Dielectric relaxation in epoxide resins hardened with different anhydrides

DIELECTRIC RELAXATION IN EPOXIDE RESINS HARDENED WITH DIFFERENT ANHYDRIDES* YE. ~ . BLYAK~fA~, T. I. BORISOVAand Ts. 1~. LEVITSKAYA High P o ly m e r Institute, U.S.S.R. Academy of Sciences Siberian Energy Research I n st i t u t e

(Received 12 May

1969)

HARDENED epoxides contain polar bonds with orientational polarization; this can be used in an electric field to assess molecular mobility. The parts of the chains containing the anhydride grouping in polymers hardened with anhydrides have an ester group, while the polymer contributes hydroxyl and ether bonds to the epoxy system. The different types and conditions of internal rotation of these groups permit the assumption of specificity of the relaxation parameters of their dipolar polarization; this again makes it possible to study the structural mobility of these parts. This report describes the study of the dipolar polarization relaxation 'of group and segmental type on the low mol.wt, oligomer diane, t to get some knowledge of the mechanism of relaxation and its connection with the structure of the setting agent used, which was an acid anhydride or an amine complex with boron trifluoride acting as a setting catalyst. EXPERIMENTAL The dielectric loss anglo (tan J) and constant (8') was measured at frequencies from 50 t o l0 s c/s in the temperature range from --150 to -~200°C, on hardened epoxy systems. The bridges used were of type P-525 and MLE-1, and also BM-271 "Tessla". The sa~nples for the above measurements were prepared from a stoiehiometrie m i x t u r e of epoxy and anhydride groups, which was poured in the slit between two metal or glass slides, followed by the thermal t r e a t m e n t of the oligomer m i x t u r e with the thermosetting agent. The object of our study was the ED-5 type epoxide:

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Dielectric relaxatiorL in epoxide resins A:NItYDRIDE (A) QUANTITYI~ER 100 g ED-5 AND Tg OF THE HARDENED SYSTEMS Anhydride

A,g

Succinic Maleic Phthalie

49 48 72

Symbol used for set system ED-5S EI)-5M ED-5P

T g ~ °C

104 137 162

Its fraction composition showed it to be a mixture of two components with n = 0 and n = 1 at 68 : 32 (° o w/w) ratio. The Table gives the weights of the thermosetting agent per 100 g of epoxide component (A) and the Tg (glass temperature) of the hardened epoxy system. The thermosetting was carried out at 120-140°C in 70-100 hr, and at 200°C in 24 hr. A polymer based on ED-5 and the amine-BFa complex (7 ~o w/w)was produced by polymerization under the same conditions, under vacuum (10 mmHg) to prevent oxidation at 200°C. The polymerization conditions ensured the reproducibility of the electrical measurements up to 200°C, which ensured the completion of the thermosetting and the stability of the steric structure of the polymer. The samples had a thickness of 0.3-0.5 ram; the electrodes were of 30-40 mm diameter and were sprayed on to the surface under vacuum. The tan 5 and e' values of the epoxy systems at above 20°C were measured in air which had been bubbled through H~SOd, CaC12 and P~O~, while a nitrogen atmosphere was used at high temperatures. This eliminated condensation of moisture at low temperatures and the polymer oxidation at higher ones on the sample surface. RESULTS

