- by Franco Ferrero
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- Engineering, Photopolymerization, Ultraviolet, Applied

The use of two dibenzo[a,c]phenazine derivatives, 10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine and 10,13-bis(4-hexylthiophen-2-yl)dibenzo[a,c]phenazine are reported as photosensitizers for diaryliodonium salt photoinitiators. Novel dyes based on the dibenzo[a,c]phenazine skeleton are shown to be efficient in carrying out the cationic photopolymerizations. Representative examples of different types of monomers including epoxide, and vinyl monomers are polymerized in the presence of the photosensitizers and diphenyliodonium hexafluorophosphate (Ph 2 I þ PF À 6 ). Polymer-izations are initiated at room temperature using long wavelength UV and visible light, and monitored by optical pyrometry. The photopolymerization of an epoxide monomer via solar irradiation is also demonstrated. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3299-3303, 2011

- by Levent Toppare and +1
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- Materials Engineering, Polymer science, Photopolymerization, Cationic polymerization

The activated-monomer cationic ring-opening polymerization of ethylene oxide, initiated with ethylene glycol and using an acid-exchanged montmorillonite clay called Maghnite-H þ as an effective catalyst, was carried out to obtain the corresponding homopolymers with narrow polydispersity ratios. The molecular weights of the obtained polymers were controlled with the feed ratio of the monomer to the initiator. The effects of the amount of the catalyst and time on the polymerization yield and viscosity of the polymers were studied. The structure was confirmed with proton nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

- by Ahmed YAHIAOUI and +1
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- Engineering, Kinetics, Cationic polymerization, CHEMICAL SCIENCES

Nanostructured organic-inorganic hybrid epoxy coatings containing zirconia domains were obtained via a cationic UV/thermal dual-cure process. Uniform distribution of the in situ generated zirconia within the polymeric network on a nanometric scale (5-25 nm) was demonstrated by AFM and TEM analyses. The UV-cured films showed increase of the refractive index by increasing the zirconium tetrapropoxide content in the photocurable formulation. Coatings with a drastic cut-off in the UV spectra still maintaining transparency in the visible light were achieved. These coatings could find advanced applications as antireflection coatings, or in the optical industry.

- by Brigitte Voit
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- Engineering, Morphology, Photopolymerization, Polymer

Alkyl-substituted ferrocenium salts have limited solubility in epoxy oligomers and produce poisonous arene by photolysis. Herein, the synthesis and photoactivity of several alkoxy-substituted ferrocenium salts as long-wavelength UV light photoinitiators have been reported. [Cyclopendadien-Fe-anisole]PF 6 , [Cyclopendadien-Fe-anisole]BF 4 , [Cyclopendadien-Fe-diphenylether]PF 6 , [Cyclopendadien-Fe-diphenylether]BF 4, and [Cyclopendadien-Fe-diethoxybenzene] PF 6 for polymerization of epoxy resin were prepared through the ligand exchange reaction between one ring of ferrocene and aromatic ether. They all display good solubility and photoinitiating activities in epoxy resins.

- by Lu Gan
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- Cationic polymerization

Synthesis and characterization of nano-sized pure and Al-doped lithium ferrite having high value of dielectric constant, Abstract Fine particles of Al doped lithium ferrite of general formula Li 0.5 Al x Fe 2.5-x O 4 (0.0 ≤ x ≤ 0.4, in... more

- by Vivek Verma
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- Engineering, Materials Engineering, Condensed Matter Physics, Organic Chemistry

The synthesis of amphiphilic lipid-polyoxazoline based on copolymers (CO-POx n ) with narrow distribution has been achieved via cationic ring-opening polymerization of 2-methyl-2-oxazoline (MOx). Lipidmacroinitiator (COTs) was obtained from commercial castor oil (CO), a widely renewable agricultural resource. CO-POx n with various length segments was synthesized from a macroinitiator COTs in order to investigate the effect of the length of the hydrophilic segment on the solution behaviour of the nonionic polymer surfactants CO-POx n . The results showed that the critical micelle concentration increased with the increase of POx content and inversely surface tension decreased. The average size of aggregates of these structures suggested the formation of vesicles or nonspherical micelles. Star-shaped morphology of CO-POx n in solid state has also been observed using environmental scanning electron microscopy (ESEM). Additionally energy dispersive X-ray (EDX) analysis demonstrated the presence of POx block in the concentric stripes of the texture.

