- Email: [email protected]
The Molecular Weight Distribution (MWD) of oligocaprolactones and the exchange reactions between chains
Molecular weight distribution of oligocaprolactones
1427
4. O. Ya. FEDOTOVA, M. L. KERBER and 1. P. LOSEV, Vysokomol. soyed. 2: 1020, 1960 (Not translated in Polymer Sei. U.S.S.R.) 5. L. B. SOKOLOV and T. V. KUDI1K, Vysokomol. soyed. 9: 698, 1960 (Not translated in Polymer Sei. U.S.S.R.) 6. G. I. KUDRYAVTSEV, L. F. BALAKLEITSEVA, A. M. SHCHETININr and L. V. CHIKURINA, Vysokomol. soyed. A10: 2205, 1970 (Not translated in Polymer Sei. U.S.S.I~.) 7. V. K. BELYAKOV, A. A. KOSOBUTSKAYA, V. M. SAVINOV, L. B. SOKOLOV, S. S. GITIS and V. M. IVANOVA, Vysokomol. soyed. A12: 610, 1970 (Translated in Polymer Sci. U.S.S.R. 3: 684, 1970) 8. S. NISHIZAKI and A. FUKAM[, J. Chem. Soc. Japan, Ind. Chem. Sec. 66: 383, 1963; 67: 474, 1964 9. Yu. A. SHLYAPNIKOV, V. B. MILLER and M. B. NEIMAN, Vysokomol. soyed. 2:1409 1960 (Not translated in Polymer Sci. U.S.S.R.) 10. O. Ya. FEDOTOVA, M. L. KERBER and B. M. KOVARSKAYA, Plast. massy, No. l, 14, 1967 11. L. H. LADY, J. J.KESSE and R. E. ADAMS, J. Appl. Polymer Sci. 3: 71, 1960 12. N. N. SEMENOV, Razvitie tcorii tsepnykh reaktsii i teplovogo vosplameneniya (Development of the Chain l~eaction Theory and of Thermal Ignition). Izd. "Znanie", 1969 13. J. MAYO, Polymer Preprints 8: 11, 1967 14. M. B. NEIMAN (Ed.), Sb.: Starenie i stabilizatsiya polimerov (The Ageing and Stabilization of Polymers). p. 11, Izd. " N a u k a " , 1964 15. V. V. KORSHAK, Sb.: Kinetika i mekhanizm obrazovaniya makromolekul (In: The Kinetics and Mechanism of Macromolecular Synthesis), p. 127, Izd. "Nauka", 1968 16. K. INGOL'D, Uspekhi khim. 33: 1107, 1964 17. T. NARAGAN, ZAKSHMI and C. MARVEL, J. Polymer Sci. 5, A - l : 1113, 1967 18. S. NISHIZAKI and A. FUKAMI, J. Chem. Soe. Japan, Ind. Chem. Sec. 68: 383, 1965
THE MOLECULAR WEIGHT DISTRIBUTION (MWD) OF OLIGOCAPROLACTONES AND THE EXCHANGE REACTIONS BETWEEN CHAINS* A. A. GURYLEVA, R . A. SHLYAKHTER a n d B. YA. TEITEL'BAUM A. ¥ c . Arbuzov I n s t i t u t e of Organic and Physical Chemistry, U.S.S.R. Academy of Sciences S. V. Lebedev All-Union Synthetic R u b b e r Research Institute (Received 26 J u n e 1972)
Turbidimetric titration was used on oligocaprolactones (OCL) with ~r n = 660-4500 to arrive at a solubility equation; the MWD and/~r values were calculated and found to agree well with the fractionation data. The M w / M n ratio was found to depend on the possibility of exchange reactions between chains and to increase with growing 7~., u n t i l approaching the value of 2. The 21~w changes, when a mixture of two artificial * Vysokomol. soyed. A16: No. 6, 1235-1240, 1974.
1428
A. A. G ~ v A
et al.
