Effect of active additives on the time-temperature dependence of polymer strength

Effect of active additives on the time-temperature dependence of polymer strength

EFFECT OF ACTIVE ADDITIVES ON THE TIME-TEMPERATURE DEPENDENCE OF POLYMER STRENGTH* S. 1~. ZHURKOV, V. R . REGEL a n d T. P. SANFIROVA A. F. Ioffe Phys...

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EFFECT OF ACTIVE ADDITIVES ON THE TIME-TEMPERATURE DEPENDENCE OF POLYMER STRENGTH* S. 1~. ZHURKOV, V. R . REGEL a n d T. P. SANFIROVA A. F. Ioffe Physieo-tectmieal Institute (Reveived 4 September 1964)

IN [1] WE dealt with the polo shift effect observed for certain polymers in the s t u d y of the time-temperature dependence of their strength. This effect consisted in the following. From the equation for the lifetime v: .c=l:oe(~-ya)ltT

where %, u0 and ? are constant coefficients, it follows t h a t log ~ as a function of the reciprocal temperature 1 / T at different stresses must apper as a fan of lines converging a t the pole, which should be on the ordinate axis, i.e. at 1/T-----O. This is actually observed for most polymers [1-4]. B u t in a number of cases the pole is not in the normal position on the ordinate axis [1]. ZoE "E,sec

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FIe. 1. Temperature-time dependence of the strength of pure PMMA without additives: a--log v v. a at different temperatures: 1-- --50 °, 2-- --18~, 3-- --50°; b--log T v. 1/T at different stresses (a, kg/mm2): 1--9, 2--7, 3--5. * Vysokomol. soyed. 7: No. 8, 1339-1343, 1965. 1486

1487:

Effect of active additives

The study of this departure from normality, which was carried out in [1], led us to conclude t h a t the pole shift effect in poly,,~ers is connected with the development of secondary radical reactions. Indeed, it was found experimentally t h a t for polymers degraded accordi-£ to a random law, the pole was in the right place. But where this was not followed, the shif~ was to be observed, the more so where the degradation was accompanied b y secondary b y radical reactions.

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FIG. 2. ]~rsrnple of the strong influence of impurities on the position of the pole: A--PMM~ with 1% hydroquinone: a--log~----f(~) at: 1 - - --50°; 2 - - 1 8 °, 3 - - 5 0 ° ; b--logr.=.f(I/T) at (~, kg/mm'): 1--8, 2--6, 3--4. B--PMMA with 7% diphonylmethacryl~m;cle- a--log ~ = f ( ~ ) at: 1 - - - - 5 0 °, 2 - - 1 8 °, 3--500; b - - l o g ~ . f ( l / T ) at (~, kg/mm=): 1 - - 7 , 2 - - 5 , 3--3"5.

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S. ~N]'.ZHURKOV e~ al.

To be certain of the accuracy o£ our proposition regarding the reason for the pole shift in polymers, we u n d e r t o o k experiments in which we a t t e m p t e d to influence the effect by adding inhibiting and activating additive which initiated or suppressed the secondary radical reactions. The metarials which initiate these reactions should increase the pole shift to the right of the ordinate axis, and those suppressing them should reduce it, shifting the pole to the left, closer to its normal position. Zogz;~ec

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FIG. S. Example showing the comparatively slight (as compared with Fig. 2) influence of impurities on the pole position: A--PMMA with 0"5~/o antioxidant: a--log ~=f (a) at 1---25 °, 2--18°; 3--50°; b--log 7:=f(1/T) at (a, kg/mma): 1--8, 2--6, 3--4. B--PMMA with 0.5% tinuvine: a--log v = f (a) at: 1-- --25 °, 2-- 18°, 3--50°; b--log v = f (I/T) at (a, kg/mm~): 1--8, 2--6, 3--4.

Effect of active additives

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I n the present work, to check this proposition, we studied the influence of various stabilizers, antioxidants, inhibitors and radical reaction initiators on t h e pole shift effect in polymethylmethacrylate (PMMA). The additives used were well known inhibitors, stabilizers and initiators [5-7]. The lifetime z as a function of stress ~ and temperature T was determined on specimens of thin PMMA film. The film was prepared from PMMA solution in dichloroethane or acetone, in which the test additives had previously been dissolved. Both the procedure for preparing the films and the specimens, and also for the time to rupture tests and determination of the pole position, were exactly the same as used in [1]. The results are shown in Figs. 1-4, in the form of the function log ~ v. (graphs a in Figs. 1-4) and log ~ v. I / T calculated from these graphs (graphs b Figs. 1--4). ~ v , sec

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FIG. 4. Example showing the increase in pole shift due to the addition of 2% benzoyl peroxide: a--log=f(~) at 1--25 °, 2--18 °, 3--50°; b--log~-~f(l/T) at (a, kg/mm2): 1--8, 2--6.5,

3--5.

I t is evident from these results t h a t the a~ldition of radical reaction inhibitors and initiators has considerable effect on the pole shift. Additives which suppress the radical reactions cause the pole to shift to the left, towards its normal position on the ordinate axis (Figs. 2 and 3). But the addition of a radical reaction initiator, benzoyl peroxide, gives a big shift to the right (Fig. 4). The experiment showed t h a t different stabilizers and inhibitors give different pole shift effects. The effect is greatest for the addition of 1% hydroquinone and 70/o diphenylmethacrylamide (Fig. 2).* With these additives the pole shifted from the po* The stabilizer 4iphenylmethacryllamidewas kindly presented to us by P. A. Sokolova, the others, and the antioxid~mt, by Ye. N. Matveyeva.

