Poly(methyl methacrylate)-kaolinite nanocomposites prepared by interfacial polymerization with redox initiator system

Interfacial intercalative polymerization of methyl methacrylate (MMA) was developed to prepare PMMA-kaolinite nanocomposites using a redox initiator system, based on dodecylamine as reductant, immobilized into kaolinite by successive intercalation while the oxidant component of the redox system (K₂S₂O₈) was applied from aqueous phase. The X-ray diffraction (XRD) was used to prove the functionalization of the clay with the amine before starting the polymerization reaction. The progress of the polymerization reaction through the involvement of the amine in the initiation process was confirmed not only by successfully performing the reaction at 50 °C, a temperature at which the K₂S₂O₈ cannot start the polymerization alone, but also by the enhancement of polymerization rate and drop in activation energy required to start the polymerization. The produced PMMA/kaolinite nanocomposites were examined by XRD and transmission electron microscope as well; both confirmed the defoliation of the kaolinite layers into homogeneously distributed platelets within the polymer phase which supports the effectiveness of the redox initiation in the intercalative polymerization. Furthermore, more explanation about the interfacial structure of the nanocomposites was given using Fourier transform infrared. The thermal gravimetric analysis revealed a very similar behavior above 300 °C with respect to the pure PMMA prepared under the same reaction conditions while in the range from 220 °C to 320 °C, the degradation was earlier in the case of the nanocomposites due to the presence of the dodecylamine; on the other hand, the glass transition temperatures were increased remarkably as assigned by differential scanning calorimetry in comparison with the pure PMMA.     

Determination of TOCl, TOBr and TOI in drinking water by pyrolysis and off-line ion chromatography

The objective of this research was to determine the optimum total organic halogen (TOX) protocol for use with ion chromatographic (IC) detection to analyze total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI) in drinking water simultaneously. Two commercial analyzers (one using a pure O₂ carrier and one using O₂/CO₂ mixture) and three commercially available activated carbons (two coconut-based and one bituminous coal-based) were examined in this study. Results showed that the pyrolytic analyzer using pure O₂ and off-line IC combined with a standard TOX carbon (coconut-based) achieved the most complete recovery of TOCl, TOBr and TOI for both model compounds and real samples. There was no obvious difference between the two analyzers when used in microcoulometric detection mode. The TOX method is moderately sensitive to nitrate rinse volume. The monohaloacetic acids were partly washed out during sample preparation. This problem was solved by a modified nitrate rinsing solution.     

Atomization-Induced High Intrinsic Activity of a Biocompatible MgAl-LDH Supported Ru Single-Atom Nanozyme for Efficient Radicals Scavenging

Developing efficient nanozymes to mimic natural enzymes for scavenging reactive radicals remains a significant challenge owing to the insufficient activity of conventional nanozymes. Herein, we report a novel Ru single-atom nanozyme (SAE), featuring atomically dispersed Ru atoms on a biocompatible MgAl-layered double hydroxide (Ru₁/LDH). The prepared Ru₁/LDH SAE shows high intrinsic peroxidase (POD)-like catalytic activity, which outperforms the Ru nanoclusters (NCs) nanozyme by a factor of 20 and surpasses most SAEs. The density functional theory calculations reveal that the high intrinsic POD-like activity of Ru₁/LDH can be attributed to a heterolytic path of H₂O₂ dissociation on the single Ru sites, which requires lower free energy (0.43 eV) compared to the homolytic path dissociation on Ru NC (0.63 eV). In addition, the Ru₁/LDH SAE shows excellent multiple free radicals scavenging ability, including superoxide anion radical (O₂⋅⁻), hydroxyl radical (⋅OH), nitric oxide radical (NO⋅) and 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH⋅). Given the advantages of Ru₁/LDH with high enzymatic activities, biosafety, and ease to scale up, it paves the way for exploring SAEs in the practical biological immunity system.     