The t a n ~- a n d ~'-values o f t h e studied a n h y d r i d e - h a r d e n e d epoxides are s h o w n as a f u n c t i o n of t e m p e r a t u r e a t frequencies of 50, l0 s a n d l0 s c/s in Figs. 1 a n d 2. T w o regions of t a n 3max were found; these shifted t o w a r d s higher t e m p e r a t u r e s on increeosing t h e f r e q u e n c y . These r a n g e d from - - 5 5 to - - 4 0 ° C a n d f r o m 120 to 200°C, a n d each was a c c o m p a n i e d b y a n increase in e', which was more p r o n o u n c e d in the h i g h - t e m p e r a t u r e process. The r e l a x a t i o n of dipolar polarization a t high t e m p e r a t u r e could be associated with s e g m e n t a l m o v e m e n t , as there was a n a b r u p t n a r r o w i n g of the A H 1 N M R lines (Fig. 3). (The m e a s u r e m e n t s of the N M R line w i d t h - t e m p e r a t u r e f u n c t i o n on our epoxides were m a d e b y V. N. M a s t k h i n a n d A. V. Golovin of the Catalysis I n s t i t u t e , Siberian B r a n c h , U.S.S.R. Acad e m y of Sciences). The dipole process a t lower t e m p e r a t u r e s a n d also the g r a d u a l decrease of A H ~ m u s t be a t t r i b u t e d to the m o v e m e n t of individual g r o u p s in the b r a n c h e s a t T < T g . The changes in t h e chemical s t r u c t u r e of t h e t h e r m o s e t t i n g a g e n t w i t h i n the studied s y s t e m s g r e a t l y affected t h e t e m p e r a t u r e T M a t which t a n 6 passes t h r o u g h the p e a k o f dipole-segmental losses, b u t h a d less effect on t h a t of dipole-group losses (at fixed frequencies). The a n h y d r i d e h a r d e n e r f o r m e d linear O--C--R--C--O-g r o u p s in the chain, R = - - C H 2 - - C H z - - , --CH=CH--,

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D i e l e c t r i c r e l a x a t i o n in e p o x i d e resins

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FIG. 2. T h e g - v a l u e s of: a - - E D - 5 S ,

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or a phenylene radical; the addition took place in the ortho-position in systems ED-5S, E D - 5 ~ and ED-5P. The double bond of mzleic anhydride, and still more so the benzene ring in system ED-5P, raised T M of the dipole-segmental losses when comparing with ED-5S (the T M were 127, 162 and 179°C respectively for ED-5S, ED-5M and ED5P) resulting in an increase in the relaxation times of segmental polarization and in Tg. The effect is the reverse on the ~ t of dipole-group losses, i.e. the cl~nge from ED-5S to ED-5M and ED-5P caused tan gmax to shift -to low temperatures, although this shift did not exceed 10°C. The presence or absence of ,oonaromatic. group had practically no effect on the parameters of the dipole-group losses.

I760

.YE: M. BLYAKH,MANet al.

The T~ of the dipole-group losses, and thus also the relaxation times of polarxzation of the particular form, had been shown earlier to decrease on reducing the number of aromatic rings-present in the oligomer structure [1]. Bearing this in mind, it can be assumed that the dipole-group polarization is linked with the movement of polar groups in t h e epoxide as such, i.e. of the C O - - ( - ~ ethers or hydroxyl, while the carbonyl groups do not make any significant contribution. T h i s assumption was verified b y studying the dielectric relaxation of a system based on ED-5, which was hardened b y means of an amine-BFa complex as catalyst. The resulting polsmer was therefore free from carbonyl groups. The tan 6-temperature plot in Fig. 4 for this polymer shows a peak at T < T g (as before, we shall assess the start o f segmental movement and Tg on the basis of the temperature of abrupt narrowing of the A H 1 N M R line; Fig. 3). The tan 6ma~ of the dipole=segmental losses, which is to be expected on the basis of Fig. 3 at T >140°C, does not exist because of the larger loss of transverse conductivity a t 100-120°C. tan6 0.070 0"050 0"050

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FIO. 4. Tan ~$as a function of temperature for ED-5 polymerized in the presence of the amine-BFa complex: 1--50 c/s, 2--108 c/s, 3--10 e c/s. The dipole-group tan 5ma~-values were similar for both the thermosetting agents used. Figure 5 shows the logarithm of the frequency f~ at which tan 6 passes through the peak as a function of temperature, and thus also the relaxation times of the dipole-group polarization of all the studied systems; the responses were practically identical, and also the respective activation energies (14 kcal/mole), which were calculated from the data in Fig. 5. The agreement of the tan 5max and the relaxation times permits the assumption that the dipole-group polarization of all the studied polymers is linked with the mobility of all the groups of similar structure; as shown earlier, these kinetic

