Spontaneous Thermal Polymerization Research Articles

Kinetic analysis of the spontaneous thermal polymerization of acrylic acid

Acrylic acid is a monomer that has been responsible for a number of severe explosions worldwide as a result of thermal runaway. The present work was intended to lead to an improved understanding of the kinetics of the thermal polymerization and Michael addition reaction (MAR) of acrylic acid. Sealed cell differential scanning calorimetry was carried out, and the kinetics of the thermal polymerization of acrylic acid were assessed on the basis of the model-free Friedman method. In addition, microcalorimetry using a Thermal Activity Monitor IV apparatus was conducted to determine the kinetic parameters for the MAR. The rate constant for the MAR was found to be k (s−1) = 3.45 × 105 × exp (− 9.48 × 103/T (K)), while the activation energy was 78.8 kJ mol−1. The progress of the MAR was fitted with an n-order reaction model, and the reaction order as well as the rate constant was determined to be linearly proportional to temperature. By employing a modified n-order reaction model in which the reaction order was a linear function of temperature, we obtained a reaction rate equation for the MAR that closely reproduced the experimental results over a wide temperature range.

Method of Moments Applied to Most-Likely High-Temperature Free-Radical Polymerization Reactions

Many widely-used polymers are made via free-radical polymerization. Mathematical models of polymerization reactors have many applications such as reactor design, operation, and intensification. The method of moments has been utilized extensively for many decades to derive rate equations needed to predict polymer bulk properties. In this article, for a comprehensive list consisting of more than 40 different reactions that are most likely to occur in high-temperature free-radical homopolymerization, moment rate equations are derived methodically. Three types of radicals—secondary radicals, tertiary radicals formed through backbiting reactions, and tertiary radicals produced by intermolecular chain transfer to polymer reactions—are accounted for. The former tertiary radicals generate short-chain branches, while the latter ones produce long-chain branches. In addition, two types of dead polymer chains, saturated and unsaturated, are considered. Using a step-by-step approach based on the method of moments, this article guides the reader to determine the contributions of each reaction to the production or consumption of each species as well as to the zeroth, first and second moments of chain-length distributions of live and dead polymer chains, in order to derive the overall rate equation for each species, and to derive the rate equations for the leading moments of different chain-length distributions. The closure problems that arise are addressed by assuming chain-length distribution models. As a case study, β-scission and backbiting rate coefficients of methyl acrylate are estimated using the model, and the model is then applied to batch spontaneous thermal polymerization to predict polymer average molecular weights and monomer conversion. These predictions are compared with experimental measurements.

Calcium-doped fluorescent carbon nanoparticles: Spontaneous thermal synthesis, pH-sensitive fluorescence off-on, and mechanism

Spontaneous thermal polymerization and carbonization assisted by calcium oxide was proposed for the first time to develop an incomparable synthetic route for the production of calcium-doped fluorescent carbon nanoparticles (FCNPs). This unique approach shares numerous virtues such as eco-friendly, moderate and controllable reaction, and uninvolved poisonous chemicals and intricate operations. Apart from several excellent photoluminescence properties of ordinary fluorescent nanomaterials, the FCNPs exhibited unexceptionable features in stark contrast to previous reports, especially possessing pH-sensitive fluorescence “off-on”, thermosensitivity, and superior optical performances under alkaline condition. Furthermore, the formation processes dramatically influencing the nucleation and growth of FCNPs were meticulously discussed according to the detailed material characterization. These investigations revealed the function of doping calcium and the fabrications of carbogenic cores coupled with oxygen-containing groups served as photoluminescence center and edge. It can be speculated that the synthesis of FCNPs will inaugurate new avenues for the design of multifunctional composites with other biomaterials and expand their applications in extreme alkaline conditions.

