Study of molecular motion and structure in solid polyethylene of varied molecular mass by the nuclear magnetic relaxation method

Molecular motion in solid polyethylene

287

11. Yu. V, ZELENEV, G. M. BARTENEV and DEMISHEV, Zavodsk. lab. 29: 7, 868 12. T. ALFREY, Mekhanicheskiye svoistva vysokopolimerov (Mechanical Properties of High Polymers) Inost. lit., Moscow, 1962 13. A. P. MOLOTKOV, G. A. KLIMENKO and Yu. V. ZELENEV, Prognozirovaniye ekspluatatsionnykh svoistv polimernykh materialov (Prediction of the Working Properties of Polymer Materials), p. 44, KISI, Kazan, 1976 14. G. A. KLIMENKO, A. P. MOLOTKOV and L. I. BOGDANOV, Vysokomol. soyed. 17: 2574, 1975 (Not translated in Polymer Sci. U.S.S.R.) 15. A. A. ASKADSKII and G. L. SLONIMSKII, 1bid. A13: 1917, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 8, 2158, 1971) 16. A. A. ASKADSKH, G. L. SLONIMSKII, M. I. MATVEYEV and V. V. KORSHAK, Ibid. A18: 2067, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 9, 2363, 1976)

PolymerScienceU.S.S.R.Vol. 27,/'40. 2, pp. 287-295, 1985 Printed in Poland

0032-3950185 $10.00+ .00 © 1986PergamonPress Ltd.

S T U D Y OF MOLECULAR MOTION A N D STRUCTURE IN SOLID POLYETHYLENE OF VARIED MOLECULAR MASS BY THE NUCLEAR MAGNETIC RELAXATION M E T H O D * V. D . FEDOTOV a n d N . A . ABDRASHITOVA Kirov Chemico-Technological Institute, Kazan (Received 1 June 1983)

A three-component analysis of the decays of transverse magnetization is made in seven samples-of linear PE over a wide temperature range providing information on the relative intensities of the components of the decays, the times of spin-spin relaxation 7'2 and the second moments o2 of the signals of each phase. From the temperature dependence of 7'2 and tr2 the authors determine the temperatures of the ~ and fl transitions of the intermediate and amorphous phases and also the apparent activation energies corresponding to these transitions. The parameters of the phasic structure and the characteristics of the transitions thus obtained are compared with the parameters of structure obtained from analysis of the data on X-ray diffraction of similar samples. MUCH w o r k using different m e t h o d s i n c l u d i n g N M R a n d X - r a y diffraction has been d o n e o n p a r t i a l l y crystalline PE. A n u m b e r o f recent studies have s h o w n t h a t solid P E h a s a c o m p l e x structure c h a r a c t e r i z e d b y the presence as a m i n i m u m o f three different phases: crystalline, i n t e r m e d i a t e a n d a m o r p h o u s [1-6]. But a g r e e m e n t on the c o n t e n t o f each o f these p h a s e s is far f r o m always reached. T h e p o i n t is t h a t the different p h y s i c a l m e t h o d s m e a s u r e different p h y s i c a l m a g n i t u d e s differing in sensitivity to the h e t e r o * Vysokomol. soyed. A27: No. 2, 263-269, 1985.

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V.D. FEDOTOVand N. A. ABDRA~HI"rovA

geneity o f structure. In addition, in heterogeneous systems the form of the signals recorded is usually so complex as to present major difficulties in obtaining correct information from them on the phasic structure, The method of isolating the a m o r p h o u s halo from the diffraction curve outlined in [6] and observed in study of PE by X-ray diffraction gave the best agreement between the experimental data and existing model notions on the structure of PE within the triphase structure of PE. On the other h~nd, Bergmann et al. [1 ] developed a method o f analysing the complex N M R wide line spectra helping to resolve the N M R signals in PE into three components each of which has its own form because of the pa~icip a t i o n o f chains of different phases in the different forms of molecular motion. With this approach change in the character of motion alters the form of the components and hence also the n u m b e r of nuclei corresponding to a given structural phase, which often does not tally with the results of structural methods. In w o r k on nuclear relaxation in PE [3-5, 7] a different approach to analysis o f the multicomponent N M R signals has been developed. With this approach each structural phase of the polymer has its own spin system and to it corresponds it~ own signal of a definite form. With change in the type of molecular motions in a given phase the f o r m of the signal m a y change but the phase structure m a y remain unchanged. Using such notions it was possible to. show in o n e PE sample good agreement between the results of investigation of PE by the N M R pulse method and X-ray diffraction and also to analyse the relaxation transitions within a triphasic model of the structure of PE

