Polymerization in magnetic field. XVI. Kinetic aspects regarding methyl methacrylate polymerization in high magnetic field

The effect of a high magnetic field of 7 T in the reaction of methyl methacrylate polymerization is emphasized. The intervening magnetokinetic modifications are correlated with the system of radical initiation with benzoyl peroxide, 2,2′‐azobis(2‐methylpropionitrile), 4,4′‐azobis(4‐cyanopentanoic acid), and 1,1′‐azobis(cyclohexane‐1‐carbonitrile). The characterization of the synthesized polymers is correlated with the reaction conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5678–5686, 2004     

Separation and structural analysis by 1H-NMR of the telomers of methyl methacrylate with thiophenol

The stereoselectivity of the addition step and the transfer step of the radical telomerization of methyl methacrylate with thiophenol has been studied by determining the structure and the amount of each isomer by ¹H-NMR. We found, in this case, that the addition step gave preferentially a diad r and that the transfer step gave preferentially a diad m. On the other hand, the tacticity observed for higher telomers is preferentially syndiotactic, similar to that of the poly(methyl methacrylate) prepared by radical initiation. The propagation process for radical telomerization obeys, as for the radical polymerization, Bernoulli's statistics.     

Factors affecting the TMPTA radical polymerization photoinitiated by phenyltrialkylborates paired with tri-cationic hemicyanine dye. Kinetic studies

This article introduces tri-cationic hemicyanine dye employed as a visible-light photoinitiator of acrylic monomers polymerization. This dye, in combination with borate anions, was found to be a very effective photoinitiating system. The kinetics of trimethylolpropane triacrylate polymerization was studied by a microcalorimetric method. The photoredox pair concentration, the co-initiator structure as well as the light intensity strongly affected the progress of the polymerization, leading, for example, to an increase in the polymerization rate and quantum yield of the process. The efficiency of these photoinitiators was discussed on the basis of the free energy change for electron transfer from a borate anion to an excited hemicyanine dye cation. The ?G _el values were estimated for photoredox pairs containing a series of phenyltrialkylborate anions and one styrylpyridinium dye cation. The relationship between the rate of polymerization and the free energy of activation for electron transfer reaction gives the dependence predicted by the classical theory of electron transfer. The photoinitiating abilities of the selected novel photoredox pairs (BPB61, BPB7, BPB8, and BPB9) are comparable with the photoinitiating efficiency of commercially available photoinitiators.     

Secondary and tertiary oxonium ions in the polymerization of 1,3-dioxolane initiated with HOSO2 CF3: 1H-NMR studies

In the polymerization of 1,3-dioxolane (DXL) initiated with trifluoromethanesulfonic acid (TFAc) the proton originated from acid [underlined in the scheme (1)] may form either the hydroxy end-group or the secondary oxonium ion: (1) where is a part of linear or cyclic macromolecule (or monomer). In ¹H-NMR spectra, due to the fast exchange, only one averaged signal of proton is observed, its chemical shift reflecting the relative concentration of both species. The chemical shift of proton, measured at different monomer and initiator concentrations changes, indicating that the proportion of macromolecules bearing OH end-groups increases with increasing [monomer]_o/[initiator]_o ratio. This observation is fully consistent with a mechanism, according to which secondary oxonium ions are formed by inter-or intramolecular reaction between growing species and OH end-groups of linear macromolecules.     

Studies on the polymerization of ethyl acrylate. I. Kinetic studies

Kinetic studies on the polymerization of ethyl acrylate have been carried out and the various rate constants and their corresponding activation energies determined.     

An in situ study of the t-butyllithium initiated polymerization of butadiene in d-heptane via small angle neutron scattering and 1H-NMR

We present a combined 1H-NMR and small angle neutron scattering in situ study of the anionic polymerization of butadiene using t-butyllithium as the initiator. Both initiation and propagation phases were explored. This combined approach allows the structural and kinetic characteristics to be accessed and cross compared. The use of the D22 instrument (ILL Grenoble) permits the attainment of Q approximately equal to 2 x 10(-3) A. This, in turn, led to the identification of coexisting large-scale and smaller aggregates during all stages of the polymerization. The smaller aggregates contain most of the reacted monomers. Their structure changes from high functionality wormlike chains at early stages of the reaction to starlike aggregates where the crossover occurs at a degree of polymerization of approximately equal to 40. The initiation event involved these small, high functionality (approximately equal to 120) aggregates that apparently consisted of cross-associated t-butyllithium with the newly formed allylic-lithium head groups. As the initiation event progressed the initiation rate increased while the functionality of these small aggregates decreased and their size increased. Propagation, in the absence of initiation, was found to have a rate constant that was molecular weight dependent. At approximately 11 kg/mol the measured polymerization rate was found to increase while no further structural changes were seen.     