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S.lq. ZHURKovet al.

sition corresponding to 1.4× lOS/T on the ordinate axis to one corresponding to the coordinate 0.5 × 108/T. A less marked, but nevertheless appreciable shift was found for the addition of 0 . 5 ~ antioxidant, which is a thermostabilizert, or 0"5~/o tinuvine ~, a light stabilizer. I n these cases the pole shifted to a position corresponding to 1.0× lOS/T on the abscissa. Finally, Figure 4 shows the pole shift to the right as compared to the pole of pure PMMA. The same kind of shift was found for the addition of 2 ~ benzoyl peroxide impurity. I t can be seen t h a t in this case the pole shifted to the right, to 2.0 × 10s/T on the coordinate axis. I t is interesting to note t h a t the pole shift as a function of the concentration of .additive also reveals some analogy between the effect of stabilizers on the thermal degradation and mechanical properties of PMMA. We have not studied this question in detail, but it can b e mentioned in the light of the present experiments. We know from studies o f polymer stabilization [5, 6] t h a t there is a certain optimum amount of each stabilizer which produces the optimum stabilizing effect. More or less of the stabilizer in question, reduces the stabilization. Consistent with this, in our experiments also, it was found that if a larger amount of stabilizer was purposely added, this reduced its effect on the pole shift. We tested this b y adding a large amount of hydroquinone (up to 30%) and antioxidant (up to 3 ~ ) to PMMA. I n both cases the effect of the additive on the position of the pole fell noticeably when the concentration was raised above the optimum. I n the present work experiments to ascertain the effect of active additives on the temperature-time dependence of the strength of polymers were only performed on the one polymer, PMMA. But it is suggested t h a t the same kind of effects must obtain for other polymers for which degradation does not follow the random law and, consequently, the pole shift effect is to be found. I n our opinion, our experimental results confirm the proposition of [1], t h a t the reason for the pole shift effect in polymers is to be found in the seconda r y radical reactions which influence the rate of the breakdown process. These results provide a further argument in favour of the kinetic representations of the nature of polymer degradation, in particular, regarding the close connection between the process of breakdown and the thermal degradation of the polymers. CONCLUSIONS

(1) Active additives have been found to influence the pole shift effect in the log ~ - f ( 1 / T ) coordinates. • (2) Radical reaction inhibitors are found to shift the pole to the left Of its normal position on the ordinate axis, .while catalysts shift it to the right. The antioxidant was 2,2'-methylene-bis-4-methyl.6-tert.butylphenol. Tinuvine is 2-(2-oxy-5-methylphenylbenzocreso]).

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This is a further argument in favour of the kinetic representations of the nature of polymer breakdown, and of the close relation between the processes of breakdown and thermal degradation. Translated by V. ALFORD REFERENCES

1. 2. 3. 4. 5.

S.N. ZH1UR~OV,V. R. REGEL and T. P. SANFIROVA, Vysokomol. soyed. 6: 1092, 1964 S. N.~ZHURKOV and S. A. ABASOV, Vysokomol. soyed. 8: 441, 1961 S. N. ZHURKOV and S. A. ABASOV, Vysokomol. soyed. 8: 450, 1961 S. N. Z/HYRKOV, S. A. ABASOV, Vysokomol. soyed. 4: 1703, 1962 N. Ya. GORDON, Stabili~atsiya sintetioh, polimerov. (Stabilization of Synthetic Poly. mers.) Gost. ]~hlrr~. izdat., Moscow, 1963 6. Stareniye i stabilizatsiya polimerov. (Ageing and Stabilization of Polymers.) Izd. Naulm, Moeoow, 1954

7. S. Ye. BRESLER, A. T. 08MINSKAYA, A. T. POPOV, Ye. M. SOMINSKII and S. Ya. FRENlg!~?, Kolloidn. zh. 26: 403, 1958

PREPARATION OF O R G A N O D ~ O N S POL~ORIDE

OF C ~ O R I N A T E D *

P . I. ZUBOV, A. M. SMIRNOVA and T. V. RAIKOVA Institute of Physical Chemistry, U.S.S.R. Academy of Sciences (R~ived 4 S6pt~mber 1964)

ONE o f the m o s t common defects of polymer coatings is the high viscosity of the solutions, which restricts t h e application of high concentration solutions and, besides this, necessitates considerable consumption of solvents. The amount of dry residue can be increased without raising the viscosity if the macromolecular interaction is weakened b y adding a poor solvent to the solution. This causes globularization of the macromolecules or aggregates thereof (bundles) [1, 21, and ultimately leads to the formation of colloidally disperse systems. Formation of disperse systems, and consequently the increase in the dry residue, is best brought a b o u t in the process of the monomer polymerization in a solution of another polymer, or under conditions where the reaction products h a v e poor solubility in t h e solvent in question. The advantmge of this method is t h a t an improvement in the physicochemical properties of the film former can be brought about at the same time. * Vysokomol. soyed. 7: No. 8, 1344-1347, 1965.