[4, 8, 9] This work discusses the results of analysis of the curves of decay of transverse magnetization observed over a wide temperature range in a series of PE samples differing in M M and degree of branching. Since similar samples have been studied in the K a r p o v Phys. Chem. Research Institute by X-ray diffraction [10] it was possible not only to trace the influence of the molecular structure of PE on its phase structure and molecular dynamics and check the correspondence of the data of the two methods But also to touch on the problem of a correlation between the parameters of structure and the characteristics of the relaxation transitions. In the work we studied samples of linear PE (LPE) with Mw = 5 × 104 (sample 1), 105 (sample 2), 3 x 105 (sample 3), 4.3 x 105 (sample 4), 8 x l0 s (sample 5) and 3 x 106 (sample 6). For the samples 1, 3, 4--6 the ratio M w / M , = 2 - 3 , ramification 0,5 branches per 1000 carbon atoms. For sample 2 PE of commercial production grade Hostalen the ratio Mw/M~= 10, with five branches per 1000 carbon atoms. All the samples were obtained in the Karpov Phys. Chem. Research Inst. and studied by the method of X-ray diffraction in [10]. In addition, we studied a sample of branched PE (BPE) of grade 16802-070 (GOST 16337-70) (sample 7). All the samples were crystallized from the melt on slow cooling to room temperature and annealed for 5 hr at 125 (LPE) and 100 (BPE) °C. The measurements were made with the pulse NMR relaxometer working at the frequency 21.5 MHz [11] in the temperature interval - 1 2 0 - + 125°C, Analysis of the decay curves of transverse magnetization (DTM) was based on the expression obtained in [7] and consisting of three terms corresponding to the three structural phases of the polymer-crystalline, intermediate and amorphous A(t)=Pc

sin b t -"s~---+ e

bt

2 +ple-O21I(t/,l)+pae . . . . .r,~+/+,~,

(1)

Molecular motion in solid polyethylene

299

~here a2+ b2/3 = azc, tr2t, e2, are the second moments of the absorption lines; r,. i are the correla-

tion times of segmental motion; Pc, Pi and P, are the relative intensities of the components of the signal from each phase of PE; f ( t / T ) = e - t / ' - 1 + t/z is a function equal to t2/2 at low (~:~r°'s) and tv at high (r<
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V. D. FEDOTOV a n d N. A. A B D ~ T O V A

290

' Thus, both methods have established that the phase structure of PE may be welt described within the triphase model and depend on the molecular structure (MM and ramification), which makes it possible to regulate it appropriately and prepare samples. with,a different phasic structure. Molecular motion. To simplify the analysis of the data in terms of molecular motion: weshall as in [9] take as ~ the relaxation transition of a particular non-crystalline p h a s e the process associated with the development in it of liquid-like movements which may be found from change in the form of the corresponding component of the signal from Gaussian to exponential. The start of fall in the value of the second moment not accompanied by change in the form of the signal is associated with the fl-relaxation process due to development of local, anisotropic movements of portions of the main chain of the given phase. Figure 2 presents the temperature dependence of the second moments of each phase at temperatures below the corresponding:~-transit~ons and Fig. 3 that of the spin-spin relaxation times of the amorphous arid intermediate phases for temperatures above those of the ~-transitions, in all the PE samples studied. In Fig. 2 these temperatures are denoted by arrows.

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Molecular motion in solid polyethylene

291

Figure 2 shows that the temperature dependence of the second moments of the crystalline and amorphous phases a2c and tr2a and correspondingly the temperatures of the fl-transitions in them T~ and T~ for the LPE samples are much the same. In the intermediate phase the temperature of the fl-transition Ta and the course of the temperature dependence at high temperatures > T~ change from sample to sample. It should be noted that in the amorphous phase the value of the second moment at high temperatures passes to a plateau with a value ,,~5 Oe 2 while in the intermediate and crystalline phases fall in the second moments occurs down to 10-12 Oe 2 and is then interrupted by the start of the more general 0t process. The temperature dependence of the second moments for each of the BPE phases is similar to that observed for LPE but shifted to the region of low temperatures. T z , SeC

