Phenolics Dynamic Mechanical Analysis

In the absence of co-reactants, it is supposed that the polymerization is promoted by traces of water or other nucleophiles, since very pure monomer does not gel even after extended heating. Conversely, gelation may be accelerated by addition of phenols such as bisphenol A. Dynamic mechanical analysis of cured resins confirms that they are practically identical whether or not the phenol is added. 

Dynamic mechanical analysis (DMA) is a sensitive method for glass transition temperature measurement, for detection of side-chain and main-chain motions, and for local mode relaxation measurements. Loeal mode relaxation can not be measured by DSC. DMA can give information about the crosslinking process of modified phenolic prepolymer [218] and about the erosslinked material [132]. During DMA measurements, sinusoidally varying stress of frequency is applied to the sample. Frequency and the stress are connected by equation 57, where is the maximum stress amplitude and is the phase angle at which the stress proceeds the strain. 

Dynamic mechanical analysis (DMA) measures a compound s modulus (stiffness) as its temperature is raised. This instrument has provided interesting insights into the properties of phenolics as well as those of DAPs, thermoset polyesters, silicones, and epoxies, by indicating the ability of thermosets to retain their modulus at elevated temperatures. DMA can also be used to determine thermal transition temperatures of the sample. 

Dynamic mechanical analysis provides a useful technique to study the cure kinetics and high temperature mechanical properties of phenolic resins. The volatile components of the resin do not affect the scan or limit the temperature range of the experiment. However, uncured samples must be supported by a braid, a scrim, or paper. This does not influence the kinetic results and can be corrected in the calculations of dynamic mechanical properties (qv). Recent DMA work on phenolic resins has been used to optimize the performance of structural adhesives for engineered wood products and determine the effect of moisture in wood product on cure behavior and bond strength (75-77). 

Differential scanning calorimetry (DSC), DMA and TG were used by Tabaddor and co-workersl l to investigate the cure kinetics and the development of mechanical properties of a commercial thermoplastic/ thermoset adhesive, which is part of a reinforced tape system for industrial applications. From the results, the authors concluded that thermal studies indicate that the adhesive was composed of a thermoplastic elastomeric copolymer of acrylonitrile and butadiene phase and a phenolic thermosetting resin phase. From the DSC phase transition studies, they were able to determine the composition of the blend. The kinetics of conversion of the thermosetting can be monitored by TG. Dynamic mechanical analysis measurements and time-temperature superposition can be utilized to... 

Journal of Applied Polymer Science 81, No.8,22nd August 2001, p.1902-13 DYNAMIC MECHANICAL ANALYSIS STUDY OF THE CURING OF PHENOL-... 

Using dynamic mechanical analysis the curing reactions of typical phenol-formaldehyde novolac resins were followed. The evolution of various rheological parameters was recorded for samples of the resins on cloth. A third-order phenomenological equation described the curing reaction. The influences of the structure, composition and physical treatment on the curing kinetics were evaluated. 20 refs. 

In this communication we present the results of an FTIR study of the blend system poly(bis-phenol A-carbonate) (PC) - PCL. This is a complex blend system which contains two crystallizable polymers with large differences in the crystalline melting points (T ) and glass transition temperatures (Tg). Cruz, et al.have demonstrated from thermal analysis and dynamic mechanical testing that blends of PC and PCL have a single Tg which is dependent only on the composition of the blend and conclude that the amorphous phase is miscible. These authors also concluded that the miscible amorphous phase results primarily from physical rather than chemical interactions between the polymers. 

As an example a model of die liquid-phase oxidation of the ethylbenzene in the presence of inhibitors, the iora-substituted phenols and the butylated hydroxytoluene, was selected. The identified dynamics of die value contribution of steps in the reaction mechanism is complicated. The dominant steps for die different time intervals of the inhibited reaction were determined. The inhibition mechanism of die ethylbenzene oxidation by sterically unhindered phenols is conditioned by establishing equilibrium (7.24) in the reaction of the chain carrier, the peroxyl radical, with the inhibitor s molecule (within sufficiently wide interval of the inhibitor s initial concentration), followed by the reaction radical s quadratic termination with the participation of the phenoxyl radical. The value analysis has established that the efficient inhibitor with low dissociation energy of the phenolic 0-H bond promotes shifting the mentioned equilibrium from the chain carrier to the direction of the phenoxyl radical formation. 

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