A gel point method for the estimation of overall apparent activation energies of polymerization

Gough, L. J.; Smith, I. Trevor

doi:10.1002/app.1960.070030914

Cited by 54 publications

(19 citation statements)

References 3 publications

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“…Whereas the order and the rate constant show considerable discrepancies, most activation energies determined by DSC methods are consistent with the values of 58-67 kJ/mole and 58-71 kJ/mole obtained from the gel point [36] and electrical resistance [37] measurements. On this basis it can be concluded that the network structure formed has very little effect upon the activation energy of the hardening of epoxy resins.…”

Section: Curin9 Reactionssupporting

confidence: 77%

Thermal analysis of thermosetting resins

Erä

Mattila

1976

Journal of Thermal Analysis

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Applications of thermoanalytical methods for the study of resinification, curing and thermal degradation of phenolic and epoxy resins are reviewed. The curing properties of PF resins and various epoxy systems~ determined by thermal methods~ are illustrated.Phenolic and epoxy resins are the most common thermosets utilized by the plastics-processing industry. In the cured state they are infusible, insoluble, covalently-cross-linked, thermally stable network polymer structures. The formation of this network structure is responsible for the desirable physical properties which are typical of thermosetting resins over a broad temperature range.Owing to their intractable nature, the thermosetting resins are difficult to study by chemical means. Numerous investigations have shown that thermoanalytical techniques offer valuable tools for the study of the formation, the curing characteristics and the thermal degradation of these resins.The purpose of this paper is to survey the thermoanalytical methods such as differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical methods, which have been successfully applied to the elucidation of the thermal characteristics of phenolic and epoxy resins. Phenol-formaldehyde resinsWhen phenol reacts with formaldehyde four major reactions occur: a) addition to give methylol phenols; b) condensation of a methylol phenol and a phenol to give a methylene bridge; c) condensation of two methylol groups to give an ether bridge; d) decomposition of ether bridges to methylene bridges and formaldehyde.The reaction is catalyzed by acids or by bases to give novolacs or resols respectively. The nature of the product is dependent on the type of catalyst and the molar ratio of the reactants. Addition and condensation are exothermic reactions, and therefore thermoanalytical methods are particularly suited for elucidation

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Section: Curin9 Reactionssupporting

confidence: 77%

Thermal analysis of thermosetting resins

Erä

Mattila

1976

Journal of Thermal Analysis

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“…15,26 The assumption is typically made that the curing kinetics involves only a single reaction with single activation energy. While this is often not the case, the single activation energy value so obtained can be considered to be representative of the multiple reactions in progress.…”

Section: Activation Energy Of Crosslinkingmentioning

confidence: 99%

Rheological study of crosslinking and gelation in bismaleimide/cyanate ester interpenetrating polymer network

Fan

Yue

2001

J of Applied Polymer Sci

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In searching for high performance polymer resins that have a combination of low dielectric constant and loss, high temperature resistance, ease of being processed, and other desirable properties, an interpenetrating polymer network (IPN) based on cyanate ester (CE) and 2,2Ј-diallylbisphenol A (DBA) modified bismaleimide resin (BMI) was prepared via prepolymerization followed by thermal curing. This work discusses the use of multiple waveform rheological technique to investigate the crosslinking and gelation behavior of this resin system at various temperatures. The gel point can be accurately determined from a single experiment using this technique. At the point of gelation, both the storage modulus (GЈ) and loss modulus (GЉ) of the IPN follow a similar power law equation with oscillation frequency used in the rheological measurement. Both the relaxation exponent n, a viscoelastic parameter related to the cluster size of the gel, and gel strength S, related to the mobility of the crosslinked chain segments, were determined via a curve fitting method. Both n and S were found to be temperature dependent in this BMI/ DBA-CE IPN system. The apparent activation energy of gelation or curing reaction was found to be approximately 47.6 kJ/mol.

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“…These observations indicate that the network formation proceeded faster with increasing temperature, whereas the gel texture is rather loose. There are some discussions in the literature regarding an apparent activation energy for the gelation reaction calculated from the gel time at different temperatures [29,31]. Because gelation represented a specific extent of reaction, the temperature dependence of the time to gel should be described by the Arrhenius equation…”

Section: Effect Of Temperaturementioning

confidence: 99%

Sol–gel transition study and pyrolysis of alumina-based gels prepared from alumatrane precursor

Ksapabutr¹,

Gülari²,

Wongkasemjit³

2004

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Alumina gels were prepared by the sol-gel method using alumatrane or tris(alumatranyloxy-i-propyl)amine as precursor synthesised directly from the reaction of inexpensive and readily available compounds, aluminium hydroxide and triisopropanolamine (TIS), via the one step process. Sol-gel process parameters, such as gel time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and hydrolysis ratio. The sol-gel transition of alcoholic alumatrane solutions was monitored by multiple waveform rheological measurements. The gel time could be determined from the evolution of the storage (G ) and loss (G ) moduli versus time at different frequencies using the Winter Chambon criterion (convergence of the loss tangents at the gel point). Increasing pH values, hydrolysis ratio and/or temperature accelerated the kinetics of hydrolysis-condensation reactions and thus reduced the gel time. The apparent activation energy of the cross-linking leading to the gelation calculated from the gel times at various temperatures was found to be approximately 139 kJ mol −1 and independent of hydrolysis ratio. Alumina materials prepared from the heat treatment of obtained gel at 500 • C were analysed using X-ray diffraction and the BET method.

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A gel point method for the estimation of overall apparent activation energies of polymerization

Cited by 54 publications

References 3 publications

Thermal analysis of thermosetting resins

Thermal analysis of thermosetting resins

Rheological study of crosslinking and gelation in bismaleimide/cyanate ester interpenetrating polymer network

Sol–gel transition study and pyrolysis of alumina-based gels prepared from alumatrane precursor

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