1-[2′-(Heptaphenylcyclotetrasiloxanyl)ethyl]-1,3,3,5,5-pentamethylcyclotetrasiloxane (II) was prepared from 1-[2′-(methyldichlorosilyl)ethyl]-1,3,3,5,5,7,7-heptaphenylcyclotetrasiloxane (I) and tetramethyldisiloxane-1,3-diol. Acid-catalyzed ring-opening of II in the presence of tetramethyldisiloxane gave 1,9-dihydrido-5-[2′-(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane (III) and 1,9-dihydrido-3-[2′-(heptaphenylcyclotetrasiloxanyl)ethyl]nonamethylpentasiloxane (IV). Both acid- and base-catalyzed ring-opening polymerization of II gives highly viscous, transparent polymers. The structures of I–IV and polymers were determined by UV, IR, 1H, 13C, and 29Si NMR spectroscopy. In addition, molecular weights obtained by GPC and NMR end group analysis were confirmed with mass spectrometry. On the basis of 29Si NMR spectroscopy, the polymers appear to result exclusively from ring-opening of the cyclotrisiloxane ring. No evidence for ring-opening of the cyclotetrasiloxane ring was observed. Polymer properties were determined by DSC and TGA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 137–146, 2006

Photoinitiated cationic polymerization of mono-and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4-epoxycyclohexylmethyl-3 0 ,4 0 -epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real-time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC-containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914-4920, 2007

- by Mehmet Tasdelen
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- Materials Engineering, Photochemistry, Photopolymerization, Polymer

Real-time Fourier Transformation Infrared (FTIR) spectroscopy with a fiber optic transmission probe (TR) was used to monitor the polymerization of isobutylene (IB) initiated by a-methylstyrene epoxide (MSE) and 1,2-epoxi-2,4,4-trimethylpentane (TMPO-1) in conjunction with TiCl 4 and BCl 3. In the presence of an equimolar amount of BCl 3 , MSE and TMPO-1 underwent ring opening via S N 1 mechanism. In contrast to TiCl 4 -coinitiated reactions, no oligoether formation via S N 2 mechanism was observed. TMPO-1 with excess BCl 3 initiated IB polymerization, yielding a telechelic PIB carrying a-primary OH and x-tertiary Cl functionalities with 70% initiator efficiency.

- by Serap Soytas
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- Materials Engineering, FTIR, Polymer, Cationic polymerization
- by Charles Kausch
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- Engineering, Photopolymerization, Cationic polymerization, Contact angle

Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine-telechelic PIB oligomers (NH 2 -PIB-NH 2 ) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB-based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain-extended and chain-extended polyureas showed a linear dependence on the urea hard segment content. PIB-based polyureas prepared with NH 2 -PIB-NH 2 of M n ¼ 2500 g/mol, 4,4 0 -methylendbis(cyclohexylisocyantate), and 1,6diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 C for 12 h. With increasing hard segment content, elongation at break decreased from $ 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB-based polyureas were unprecedented. Although commercial ''oxidatively resistant'' thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties.

- by iskender yilgor and +1
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- Materials Engineering, Cationic polymerization, Hardness, Thermal Stability

The photoinitiated ring-opening cationic polymerization of a monofunctional benzoxazine, 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine, with onium salts such as diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate as initiators was examined. The structures of the polymers thus formed were complex and related to the ring-opening process of the protonated monomer either at the oxygen or nitrogen atoms. The phenolic mechanism also contributed, but its influence decreased with decreasing monomer concentration. Thermal properties of the polymers were also investigated by differential scanning calorimetry and thermogravimetric analysis.