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The temperature dependence of the relaxation times T2a and T21 given in Fig. 3 is well described by straight lines in Arrhenius coordinates although in samples 2-5 an inflexion is seen indicating sharp change in the slope of this dependence. From the temperature dependence of the relaxation times we determine the apparent activation energies (Ea and El), the values of Ea (E" and E~") being obtained for each of the samples 2-5 corresponding to the low and high temperature portions of the functions T~ (l/T}

292

V. D . F~ooTov and N . A..A.BDRASHITOVA

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Molecular motion in solid polyethylene

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respectively. In addition, the temperatures of the inflexion (T*) of these functions were determined. Following the formalism developed in [8, 12, 13] from the ratio of the apparent to the true activation energy E ° we determine the parameters of width of the spectrum of the correlation times from the formula ~ = 2E/E°+ E assuming that the spectrum of the correlation times is determined by the Fuoss-Kirkwood function [14] and the true value E ° for the • transitions in the amorphous and intermediate phases of all polymers is identical and amounts to ,,~50 kcal/mole [8]. The values of the activation energies, the temperature of the ~ and fl transitions and the parameters of the width of the spectra of the correlation times determined for seven PE samples are given in the Table together with some data on structure obtained by X-ray diffraction in [10]. We would note the main aspects of the data obtained. The temperatures of the fl transitions in the crystalline and amorphous phases do not depend but in the inteimediate phase closely depend on Mw. In the samples with mean MM inflexions are observed in the curves of the temperature dependence T2, the temperatures of the inflexions coinciding with that of the fl transition in the crystalline phase. The magnitudes T~, T~ and El reach maximum values in the region of mean (3 x 10) s MM while the magnitudes T~, T~ and E a are independent of Mw. Comparison of the structural and dynamic parameters. Having at our disposal the results of experiments run by both methods on the same samples let us try to establish some links between the two facets of the structure of PE-static and dynamic, confining ourselves to the most obvious correlations between the parameters of structure and molecular motion. From comparison of the results of the two methods given in the Table and Figures one may draw the following conclusions. 1. The temperatures of the ~ transitions of the non-crystalline phases correlates with their density determined by the X-ray method (20maz), the magnitude T~, like the X-ray density, does not depend on Mw while the magnitudes T~ and 20mazare linked by a linear relation (Fig. 4). 2. The temperatures of the • transitions of the amorphous.and intermediate phases do not correlate with their density but with their content i.e. the phase structure. It was found that these temperatures are linked by a linear relation to the intensity of the crystalline phase and do not correlate with the global intensity of the crystalline and intermediate phases. Extrapolation of both linear relations T~'~(Po) to a zero degree of crystallinity leads to the temperature ~ - 90--100°C. From the physical meaning of such extrapolation this temperature may be taken as Tg of the hypothetical amorphous PE (Fig. 5). This conclusion is confirmed by the analogous relation found by us in study of various PEPT samples [15]. From Fig. 5b it will be seen that the dependence of T~ on Pc in the ease of PEPT is well approximated by a straight line which at Pc = 0 shows a tamperature close to Ts of purely amorphous PEPT (360 K). 3. The extremal behaviour of the temperature functions of the relaxation times presence of an inflexion in the samples with mean MM) and some of their parameters

V. D. F~atrrov and N. A. ABV~,SmTOgA

294

(El, T ~, i) correlates with the extremal dependence on M M of such structural parameters as the temperature changes in X-ray density and relative disorientation of the chains o f the intermediate phase. Although in references [6, 10] the authors propose a model o f the structure of PE which explains quite well the extremal behaviour of the structural parameters, we consider that at present there are insufficient grounds for making a

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Fio. 4. Temperature of the fl transition T~ as a function of density determined by the X-ray method for the intermediate phase of PE. l~o. 5. Temperatures of the ct transitions in amorphous T~ (1) and intermediate T~ (2) phases of PE (a) and in the amorphous phase of PETP (b) as a function of the relative intensity of the component of the DTM curve related to the crystalline phase P~ .of the polymer. correct description of the above established links between the statistical and dynamic aspects o f structure within the molecular model. The quality between the temperatures T~#and T* may be explaived by the fact that the local movements developing at a given temperature in the crystalline phase remove the limitations on the mobility of some chains of the amorphous phase (for example, of the through molecules or free ends) which in turn leads to narrowing of the spectrum of the correlation times of segmental motion ( J " ~ J ' ) and as a consequence to increase in the apparent activation energy o f this motion. The presence of approximate equality of the temperatures T~ and T~ points to a mutual link betw.een the local movements in the intermediate and large scale movements in the amorphous phases. T h e authors are grateful to Yu. K. Ovchinnikov for useful discussion. .Translated by A. Cgozg REFERENCES 1. K. BERGMANN and K. NAWOTKI, Kolloid. Z. und Z. fur Polymere 250: 1094, 1972;K. BERGMANN, J. Polymer Sci. Polymer Phys. Ed. 16: 1611, 1978 :