OCL fractions w i t h d i f f e r i n g / ~ r was h e a t e d at a n u m b e r of t e m p e r a t u r e s , were u s e d to e s t i m a t e t h e a c t i v a t i o n energies of t h e e x c h a n g e processes; this was f o u n d to b e 14 keal/mole in t h e presence of 0-1 °/o tin d i b u t y l diIaurate as catalyst, and 24 k e a l / m o l e w i t h o u t i~. A similar result was found b y analysing t h e p r i m a r y t u r b i d i m e t r i c d a t a 7 , - - v o l u m e fraction of p r e c i p i t a n t producing t h e p r e c i p i t a t i o n of h a l f t h e OCL p r e s e n t in t h e solution.
I~ THE synthesis of high molecular weight (mol.wt.) products from oligomers-it is important to know the average mol.wt, and of the mol.wt, distribution (MWD) of the oligomers used, and also of the possibility of controlling these values by mixing samples of different Mn while considering the exchange reactions which occur between chains. The frequent uses of oligomers in industry present this investigation with the problem of finding a rapid and sufficiently accurate method of determining the polydispersity. The turbidimetric titration used to study polymers with large mol.wt, is one of the rapid methods giving such information. Recent publications [1-3] describe the possibility of selecting conditions in which the turbidimetric method will give results which are in good agreement with those of fractionation when oligomers of different origins are used. Oligomers with hydroxyl end groups which are used to synthesize methane elastomers are of special interest. OCL produced by cationic polymerization from e-caprolactone in the presence of a diol [4] belong to this groups. The mechanism of OCL synthesis is by living chain propagation which ensures a narrow MWD. The composition of the OCL macromolecules with ester groups in the main chain, and with hydroxyl end groups will facilitate the exchange reactions between chains, which is typical of hetero-chain polymers regardless of the synthesis used. These exchange reactions must naturally alter the MWD. If they progress to an equilibrium, the polymer will possess the most probable distribution at which the Mw/Mn will equal 2. Polyester type oligomers will have a much lower ratio, but it will approach 2 when ~rn increases [5]. This report describes the results of a study of the MWD of OCL (with Mn ~660A4500) and the exchange reaction between chains. EXPERIMENTAL F r a c t i o n a t i o n and t u r b i d i m e t r i c t i t r a t i o n methods were used in the study. The l a t t e r h a d t h e curves a u t o m a t i c a l l y r e c o r d e d [6]. T h e initial v o l u m e of t h e solution was 10 ml, t h e m e t e r i n g r a t e of t h e preci~oitant 0.32 m l / m i n , and m i x i n g was a t 240 r.p.m. Benzeno was used as t h e solvent, petrole~um ether as t h e precipitant; b o t h were purified as described b y Weissberger and co-authors [7], and t h e t i t r a t i o n was carried o u t at 25°C. T h e OCL crystallized at a lower t e m p e r a t u r e , which u p s e t the m a i n condition for t h e fractionation, i.e. t h e p o l y m e r s e p a r a t i o n in t h e liquid phase [8] b u t it was difficult to precipitate it a t a higher t e m p e r a t u r e .
RESULTS
The large changes in solubility of OCL when the M~ changes ensured easy fractionation of the sample in the selected titration conditions (Fig. 1). To establish that the turbidimetric characteristics were independent of M we titrated
Molecular weight distribution of oligoeaprolactones
1429
separate fractions (or narrow M W D samples) at several concentrations (from 0.01 to 0.15 g/dl). A solubility equation connecting volume fraction 7 of the precipitant at any point of the titration curve with the solution concentration and the mol.wt. M was produced from the experimental curve processed according to [9]. 7----1.15--0-35 log c--0"19 log M~-0"08 log c log M The calculated value of M, equivalent to the experimental 7, was found for any OCL sample according to this equation and the distribution curve was plotted. The reliability of the turbidimetric titration data was assessed b y comparing the latter with the results of column fractionation. D 2-
e
z/
g.65
075
0.85/
FIG. 1. The OCL turbidimetric titration curves for/~r n of: 1 -- 660; 2-- 1560; 3-- 1900; 4--2300; c=0.05 g/dl. OCL samples with ~ / n ~ 2 3 0 0 and 660 were fractionated b y extraction from a thin film at 30°C [5] using the same solvent-precipitant system as for the titration. The mol.wt, of the isolated fractions were determined b y ebullioscopy in benzene. Figure 2 shows the integral MWD curves of the sample with ~rn ~ 2300 which were plotted from the fractionation and turbidimetrie data; they demons'trate the good agreement of the results from the two methods. The objectivity of the data was verified b y the frdetionation method and the results from samples under identical conditions in methylethylketone (MEK)n-hexane confirmed it. The latter system is less "severe" and gives better separation as it provides a broader range of volume fractions of the precipitant in which precipitation (or solubflization) of OCL will take place. Complete precipitation is produced b y such large volume fractions of the precipitant that a turbidimetric titration would be impossible in a vessel of limited volume. The system benzene-petroleum ether was therefore chosen for the titration. Comparison of the results from both the systems shows at the same time the full agreement of mol.wt, characteristics (Table 1). One can therefore regard the calculated MWD as reliable and also their changes based on turbidimetric titrations.