Living cationic polymerization of styrene was achieved with a series of initiating systems consisting of a HX-styrenic monomer adduct (X = Br, Cl) and ferric chloride (FeCl3) in conjunction with added salts such as tetrabutylammonium halides (nBu4N+Y−; Y− = Br−, Cl−, I−) or tetraalkylphosphonium bromides [nR′4PBr; R′ = CH3CH2–, CH3(CH2)2CH2–, CH3(CH2)6CH2–] or tetraphenylphosphonium bromide [(C6H5)4PBr] in dichloromethane (CH2Cl2) and in toluene. Comparison of the molecular weight distributions (MWDs) of the polystyrenes prepared at different temperatures (e.g., −25 °C, 0 °C and 25 °C) showed that the polymerization is better controlled at ambient temperature (25 °C). The polymerization was almost instantaneous (completed within 1 min) and quantitative (yield ∼100%) in CH2Cl2. In CH2Cl2, polystyrenes with moderately narrow (Mw/Mn ∼ 1.33–1.40) and broad (Mw/Mn ∼ 1.5–2.4) MWDs were obtained respectively with and without nBu4N+Y−. However, in toluene, the MWDs of the polystyrenes obtained respectively with and without nBu4N+Y−/nR′4P+Br− were moderately narrow (Mw/Mn = 1.33–1.5) and extremely narrow (Mw/Mn = 1.05–1.17). Livingness of this polymerization in CH2Cl2 was confirmed via monomer-addition experiment as well as from the study of molecular weights of obtained polystyrenes prepared simply by varying monomer to initiator ratio. A possible mechanistic pathway for this polymerization was suggested based on the results of the 1H NMR spectroscopic analysis of the model reactions as well as the end group analysis of the obtained polymer.

- by Atanu Mandal
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- Engineering, Polymer, Cationic polymerization, Solvent Effect

Novel, well-defined, temperature-and/or pH-sensitive copolymer architectures were prepared by atom transfer radical (co)polymerization (ATRP) of a temperature-sensitive poly(methyl vinyl ether) (PMVE) macromonomer, obtained via living cationic polymerization of MVE initiated with inimer 3,3-diethoxypropyl acrylate. Temperature-sensitive comb architectures were obtained by ATRP homopolymerization (Me 6 TREN/ CuBr in toluene) of the PMVE macromonomer. ATRP copolymerization of the PMVE macromonomer with tert-butyl acrylate, a hydrolyzable precursor for pH-sensitive acrylic acid (AA), gives statistical graft copolymers. Palm-tree block copolymers containing a linear PtBA (PAA after hydrolysis) block and a branched block based on PMVE macromonomers were also prepared and fully characterized. Using turbidimetry, dynamic light scattering, FT-IR, and NMR, the temperature and/or pH responsiveness of those (co)polymer architectures are compared with the properties of previously synthesized linear block copolymers containing PMVE and PtBA or PAA.

- by Jean-françois Gohy
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- Engineering, Ph, Cationic polymerization, Macromolecules

The polymerization of N-vinyl-2-pyrrolidone catalyzed by the Maghnite-H þ (Mag-H) was investigated. Mag-H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of N-vinyl-2-pyrrolidone (NVP) is initiated by Mag-H at 30 8C in bulk and in solution. The effect of the amount of Mag-H, the temperature and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nitrobenzene than that in toluene. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag-H. q

- by Mohammed Belbachir
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- Engineering, Polymer, Cationic polymerization, Solvent Effect

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(2,3-dihydroxypropyl methacrylate) or poly(ethylene glycol) methacrylate (PEGMA) and hydrophobic polyisobutylene chains. This conetworks were prepared by a two-step polymer synthesis. In the first step, a cationic copolymer of isobutylene and 3-isopropenyl-a,a-dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB-IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2-hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA-multifunctional PIB-based crosslinker, PIB(MA) n , with an average functionality of approximately four per chain, was copolymerized with 2,3-dihydroxypropyl methacrylate or poly(ethylene glycol) methacrylate by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 11-60 mol % of DHPMA or 10-12 mol % of PEGMA. The synthesized conetworks were characterized with solid-state 13 C-NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proved by swelling in both water and n-heptane. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4074-4081, 2007

