Structure of diepoxide–diamine network polymers. I. Average network properties

Charlesworth, John M.

doi:10.1002/pol.1979.180170908

Cited by 19 publications

(10 citation statements)

References 18 publications

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“…3) extrapolate through the origin. This is the behavior which is expected since in these systems the sol fraction has been shown to increase rapidly as v becomes small (37), and therefore T, must also become small. The theoretical values of T, calculated using E q 10, 14, and 15, listed in Table 2, confirm that this is the case.…”

Section: + 30°mentioning

confidence: 61%

Effect of crosslink density on molecular relaxations in diepoxide‐diamine network polymers. Part 2. The rubbery plateau region

Charlesworth¹

1988

Polymer Engineering & Sci

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A comparison of the predictions of the theory of rubber elasticity with the experimentally observed variation of the shear storage modulus, G, as a function of crosslink concentration shows that deviations occur when the network strand concentration in diepoxide-diamine polymers exceeds approximately 1.5 mole kg-'. The rapid rise in G above this level is accounted for in terms of the increasing importance of non-Gaussian chain statistics and steric interactions. It is also established that the contribution from entanglements is significant and the behavior over the entire crosslink density range can be described by the following equationwhere v and cTe are the concentrations of elastically active strands which originate from fixed points and entanglements respectively, $ is a n empirical constant related to the importance of the non-ideal behavior, and I # J is the socalled "front factor". This latter constant is found to depend on the functionality of the network junctions, varying from 0.9, for a system with tetrafunctional junctions, to an average of 0.53 for those networks with trifunctional junctions.

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Section: + 30°mentioning

confidence: 61%

Effect of crosslink density on molecular relaxations in diepoxide‐diamine network polymers. Part 2. The rubbery plateau region

Charlesworth¹

1988

Polymer Engineering & Sci

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“…(A5) of Ref. 21; this has been corrected. From these results it appears that, for any reasonable combination of kinetic parameters, the gel point should occur below 30% conversion of epoxy groups.…”

Section: Gelation Theory Applied To Epoxy Mixturesmentioning

confidence: 99%

Chemorheology of an epoxy resin system under isothermal curing

Hou¹,

Huang

Hinkley

1990

J of Applied Polymer Sci

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SynopsisThe chemorheological properties of a commercial Hercules 3501-6 resin system were studied under isothermal curing conditions between 375 and 435 K. For cure temperatures 2 385 K, the storage modulus curing curves, G'( t ) , exhibited abrupt changes in slope which occurred at various times depending on the curing temperatures. These slope changes were attributed to the onset of gelation. Crossover points between G'( t ) and G"( t ) curves were observed for curing temperatures 2 400 K. The gelation and the crossover points obtained from the chemorheological measurements, therefore, defined two characteristic resin states during cure. Although gelation theory did not predict them correctly, the degree of cure in each of these states was approximately the same for every cure temperature. The temperature dependency of the viscosities in the characteristic resin states, and the rate constants of increase in moduli a t different stages of curing were analyzed.Various G'( t ) and G"( t ) isothermal curing curves were also shown to be capable of being superimposed to one another by the principle of time-temperature superposition. The resultant shift factors a,( T ) and a,( T ) were shown to follow Arrhenius type relationships. Values of the activation energy suggested that the reaction kinetics, instead of the diffusion mechanism, was the limiting step in the overall resin advancement for cure at temperatures 2 385 K.

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“…The formation of p-dioxane rings is, however, of minor relevance for non-stoichiometric reactions 28 , although it can be responsible for the consumption of about 1/16 of all epoxy rings.…”

Section: Introductionmentioning

confidence: 99%

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

2003

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An investigation was carried out on the room temperature ageing of off-stoichiometric DGEBA/TETA epoxy formulations. The results obtained show that the epoxy rich mixtures have their inherent brittleness increased by the ageing treatment due to recrystalization of the unreacted epoxy monomers, although homopolymerization could also play a minor role. The initial reaction steps dominated by the amine addition reactions control the macromolecular structure and the mechanical performance of the stoichiometric and near stoichiometric formulation with excess of epoxy monomer. Plasticization due to absorbed -OH results on a significant increase of the deformability of these formulations. The amine rich mixtures have the more stable structures, although plasticization due to moisture absorption from the surrounding environment also produces an increase on the deformability of all, but one, of the formulations investigated. keywords: epoxy resins, ageing, mechanical propertiesoff-stoichiometric mixtures. For the particular system made of the triethylene tetramine, TETA, hardener and the DGEBA monomer the variation of the hardener to monomer ratio promotes strong changes on the mechanical behavior [18][19][20][21] . Of particular interest with respect to these changes is the very sharp increase in the impact strength, when amine rich mixtures were used 21 . The problem of working with off-stoichiometric mixtures is that latent reaction sites could remain on the macromolecular structure developed and under the proper conditions the structure can evolve, resulting in changes on the mechanical performance of the material. Temperature is clearly one external parameter that could cause changes to the system, but, even at room temperature, ageing due to exposure of the epoxy resin to humid environments could also be important [22][23][24] . The changes observed on the mechanical properties when the epoxy monomer to hardener ratio is varied, and the possible changes due to aging, are a direct consequence of the different macromolecular structures that are developed and/or the possible reactions that could occur given a

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Structure of diepoxide–diamine network polymers. I. Average network properties

Cited by 19 publications

References 18 publications

Effect of crosslink density on molecular relaxations in diepoxide‐diamine network polymers. Part 2. The rubbery plateau region

Effect of crosslink density on molecular relaxations in diepoxide‐diamine network polymers. Part 2. The rubbery plateau region

Chemorheology of an epoxy resin system under isothermal curing

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

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