Unstable 1,1,2,2-Tetramethyl-1,2-disilacyclobutane and Its Polymerization. Vibrational Spectroscopy and Quantum-Chemistry Study

The structure of 1,1,2,2-tetramethyl-1,2-disilacyclobutane (1) has been investigated by experimental means, by Raman and IR spectra, and by quantum-chemical calculations at various levels of theory. All the data obtained show that the four-membered ring of 1 is puckered, the ring puckering mode being 80 cm–1 and the barrier to planarity 1.76 kcal/mol (617 cm–1). Temperature investigations of the Raman spectrum have shown that the liquid 1 solidifies into a plastic mesophase at ∼210 K and crystallizes below ∼110 K. Strain energies (SEs) for 1, the parent molecule 1,2-disilacyclobutane (2), and, for comparison, their 1,3-isomers (3 and 4) were estimated as enthalpies of corresponding homodesmic reactions taken with a reversed sign. These values (in kcal/mol) for 1 (8.6) and 2 (12.4) appeared lower than those for 3 (18.3) and 4 (19.6). To rationalize these results, a QTAIM topological analysis of electron density distribution was carried out for 1–4. Examination of the molecular graphs has demonstrated that the Si–Si bond paths (BPs) in 1 and 2 are significantly bent (“banana” bonds), thus decreasing the SE of these molecules. The corresponding Si–Si BP lengths are increased by Δ ≈ 0.03 Å in comparison to the corresponding endocyclic Si–Si interatomic distances, while the Si–C BPs in all four molecules are nearly straight lines (Δ ≈ 0.002 Å). Monitoring of the process of 1 polymerization on heating to room temperature has revealed that this process is not spontaneous, as was supposed previously, but is initiated by minor radical impurities. Indeed, the value of the ring-opening enthalpy for 1 was calculated as 70 kcal/mol, too high for spontaneous thermal polymerization to occur.

Experimental study of the spontaneous thermal homopolymerization of methyl andn‐butyl acrylate

AbstractThis article presents an experimental study of the spontaneous thermal homopolymerization of methyl acrylate (MA) andn‐butyl acrylate (nBA) in the absence of any known added initiators at 120 and 140°C in a batch reactor. The effects of the solvent type, oxygen level, and reaction temperature on the monomer conversion and polymer average molecular weights were investigated. Three solvents, dimethyl sulfoxide (DMSO; polar, aprotic), cyclohexanone (polar, aprotic), and xylene (nonpolar) were used. The spontaneous thermal polymerization of MA andnBA in DMSO resulted in a lower conversion and higher average molecular weights in comparison to polymerization in cyclohexanone and xylene under the same conditions. The highest final conversion of both monomers was obtained in cyclohexanone. The high polymerization rate in cyclohexanone was most likely due to an additional initiation mechanism where cyclohexanone complexed with the monomer to generate free radicals. Bubbling air through the mixture led to a higher monomer conversion during the early stage of the polymerization and a lower polymer average molecular weight in xylene and cyclohexanone; this indicated the existence of a distinct behavior between the air‐ and nitrogen‐purged systems. Matrix‐assisted laser desorption/ionization time‐of‐flight analysis of the polymer samples taken from nitrogen‐bubbled batches did not reveal fragments from initiating impurities. On the basis of the identified families of peaks, monomer self‐initiation is suggested as the principal mode of initiation in the spontaneous thermal polymerization of MA andnBA at temperatures above 100°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Self-Initiation Mechanism in Spontaneous Thermal Polymerization of Ethyl and n-Butyl Acrylate: A Theoretical Study

In this study, the mechanism of self-initiation in spontaneous thermal polymerization of ethyl and n-butyl acrylate is explored using first-principles calculations. Density functional theory (with B3LYP functional and 6-31G* basis set) was used to study [4 + 2] and [2 + 2] cycloaddition reactions on the singlet and triplet potential energy surfaces. Diels-Alder (DA) dimers of ethyl acrylate [6-ethoxy-2-ethoxycarbonyl-3,4-dihydro-2H-pyran (EDP)] and of n-butyl acrylate [6-butoxy-2-butoxycarbonyl-3,4-dihydro-2H-pyran (BDP)] were found to form on the singlet surface via the concerted pathway proposed by Mayo. The formation of diethyl cyclobutane-1,2-dicarboxylate (DECD) and dibutyl cyclobutane-1,2-dicarboxylate (DBCD) via a nonconcerted pathway was identified on the singlet surface of ethyl and n-butyl acrylate, respectively. The presence of a diradical transition state for the formation of the DECD and DBCD was predicted. Triplet potential energy surfaces for the formation of diradical dimer of ethyl and n-butyl acrylate were computed, and the presence of a triplet diradical intermediate was identified for each of the monomers. A low energy monoradical generation mechanism was identified to be involving hydrogen abstraction by a third acrylate monomer from the triplet diradical species. The molecular structure of the computed monoradical species was found to correlate with chain initiating species of the dominant series of peaks in previously reported electrospray ionization-Fourier transform mass spectra of spontaneously polymerized samples of ethyl and n-butyl acrylate. In view of these observations, it is concluded that this self-initiation mechanism is most likely the initiating mechanism in spontaneous thermal polymerization of alkyl acrylates.