1430
A.A.
GURYLEVA et al.
The results given in Table 1 comply with the dependence of polydispersity coefficients on the mol.wt., which is generally similar to that found for polyethylene-, polydiethylene- and polytriethyleneglycol adipates [5]. These results W 1"0o2
0.80"80"40"20
I #
2
I 6~bT~/O"3
:FIG. 2. The M W D integral curves for OCL and .3~rn=2300 using: 1 - - f r a e t i o n a t i o n ; 2 - - t u r b i d i m e t r i c titration. ( W - - w e i g h t f r a c t i o n integral).
indicate the existence of an exchange reaction between chains during the syntheses of OCL (cyclic products can be present here, as in the majority of oligomeric polyesters; these must broaden the MWD, but this problem is not being discussed here). T A B L E i . T H E AVERAGE
mol.wt.
AND P O L Y D I S P E R S I T I E S OF O C L
E x p e r i m e n t a l results
Calculated f r o m f r a c t i o n a t i o n in s y s t e m
Sample, No.
.Z~n × 10 -2 (ebulliometry)
/]S/wX 10 -a (lightscattering)
MEK-n-hexane
_#s: ~ I ,
2 3 4*
6-0 15 19 23
5 6175
45 18 18.5
1
1200 2550 3000 4900
5
780 1560 1900 2600
3
4300 8600 2190 2300 2400 2550
Mn
benzene-petroleum ether
t u r b i d i m e t r y in benzene-petroleum ether
iw
1.54 720 108 1.63 1-58 1.88 2470 452 2200 406 2.00 1.05 1.06
* Fraetionated twice in system benzene-petroleum ethcr. t Produced at 60°C without catalyst. $ Produced at the same temperature with 0"1% tin dibutyl dilaurate as catalyst.
150
1.83
1.84
75£ 1470 1790 2200
1160 2300 2690 4070
1.55 1.56 1.50 1.85
143l
Molecular weight distribution of oligoeaprolaetones
The fairly large differences in 21~ values, according to ebullioscopic measurements and fractionation of samples 6 and 7 (Table 1), seem to be explained b y the presence of some original lactone in the samples. The unusually narrow MWD in these (Mw/M~=I'05 and 1.06) led to the assumption of exchange reactions between chains not taking place during their synthesis. This fact can be associated with the low temperature used (60°C for these two, 150°C for the others). As one of the samples (No. 7) was synthesized over a catalyst, and No. 6 without, one can conclude that the catalyst (tin dibutyl dilaurate) will hardly affect the inter-chain exchange reaction. W
l.ol
0~8 O#
0.4 t2# 0"2 0
~3
2
I
I
4
I
I
#
I
H~lO-8
I
8
FiG. 3. The effect of inter-chain exchange reaction~ on the MWI). 1--OCL with 71~, 4860; 2--OCL with M~ 730; 3-8--mixture of OCL 1 and 2 at 1 : 2 ratio (_71~n-~1090) after heating to 100°(3 for (hr): 3--15; 4--31; 5--50; 6--76; 7--100; 8--150. The inter-chain exchange reactions were investigated on the Jlw of specially prepared OCL mixtures, using samples 1 and 4 fractions with/]]rn-~ 750 and 5000 (Table 1; the correct figures were 730 and 4860 during the study of the uncatalyzed exchange, and 780 and 5260 during that catalyzed b y 0.1 ~/o w/w tin dibutyl dilaurate). The fractions were mixed at a 1 : 2 ratio b y weight, the mixtures sealed in ampoules under less than 6 x 10 -8 m m H g vacuum, and were then heated at 100, 120, 150 and 180°C in the case of uncatalyzed, 60, 90, 120 and 150°C in that of catalyzed exchange. Samples were taken at regular intervals and solutions prepared of the required concentrations. The latter were titrated as described above and the titration curves, together with the given equation, used to calculate the MWD of each sample. As Fig. 3 shows, the distribution curve for the mixture heated at 100°C without catalyst shifts towards the low mol.wt, component as the temperature rises,