- by Petr Vlček
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- Materials Engineering, Kinetics, Hydrogels, Polymer

In this article, germanes are presented as new coinitiators for both radical and cationic photopolymerization processes. For the free radical polymerization process, the newly proposed structures are characterized by efficiencies similar or better than the reference amine. Germyl radicals are also found to be excellent initiators for free radical promoted cationic photopolymerization (FRPCP) of an epoxy resin. The associated reactivity is even better under air. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3042–3047, 2008

- by ROZ ALI
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- Materials Engineering, Radiation, Photopolymerization, Polymer

Polylactides can be prepared by direct polycondensation of lactic acid, or better, by ring-opening polymerization of cyclic dilactides (usually called lactides). These lactides exist in the form of four stereoisomers two of which (L L ,L L -and rac. -D D ,L L -) are technically produced in large quantities. These lactides can by polymerized via four dierent classes of initiators and reaction mechanisms. The characteristics mechanistic and preparative features of the cationic polymerization, anionic polymerization and of the coordination±insertion mechanism are described. Furthermore, copolymerizations of lactides with glycolide or e-caprolactone and their analytical problems are discussed. Finally, a new type of wound dressing based on transparent are resorbable ®lms of copolylactides is mentioned. Ó

Block copolymers of cyclohexene oxide (CHO) and ketonic resin were prepared by using ketonic resins as free radical photoinitiators via two-step procedure. In the first step, cyclohexanone-formaldehyde and acetophenone-formaldehyde resins were modified during their preparation with benzoin and benzoin isobutyl ether. Then, AB or ABA type block copolymers depending on the resin employed were obtained by irradiation of these resins in the presence of pyridinium salt and CHO as a cationically polymerizable monomer. By this way, block copolymers of CHO with ketonic resin were prepared and characterized by GPC, DCS, FTIR, and 1 H NMR spectral measurements.

- by Selin Ergun and +1
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- Engineering, Photopolymerization, Block Copolymer, Cationic polymerization

The synthesis of poly(p-phenylene methylene) (PPM)-based block copolymers such as poly(p-phenylene methylene)-b-poly(e-caprolactone) and poly(p-phenylene methylene)-b-polytetrahydrofuran by mechanistic transformation was described. First, precursor PPM was synthesized by acid-catalyzed polymerization of tribenzylborate at 16 C. Then, this polymer was used as macroinitiators in either ring-opening polymerization of e-caprolactone or cationic ring-opening polymerization of tetrahydrofuran to yield respective block copolymers. The structures of the prepolymer and block copolymers were characterized by GPC and 1 H NMR investigations. The composition of block copolymers as determined by 1 H NMR and TGA analysis was found to be in very good agreement. The thermal behavior and surface morphology of the copolymers were also investigated, respectively, by differential scanning calorimetry and atomic force microscopy measurements, and the contribution of the major soft segment has been observed. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4021-4026, 2011

- by Deniz Gunes
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- Materials Engineering, Polymer, Cationic polymerization, Block Copolymers

The synthesis of a novel series of hybrid monomers containing cationically polymerizable cycloaliphatic epoxide and 1-propenyl ether functional groups in the same molecule has been conducted. Detailed structure-reactivity studies of the diaryliodonium salt-induced cationic photopolymerizations of these monomers indicate that the rate of epoxide ring-opening polymerization is markedly enhanced by the presence of the 1-propenyl ether group. At the same time, the polymerization of the 1-propenyl ether groups in such hybrid monomers is retarded. A mechanism involving the free-radical-induced decomposition of the photoinitiator has been proposed which serves to amplify the rate of the photoinitiated cationic epoxide ring-opening polymerization.