2. K. FUJIMOTO, T. NISHI and R. KADO, Polymer 3. 3: 448, 1972; R. KITAMARU, F. HORII and H. HYON, J. Polymer Sci. Polymer Phys, Ed. 15: 821, 1977 3. V. D. FEDOTOV, Yu. K. OVCHINNIKOV, N. A. ABDRASHITOVA and N. N. KUZ'MIN, Vysokomol. soyed. A19: 327, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 2, 378, 1977) 4. V. D. FEDOTOV, A. EBERT and H. SCHNEIDER, Phys. Star. Solid 63:1209, 1981

Three-dimensional polymerization of diamond

295

5. V. D. FEDOTOV and N. A. ABDRASHITOVA, In: Proc. of the XX Congress AMPERE. p. 118, Springer-Verlag, Berlin, 1979 6. Yu. K. OVCHINNIKOV, N. N. KUZ'MIN, G. S. MARKOVA and N. F. BAKRYEV, Vysokomol. soyed. A22: 1742, 1978 (Translated in Polymer Sci. U.S.S.R. 22- 8, 1908, 1978) 7. V.D. FEDOTOV and N. A. ABDRASHITOVA, Vysokomol. soyed. A22: 624, 1980 (Translated in Polymer Sci. U.S.S.R. 22" 3, 688, 1980) 8. Vysokomol. soyed. A19: 2811, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 12, 3246, 1977), A21: 2275, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 10, 2511, 1979) 9. Vysokomol. soyed. A23: 1, 61, 1981 (Translated in Polymer Sci. U.S.S.R. 23- 1, 70, 1981) 10. N. N!. KUZ'MIN, Yu. K. OVCHINNIKOV and N. F. BAKEYEV, Vysokomol. soyed. A22: 1372, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 6, 1507, 1980) i i . A. N. TEMNIKOV and V. D. FEDOTOV, Pribor. i tekh. eksp., 51,151, 1980 12. V. M. CHERNOV and V. D. FEDOTOV, Vysokomol. soyed. 23: 931, 1981 (Not translated in Polymer Sci. U.S.S.R.) 13. V. D. FEDOTOV, Sovremennye metody YaMR i EPR v khimii tverdogo tcla (Current N M R and ESR Methods in Solid Body Chemistry). p. 38, OIKhF, Akad. Nauk SSSR, 1982 14. R. M. FUOSS and J. G. KIRKWOOD, J. Amer. Chem. Soc. 63: 385, 1941 15. V. D. FEDOTOV and G. M. KADIYEVSKII, Vysokomol. soyed. A20: 1565, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 7, 1766, 1978)

polymer ScienceU.S.S.R.Vol. 27, No. 2, pp. 295-302. 1985 Printed in Poland

0032-3950/85 $10.00+ .00 © 1986 Pergamon Press Ltd.

THREE-DIMENSIONAL POLYMERIZATION AND GROWTH OF DIAMOND IN A HETEROGENEOUS MEDIUM AT HIGH PRESSURES AND TEMPERATURES* A. V. LYSENKO, M. YA. KATSAI a n d A. A. SHUL'ZHENKO Institute of Ultra-Hard Materials, Ukr.S.S.R. Academy of Sciences

(Received 4 June 1983)

The authors have studied the structural and kinetic patterns of the crystallization of threedimensional covalent diamond networks in the metallic melt N i - M n - C at a pressure of 4.2 GPa and temperature 1500 K. The kinetic region and kinetic constants of the process have been determined. The role of the metals as solvents of carbon and a medit~m activating the radical polymerization of three-dimensional covalent networks is studied. The mechanism of synthesis of diamond based on the mono-, bi- and trimolecular reactions taking place in the activated complexes is considered. * Vysokomol. soyed..4,27: No. 2, 270--275, 1985.