Cinetique de polymerisation du styrene en presence de peroxyde de benzoyle p,p′ bis-bromomethyle synthese de polymeres peroxydes

The free radical polymerization of styrene has been studied by using p,p′-bisbromomethyl benzoyl peroxide as initiator containing a chain transfer group. The rate constant of decomposition (k_d) of this peroxide has been determined at various temperatures, as well as the efficiency factor f and the transfer constant to initiator C₁. At 60°, f = 0·70 ± 0·05 and C₁ = 0·5. Polystyrene containing peroxide groups has been prepared by using this initiator. The highest yield in polymeric peroxide has been obtained for polymerization in emulsion at 40°.     

The interaction between polymerization initiators and inhibitors in solution—IV: The reaction of benzoyl peroxide with hydroquinone in solution

The reaction between benzoyl peroxide and hydroquinone in a wide variety of solvents has been investigated by isolation and identification of the products. Benzoic acid, p-benzoquinone and benzoyloxy derivatives of p-benzoquinone are obtained under all conditions. Their relative amounts are largely determined by the molar ratios of the reactants and the nature of the solvent. In strongly polar solvents of high solvation power, p-benzoquinone is formed in preference to its derivatives. Nevertheless, the yield of 2,5-dibenzoyloxy p-benzoquinone reaches a maximum in acrylonitrile. Only in this solvent, at equal molar ratios of reactants, is full substitution in the hydroquinone nucleus achieved with the formation of tetrabenzoyloxy hydroquinone. These facts, together with the partial polymerization of acrylonitrile at room temperature at slightly higher peroxide/hydroquinone ratios and the complete suppression of the polymerization when perchloric acid is added, could be explained by a heterolytic mechanism involving the formation and controlled separation of ion pairs derived from the reactants.     

Application of Endo-β-1,4,d-mannanase and Cellulase for the Release of Mannooligosaccharides from Steam-Pretreated Spent Coffee Ground

Spent coffee ground (SCG), a present waste stream from instant coffee production, represents a potential feedstock for mannooligosaccharides (MOS) production. MOS can be used in nutraceutical products for humans/animals or added to instant coffee, increasing process yield and improving product health properties. The SCG was evaluated for MOS production by steam pretreatment and enzymatic hydrolysis with a recombinant mannanase and a commercial cellulase cocktail (Acremonium, Bioshigen Co. Ltd, Japan). The mannanase was produced using a recombinant strain of Yarrowia lipolytica, used to produce and secrete endo-1,4-β,d-mannanase from Aspergillus aculeatus in bioreactor cultures. Endo-1,4-β,d-mannanase was produced with an activity of 183.5 U/mL and 0.23 mg protein/mL. The enzyme had an optimum temperature of 80 °C, and the activity in the supernatant was improved by 150 % by supplementation with 0.2 % sodium benzoate and 35 % sorbitol as a preservative and stabiliser, respectively. The steam pretreatment of SCG improved the enzymatic digestibility of SCG, thus reducing the required enzyme dosage for MOS release. Combined enzymatic hydrolysis of untreated or steam-pretreated (150, 190 and 200 °C for 10 min) SCG with mannanase and cellulase cocktail resulted in 36–57 % (based on mannan content) of MOS production with a degree of polymerization of up to 6. The untreated material required at least 1 % of both mannanase and cellulase loading. The optimum mannanase and cellulase loadings for pretreated SCG hydrolysis were between 0.3 and 1 and 0.4 and 0.8 %, respectively. Statistical analysis suggested additive effect between cellulase cocktail and mannanase on MOS release, with no indication of synergism observed.     

