Effect Of Glass Transition Temperature Research Articles

Molecular dynamics of the frozen‐in glassy state of Ni80P20

AbstractA molecular dynamics approach is used for the dynamic structure simulation of the Ni80P20 glassy‐like system. Calculations are made considering the rapid cooling from melt and the effect of glass transition temperature. Comparison with the experimental data is given with a reasonable correspondence.

Computer‐simulated ESR spectra of irradiated poly(olefin oxides)—effect of glass transition temperature on the ESR spectra

AbstractInvestigations on the effects of γ irradiation on poly(methylene oxide) (POM) and poly(ethylene oxide) (PEO) have been made employing electron spin resonance (ESR) spectroscopy. The ESR sextet and doublet spectra, recorded for POM and PEO, respectively, on irradition in air at room temperature are broadened as the temperature is lowered and show a reversible change in line shape with temperature. The spectra are analyzed by computer simulation, employing Lorentzian line‐shape functions and the least‐squares method of total curve fitting. The component spectra are evaluated and are assigned. Superposition of the component quartet, triplet, and doublet spectra, corresponding to the radicals ĊH3, ĊH2O , and OĊHO , respectively, together with a singlet due to the radicals ȮCH2 is considered to be the best fit to the observed spectrum for POM. The doublet spectrum recorded for PEO has been assigned to the radicals ĊHO . The reversible broadening of the spectra has been associated with the mechanism of molecular motions around the glass transition temperatures of these polymers.

ESR of Cu2+and Tl2+ in thallium borate glasses

The electron spin resonance (ESR) and optical absorption spectra of Cu2+ were measured in thallium borate glasses in order to investigate the effects of glass transition temperature,T g, upon the responses of cupric ion in alkali borate glasses. The ESR of Tl2+ induced byγ-ray irradiation was also obtained. An abrupt increase in the covalency of in-plane Cu2+-Oπ-bonding was observed in the Tl2O system as well as in the Na2O system in a similar B2O3 composition range althoughT g for the Tl2O glasses has little dependency on the composition compared with the Na2O glasses. The trend in the variation of the S-character of the Tl2+ unpaired electron with composition agreed with that of the covalency of in-plane Cu2+-Oπ-bonding. The structure of the anion group present in Tl2O glasses was also examined by laser reman spectroscopy.

Cyclopolymerization. VI. Polymerization mechanism of N‐methyl‐N‐allylmethacrylamide at lower temperature

AbstractMechanistic investigations on the polymerization of N‐methyl‐N‐allylmethacrylamide (MAMA) at lower temperature were carried out based upon the ESR studies of MAMA and its monofunctional counterparts irradiated with 60Co γ rays. Cyclopolymerizability of MAMA was also studied in connection with the hindered rotation about its amide CN bond. The propagating radical observed is only related to the methacryl group but not to the allyl group both in MAMA and its monofunctional counterparts. Polymerization at −78°C yielded a polymer with a lower degree of cyclization(88.8%) as compared with that of polymers formed at higher temperatures (93.5% above 0°C). A structural study revealed that the increment of the unsaturation in the poly‐MAMA obtained at −78°C is due to the allyl group and the content of pendant methacryl group is almost unchanged over the temperature range from −78 to 120°C. These results led to the conclusion that the polymerization of MAMA at −78°C proceeds mainly through the methacryl group, the rate‐determining step is the cyclization reaction, and, in addition, cyclization reaction scarcely occurs when it polymerizes through the allyl group. Since MAMA is frozen into a glassy state, the effect of glass transition temperature (Tg) has been studied and it was suggested that the polymerization of MAMA proceeds only above Tg.

The Relationship of Glass Transition Temperature to Adhesive Strength

Abstract The effects of glass transition temperature (Tg ) on mechanical properties have been further demonstrated by the observation of adirect relationship between the Tg of an epoxy adhesive and its lap shear bond strength to metal at elevated test temperatures. An additive (coupling agent) which lowers the Tg from a point near or above the test temperature to below it causes a subsequent decrease in the strength of the system and generally increased cohesive failure. Therefore effects on the Tg of the adhesive are more important than on interfacial properties. The end result is that differential thermal analysis (DTA) can be utilized as a effective screening method for adhesives and additives, and can be a good indicator of maximum use temperature. From these data Tg can also be used to estimate adhesive strength at a given use temperature.

Polymers: Their Stucture and Dielectric Properties

Polymers, with their high molecular weight and great lenghts vs. relatively small diameters, tend to have very complex physical and dielectric properties. The dielectric properties, like the mechanical properties, are dependent on the mobility of their constituent parts and are therefore quite sensitive to both temperature and frequency. The effects of glass transition temperature, melting point, impurities, and atomic structure on the dielectric properties are discussed with specific examples from the literature. Conduction and breakdown are covered rather briefly with emphasis on the need for fundamental structural studies in this area.