SYNTHESIS AND POLYMERIZATION OF ALIPHATIC TERTIARY AMINO-GROUP N-SUBSTITUTED ACRYLAMIDES

Aliphatic tertiary amino-group N-substituted acrylamides, N-acryl-N′-methylpiperazine (AMP)and N-methacryl-N′-methylpiperazine (MAMP) were synthesized directly from N-methylpiperazinewith corresponding acryloyl chlorides and characterized by elementary analysis of their picrates,~1H-NMR, IR and MS. AMP did not polymerize with benzoyl peroxide (BPO), but could poly-merize with lauroyl peroxide (LPO). The rate equation of the polymerization was given as R_P=K_P [AMP]~(1.5)[LPO]~(0.5) and the overall activation energy of this polymerization system was 10.8Kcal/mol. The redox nature of LPO with the monomer itself was suggested. Even though AMP and MAMP hardly proceed the polymerization initiated with BPO, butunder lower concentration would form redox system with BPO to initiate the polymerization of MMAreadily. The rate equation of the polymerization of MMA initiated with MAMP-BPO systemwas given as R_P=K_P [MMA] [MAMP}~(0.5) [BPO]~(0.5) and the overall activation energy was 10.2Kcal/mol. The analysis of the obtained polymers confirmed that MAMP not only initiated the poly-merization of MMA by combining with BPO, but also took part in the polymer chains impartingthem with better biocompatibility.     

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.     

Synthesis of PMMA‐b‐PBA block copolymer in homogeneous and miniemulsion systems by DPE controlled radical polymerization

In this research, poly(methyl methacrylate)‐b‐poly(butyl acrylate) (PMMA‐b‐PBA) block copolymers were prepared by 1,1‐diphenylethene (DPE) controlled radical polymerization in homogeneous and miniemulsion systems. First, monomer methyl methacrylate (MMA), initiator 2,2′‐azobisisobutyronitrile (AIBN) and a control agent DPE were bulk polymerized to form the DPE‐containing PMMA macroinitiator. Then the DPE‐containing PMMA was heated in the presence of a second monomer BA, the block copolymer was synthesized successfully. The effects of solvent and polymerization methods (homogeneous polymerization or miniemulsion polymerization) on the reaction rate, controlled living character, molecular weight (M_n) and molecular weight distribution (PDI) of polymers throughout the polymerization were studied and discussed. The results showed that, increasing the amounts of solvent reduced the reaction rate and viscosity of the polymerization system. It allowed more activation–deactivation cycles to occur at a given conversion thus better controlled living character and narrower molecular weight distribution of polymers were demonstrated throughout the polymerization. Furthermore, the polymerization carried out in miniemulsion system exhibited higher reaction rate and better controlled living character than those in homogeneous system. It was attributed to the compartmentalization of growing radicals and the enhanced deactivation reaction of DPE controlled radical polymerization in miniemulsified droplets. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4435–4445, 2009     

Synthesis and Polymerization Kinetics of Polystyrene Grafting using Azo-groups Bounded SiO2 as an Initiator

This work presents a new method for synthesis of inorganic/organic hybrid nanoparticles via the in-situ polymerization by the use of the azo-groups bounded silica nanoparticles as a radical initiator and styrene as a model vinyl-monomer. The synthesis and the structure of silica/polystyrene (SiO₂/PS), and the polymerization kinetics of the styrene initiated by the azo-groups bounded SiO₂ nanoparticles are studied with techniques such as FTIR, XPS, DSC, GPC, and TEM. Results show that the SiO₂-g-PS nanoparticles are synthesized successfully, and the resulting hybrid nanoparticles have a core-shell structure with SiO₂ in the core and the polystyrene on the outside layer. The percentage of the grafted PS on the SiO₂ surface increases with the progress of the polymerization before 6 h, and the largest amount of the grafted PS reaches 33% of the silica nanoparticles.

Consequently, the size of the nanoparticles increases ca. 20 nm upon the polystyrene grafting. The molecular weight of the grafted PS increases with the polymerization, and it has reached a much large value in the first several polymerization hours while it keeps a constant value approximately in the following polymerization process. Meanwhile, the polydispersity index of the grafted PS gradually increases with the progress of the polymerization. These phenomena agree with the theory of the traditional free radical polymerization very well.     

STUDIES ON THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY METAVANADATE-CONTAININ G ANION EXCHANGER-THIOUREA REDOX SYSTEM

The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by metavanadate-containing anion exchange resin (PV)-thiourea (TU) redox system at 20—40℃. has been investigated. The overall rate of polymerization (R_p) is given byR_p=1.92×10~4e~(-6.860/RT) [AN]~(1.2) [PV]~(0.44) [TU]~(1.0)[HNO_3]~(1.0)The kinetic parameters differed from those of V~(5+)-TU system indicated that the generation of the primary radicals is mainly a difffusion-controlled reaction. The effect of macromolecular field arisen from the polymer matrix exerts a great influence on the polymerization process.     

