The role of cationic monomers in emulsion polymerization

[2-(methacryloyloxy)ethyl] trimethylammonium chloride (MATMAC), and vinylbenzyl trimethyl ammonium chloride (VBTMAC) were chosen to be used as ionic comonomers in the emulsion polymerization of styrene. The cationic nature of the two comonomers is the same (quaternary ammonium salts), however the styrene derivate (VBTMAC) is more hydrophobic than the methacrylic one (MATMAC). With the more hydrophobic cationic comonomer (VBTMAC) higher conversions were obtained due to the in situ creation of an amphiphilic copolymer with styrene and faster rates of polymerization were observed by increasing the cationic comonomer concentration. The same behavior was observed with the more hydrophilic cationic comonomer (MATMAC) at concentrations up to 0.012 M. At higher concentrations the ionic strength controls the colloidal stability of the system and coagulation occurs.     

The synthesis and cationic polymerization behavior of ambifunctional monomers

The synthesis of a novel series of ambifunctional monomers containing cationically polymerizable vinyl and 1-propenyl ether or 1-butenyl ether groups in the same molecule has been carried out. Studies of the onium salt-induced photopolymerizations of these monomers indicate that both functional groups are highly reactive and that they undergo extensive copolymerization. © 1996 John Wiley & Sons, Inc.     

Photoinitiated cationic polymerization of epoxy alcohol monomers

A series of epoxy alcohols were prepared by simple, straightforward methods. These compounds were very reactive monomers that polymerized rapidly on UV irradiation in the presence of cationic photoinitiators. The kinetics of the cationic photopolymerization of these monomers were studied with diaryliodonium salt photoinitiators and real‐time IR spectroscopy. The rate of epoxide ring‐opening polymerization was enhanced markedly by the presence of the hydroxy group. Using model compounds, the monomers were shown to polymerize via an activated monomer mechanism. Simple epoxy alcohols polymerized to give polymers with a hyperbranched structure. The novel monomers also were observed to accelerate the rate of the photopolymerization of mono‐ and multifunctional epoxides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 389–401, 2000     

Verification of transfer-suppressed cationic polymerization of vinyl monomers

A general approach to a transfer-suppressed proceeding of cationic vinyl polymerization is put forward. The fundamental principle of the method consists in stabilization of the counter-ion by interaction with acceptors. This results in an orbital controlled cation-anion interaction and by this, suppression of side reactions, for example chain transfer due to lowering the ß-hydrogen acidity of the growing cation and the specific monomer solvation of the propagation transition state. It is shown that picric acid, initiated polymerization of p-methoxyatyrene and vinyl ethers, runs free of transfer in contrast to LEWIS-acid initiated systems. Cationic polymerization, initiated by iodine based systems, are in the same category as demonstrated by molecular weight distributions, monomer addition experiments, thermokinetical data and UV-spectroscopical measurements. The results are discussed in the framework of a general energetic scheme of propagation via cation-anion orbital controlled interactions with propagating ion pairs.     

Reactivities of carbocations and monomers in carbocationic polymerization and copolymerization

In carbocationic polymerization and copolymerization, a recent publication concluded that the substituent effect on carbocation reactivity is much larger than its effect on monomer reactivity, and this by a factor 10⁶ in the case of the rate constant k_12capp for p‐methylstyrene addition (monomer M₂) on, respectively, poly(p‐methoxystyrene)^± or poly(p‐methylstyrene)^± (M). This conclusion is disputed, as well as the assumption that the rate constants of capping (k_12capp) obtained in deactivation reactions of poly(p‐methoxystyrene)^± are identical with cross propagation rate constants in copolymerization (k_12copol). It is shown that the large calculated k_12capp are based on propagation constant values for p‐methylstyrene (k ≈ 10⁹) obtained by the diffusion‐clock method. They are 10⁴ times smaller as found for all styrenes, that is, between 10⁴ and 10⁵ when they are based on the ionic species concentrations. In such a case, the available data are still in agreement with an approximate compensation between the reactivities of a monomer and of the corresponding carbocation. It is also shown that copolymerization data for styrenes are not compatible with k values near to diffusion control, and that variations of log k_12capp and log k_12copol with the nucleophilicity parameter N of the monomers indicate a much lower selectivity of the monomers in the case of copolymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2666–2680, 2010     

The synthesis and cationic polymerization of multifunctional silicon-containing epoxy monomers and oligomers

Several series of multifunctional silicon-containing epoxide monomers and oligomers have been prepared using rhodium catalyzed hydrosilation reactions. Dialkyl and diarylsilanes can be condensed with vinyl epoxides to give high yields of the desired diepoxides while the hydrosilation of alkyl and aryl silanes yields a mixture of di and tri epoxy substituted products. The condensation of αω,? Si? H difunctional compounds with vinyl epoxides can be carried out regioselectively to give α-hydrogen-ω-epoxy intermediates, which can be further reacted with di and tri olefins bearing terminal double bonds to give a series of well characterized epoxy functional oligomers. An investigation of the photoinitiated cationic polymerization of the monomers and oligomers, which were prepared during the course of these studies, was carried out. © 1994 John Wiley & Sons, Inc.     