Suspension polymerization of vinyl chloride initiated by in situ generated diisobutyryl peroxide

It was found that diacyl peroxides can be formed in situ in a polymerization medium by the reaction of an acid anhydride with hydrogen peroxide. For the specific application to aqueous vinyl chloride polymerization, an initiator system based on the base-catalyzed reaction of isobutyric anhydride with hydrogen peroxide to produce diisobutyryl peroxide gave very good results. In contrast, the acid chloride was completely ineffective as a peroxide precursor in this reaction. Studies pointing to diisobutyryl peroxide as the initiating species; investigations of reactant stoichiometry; and comparison of the in situ system with preformed diisobutyryl peroxide were conducted. It was shown that this system makes possible the polymerization of vinyl chloride at 30°C at rates comparable to those obtained with dialkyl peroxydicarbonates at 50°C, thus demonstrating the ability of this system to initiate vinyl chloride polymerization at low temperature. The rates of vinyl chloride polymerization with the use of different concentrations of in situ diisobutyryl peroxide at 30, 40, and 50°C were determined. Similarly, polymerization rates with the use of combinations of in situ diisobutyryl peroxide and n-propyl peroxydicarbonate were determined. The data obtained demonstrate rapid initiation of the polymerization reaction and a reduction in polymerization time made possible by this dual initiator system. These results were verified in pilot-plant and commercial-scale PVC polymerizations.     

Polar-Group Activated Isospecific Coordination Polymerization of ortho-Methoxystyrene: Effects of Central Metals and Ligands

Stereoselective polymerization of polar vinyl monomers has been a long-standing challenge because the employed transition-metal catalysts are easily poisoned by polar groups of monomers. In this contribution, a series of β-diketiminato rare-earth metal complexes 1 – 5 (L^1–5Ln(CH₂SiMe₃)₂(THF)_n, Ln=Gd–Lu, Y, and Sc) were successfully synthesized. In combination with AliBu₃ and [Ph₃C][B(C₆F₅)₄], complexes 1 c (Tb)– 1 g (Tm) exhibited high activities and excellent isoselectivities for the polymerization of ortho-methoxystyrene (oMOS), in which, the polar methoxy group of oMOS did not poison but activated the polymerization through σ–π chelation to the active species together with the vinyl group. Moreover, the large Gd-attached precursor 1 b showed a higher activity, albeit with a slightly decreased isoselectivity. The small Sc-attached precursor 1 i was completely inert. Meanwhile, the spatial steric arrangement and the coordination mode of the β-diketiminato ligand could clearly affect and even block oMOS polymerization. This work sheds new light on the coordination polymerization of polar monomers.     

Rate constants of substantial initiation in free-radical polymerization: A new method for determination of conversion dependences

A new method for determination of the conversion dependence of substantial initiation rate constants k _i = f(C) in free-radical polymerization processes has been developed. On the basis of the known data on k _i1 = f(C) dependences for initiator I₁ and the kinetic analysis of a single trivial and simple experiment, this method allows one to calculate k _i2 = f(C) function for any other initiator I₂ under the same conditions (monomer, temperature). The reference experiment includes measurements of polymerization rates in the presence of initiator I₁ in a wide conversion range from 0 to 100% and in the presence of I₂, on the condition that the rates of initiation are equal w _i1 = w _i2, thus ensuring equal initial rates of polymerization. The above-described approach has been approved for the polymerization of styrene, methyl methacrylate, and vinyl acetate initiated with AIBN and benzoyl peroxide.     

Stable free radical polymerization of n-butyl acrylate in the presence of high-temperature initiators

Living radical polymerizations of acrylate are known to be difficult to achieve using TEMPO as a mediator. The stable free radical polymerization (SFRP) of acrylate tends to stop at low monomer conversion due to the accumulation of TEMPO in the medium as a result of unavoidable bimolecular termination. Rather than solving this problem by destroying the excess nitroxide using ascorbic acid or glyceraldehyde associated with pyridine as reported recently, high temperature initiators were used to slowly and continuously generate new radicals throughout the polymerization to consume the excess TEMPO molecules. Polymerizations of n-butyl acrylate initiated by the alkoxyamine unimer (1-benzoyloxy)-2-phenyl-2-(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)ethane (BST) were performed between 130 °C and 134 °C in the presence of a series of high temperature peroxide and azo initiators. The best results in this study were obtained by the continuous addition of small amounts of di-tert-amyl peroxide throughout the polymerization. Under these conditions, the acrylate polymerizations fulfilled the criteria of a controlled polymerization process although the molecular weight distributions were slightly broad (M_w/M_n ∼ 1.5).     