Kinetic study of the radical polymerization behavior of N‐(1‐phenylethylaminocarbonyl)methacrylamide

Polymerization of N‐(1‐phenylethylaminocarbonyl)methacrylamide (PEACMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was kinetically studied in dimethyl sulfoxide (DMSO). The overall activation energy of the polymerization was estimated to be 84 kJ/mol. The initial polymerization rate (R_p) is given by R_p = k[MAIB]^0.6[PEACMA]^0.9 at 60 °C, being similar to that of the conventional radical polymerization. The polymerization system involved electron spin resonance (ESR) spectroscopically observable propagating poly(PEACMA) radical under the actual polymerization conditions. ESR‐determined rate constants of propagation and termination were 140 L/mol s and 3.4 × 10⁴ L/mol s at 60 °C, respectively. The addition of LiCl accelerated the polymerization in N,N‐dimethylformamide but did not in DMSO. The copolymerization of PEACMA(M₁) and styrene(M₂) with MAIB in DMSO at 60 °C gave the following copolymerization parameters; r₁ = 0.20, r₂ = 0.51, Q₁ = 0.59, and e₁ = +0.70. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2013–2020, 2005     

Radical polymerization behavior of ethyl ortho-formylphenyl fumarate involving intramolecular hydrogen abstraction

The radical polymerization behavior of ethyl ortho-formyl-phenyl fumarate (EFPF) using dimethyl 2,2′-azobisisobutyrate (MAIB) as initiator was studied in benzene kinetically and ESR spectroscopically. The polymerization rate (R_p) at 60°C was given by R_p = k[MAIB]^0.76[EFPF]^0.56. The number-average molecular weight of poly(EFPF) was in the range of 1600–2900. EFPF was also easily photopolymerized at room temperature without any photosensitizer probably because of the photosensitivity of the formyl group of monomer. Analysis of ¹H? and ¹³C-NMR spectra of the resulting polymer revealed that the radical polymerization of EFPF proceeds in a complicated manner involving vinyl addition and intramolecular hydrogen-abstraction. The polymerization system was found to involve ESR-observable poly(EFPF) radicals under the actual polymerization conditions. ESR-determined rate constant (2.4–4.0 L/mol s) of propagation at 60°C increased with decreasing monomer concentration, which is mainly responsible for the observed low de-pendency of R_p on the EFPF concentration. Copolymerizations of EFPF with some vinyl monomers were also examined. © 1995 John Wiley & Sons, Inc.     

Vinyl polymerization with a binary system of p‐chlorobenzenediazonium salt and sodium tetraphenylborate

A combined system of sodium tetraphenylborate (STPB) and p‐chlorobenzenediazonium tetrafluoroborate (CDF) serves as an effective initiator at low temperatures for acrylate monomers such as methyl methacrylate (MMA), ethyl acrylate, and di‐2‐ethylhexyl itaconate. The polymerization of MMA with the STPB/CDF system has been kinetically investigated in acetone. The polymerization shows a low overall activation energy of 60.3 kJ/mol. The polymerization rate (R_p) at 40 °C is given by R_p = k[STPB/CDF]^0.5[MMA]^1.6, when the molar ratio of STPB to CDF is kept constant at unity, suggesting that STPB and CDF form a complex with a large stability constant and play an important role in initiation and that MMA participates in the initiation process. From the results of a spin trapping study, p‐chlorophenyl and phenyl radicals are presumed to be generated in the polymerization system. A plausible initiation mechanism is proposed on the basis of kinetic and electron spin resonance results. A large solvent effect on the polymerization can be observed. The largest R_p value in dimethyl sulfoxide is 11 times the smallest value in N,N‐dimethylformamide. The copolymerization of MMA and styrene with the STPB/CDF system gives results somewhat different from those of conventional radical copolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4206–4213, 2001     

Kinetic aspects of styrene minisuspension polymerization using a mixture PVA-SDS as stabilizer: Effect of the time of addition of SDS

The styrene minisuspension polymerization at 70 °C using AIBN as initiator and Polyvinil alcohol (PVA) and mixture PVA-sodium dodecil sulfate (SDS) as stabilizers was studied focusing on the kinetic behavior of the process after the SDS was added (PVA is present from the beginning and SDS is added at a given time t_SDS). It was confirmed that the addition of SDS to the system initially stabilized with PVA highly enhances the colloidal stability of the polymer particles because of the association formed between SDS and PVA molecules. It was observed that when SDS is added the rate of polymerization, the average molecular weight and final latex viscosity increase. The earlier the addition of SDS the more marked these increments. This behavior is explained in terms of the colloidal stability of the particles formed via emulsion polymerization and its effect on kinetic aspects such as the evolution of molecular weight and particle size distributions during the minisuspension polymerization.     

