A study of the variables which influence the response of the evaporative analyzer has been undertaken. The instrument appears to function adequately as a mass detector In liquid chromatographic applications, provided the solute is considerably less volatile than the solvent at the operating temperature. Furthermore at the normal atomization air
The effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide-diamine polymers are reported. Activation enthalpies and intensities for the p relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation intensity. In the case of nonstoichiometric networks, variations in the intensity of the p relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the y relaxation (-140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.
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.
The relative reactivity of the functional groups present in aromatic amine and diepoxide monomers has been investigated by gel permeation chromatography. The ratio of rate constants for the consumption of the secondary and primary amine hydrogens involved in the reaction between aniline and phenyl glycidyl ether has been calculated to equal approximately 0.5. In the case of the reaction between N‐methy aniline and diglycidyl ether of bisphenol A (DGEBA) the rate constant ratio for the consumption of the first and second epoxide groups in the DGEBA molecule is also approximately 0.5. In contradiction to previously published data these results suggest that substitution effects are unimportant for aromatic amines as well as DGEBA. Furthermore, etherification side reactions, consuming epoxide groups at the expense of the amine–epoxide reaction, also appear to be insignificant.
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