A device for sample agitation in an accelerating rate calorimeter

A stirring bar type agitation system has been designed and characterized for the accelerating rate calorimeter (ARC). The device allows stirring of the contents of a standard ARC sample container at stirring rates of up to 500 rev. min^?1, depending on sample viscosity. Experiments on a well-characterized thermal decomposition reaction, such as that of di-t-butyl peroxide, indicate that the device does not degrade the measurement of the energy of reaction, ΔE_v, the Arrhenius activation energy, E_a, or the pre-exponential factor, A.The utility of this stirring apparatus is demonstrated by examining the runaway data of a suspension polymerization. The results indicate that a polymerization “kill” agent can be successfully used for that particular reaction.     

Radical/Cation Transformation Polymerization and Its Application to the Preparation of Block Copolymers

Abstract

ESR study on the primary radicals obtained by decomposition of azo-compounds showed that primary radicals with electron donating substituents were transformed to the corresponding cations in the presence of electron acceptors such as ph₂I⁺PF^? ₆. Accordingly, propagating radicals are transformed to the corresponding cations in the polymerization of p-methoxy-styrene (MOS), n-butyl vinyl ether (BVE), and N-vinylcarbazole (VCZ) with azoinitiators such as AIBN in the presence of electron acceptors such as Ph₂I⁺PF^? ₆. In the case of BVE, the polymer formation was caused by cationic species produced by the transformation of the initiating radical. The polymerizations of MOS and VCZ were ascribed to the transformation of the growing radical to the corresponding cation during the propagation step which was classified as the radical/cation transformation polymerization. Block copolymers of MOS/cyclohexene oxide (CHO) and VCZ/CHO were effectively prepared by the radical/cation transformation polymerization of the appropriate monomers in the presence of AIBN, electron acceptor and CHO. The formation of block copolymers was characterized by turbidimetry, thin-layer chromatography, and solubility tests.     

Synthesis of well-defined, polymer-grafted silica nanoparticles via reverse ATRP

The surface grafting onto ultrafine silica via reverse ATRP of methyl methacrylate initiated by peroxide groups introduced onto the surface and conventional ATRP of Styrene initiated by the hybrid nanoparticles were investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polymer layer. The polymerization was closely controlled in solution at quite low temperature such as 70 °C. In both cases, linear kinetic plots, linear plots of molecular weight (M_n) versus conversion, in hydrodynamic diameter with increasing conversion, and narrow molecular weight distributions (M_w/M_n) for the grafted polymer samples were observed. Hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved polymer using GPC. Ultrathin films of hybrid nanoparticles were examined using TEM and AFM.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Effect of thiourea on the radical polymerization of vinyl monomers. Part III. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with various organic peroxides as initiator

The effect of diphenyl thiourea (DPTU) on the radical polymerization of methyl methacrylate (MMA) has been studied in benzene solution at 50°C. with the use of cumene hydroperoxide (CHP), p-menthane hydroperoxide (PMHP), tert-butyl perbenzoate (tBPBz), di-tert-butyl peroxide (DBP), and dicumyl peroxide (DCP) as initiators. In the CHP-initiated polymerization, the rate of polymerization increased appreciably on addition of DPTU with a linear dependence on the square root of DPTU concentration up to a maximum which was observed when the ratio of the concentration of CHP to DPTU was 2.5. Then the rate decreased gradually with increasing DPTU concentration in the range greater than the above ratio. It was found from kinetic studied that the overall polymerization rate R_p was expressed by the equation: R_p = K[peroxide]^1/2 [DPTU]^1/2[MMA], where K is the rate constant, α = 1.2 for CHP and α = 1.0 for tBPBz. It was thought that the acceleration effect observed was due to a redox reaction caused by the interaction of a peroxide–monomer and/or a peroxide–solvent complex with DPTU, and the decrease in the polymerization rate which was observed over a certain concentration of DPTU was due to the action of the oxidized product of DPTU as a transfer agent. The effect of substituents was studied by using para and meta-substituted DPTU. It was found that the polymerization rate increased as electron-donating substituents are added to the benzene ring of DPTU with considerable dependence on Hammett's equation (p = ?0.36). The acceleration effect is also observed for PMPH-and tBPBz-initiated polymerizations, whereas the DCP- and DBP-initiated systems show no effects on the polymerization rate.     