- by Suresh Rajaraman
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- Engineering, Photopolymerization, Cationic polymerization, Macromolecules
- by Daniel Romero Nieto
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- Modeling, Cationic polymerization, Monomer, Macromolecular

Two benzotriazole derivative dyes 4,7-bis(2,3-dihydrothieno [3,4-b][1,4]dioxin-5-yl)-2-dodecyl-2H-benzo[1,2,3]triazole, and 2-dodecyl-4,7-bis(4-hexylthiophen-2-yl)-2H-benzo[d] triazole are shown to work as efficient photosensitizers for a diphenyliodonium salt initiator in cationic photopolymerization of epoxide and vinyl monomers. Substituted thienyl groups are attached to benzotriazole backbone to extend conjugation and enhance electron density of the molecules. Thereby, it was possible to initiate polymerizations at room temperature using long wavelength UV and visible light. The progress of photopolymerizations was monitored using optical pyrometry. The photopolymerization of an epoxide monomer using solar irradiation was also demonstrated. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 729-733, 2011

ABSTRACT The adsorption of a cationic surfactant, dodecyltrimethylammonium bromide (C12TAB), from aqueous solutions on graphitized carbon black has been investigated from 288.15 to 318.15 K using a versatile, automated measuring system, which has been designed for the simultaneous measurement of the adsorption isotherm and the calorimetric enthalpies of displacement at the solid/liquid interface. At low concentrations, the surfactant molecules form a flat monolayer on the graphite surface. The enthalpy of monolayer formation is apparently not (or only slightly) dependent on the temperature and is independent of the surface coverage (−61 kJ·mol-1). The adsorption proceeds further as the concentration in the bulk solution is increased to the cmc. In this region, the enthalpy of displacement is again nearly independent of the surface coverage but depends strongly on the temperature: −10.7, −17.5, and −29 kJ·mol-1 at 288.15, 298.15, and 318.15 K, respectively. The mechanism of the adsorption and the morphology of the high-density adsorbate structure have been analyzed in terms of the classical reorientation model (reorientation of the adsorbed surfactant molecules from a horizontal to a vertical orientation, accompanied by further adsorption from the bulk solution) and in terms of a recent concept of interfacial aggregation (formation of half-cylindrical surface micelles templated by an epitaxially bound surfactant monolayer). The results of the thermodynamic analysis strongly support the formation of C12TAB half-cylinders at the graphite/water interface.

- by Zoltan Kiraly
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- Engineering, Chemistry, Cationic polymerization, Physical sciences

Reaction conditions have been found which allow the synthesis of polyindanes with improved molar mass. The properties of four different polyindanes are described and compared with those of polyindanes with low molar mass from former investigations. The range of glass transition temperatures which can be achieved with polyindanes has been extended from-10 "C to 293 "C. In addition, one of the newly snythesized polyindanes exhibits crystallinity with a melting point of 253 "C. This is in sharp contrast to all other polyindanes investigated up to now, which were completely amorphous.

- by Gerhard Maier
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- Materials Engineering, Cationic polymerization, Polycondensation

The thermal cationic curing of mixtures, in various proportions, of diglycidylether of bisphenol A with two substituted condensed bis(γ-lactone)s initiated using scandium, ytterbium and lanthanum triflates or a conventional boron trifluoride monoethylamine (BF 3 •MEA) initiator was investigated. The evolution of the various reactive groups was followed by means of attenuated total reflection Fourier transform infrared spectroscopy. The formation of mono-spiroorthoesters (monoSOE)s and bis-spiroorthoesters (bisSOE)s is discussed. The polymerization of bisSOE structures led to the formation of ether-ester-ketone repeat units, which implied the cationic polymerization took place by a tandem reaction. The use of scandium triflate as an initiator led to the highest chemical incorporation of lactone in the network. Moreover, this initiator was the most active, incorporating a higher proportion of lactone in a shorter time. In contrast, the conventional BF 3 •MEA initiator incorporated the lowest proportion of bislactone in the cured material.

- by Angels Serra
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- Materials Engineering, Chemical Engineering, Analytical Chemistry, FTIR spectroscopy
- by MARIA FERNANDA SANCHEZ HERNANDEZ
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- Modeling, Cationic polymerization, Monomer, Macromolecular
- by Bunyamin Karagoz
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- Engineering, Materials Engineering, Chemical Engineering, Free Radicals

The effect of the degree of branching (DB) of a hyperbranched polyester (GBPEX) added as a modifier of new thermosets obtained from diglycidylether of bisphenol A has been studied. The use of ytterbium triflate as cationic initiator allows the hydroxyl chain-ends in the GBPEX to become covalently linked to the matrix through the monomer activated propagation mechanism. The curing process has been studied by DSC and rheology. The DB of the modifier does not affect appreciably the thermal stability and the chemical reworkability but shrinkage exhibits a significant reduction on increasing the DB. Thermomechanical characteristics are also improved with increasing the DB of the modifier.