Radical Polymerization of Methyl Methacrylate by Captodative Substituted Morpholino Succinonitrile

Radical polymerization of methyl methacrylate (MMA) by captodatively substituted morpholino succinonitrile was studied kinetically at 90 and 130°C by comparison with that of styrene. The polymerizations of MMA and styrene at 90°C proceeded at moderate rates to give polymers which show unimodal size exclusion chromatography (SEC) curves. Both polymerizations at 130°C were significantly fast to give polymers with bimodal SEC curve. A higher molecular weight fraction of the obtained polymer may mostly formed by a spontaneous thermal polymerization in styrene polymerization, but in MMA polymerization produced mainly by dissociation of the domant species. The rate constant of the activation of captodative-capped poly(MMA) domant was smaller than that reported for nitroxide-mediated styrene polymerization.

New dicyano-containing cyclopolymers having high stereoregularity derived from dimethacrylmalononitrile

New monomers for cyclopolymerization were synthesized through phase transfer catalyzed reaction between methyl or ethyl α-(chloromethyl)acrylate and malononitrile. The dicyano-containing diacrylates obtained undergo AIBN-initiated or spontaneous thermal polymerization in bulk to give soluble cyclopolymers with virtually complete cyclization (cyclization efficiency f c > 0.99) and η sp /c of 0.15-0.50 dL/g. 13 C NMR data confirmed cyclic structures for the repeat units and suggests exclusive six-membered ring formation with cis-dominated configurations (70-95%) of the recurring cyclohexane ring

Radical and spontaneous thermal polymerizations of some captodative‐substituted acrylates

AbstractThe polymerization of some captodative‐substituted acrylates was examined in the presence and absence of 2,2′‐azoisobutyronitrile (AIBN) at 60 °C. Methyl acrylates, substituted by acetoxy, methoxy and ethylsulfenyl groups in α‐position, and tert‐butyl α‐methoxyacrylate homopolymerized with and without this initiator. The rate of AIBN‐initiated homopolymerization of methyl α‐acetoxyacrylate was as high as that of methyl methacrylate in spite of the captodative‐substituted monomer, and these acrylates also gave polymers spontaneously in remarkably high yield even under conditions under which styrene and methyl methacrylate are not polymerized. Copolymers of these monomers with styrene also were obtained in the presence and in the absence of AIBN. The mechanism of the initiation of the spontaneous thermal polymerization is discussed on the basis of ESR spectra, reaction intermediates and radical inhibition experiments.

The spontaneous thermal polymerization of methyl methacrylate: 5. Experimental study and computer simulation of the high conversion reaction at 130°C

The thermal polymerization and oligomerization of methyl methacrylate was studied at 130°C up to almost total monomer conversion. Using the rate constants for chain initiation and the diverse oligomerization steps given in our previous papers as well as literature values for chain propagation and termination, the kinetics of the complex reaction system was simulated with the computer program REMECH of DeTar. The good agreement between experimental and calculated concentration and molecular weight data indicates that the assumed reaction mechanism and the associated set of reaction constants are essentially correct.

Die thermische polymerisation von methylmethacrylat, 2. Bildung des ungesättigten dimeren

AbstractThe spontaneous thermal polymerization of methyl methacrylate (MMA) is accompanied by the production of serveral oligomers among which a linear unsaturated dimer H‐1 (dimethyl 1‐hexene‐2,5‐dicarboxylate) is predominant. The reaction kinetics of this dimer formation was investigated in bulk and in solution. The temperature dependence of the second order dimerization constant was determined as Reaction mechanisms for the thermal dimer formation of MMA are discussed.

Die thermische Polymerisation von Methylmethacrylat, 1. Polymerisation in Substanz

AbstractSpecial purification of the monomer and careful preparation of the reaction setup allowed a thorough study of the spontaneous thermal polymerization of methyl methacrylate over a wide range of temperatures (0–140°C). The rates of polymerization are notably lower than the few data previously reported in literature, and the degrees of polymerization slightly higher. The thermal initiation reaction is superimposed by radical production due to the natural ionising radiation (cosmic radiation etc.). This additional initiation becomes significant at temperatures below 60°C. New and more reliable monomer chain transfer constants are given.