Docosyl acrylate modified polyacrylic acid: synthesis and crystallinity

Copolymers of n-docosyl acrylate and acrylic acid were synthesized in tetrahydrofuran by conventional free radical polymerization using benzoyl peroxide as initiator. The increase in crystallinity of the copolymers with increasing C₂₂ acrylate mole fraction was studied. It was found that even with very low mole fraction of C₂₂ acrylate (0.14) in the polymer chain the copolymers shows significant crystallinity (crystallinity fraction 0.23 against 0.52 for homopolymer of C₂₂ acrylate).     

Irradiation effects of 6 MeV electron on electrical properties of Al/Al2O3/n-Si MOS capacitors

The influence of 6 MeV electron irradiation on the electrical properties of Al/Al₂O₃/n-Si metal–oxide–semiconductor (MOS) capacitors has been investigated. Using rf magnetron sputtering deposition technique, Al/Al₂O₃/n-Si MOS capacitors were fabricated and such twelve capacitors were divided into four groups. The first group of MOS capacitors was not irradiated with 6 MeV electrons and treated as virgin. The second group, third group and fourth group of MOS capacitors were irradiated with 6 MeV electrons at 10 kGy, 20 kGy, and 30 kGy doses, respectively, keeping the dose rate ～1 kGy/min. The variations in crystallinity of the virgin and irradiated MOS capacitors have been compared from GIXRD (Grazing Incidence X-ray Diffraction) spectra. Thickness and in-depth elemental distributions of individual layers were performed using Secondary Ion Mass Spectrometry (SIMS). The device parameters like flat band voltage (V_FB) and interface trap density (D_it) of virgin and irradiated MOS capacitors have been calculated from C vs V and G/ω vs V curve, respectively. The electrical properties of the capacitors were investigated from the tan δ vs V graph. The device parameters were estimated using C–V and G/ω–V measurements. Poole–Frenkel coefficient (β_PF) of the MOS capacitors was determined from leakage current (I)–voltage (V) measurement. The leakage current mechanism was proposed from the β_PF value.     

Radical/Cation Transformation Polymerization and Its Application to the Preparation of Block Copolymers

Propagating radicals could be transformed into corresponding cations in the radical polymerization process of vinyl monomers in the presence of an electron acceptor. The electron transfer reaction from the propagating radicals to the acceptor was confirmed by an electron spin resonance study and by the model compound reaction. The radical/cation transformation polymerization was effectively applied to the preparation of a new type of block copolymer compound of radically polymerized segments and cationically polymerized segments by the one shot method. Thus, a block copolymer of p-methoxystyrene (MOS) and cyclohexene oxide (CHO) was prepared by the radical polymerization of MOS in the presence of Ph₂I⁺PF⁻₆ and CHO. The formation of the block copolymer was confirmed by extraction separation, ¹H-NMR (nuclear magnetic resonance), thin layer chromatography and turbidimetric titration. © 1997 John Wiley & Sons, Ltd.     

Introduction of peroxide groups onto carbon black surface by radical trapping and radical graft polymerization of vinyl monomers initiated by the surface peroxide groups

The introduction of peroxide groups onto carbon black surface was achieved through the trapping of the peroxide radicals formed by the decomposition of polymeric peroxide, such as poly(tetraethylene glycol peroxyadipate) (ATPPO), and bis-peroxide, such as 1,1′-bis (t-butyldioxy)cyclohexane (Perhexa-C), by the surface: the amount of peroxide groups introduced onto carbon black surface by the treatment with ATPPO and Perhexa-C were determined to be 0.07 mmol/g and 0.12 mmol/g, respectively. The polymerization of vinyl monomers with positive e-value, such as methyl methacrylate and 2-hydroxyethy methacrylate, was successfully initiated by the peroxide groups introduced onto carbon black surface. During the polymerization, the corresponding polymers were effectively grafted onto the surface as a result of the propagation of polymer from the surface radicals formed by decomposition of the peroxide groups. The polymerization of vinyl monomers with negative e-value, such as styrene and vinyl acetate, however, was scarcely initiated by the peroxide groups on carbon black. This may be due to the fact that surface active radicals, which were formed by the hydrogen abstraction from carbon black by fragment radicals, inhibit the polymerization of vinyl monomers with negative e-value. © 1996 John Wiley & Sons, Inc.     

