Determining the gel point of an epoxy-hexaanhydro-4-methylphthalic anhydride (MHHPA) system

Boey, Freddy; Qiang, Wei

doi:10.1002/(sici)1097-4628(20000523)76:8<1248::aid-app5>3.0.co;2-0

Cited by 40 publications

(31 citation statements)

References 28 publications

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“…The critical exponent D therefore, assumes a high level of importance in understanding the formation of the gelled material as it provides a framework to understand the dynamic mechanical properties of a polymer structure at gelation. The value of D determined for a wide range of epoxy amine networks has been shown to be consistently around 0.70, [38,39] although Scanlon and Winter showed that it is not a universal constant and is dependent upon precursor composition. Other polymer systems have been shown to produce values ranging from 0.2 to 0.70.…”

Section: Network Formationmentioning

confidence: 99%

Reaction Kinetics and Phase Transformations During Cure of a Thermoplastic‐Modified Epoxy Thermoset

Varley

2007

Macro Materials & Eng

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A comprehensive thermal and rheological characterisation of a commercially important aerospace resin system modified with a thermoplastic toughener is presented here. The primary focus has been the understanding of how the cure kinetics and mechanism relate to other processes such as phase separation during cure. Differential scanning calorimetry has shown that thermoplastic modification does not affect the cure mechanism significantly and that the process was dominated by an autocatalytic process up to vitrification after which diffusion‐controlled processes dominate regardless of thermoplastic concentration. Thermoplastic addition at 10 wt.‐% PEI was found to increase the final cure conversion compared with the neat resin and inhibit the onset of diffusion control below a cure temperature of 160 °C. At 20 wt.‐% PEI concentration the final conversion and the onset of diffusion control were similar until 150 °C, after which they displayed lower values than the neat resin. Rheological analysis showed that the phase separation process could be followed conveniently through the changes in viscosity and exhibited effects consistent with expected variations in morphology. The 10 wt.‐% PEI system displayed abrupt increases in viscosities which were indicative of a dispersed particulate morphology, while the 20 wt.‐% PEI system displayed more complex behaviour consistent with a phase‐inverted or co‐continuous structure. The gelation process was shown to obey a power law model although the local environment or morphology of the reactive epoxide group at higher PEI concentrations was shown to affect the fit to the model.

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Section: Network Formationmentioning

confidence: 99%

Reaction Kinetics and Phase Transformations During Cure of a Thermoplastic‐Modified Epoxy Thermoset

Varley

2007

Macro Materials & Eng

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“…Accurate knowledge on the gelation time would therefore allow the estimation of the optimal temperature and time for which the sample should be heated before being allowed to set in the mold. 31 It was found that the application of the G 0 -G 00 crossover method for gelation point determination is only effectively suitable for some specific polymers as given by the Winter's criterion. 32 Mehran Hayaty has reported that the crossover of G 0 and G 00 of the EP system does not occur at the frequency ranges.…”

Section: Resultsmentioning

confidence: 99%

Preparation and characterization of cyanate/epoxy foam

Fan

Tian

Chen

et al. 2015

High Performance Polymers

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A new type of cyanate (CE)/epoxy (EP) foam with bisphenol-A dicyanate ester prepolymer and diglycidyl ether of bisphenol-A (BADCy/DGEBA) has been successfully prepared through a two-step process. The structure and properties of CE/EP foam were studied. The results reveal that the CE/EP foams, with relatively uniform cell structure, were composed of closed cells as confirmed by scanning electron microscopy. The compressive strength increased from 0.507 MPa to 3.021 MPa, and the compressive modulus (E) increased from 15 MPa to 123 MPa as the density increased from 0.103 g cm À3 to 0.305 g cm À3. Dynamic mechanical analysis revealed that the CE/EP foams possessed a high glass transition temperature (T g ) (203 C) and that density had only a little impact on T g . Moreover, the excellent thermal stability presented with the onset of weight loss taken at 5% value was above 320 C, and the residual weight of the foam was more than 21.6% at 800 C. With increase in the density of CE/EP foams, the dielectric constants (") gradually decreased. For the foam with density of ¼ 0.162 g cm À3 , the value of " was as low as 2.28 at the frequency of 10 kHz.