- by Albena Lederer
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- Engineering, Materials Engineering, Cationic polymerization, CHEMICAL SCIENCES

The design and synthesis of new pyrazole derivatives have long been the focus of numerous biological and pharmacological studies. In particular, this important class of heterocyclic compounds have attracted considerable attention due to... more

- by Mauricio Fuentealba
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- Chemistry, Inorganic Chemistry, Organic Chemistry, Medicinal Chemistry

Novel magnetic nanocomposite alginate beads are fabricated for the simultaneous removal of cationic, anionic and organic pollutants in highly acidic water. Copper, phosphate and toluene are used as representative cationic, anionic and organic pollutants respectively. The alginate beads were impregnated with a nanocomposite material composed of zeolites, activated carbon, layered double hydroxides and magnetic nanoparticles bound together by xanthan gum. A 3:4:1 aspect ratio (alginate: nanocomposite: xanthan gum) is used for fabrication of the beads. The beads show removal percentage for phosphate at 97.9%, copper at 81.8% and toluene at 43.4% and adsorption capacities of 60.24 mg g-1 , 120.77 mg g-1 and 25.52 mg g-1 respectively. Isothermal studies show that the Langmuir isotherm model is the governing equation for sorption. Pseudo-second-order model is the governing equation for the kinetics of sorption. The sorption process is also spontaneous and exothermic. This sorbent shows great potential to be used for simultaneous removal of cationic, anionic and organic pollutants removal in water.

- by Spancer Msamadya
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- Chemistry, Adsorption, Cationic polymerization
- by Mariaenrica Frigione
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- Materials Engineering, Mechanical Engineering, Materials Science, Kinetics

With certain cationic initiators benzoxazine rings can be opened and polymerized at room temperature. Fourier transform infrared spectroscopy, 1 H and 13 C nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis have been used to monitor the polymerization process and to characterize the obtained polymers. High performance bisphenol-A/aniline based polybenzoxazine with glass transition (T g) at 220ЊC and char yield of approximately 60% at 800ЊC under nitrogen is obtained.

- by Hatsuo Ishida
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- Engineering, Polymer, Differential scanning calorimetry, bisphenol A

Acidic bismuth salts, such as BiCl 3 , BiBr 3 , BiJ 3 , and Bi-triflate catalyzed the ring-opening polymerization of 2-methoxazoline (MOZ) in bulk at 100 8C, whereas less acidic salts such as Bi 2 O 3 or Bi(III)acetate did not. Bi-triflate-catalyzed polymerizations of 2-ethyloxazoline (EtOZ) were performed with variation of the monomercatalyst ratio (M/C). It was found that the molecular weights were independent of the M/C ratio. The formation of cationic chain ends and the absence of cycles was proven by reactions of virgin polymerization products with N,N-dimethyl-4-aminopyridine or triphenylphosphine. The resulting polymers having modified cationic chain ends were characterized by 1 H NMR spectroscopy and MALDI-TOF mass spectrometry. The polymerization mechanism including chain-transfer reactions is discussed.