Graft polymerization of methyl methacrylate from silica initiated by peroxide groups introduced onto the surface

The surface grafting onto ultrafine silica by the radical polymerization of methyl methacrylate (MMA) initiated by peroxide groups introduced onto the surface was investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. The content of diisopropylbenzene peroxide and tert-butyl peroxide groups introduced onto the silica according to the above method was determined to be 0.11 and 0.08 mmol/g, respectively. It was found that the polymerization of MMA is initiated by silica having these peroxide groups. In the polymerization, polyMMA was grafted onto silica surface: the percentage of grafting reached about 70%. Therefore, it was concluded that the polymerization of MMA is initiated by surface radicals formed by the decomposition of peroxide groups on silica and polyMMA is grafted through the propagation from the surface. During the polymerization, ungrafted polyMMA was also formed because of the formation of initiator fragments by the decomposition of peroxide groups: the grafting efficiency of the graft polymerization was 30–40%. PolyMMA-grafted silica produced a stable colloidal dispersion in organic solvents for polyMMA. © 1992 John Wiley & Sons, Inc.     

A novel synthetic method for preparing poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene alloy in reactor containing aqueous medium

Considering the defect of solution polymerization of 2,6-dimethylphenol (DMP), the low molecular weight of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in water and difficulty in processing of PPO, a novel one-pot synthetic method for preparing PPO/PS alloy in reactor containing aqueous medium was proposed based on green chemistry. In the presence of styrene, DMP was polymerized to form PPO, and then styrene was in situ polymerized under the initiation of dibenzoyl peroxide (BPO) and dicumyl peroxide (DCP), finally thermodynamically compatible PPO/PS alloy was prepared. It was found that the introduction of styrene during the oxidative polymerization of DMP could increase the molecular weight of PPO. When styrene content was 50 wt%, for the synthesized PPO/PS alloy the yield and the weight-average molecular weight were determined to be 95% and 1.7 × 10⁵ for PPO, 93% and 2.0 × 10⁵ for PS, respectively.     

Radical/cation transformation polymerization and its application to the preparation of block copolymers

p-Methoxystyrene (MOS), butyl vinyl ether (BVE), and N-vinylcarbazole (VCZ) were polymerized in high yield by azoinitiators such as 2, 2'-azodiisobutyronitrile (AIBN) in the presence of electron acceptors such as Ph₂I⁺PF₆⁻. An electron paramagnetic resonance (ESR) study of the model radicals of the propagating radical showed the transformation of the radical to the corresponding cation in the presence of the electron acceptors. In the case of BVE, the polymer formation was caused by cationic species produced by the transformation of the initiating radical. The polymerizations of MOS and VCZ were ascribed to the transformation of the growing radical to the corresponding cation during the propagation step which was classified as the radical/cation transformation polymerization. Block copolymers of MOS/cyclohexene oxide (1, 2-epoxycyclohexane) (CHO) and VCZ/CHO were effectively prepared by the radical/cation transformation polymerization of the appropriate monomers in the presence of AIBN, electron acceptor and CHO. The formation of block copolymers was characterized by turbidimetry, thin-layer chromatography, and solubility tests.     

Methyl methacrylate polymerization initiated by triethylborane–peroxide mixtures

The polymerization of methyl methacrylate initiated by triethylborane or triethylborane–peroxide mixtures was studied. The rate of initiation by a mixture of triethylborane and tert-butyl peroxide was found to be first-order in peroxide. The order in triethylborane changes from one at low triethylborane/peroxide to nearly zero at high triethylborane/peroxide. The possibility of a mechanism involving a fast reaction followed by a slow reaction that would initiate the polymerization is discussed.