Permanganate-Pyruvic Acid Initiated Polymerization of Methacrylamide

A combined system of potassium permanganate and pyruvic acid was found to initiate radical polymerization of vinyl monomers, especially acrylamides. From kinetic investigations of the polymerization of methacrylamide, it was found that this initiator induced a radical polymerization which proceeded with an overall activation energy of 15.7 kcal/mol. The rate is given by

R_p=K[methacrylamide] ¹ [pyruvic acid]° [KMnO₄]¹ in aqueous and water-DMF mediums. In the presence of DMF the initial rate was found to decrease but the kinetic equation remained the same. The investigations were done at 35 ± 0.2°C in nitrogen.

Besides the clinical importance of pyruvic acid found in blood, urine, muscles, etc., it is a good initiator in conjunction with KMnO₄ for vinyl polymerization. It is therefore interesting to study the polymerization of methacrylamide using the KMnO₄-pyruvic acid redox couple in aqueous systems in order to find whether this system follows the same kinetic features of vinyl polymerization by a radical mechanism.     

Kinetic study of the living cationic polymerization of isobutylene using t-Bu-m-DCC/TICL4/2,4-dimethylpyridine initiating system

Kinetics of the living cationic polymerization of isobutylene, initiated by the system t-bu-m-DCC/TiCl₄/2,4-dimethylpyridine (2,4-DMP), were studied as a function of concentration of the various components of the initiation system, solvent polarity, and presence of the protic acid scavenger, 2,6-di-tert-butylpyridine (DTBP). Under a variety of conditions, the effective number of growing chains in a given polymerization remained constant and Mn increased linearly with monomer conversion. The system was found to yield an essentially homogeneous reaction mixture in hexanes/methyl chloride cosolvents, with only a small amount of precipitate, probably 2,4-dimethylpyridinium salts resulting from proton scavenging by the tertiary amine. It was found that increasing [TiCl₄] strongly increased the rate while increasing [2,4-DMP] weakly decreased the rate. Evidence of a retardation of the polymerization rate by the soluble TiCl₄:2,4-DMP complex was observed. The addition of DTBP as a protic acid scavenger, with or without 2,4-DMP, very weakly decreased the rate of polymerization. Increasing the fraction of methyl chloride in the solvent mixture caused an increase in the rate of polymerization. All of the results were consistent with a propagation mechanism in which an equilibrium exists between dormant and ionized, active chain ends.     

Polymerization of acrolein and methyl vinyl ketone induced by amine–water and pyridine–phenol systems

It was reported that acrolein (AL) in tetrahydrofuran (THF) polymerizes at temperatures below 0°C in the presence of pyridine (Py) and water. To clarify this polymerization mechanism the polymerization of AL and methyl vinyl ketone (MVK) by an initiation system such as Py–water, triethylamine (Et₃N)–water, or Py–phenol(Ph) was carried out. The polymerization rate (R_p) of MVK in the Et₃N–water system was expressed by the same equation, R_p = k [Et₃N] [H₂O] [MVK]², used for AL in the Py–water system. Meanwhile, β-hydroxypropionaldehyde, β-phenoxypropionaldehyde, γ-ketobutanol, and β-phenoxy-1-methylpropionketone were obtained as the initial addition products. The polymer of AL obtained was composed of polymer units of vinyl and aldehyde polymerization, but the structure of MVK polymer obtained by the Py–water system was composed of only vinyl polymerization units. The polymerization of MVK by the Py–Ph system did not occur, however. These results were discussed in terms of the initiation and propagation mechanisms.     