Cationic polymerization of styrenes by activated covalent species. Direct 1H-NMR observation of complexes of 1-phenylethyl acetates with lewis acids

Complexes of boron trichloride, boron tribromide, and ethylaluminumdichloride with various acetates were directly observed by ¹H-NMR. Complexes of secondary and tertiary acetates which model macromolecular active species in polymerization of styrene and isobutene are stable at ?75°C, but decompose at temperatures above ?30°C to yield corresponding chlorides or bromides. The stability of complexes depends on the Lewis acid, the alkyl group in the ester, and the structure of acetate. Rates of the bimolecular exchange of complexes with excess acetate were calculated from dynamic NMR to be k_ex = 2 × 10¹ L mol^?1 s^?1 (?65°C) and k_ex = 5 × 10⁴ L mol^?1 s^?1 (?75°C) for 1-phenylethyl acetate with BCl₃ and EtAlCl₂, respectively.     

Gamma radiation-initiated polymerization of styrene at high pressure. I. Kinetic parameters with intermittent irradiation

By adapting the rotating sector technique to provide an intermittent source of cobalt-60 radiation the activation volumes for all reaction steps of the bulk polymerization of styrene have been shown to be independent of pressure up to 208 MPa. The activation volumes determined for polymerization, initiation, propagation and termination were, respectively, ΔV^≠_pol = ?20.5 ± 0.22, ΔV^≠_i = +2.0 ± 0.18, ΔV^≠_p = ?18.6 ± 0.44, and ΔV^≠_t = +5.8 ± 0.55 cm³ mol^?. The values for the effect of pressure on the degree of polymerization ΔDP and the radical lifetime Δτ were, respectively, ?22.6 ± 0.16 and ?3.9 ± 0.29. The average radical lifetime increased from 4.5 s at atmospheric pressure to 6.3 s at 208 MPa. Because ΔV^≠_t is less than ΔV^≠_t and both are positive, the molecular weight increased with pressure at a faster rate than the polymerization rate. Although fewer radical chains were initiated per second under pressure the macroradical concentration increased with pressure because of the longer average lifetime of the radicals.     

MC-determination in elastomers by 1H-NMR relaxation and 2H-NMR spectroscopy

We show how ¹H–NMR transversal relaxation and ²H–NMR spectroscopy can be used for the determination of the number average molecular mass M_C in typical elastomers at temperatures well above the glass transition temperature. M_C-results of the different NMR methods are compared among one another and with M_C-results of other common independent methods. Moreover, the NMR measurements provide a number of additional useful parameters: correlation times, portions of dangling chain ends and of sol molecules, molecular order.     

Block copolymerization. VII. Kinetic studies on the polymerization of pivalolactone with polystyrene dicarboxylates and polyacrylonitrile dicarboxylates

The rate of anionic polymerization of pivalolactone with polystyrene dicarboxylates decreased with conversion, suggesting deactivation of the propagating chain end by precipitation of the polymer during polymerization. The presence of unreacted initiator was explained by slow initiation for formation of a living polymer of pivalolactone. Various factors affecting block efficiency were discussed, and high efficiency was obtained for the preparation of block copolymers containing a long pivalolactone segment by using more nucleophilic polystyrene dicarboxylates. Block copolymer of acrylonitrile and pivalolactone was prepared from polyacrylonitrile dicarboxylates.     