- by Hans Kricheldorf
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- Materials Engineering, Maldi Tof, Cationic polymerization, Reaction Mechanism

Clay-based nanocomposite polymers have been synthesized by photoinitiated crosslinking polymerization of acrylate and epoxy functionalized oligomers. The solvent-free resin containing a small amount (3 wt%) of organophilic clay was cured within seconds upon UV irradiation at ambient temperature. The polymerization reaction was followed by infrared spectroscopy and shown to proceed at a great extent in thick samples (2 mm), due to the higher exotherm and the resulting rise in temperature. The organoclay was shown to have no slowing down effect on the photopolymerization of both acrylate and epoxy resins. The addition of clay nanoparticles was found to reduce the gloss of UV-cured coatings due to an enhanced surface roughness. The viscoelastic and tensile properties of the nanocomposite photopolymer were comparable to those of the neat UV-cured polymer, while their resistance to moisture was significantly increased. q

- by Khalid Zahouily
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- Materials Engineering, Chemical Engineering, Kinetics, Nanocomposites

This paper discusses the kinetic simulation of TiCl 4 --coinitiated living carbocationic isobutylene (IB) polymerizations governed by dormant-active equilibria, using a mechanistic model. Two kinetic models were constructed from the same underlying mechanism: one using a commercial simulation software package (Predici Ò ), and the other using the method of moments. Parameter estimation from experimental batch reactor data with Predici yielded a rate constant of propagation k p = 4.64 · 10 8 ± 2.75 · 10 8 L/mol s, with no constraints imposed. This agrees with k p data measured with diffusion clock and competition methods, but disagrees with kinetically obtained k p values. Estimation of rate constants with Predici Ò and the GREG parameter estimation software packages revealed that it was difficult to estimate the complete set of kinetic parameters, due to correlated effects of the parameters on model predictions. Estimability analysis confirmed that some of the strongly correlating parameters could not be estimated simultaneously using the available experimental data. Using k p = 6 · 10 8 ± 2.75 · 10 8 L/mol s measured by Mayr, and using starting estimates of other rate constants defined by experimentally observed correlations, yielded the set of rate constants required for the simulations. Both kinetic models yielded good agreement with experimental data, with the exception of M w values that slightly diverged from the theoretically predicted ÔM w ÀM n = constantÕ relationship. This may indicate the occurrence of a minor side reaction. However, the k p /k À1 = 17.5 L/mol average run length calculated from measured and simulated MWD data agrees well with earlier literature values.

- by Sohel Shaikh
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- Materials Engineering, Chemical Engineering, Kinetics, Modeling

Free-radical/cationic hybrid photopolymerizations of acrylates and epoxides were initiated using a three-component initiator system comprised of camphorquinone as the photosensitizer, an amine as the electron donor, and a diaryliodonium salt. Thermodynamic considerations revealed that the oxidation potential of the electron donor must be less than 1.34 V relative to SCE for electron transfer with the photoexcited camphorquinone to take place. This electron transfer leads to the production of the active centers for the hybrid polymerization (two radicals and a cation). Further investigation revealed that only a subset of electron donors that meet the oxidation potential requirement resulted in polymerization of the epoxide monomer; therefore, a second requirement for the electron donor (pK b higher than 8) was established. Experiments performed using a combination of electron donors revealed that the onset of the hybrid system's cationic polymerization can be advanced or delayed by controlling the concentration and composition of the electron donor(s). These studies demonstrate that a single three-component initiator system can be used to initiate and chemically control the sequential curing properties of a free-radical/cationic hybrid photopolymerization and is a viable alternative to separate photoinitiators for each type of polymerization.

- by Joel Oxman
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- Materials Engineering, Photopolymerization, Free Radical, Polymer

- by Ricardo Ortiz
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- Materials Engineering, Kinetics, Morphology, Photopolymerization

The system N-vinyl-2-pyrrolidone (VP)/polydimethylsiloxane diglycidylether (PDMS-DGE) is a typical example of an oil-in-oil emulsion formed by two non-miscible liquids, where both phases are polymerizable in a 'one-pot' procedure by two distinct reaction mechanisms. These oil-in-oil emulsions were characterized by their stability and by the particle size of the dispersed VP phase. Non-aqueous dispersions (NADs) are obtained in a first step by free radical polymerization of the dispersed VP phase. The reaction kinetics, studied as a function of the initiator type and concentration, show that the polymerization rate is mainly influenced by the partition coefficient of the initiator between both phases. The NAD particle size could be tailored from a micrometer to a nanometer range by in situ formation of PVP-PDMS graft copolymer. Hydrophilic-hydrophobic two-phase materials can be obtained by polycondensation, in the presence of polyamines, of the epoxy-functionalized PDMS continuous NAD phase.