Radiation-induced polymerization of glass-forming systems. II. Effect of temperature on the polymerization rate at higher conversion

The effect of temperature and conversion on the polymerization rate at higher conversion was investigated with regard to the γ-ray-induced polymerization of hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the supercooled phase. The polymerization rate changed from acceleration to depression at various conversions, depending on the polymerization temperature. It was found that T_v at which the viscosity of the system became ca. 10³ cpoise influenced the shape of the polymerization time–conversion curve. The experimentally obtained conversion reflection point in the polymerization time–conversion curve agreed with the conversion where the polymerization temperature is the same as the calculated T_v of the system. When the polymerization temperature was lower than T_v of the monomer, no acceleration of the polymerization occurred. When the polymerization temperature was higher than T_v of the polymer, no depression of the polymerization rate was observed. The effect of temperature on the saturated conversion (final conversion) was also examined in terms of T_g of the polymerization system. The experimentally obtained saturated conversion agreed with the conversion where the polymerization temperature is the same as the calculated T_g of the system.     

Cationic polymerization of isobutyl vinyl ether initiated with the system aluminium trichloride/ethyl acetate,in toluene solution

The cationic polymerization of isobutyl vinyl ether initiated with the title system apparently has some features of a living polymerization (linear increase of number average molecular weight M̄_n with conversion). However, evidence is given for the occurrence of a transfer reaction resulting in the increase of the number of macromolecules, and this even for relatively low molecular weights.     

Absorption and fluorescence spectra of 9-anthrol and its chemical species in solution

The absorption, fluorescence, and fluorescence-excitation spectra of 9-anthrol (and/or anthrone) have been observed in various solvents, one of which includes a silicon-aluminium ester (diisobutoxyaluminium triethyl silane[(OBu)₂−Al−O−Si−(OEt)₃ SAE]). The fluorescence spectra of 9-anthrol shows peak wavelengths at 442 nm in benzene, 454 nm in methanol, 539 nm in triethylamine, and 550 nm in basic solution, which can be assigned to a neutral, a hydrogen-bonded neutral, an ion pair, and an anionic species of 9-anthrol, respectively. In ethanol solution including SAE, on the other hand, a new fluorescence peak appears at 473 nm. This new band originates from a complex formed between 9-anthrol and SAE. The excited-state ion pair is formed through the hydrogen-bonded form in water and the complex form in triethylamine. CNDO/S calculations support the experimental results.     

Aqueous Polymerization of Methyl Methacrylate

Aqueous polymerization of methyl methacrylate (MMA), initiated by the potassium bromate-thioglycollic acid (TGA) redox system, has been studied at 30 ± 0.2° C under positive pressure of nitrogen. The rate is given by K[MMA] [TGA] ⁰[KBrO₃]^x where × = 1 for lower KBrO₃ concentrations and 0.5 for higher KBrO₃ concentrations. The reaction has been studied over the 20–45°C range. The activation energy was found to be 65.72 kJ/mol (15.71 kcal/mol) in the investigated range of temperature. Inorganic electrolytes except MnSO₄·4H₂O and Na₂C₂O₄ depress both the rate of polymerization and the maximum conversion. All the alcohols (viz., MeOH, EtOH, iso-PrOH, tert-BuOH) and acetone depress the rate of polymerization as well as the maximum conversion.     

Electrochemical and chemical polymerization of acrylamide

The electrochemical and chemical polymerization of acrylamide (AA) has been studied. The electrolysis of the monomer in N,N-dimethylformamide (DMF) containing (C₄H₉)₄NClO₄ as the supporting electrolyte leads to polymer formation in both anode and cathode compartments. The cathodic polymer dissolves in the reaction mixture and the anodic polymer precipitates during the course of polymerization. A plausible mechanism for the anodic and cathodic initiation reaction has been given. The chemical polymerization of acrylamide that has been initiated by HClO₄ is analogous to its anodic polymerization. The polymer yield increases with an increase in concentration of the monomer and HClO₄. Raising the reaction temperature also enhances the polymerization rate. The overall apparent activation energy of the polymerization was determined to be ca. 19 kcal/mole. The copolymerization of acrylamide was carried out with methyl methacrylate (MMA) in a solution of HClO₄ in DMF. The reactivity ratios are r₁ (AA) = 0.25 and r₂ = 2.50. The polymerization with HClO₄ appears to be by a free radical mechanism. When the polymerization of acrylamide is carried out with HClO₄ in H₂O, a crosslinked water-insoluble gel formation takes place.