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“…The gel point in rheological experiments is determined using various methods, according to different definitions [42,43]: the divergence point or fixed level of the viscosity [44,45], the crossover point of the dynamic storage modulus (G') and loss modulus (G") [46], or the point at which the loss tangent becomes independent of testing frequency [47][48][49][50]. The gel point for NPU-2d, as the crossover point of G' and G" appears at 116.5°C as can be seen in Figure 8a.…”

Section: Rheological Behaviourmentioning

confidence: 99%

Polyurethanes based on thermoreversible networks designed by Diels-Alder reaction

Ursache¹,

Găină²,

Gaina³

2017

Express Polym. Lett.

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Polyurethanes appeared as a Bayer's response to the successful development of high molecular weight polyamides by E.I. Dupont, given the competition between the two companies. The need for PUs steadily increased ever since then, because of its high abrasion, chemical resistance, flexibility, and good mechanical property [1]. Nowadays they are considered one of the most versatile polymeric materials class since they can be used in many forms and in a large number of applications including elastomers [2][3][4][5], flexible and rigid foams [6][7][8], biomedical applications [9][10][11], adhesives and coatings [12][13][14], polymers for electronics [15], etc. The reaction between diisocyanates or multiisocyanates and di-or polyols generates polyurethanes with different molecular structures varying from linear to crosslinked ones depending on the structure, functionality and stoichiometry of the reactants. These thermosetting polymers cannot be reprocessed or reused if, according to the desired applications, chemical crosslinkers are used [16]. For de-crosslinking of polyurethane networks, dynamic covalent chemistry is used, especially by means of the DA and retro-DA (rDA) reactions [17]. Due to its reversibility the DA reaction also represents a choice to create self-healing properties for polymer networks [18]. Concerning polyurethane, the DA reaction was employed in thermally remendable linear polymers [19][20][21][22] and thermally reversible networks [23][24][25][26][27]. The latter were designed in three different ways: i) by polymerization reaction of monomers containing maleimide-furan cycloadduct [26,28], ii) by crosslinking of linear polyurethane containing furan or maleimide pendant groups [27,29,30] and iii) by cycloaddition DA reaction between polyurethane containing furan end groups and multimaleimide monomers [19,[23][24][25][31][32][33]. Abstract. Urethane bismaleimides (BMIs) were used in order to obtain crosslinked structures by their reaction with an aromatic trifuran compound. The Diels-Alder (DA) reaction between the maleimide and furan moieties was investigated using proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy for a model compound (CTF), due to the fact that the networks are insoluble in usual NMR solvents. The structure of the networks was confirmed by infrared spectroscopy. Thermal properties were investigated (by means of differential scanning calorimetry (DSC) and thermogravimetrical analyses (TGA)) and compared with the ones of similar compounds, previously obtained from the same BMIs and a different trifuran compound (which contains tertiary nitrogen in its structure). Mechanical and rheological properties were also investigated. The influence of the nature of the polyol from the BMIs structure and/or the influence of using a trifurylic compound with or without tertiary nitrogen on the properties of the crosslinked networks were also discussed.

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Determining the gel point of an epoxy-hexaanhydro-4-methylphthalic anhydride (MHHPA) system

Cited by 40 publications

References 28 publications

Reaction Kinetics and Phase Transformations During Cure of a Thermoplastic‐Modified Epoxy Thermoset

Reaction Kinetics and Phase Transformations During Cure of a Thermoplastic‐Modified Epoxy Thermoset

Preparation and characterization of cyanate/epoxy foam

Polyurethanes based on thermoreversible networks designed by Diels-Alder reaction

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