- by Gérard Riess
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- Materials Engineering, Chemical Engineering, Analytical Chemistry, Kinetics

Cationic dye (Methylene blue) was extracted from wastewater by using emulsified liquid membrane process. The membrane is composed of two phases: organic and aqueous. D2EHPA, SPAN 80, and acid are the composition of the aqueous phase, however, the fuel oil represents the organic phase. The effect of different parameters such as the initial concentration of cationic dye (MB), the addition of salt (KCl/ NaCl/ Na2SO4), acid (HCl/ H2SO4/H3PO4) and the extractant concentration (10, 30 and 50 ppm) was examined using Box-Behnken design. The optimization of the extraction has been shown that the extraction efficiency reach100% for the following optimum operating conditions: 30 ppm for the initial concentration of [BM]0, 10%w for the extracting (D2EHPA) with the presence of Na2SO4 and H2SO4. It can be said that the ELM method is efficient for the removal of methylene bleu.

- by Fadhel Ismail
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- Chemistry, Chromatography, Response Surface Methodology, Cationic polymerization

Abstract Applicability of a series of coumarin derivatives as fluorescent probes for monitoring progress of cationic photopolymerization processes by Fluorescence Probe Technique (FPT) has been studied using triethylene glycol divinyl ether as a model monomer and diphenyliodonium hexafluorophospate as a cationic photoinitiator. The following coumarins were evaluated: Coumarin 1, Coumarin 6H, Coumarin 102, Coumarin 120, Coumarin 151, Coumarin 343 and Coumarin 466. It has been found that despite the presence of an amino group in their structure, at low concentrations of the order of 0.1%, the Coumarins 1, 102, 343 and 466 can be used as the fluorescent probes for the cationic photopolymerization, while Coumarin 343 exhibits the best performance. At high concentrations, the aminocoumarins slow down the photopolymerization rate and extend induction period. All of the aminocoumarins are applicable as long-wavelength sensitizers for diphenyliodonium photoinitiators, enabling photopolymerization at the irradiation wavelengths, where the photoinitiator does not absorb. At short wavelengths, where both photoinitiator and probe absorb light, and at the probe concentrations below 0.1%, Coumarin 343 and Coumarin 1 accelerate the cationic photopolymerization by supplying an additional route for the photoinitiator cleavage beside its direct cleavage upon light absorption. The direct initiation and sensitization mechanisms are proposed.

- by Monika Topa
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- Materials Engineering, Chemical Engineering, Materials Science, Chemistry

Studies of the onium salt photoinitiated cationic ring-opening polymerizations of various 3,3-disubstituted oxetane monomers have been conducted with realtime infrared spectroscopy and optical pyrometry. The polymerizations of these monomers are typified by an extended induction period that has been attributed to the presence of a long-lived tertiary oxonium ion intermediate formed by the reaction of the initially formed secondary oxonium ion with the cyclic ether monomer. Because the extended induction period in the photopolymerization of these monomers renders oxetane monomers of limited value for many applications, methods have been sought for its minimization or elimination. Three general methods have been found effective in markedly shortening the induction period: (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerizing with more reactive epoxide monomers, and (3) using free-radical photoinitiators as synergists. V

- by Umut Bulut
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- Materials Engineering, Chemistry, Photopolymerization, Cationic polymerization

Substituted triphenylamine cation radical salts having anions of the type SbF6-, PF6-, BF4 and SbCl6-, were prepared and used to initiate cationic polymerization of cyclohexene oxide (CHO), tetrahydrofuran (THF), and N-vinyl carbazole (NVC), thermally in dichloromethane at room temperature. Experimental results are presented to show the effects of salt counter ion, concentration, and polymerization conditions on the yield and the molecular weight of the obtained polymer. THF polymerization was enhanced by photolysis of the reaction mixture for short time. A general mechanism for the polymerization by cation-radical salts of substituted triphenylamine is proposed.

- by Lifescience Global Canada
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- Cationic polymerization