1432
A. A. GURYLEVA et al.
until the state of equilibrium is reached. The same result was typical also for the other heat treatment temperatures. The MWD curves were used to calculate the ~r w and the kinetic curves then plotted as shown in Fig. 4a. The catalyzed exchange data were produced b y the same method.
Z
O
.q..~ l vO
.
a
Z
I
~
F
/0
1.0 0.0 o
.
I
I
/00 "/'/me,/lp Fro.4
1
I
/dO
e.o~
3.o
-0~t
-/'0
Fro. 5
Fla. 4. The kinetic curves of a: the Mw, b: the 7, changes in OCL mixture at (°C): 1--100; 2--120; 3--150; 4--180. FIC. 5. The dependence of log ~ on 1/T for kinetic curves of the type contained in Fig. 4. I - - U n c a t a l y z e d exchange; / / - - e x c h a n g e in the presence of 0.1% tin dibutyl dilaurate assessed on 1 - - M w, 2--~,~.
The inter-chain exchange reactions can also be traced in the OCL from a primary turbidimetric characteristic such as y~ (Fig. 4b). The ~÷ will become larger as heating is continued while ~r w will decrease to a limit which is identical for all the studied temperatures. This fact alone is already evidence for the changes of these values not being connected with decomposition or hydrolytic processes, although they cannot be excluded at the higher temperatures [12]. These conclusions were confirmed in special control experiments, i.e. b y heating the original components before the ebullioseopie M , determination (Table 2), and also b y turbidimetric analysis, as described above. Table 2 shows t h a t the l])n of the high and low mol.wt, components remain the same within the ebulliometric determination limits, or for that matter of the turbidimetric ones. The results lead to the conclusion that no decomposition, nor any secondary reactions, take place which would result in ~r w changes under the test conditions, and would also affect solubility. The kinetic curves contained in Fig. 4 demonstrate the strong temperature dependence of the rate of change of Mw (or ~t). It should be noted that the Mw values drop at 120 and 150°C to slightly below the equilibrium value and rise later to it. The curves for 7, are similar in shape. The minimum obviously
1433
Molecular weight distribution of oligocaprolactones
corresponds with the state of transition to a non-equilibrium MWD [8]. This phenomenon can be associated with a fairly large rate of inter-chain exchange reactions (which will result in the production of short molecules) when compared with the average rate at which the distribution equilibrium forms. The same course is also highly probable at 180°C, but its rapidity (equilibrium reached in 1 hr) did not make it possible to spot the minimum on this curve. T A B L E 2. T H E M n
OF T H E O R I G I N A L C O M P O N E N T S AND OF T H E I R M I X T U R E S A F T E R H E A T I N G
Sample High mol.wt, component Low mol.wt, component Component mixture (1 : 2)
T,°C 150 150 180
20 4860 730 1090
4950 740 1070
Heating time, hr 30 50 100
150
250
4940 4860 5000 4900 720 780 760 740 1060 1080 1100 980
1070
