Transitions curing processes

The greatest impact of the techniques has been seen in the study of polymeric materials with crystallinity and melting behaviour, glass transitions, curing processes and polymerisation representing the different types of thermal behaviour under investigation. A measure of the importance of this area of activity is reflected in the considerable number of publications and conference presentations it has generated. 

The peaks in s j dipolar (which are usually close to the peaks in e") can be used to determine the time or point in the cure process when the mean dipolar relaxation time has attained a specific value, i = 1/co, where to = 2nf is the frequency of measurement. The dipolar mobility as measured by the mean relaxation time t can be used as a molecular probe of the buildup in Tg. The time of occurrence of a given dipolar relaxation time as measured by a peak in a particular high frequency value of e"(co) can be quantitatively related to the attainment of a specific value of the resin s glass transition temperature. 

As was mentioned above (Sect. 4), for all considered polymers prepared at Tciire < T , their experimental glass transition temperature T p is close to their Tcure. The thermosetting reaction becomes quenched by vitrification, and for a new reinitiation of the cure process the polymer is to be softened by an increase of Tcure. Experimentally, in all cases, two consecutive processes take place after a sudden increase of T r (1) the softening of the polymer followed by (2) the next step of cure up to a new txdir (Fig, 25). 

It is beyond the scope of this review to discuss in detail viscoelastic properties at and after gelation. The gel point is one of the important characteristics in the epoxy resin curing process from both kinetic and rheological aspects. The gelation transition has been widely studied for epoxy resin systems [39,44,133-138] and already discussed in some of this series, such as by Malkin and Kulichikhin [28], Williams et al. [139], and Winter and Mours [140]. Rheological techniques for the determination of the gel point have been summarized for thermosetting resins by Halley et al. [29,141]. 

Aromatic polyimides have glass transition temperatures in excess of 400 °C, excellent toughness and elongation properties and dielectric constants comparable to that of inorganic dielectrics, about 3.5. An important feature relative to these applications is their ability to planarize the topography when spun on as the soluble precursor polyamic acid. The subsequent intramolecular condensation reaction to form the heterocyclic imide is typically a thermal "curing" process. 

The influence of the chemical structure of substances in PMB molecules in the curing process of epoxy materials was investigated. Stress-strain properties were determined by traditional physical-mechanical methods. Glass transition temperature was estimated by the thermomechanical method. Chemical resistance of the epoxy based coating cured by PMBs was determined by change of their impact strength after exposition in an aggressive environment within 42 days. 

Duske [6] discussed the use of thermomechanical analysis (TMA) in assessing the quality of wire insulation materials. This is particularly important for characterization of the polymer glass transition temperature, Tg, and for curing process control. TMA has been known to be a very sensitive technique for the... 

Kozlov, G. V. Bashorov, M. T Mikitaev, A. K. Zaikov, G. E. Transition nanoreactor-nanoparticle in epoxy polymers curing process. Chemistry and Chemical Technology, 2008, 2(4), 281-284. 

In this chapter the interrelation between mechanical properties, molecular mobility and chemical reactivity is discussed. Examples of how the changes in charge recombination luminescence, heat capacity and rate constants of chemical reactions can be related to the evolution of viscoelastic properties and the transitions encountered during isothermal cure of thermosetting materials are given. The possible application of the experimental techniques involved to in-situ cure process monitoring is also reviewed. 

As one can see, the value ds = 1.0 is reached at T, 363 K, which corre-sponds to linear tnactomolecule [22] and at T <363 K linearly connected chains in curing process are not formed. At T = 403 K, corresponding to the transition to stationary temperatnre regime (A 0.785), ds value is close to 1.33, i.e., to maximum spectral dimension for tightly cured macromolecules (microgels) [22]. 

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