Emulsion polymerization of vinyl acetate using a polymerizable surfactant. I. Kinetic studies

A polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (TREM LF-40; Henkel) and its nonpolymerizable counterpart were used in comparative studies of the emulsion polymerization of vinyl acetate. The conversion-time behavior differed for the two surfactants; the TREM LF-40 showed a decrease in the polymerization rate with increasing concentration while its hydrogenated derivative showed the opposite behavior, the rate increasing with increasing surfactant. Particle size analysis revealed a decreasing particle size with increasing surfactant concentration for both series of reactions. An explanation for the seemingly ambiguous results obtained for the polymerizable surfactant was sought by examining the reactivity of its vinyl group in copolymerization with vinyl acetate and its allylic group in a chain transfer reaction. The results suggest that both the copolymerization and chain transfer reactions can lead to the observed reduction in polymerization rate with increasing TREM LF-40 concentration. © 1992 John Wiley & Sons, Inc.     

Conformational studies of mercaptoacetaldehyde and mercaptoacetone by 1H-NMR,Raman and infrared spectroscopy

Molecular structures of mercaptoacetaldehyde and mercaptoacetone in the crystalline state and in solutions have been studied by ¹H-NMR, Raman and infrared spectroscopy. Both compounds exist as centrosymmetric dimers having six-membered 1,4-dithian ring skeletons in the crystalline state and in freshly-prepared dimethylsulfoxide and pyridine solutions. In equilibrium solutions, non-centrosymmetric dimers having 1,4-dithian ring skeletons and the monomer also exist. No evidence that suggests the existence of five-membered ring dimer in solutions has been obtained for both compounds. The most stable species in solution is the non-centrosymmetric dimer in the case of mercaptoacetaldehyde and the monomer in the case of mercaptoacetone.     

Characterization and electrochemical studies on poly(1-naphthylamine)-graphene oxide nanocomposites prepared by in situ chemical oxidative polymerization

Journal of Solid State Electrochemistry - Present work demonstrates the synthesis of novel poly(1-naphthylamine)-graphene oxide (PNA–GO) nanocomposites by the polymerization of NA in GO...     

丙烯酰胺在铝表面的电化学聚合涂层

铝阴极;丙烯酰胺在铝表面的电化学聚合涂层     

Kinetic studies of the polymerization of an epoxy resin modified with rhodamine B

Novel fluorescent materials were satisfactorily synthesized. With this aim, an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) was reacted with a laser dye, rhodamine B (RB), to achieve an epoxy-based prepolymer. Then, a diamine, m-xylylenediamine (MXDA), was used as hardener with the purpose of obtaining a crosslinked polymer. The curing conditions strongly influence the intended final properties and the optimization of the curing requires a reliable kinetic model. For that reason, this work presents the kinetic study of the polymerization of the epoxy resin by differential scanning calorimetry (DSC) in isothermal mode as well as by Fourier transform infrared spectroscopy (FTIR). DSC data were fitted using a Kamal autocatalytic equation. Conversion as a function of reaction time curves obtained by means of both techniques agreed well. In addition, the synthesized epoxy-based materials were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and their fluorescent properties were also analysed.     

Kinetic and ESR studies on the radical polymerization of Di-n-butyl itaconate in benzene

The polymerization of di-n-butyl itaconate (DBI) intiated with AIBN was kinetically investigated in benezene. The polymerization rate (R_p) was expressed by: R_p = k[AIBN]^0.5[DBI]^1.7. The polymerization showed a considerably low overall activation energy of 15.3 kcal/mol. The initiator efficiency of AIBN in this system decreased with increasing DBI concentration, ranging from 0.34 to 0.55°C, which is ascribable to viscosity effect due to the monomer. From an ESR study, the polymerization system was found to involve two kinds of persistent radicals, namely, primary propagating ( III ) and propagating ( I ) radicals. The relative concentration of III to I increased with decreasing monomer concentration. Azo-nitrile initiators such as AVN and ACN similarly produced two persistent radicals, while MAIB, DBPO, and PBO yielded only propagating radical I as persistent. The MAIB-initiated polymerization of DBI was also performed in benzene. Similar kinetic features were observed, that is, a higher dependence of R_p on the DBI concentration and a low overall activation energy (14.4 kcal/mol). The following rate equation was obtained at 50°C:R_p = k[MAIB]^0.5[DBI]^1.6. The initiator efficiency of MAIB decreased with increasing DBI concentration, ranging from 0.32 to 0.53 at 50°C. The concentration of propagating radical I was determined by ESR at 50 and 61°C, from which k_p and k_t were estimated. The k_p value increased with increasing monomer concentration, while the k_t one decreased with the DBI concentration. These values are much lower compared with those of MMA.     

