Thermal stability of amine-cured epoxide polymers

Note and Communication Thermal Stability of Amine-cured Epoxide Polymers THE purpose of work described herein was to determine effects of positions of amino groups on thermal stability of corresponding epoxide polymers. It was thought that thermal stabilities of diaminobenzene-epoxide polymers would decrease in the order of o-, m-, and p-diamino-benzenes because of decreasing crosslink densities between the amino groups. This was not the case, however, as will be shown later. Three crosslinked epoxide polymers were prepared by causing stoichiometric amounts of m-phenylenediglycidyl ether (MPDE) to react with o-, m-, and p-diaminobenzenes. CH.,CHCH,,OROCH.,CHCH._, + H~NR'NH,

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A linear epoxide polymer was prepared from stoichiometric quantities of m-phenylenediglycidyl ether and aminobenzene. Highly purified materials were used throughout. The crosslinked epoxide polymers were cured in a nitrogen atmosphere as follows: 96 hours at 100°C, 48 hours at 125°C, 24 hours at 160°C, 6 hours at 200°C, and 0.75 hour at 250°C. Differential thermometric (DT) apparatus was used to cure the linear polymer from 25 ° to 185°C at a heating rate of 25 deg C/min. Thermogravimetric* and differential thermometricz apparatus described previously was used to determine thermal stabilities. Thermogravimetric curves for the four polymers are shown in Figure I. Each curve is an average of three experiments. Curves for the MPDE,-odiaminobenzene, MPDE-m-diaminobenzene, and MPDE-aminobenzene polymers practically coincide. These results indicate that the three polymers have about equal thermal stabilities. It is remarkable that the linear MPD E aminobenzene polymer is as stable as the crosslinked MPDE-diaminobenzene polymers. The curve for the MPDE-p-diaminobenzene polymer differs from the others by breaking at a lower temperature and by showing a larger residual weight. On the basis of residual weight, this polymer is more stable; on the basis of temperature of initial decomposition, it is less stable. 193

NOTE AND COMMUNICATION

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/--Thermogravimetric (TG) curves of cured m-phenylenediglycidyl ether-amine polymers: (a) pdiaminobenzene; (b) o-diaminobenzene; (c) m-diaminobenzene; and (d) aminobenzene. Heating rate: 5 deg C / min in v a c u o Figure

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194

NOTE AND COMMUNICATION

As a check on the thermogravimetric results for the three crosslinked polymers, differential thermometric experiments were performed. In Figure 2, the resulting D T curves are compared with the corresponding differential thermogravimetric curves. Each set of curves shows that the MPDE-pdiaminobenzene polymer has a lower maximum rate of decomposition than the other two polymers. This maximum also occurs at a lower temperature in both cases. The differential thermometric results, therefore, enhance the validity of the thermogravimetric data. Different heating rates caused the two sets of curves in Figure 2 to appear in different temperature ranges:'. '. Exothermic D T peaks in the decomposition range are due to exothermic isomerization of residual epoxide groups '~,'~. Two findings lead to the conclusion that crosslinking is not a major factor in the thermal decomposition of the epoxide polymers studied. They are: (1) Order of thermal stability for the three crosslinked polymers did not correlate with crosslink densities between amino groups; (2) The linear polymer was just as thermally stable as the crosslinked ones. It would be informative to make a similar study of the o-, m-, and p-phenylenediglycidyl ether cured with an aromatic diamine. H. C. ANDERSON*

Chemistry Research Department, Polymer Research Group, U.S. Naval Ordnance Laboratory, White Oak, Silver Spring, Maryland 20910 (Received November 1965) *Present address: Exploratory Research Division. National Research Corporation, 70 Memorial Drive, Cambridge, Massachusetts. 02142. REFERENCES 1 ANDERSON, H. C. J. appl. Polym. Sci. 1962, 6, 484 2 ANDERSON, H. C. Analyt. Chem. 1960, 32, 1592 ANDERSON, H. C. J. Polym. Sci. 1964, C6, 175 4 FRmDMAN. H. L. J. Polym. Sci. 1964, C6, 183 5 ANDERSON. H. C. Polymer, Lond. 1961, 2, 452 LEE. L. H. J. appl. Polym. Sci. 1965, 9, 1981

On the Reliability of the Gradient Column Method for Measuring Densities of Polymer Single Crystals THE degree of crystallinity of polymer crystals grown from dilute solutions is a very important property of those samples since the structure of the so-called 'single crystals' is not yet completely elucidated. The simplest and most convenient method for determination of crystallinity is the measurement of density. With polyethylene different values are reported in the literature, One group of authors '-~ found values in the region of 0"97 indicating an amorphous fraction of about 20 per cent. On the other hand Kawai and Keller '~ obtained a value very close to, the ideal crystallographic density and concluded that no appreciable amount of an amorphous phase is present. The reasons for this discrepancy are still unknown. There are two types of observations supporting the lower value of crystallinity. First, the amorphous content can also be detected by other methods, e.g. bv X-ray scattering (literature is cited in ref. 6): secondly, the crystal195