Reactivity of oxetane monomers in photoinitiated cationic polymerization

Studies of the onium salt photoinitiated cationic ring‐opening polymerizations of various 3,3‐disubstituted oxetane monomers have been conducted with real‐time 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. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3205–3220, 2005     

Design and initiators of living cationic polymerization of vinyl monomers

This paper discusses recent developments in living cationic polymerization of vinyl monomers, specifically focusing on (a) new initiating systems, (b) kinetics and mechanism, and (c) controlled polymer synthesis. The new initiating systems were based on nucleophilic stabilization of the growing carbocations, either by counteranions (as in phosphate/ZnI₂ and Me₃SiI/ZnI₂ systems) or by added Lewis bases (as 2,6-dimethylpyridine for EtAlCl₂). The kinetic study included the determination of the lifetime of living cationic polymers. The controlled polymer synthesis by living cationic processes led to not only end- and pendant-functionalized polymers of narrow molecular weight distributions but also star-shaped polymers and sequence-regulated vinyl ether oligomers with functional groups.     

Primary processes in the photosensitized polymerization of cationic monomers

A detailed time-resolved laser spectroscopy investigation has been carried out on the electron transfer reactions of substituted thioxanthone derivatives with diphenyliodonium (Ph-I⁺) salts having different metal halide counterions (MX^?_n). Quenching of thioxanthones' triplet state has been followed under various conditions, by changing the number and nature of substituents on the thioxanthone skeletone, using anion with different nucleophilicity and employing different solvents, namely methanol and acetonitrile. A Photosensitization mechanism is proposed involving an electron transfer from thioxanthone to diphenyliodonium salt. The absorption spectra of the thioxanthone's excited state and the formed new transient are recorded and the rate constants of the excited state processes are measured. The triplet state of thioxanthone derivatives has been quenched by cationically polymerizable monomers and the quantum yield of the major processes has been evaluated. Photolytic experiments have been performed to measure the extent of acid formation. Form photopolymerization experiments using different photoinitiating systems, the rate of polymerization and percentage of monomer conversion have been determined. Both the reactivity in the excited states and the nucleophilicity of the anions affect the efficiency of the photopolymerization reaction.     

Synthesis and photoinitiated cationic polymerization of monomers with the silsesquioxane core

A synthetic scheme was developed to prepare cationically polymerizable octafunctional monomers with silsesquioxane (T₈) cores. Epoxy and 1-propenoxy functional groups were attached to the core by the hydrosilation of T with an appropriate precursor. The steric constraints and the requirements for the hydrosilation reaction are discussed. The monomers were fully characterized and then polymerized by exposure to ultraviolet irradiation in the presence of onium salt photoinitiators. The polymerization conditions for the monomers were optimized and compared with each other using real-time infrared spectroscopy. Thermal analysis was also performed on the resulting crosslinked polymers. © 1997 John Wiley & Sons, Inc.     

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

Effect of gegen ion in cationic polymerization and copolymerization of trioxane

p-Chlorophenyldiazonium hexafluorophosphate has been reported to be a superior catalyst for cationic polymerization and copolymerization of trioxane as compared to boron trifluoride dibutyl etherate (BF₃·Bu₂O)¹. In the present investigation the effect of anions derived from elements in Group VA, AsF and SbF, has been ascertained. It has been concluded that p-chlorophenyldiazonium hexafluoroarsenate is also a superior catalyst to boron trifluoride dibutyletherate (BF₃·Bu₂O), while p-chlorophenyl-diazonium hexafluoroantimonate is inferior. Copolymers with the highest polymer yield (>95%) and molecular weight (intrinsic viscosity = 4 to 5) were obtained with Simple dependences on catalyst concentration have been observed to hold for a wide catalyst concentration range ([M]/[C]) = (1 to 20) × 10⁵: For the same relationships hold. However, the polymer yield (75%) and molecular weights (intrinsic viscosity ?1) are considerably lower while the extent of chain transfer is higher. Furthermore, the polymerization proceeds with explosive violence. The quantitative aspects resulting from polymerization, for the most part, can be interpreted in terms of the extent of dissociation of the propagating ions.     