Dielectric relaxation in epoxide resins

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FzG. 5. log fmax=p(1/T) for: 1--ED-5S, 2--ED-5M, 3--ED-5P, 4--ED-5 polymerized in the presence of the aznine-BF8 complex. groups are mobile at T < T g , centralized in the structure of epoxide ED-5. Such groups are the chain segments containing hydroxyl and ether bonds, for example the - - C H 2 - - C H - - C H 2 - - O - - groups. Such a group is likely to be the kinetic unit of

f OH epoxy polymers in the glass-like state, and were also considered in the evaluations of the dynamic mechanical test results [2]. An indirect proof of this is the good agreement of the temperature-frequency coordinates in the relaxation range of OH dipole-group polarization with that of polyvinyl alcohol and the primary hydroxyl of cellulose [3]. CONCLUSIONS

(1) The parameters of the dipole-group polarization relaxation (relaxation times, activation energiesand tan ~m,x) of resin ED-5 hardened b y means of the anhydrides of succinic, maleie or o-phthalic acid, were found to be practically independent of the chemical structure of hardener within the limits of changes. The introduction of double bonds or of aromatic rings greatly increased, however, the relaxation times of the dipole-segmental polarization. (2) Comparing the results of studying the temperature-frequency correlation of tan ~ and ~' for this t y p e of thermosetting agent with those obtained by catalysed polymerization (over the amine-BF3 complex) led to the conclusion that the polar grouping responsible for the dipole-group losses at T < T g must be that part of the chain in ED-5 which contains hydroxyl and ether bonds, for example --CH2--CH--CH2--O--.

I

OH (3) The kinetic unit responsible for the dipole-segmental type polarization also includes the polar groups introduced b y the anhydride, because the structure of the latter influences the parameters of the discussed process.

Translated by :K. A. ALLE~-

1762

I . N . KIM et al. REFERENCES

1. Ts. M. LEVITSKAYA, Dielektricheskie poteri i polyarizatsiya epoksidnykh smol razlichnoi struktury. Sb: Sibir. N I I E , vyp. 16, pod red. Yu. N. Vershinina (The Dielectric Losses and Polarizations of Epoxide Resins of Different Structure. In: Sibir. N I I E 16: Yu. N. Vershinin, editor), p. 154, Izd. "Energiya", 1970 2. F. It. DAMMONT and T. K. KWEI, J. Polymer Sci. 5, A-2: 961, 1967 3. G. P. MIKHAILOV, A. I. ARTYUKHOV and T. I. BOItISOVA, Vysokomol. soyed. B9: 138, 1967 (Not translated in Polymer Sci. U.S.S.R.)

SOME STRUCTURAL STUDIES ON HIGHLY SUBSTITUTED CELLULOSE CYANOETHYLATES (CCE)* I. N. KIM, T. SAIDALIEV,V. I. SADOVNIKOVA,Yr. T. TASHPULATOV, T. G. GAFUROVand KH. U. USMA~OV Cotton Cellulose Chemical and Technical Research I n s t i t u t e (Received 12 M a y 1969)

MUCH attention has been given by investigators to the partly substituted cellulose cyanoethylates (CCE) because of t h e relatively simple production method, and the technically important properties, of which the most noticeable is the dielectric constant, and also the larger heat-, biological- and light-resistance, and the adhesion capacity. The limited solubility and the severe processing conditions, however, are an obstacle to their practical application in, for example, the production of films, fibres and plastics. We eliminated these deficiencies by synthesizing a highly substituted CCE based on cotton cellulose; the degree of substitution, ~c~----296, made the product soluble in the usual organic solvents, such as acetone, methyle~.e chloride, acetonitrile, dimethylformamide (DM-F), a methylene chloride mixture with alcohols, etc. There is hardly any reference to be found in the literature to the structural study of highly substituted CCE. This report describes the X-ray and infrared study of the structural changes which occur in cotton cellulose on changing from the natural product to the highly substituted CCE; addition work dealt with sorption properties and the density. EXPERIMENTAL The s t u d y objects were CCE samples with different degrees of substitution, amongst them also those with ~c~----296, which were produced as outlined earlier [1]; they were all * Vysokomol. soyed A12: No. 7, 1550-1554, 1970.