Silica aerogel-filled PMMA by in situ reverse atom transfer radical polymerization: kinetics and thermal studies

Hydrophobically modified silica aerogel nanoparticles (H-SiANp) were used for in situ polymerization of methyl methacrylate by reverse atom transfer radical polymerization to synthesize well-defined PMMA nanocomposites. Inherent characteristics of the prepared H-SiANp were evaluated by nitrogen adsorption/desorption isotherms, SEM, and TEM. Conversion and molecular weight determinations were carried out using GC and SEC, respectively. Addition of 3 mass% of the H-SiANp leads to decrement of conversion from 92 to 74%. Molecular weight of poly (methyl methacrylate) chains also decreases from 19,737 to 15,662 g mol^?1 by addition of only 3 mass% H-SiANp; however, PDI values increase from 1.36 to 1.82. Linear increase of ln(M₀/M) with time for all the samples shows that polymerization proceeds in a living manner. In addition, suitable agreement between theoretical and experimental molecular weight in combination with low PDI values can appropriately demonstrate the living nature of the polymerization. TG results indicate that by increasing H-SiANp content, improvements in thermal stability of the nanocomposites were obtained. DSC results show a decrease in glass transition temperature from 87.4 to 80.9 °C by addition of 3 mass% H-SiANp.

     

Thermal polymerization of difurfurylideneacetone: X-ray structural and calorimetric studies

A calorimetric study has been made of the susceptibility of difurfurylideneacetone (DIFA) and its oxidized product to thermal polymerization. It has been established that the oxidation process takes place only on the surface of the crystals. An x-ray structural study of DIFA crystals has shown that solid-phase thermal polymerization takes place in the crystal matrix through one of the two ethylenic bonds of the molecule under conditions of topochemical control.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 606–610, March, 1991.     

Polymerization of o-quinodimethanes, 1. Radical polymerization of 1-methoxy-o-quinodimethane formed in situ by thermal isomerization of 1-methoxy-benzocyclobutene

The first radical polymerization of 1-methoxy-o-quinodimethane (2) generated by thermal ring-opening isomerization of 1-methoxybenzocyclobutene (1) is described. The polymerization of 1 in the presence of a radical initiator afforded an MeOH-insoluble polymer (3) in moderate yield at temperatures above 90°C. The structure of the obtained polymer is consistent with a ring-opening polymerization. The yield of the polymer increased with the amount of initiator. Radical copolymerization with methyl acrylate was carried out. Treatment of 3 with acid gave poly(o-phenylenevinylene), quantitatively.     

Polyaniline doped with different sulfonic acids by in situ doping polymerization

Doped polyaniline (PANI) was synthesized by an “in situ doping polymerization” method in the presence of different sulfonic acids, such as methanesulfonic acid (MSA), p‐methylbenzene sulfonic acid (MBSA), β‐naphthalenesulfonic acid (β‐NSA), α‐naphthalenesulfonic acid (α‐NSA), 1,5‐naphthalenedisulfonic acid (1,5‐NSA), and 2,4‐dinitronaphol‐7‐sulfonate acid (NONSA). Morphology, solubility in m‐cresol, and electrical properties of the doped PANI were measured with the variation of the molecular structure of the selected sulfonic acids. Granular morphology was obtained when the sulfonic acids without a naphthalene ring, such as MSA and MBSA, were used. Regular tubular morphology was obtained only when β‐NSA was used. The tubular morphology can be modified by changing the substitutes, the number, and location of sulfo‐group(SOH) on the naphthalene ring. These results indicated that naphthalene ring in the selected sulfonic acids plays an important role in forming the tubular morphology of the doped PANI by the “in situ doping polymerization” method. All resulting PANI salts were soluble in m‐cresol, with the solubility depending on the molecular structure of the selected dopants. Room‐temperature conductivity for the doped PANI ranges from 10⁻¹ to 10⁰S/cm. Temperature dependence of conductivity shows a semiconductor behavior, and it can be expressed by one dimenson Variable Range Hopping (VRH) model. 1 © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1277–1284, 1999