Dual photo‐ and thermally initiated cationic polymerization of epoxy monomers

Selective inhibition of the photoinitiated cationic ring‐opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be “activated” by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring‐opening polymerization. These dual photo‐ and thermal cure systems have potential applications in adhesives, potting resins, and composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6750–6764, 2006     

Formulation and polymerization of microemulsions containing a mixture of cationic and anionic monomers

A series of polyampholytes of sodium-2-acrylamido-2-methylpropanesulfonate (NaAMPS) and 2-(methacryloyloxy) ethyltrimethylammonium chloride (MADQUAT) has been synthesized by free radical polymerization in microemulsions. The optimization of the formulation was, by a selection procedure, based on the hydrophile-lipophile balance (HLB) of the nonionic surfactants and solubility parameters of the different components. Both ionomers play an important role in the formulation owing to their amphiphilic and electrolyte characters as confirmed by surface tension and turbidimetry experiments. These effects control the HLB and interfacial properties of the microemulsions. The results are semi-quantitatively interpreted from the cohesive energy ratio (CER) concept. The reaction products are stable inverse latexes consisting of high molecular weight copolymers entrapped in water droplets particles and dispersed in an isoparaffinic oil.     

Living cationic polymerization of vinyl monomers: Mechanism and synthesis of new polymers

This paper reviews the recent progress in our research on the living cationic polymerization of vinyl compounds by the hydrogen iodide/iodine (HI/I₂) initiating system, with emphasis on its scope, mechanism, and applications to new polymer synthesis. The scope of the living cationic polymerization has been expanded to include vinyl ethers, propenyl ethers, unsaturated cyclic ethers, and styrene derivatives as monomers. The initiation/propagation mechanism was discussed on the basis of recent direct analysis on the living system by NMR and UV/visible spectroscopy. The proposed mechanism involves a quantitative formation of Hl-vinyl ether adduct [CH₃-CH(OR)-I; l] that is by itself incapable of initiating polymerization. In the presence of iodine, however, the CH-I bond of l is electrophilically activated by iodine and living propagation occurs via the insertion of vinyl ether to the activated CH-I bond. Such living polymerizations were found to proceed in not only nonpolar but polar solvents (CH₂Cl₂) as well. Quenching the living end with amines gave polymers capped with an amino group that in turn enabled us to determine the living end concentration. Applications of the HI/I₂-initiated living process to the synthesis of new bifunctional and block polymers were also described.     

Living cationic polymerization of vinyl monomers: New initiators and functional polymer synthesis

This paper focuses on two recent topics in living cationic polymerization of vinyl monomers, i.e., (a) Development of new initiating systems: RCOOH/Lewis acid for vinyl ethers; CH₃CH(C₆H₅)Cl/SnCl₄/nBu₄NCl for styrene. (b) Synthesis of shape-controlled poly(vinyl ethers): Tri-armed star polymers; Multi-armed spherical polymers. For the RCOOH-based systems, a generalized concept of living cationic polymerization was discussed on the basis of the effects of the counteranions (or R) and Lewis acids (ZnCl₂ and EtAlCl₂). The CH₃CH(C₆H₅)Cl-based system permitted a truly living cationic polymerization of styrene. The tri- and multi-armed poly(vinyl ethers) included new amphiphilic polymers of unique topology, solubility, etc., all of which were prepared by living cationic polymerization.     

Low-temperature cationic polymerization of γ-irradiated monomers during devitrification of the matrix

Ionic polymerizations of cyclopentadiene (CPD), ethylene oxide (EO) and some other monomers in a matrix of butyl chloride (BC) were achieved by low-temperature postradiation polymerization during softening of the glassy system. To conduct the polymerization, various amounts of the monomers were dissolved in BC at 273 K, and cooled to 77 K. On slow reheating of such radiolysed systems in the range of the matrix devitrification (T_g 97 K), polymerization was observed. Evidence was obtained to indicate cationic mechanisms for CPD and EO polymerization in a glassy BC matrix. No special techniques for monomer and solvent drying are required.     

Surface promoted redox cationic polymerization of epoxy monomers catalyzed by silver salts

The first example of a one‐component room temperature curing redox cationic polymerization for metal surfaces is described. A weak Lewis acid (Ag⁺) is used as a latent catalyst to likely generate a much stronger one (Fe²⁺/Fe³⁺ or Cu²⁺) at the bond line interface. Such a process has been demonstrated for 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate using [Ag(1,5‐cyclooctadiene)₂]SbF₆ with the polymerization monitored most conveniently by fourier transform infrared spectroscopy (FTIR). This system, however, demonstrates a relatively low adhesive strength even following curing for 24 h. Higher bond strengths were achieved using mixtures with other cationically polymerizable monomers (vinyl ethers, tetrahydrofuran (THF), oxetanes). Factors considered for optimization of the rates and extent of reaction were the concentrations of a vinyl ether comonomer and [AgL_n]X, the nature of the counterion (X), and of the ligand (L). The performance of the Ag(I) system was compared to that of Cu(I) and various organic cations and the activity of the redox cationic polymerizations on a range of metallic (iron, copper, and aluminium) and nonmetallic (glass and various plastics) substrates was studied. A relatively high glass transition temperature was recorded for the optimized model system and the bonding strength at elevated temperature (150–200 °C) following a room temperature cure was found to be attractive compared to selected model anaerobic acrylate compositions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012