The exchange reaction progresses more easily when a catalyst is present at any temperature. The kinetic curves do not show a minimum in such a c a s e and this could be due to the rapidity with which the equilibrium is reached in the system. No reaction occurs at 60°C however, even when the catalyst is present, and a 200 hr heating did not produce any MWD change. This confirms the earlier conclusion t h a t the very narrow MWD of samples 6 and 7 is due to the absence of exchange reactions between chains under their synthesis conditions. I t is possible on the basis of the kinetic curves for -~w and 7½ to get an idea about the activation energy of the exchange reaction from the transformation method [13]. Such an evaluation does not require any detailed knowledge of the mechanism, or kinetic order, of the reaction. By leaving out the characteristics of curves 2 and 3 in Fig. 4 one can say t h a t d a t a processing would be fully justified by this method. As a matter of fact we got good constancy of the transformation coefficient K, by e.g. selecting the 120°C data mark isotherm. The activation energies calculated from Fig. 5 were 14 and 22 kcal/mole for the catalyzed and uncatalyzed exchange reaction respectively. These values are close to those got for an exchange between a polyester and a low mol.wt. alcohol or acid [14]. The authors express their gratitude to Ye. Ye. Sidirova for assistance with the ebullioscopic determinations, T. V. Stupalova for participation in the catalyzed exchange reaction studies, and Yu. P. Vauchski for the supply of samples. Translated by K. A. Ar.~EN REFERENCES
1. A. Ire. TAVRIN and A. A. GURYI2EVA, Izd. Akad.
Nauk
SSSR, Ser. khim., 1300, 196~
2. A. A. GURYLEVA, B. Ya. TEITEL'BAD'M, R. A. SHLYAKHTER and L. P. MOSKEVICH, Vysokomol. soyed. A14: 1221, 1972 (Translated in Polymer Sei. U.S.S.R. 5:~
1370, 1972)
1434
N. S. SURKOVA et al.
3. N. G. MAL'TSEVA, I. F. TIBANOV and E. M. EIZENSHTEIN, Khim. volokna, No. 1, 26, 1971 4. N. P. APUKHTINA, L. V. MOZZHUKHINA and Yu. L. MOROZOV, Proizvodstvo i primenenie uretanovykh elastomerov (The Production and Uses of Uerthane Elastomers). Tsentral. nauch, issled, inst. tekhnol, neftekhim., 1969 5. V. I. VALUYEV, R. A. SHLYAKHTER and N. P. APUKHTINA, Vysokomol. soyed. B10: 147, 1968 (Not translated in Polymer Sci. U.S.S.R.) 6. B. Ya. TEITEL'BAUM and IV[. P. DIANOV., Zavod. labor. 30: 235, 1964 7. A. WEISSBERGER, E. PROSKAUER, J. RIDDICK and E. TUPPS, Organicheskie rastvoriteli (Organic Solvents). Izd. inostr, lit., 1958 8. S. Ya. FRENKEL, Vvedenic v statisticheskuyu teoriyu polimerizatsii (Introduction the Statistics Theory of Polymerization). p. 181, Izd "Nauka", 1965 9. A. I. SHATENSHTEIN, Yu. P. VIRSKII, N. h . PRAVIKOVA, P. P. ALIKHANOV, K. I. ZHDANOV and A. L. IZYUM~IKOV, Prakticheskoye rukovodstvo po opredeleniyu molekulyarnykh vesov i molekulyarno-vesovogo raspredeleniya polimerov (Practical Manual to Molecular Weight and Molecular Weight Distribution Determinations on Polymers). Izd. " K h i m i y a " , 1964 10. J. GOODMAN and B. F. NESBITT, Polymer 1: 394, 1960 11. J. GOODMAN and B. F. NESBITT, J. Polymer Sci. 48: 423, 1960 12. V. V. KORSHAK, G. I. TARASOVA and S. A. PAVLOVA, Vysokomol. soyed. A13: 1047, 1971 (Not translated in Polymer Sci U.S.S.R.) 13. N. M. EMA_NUEL and D. G. KNORRE, Kurs khimicheskoi kinetiki (Chemical Kinetics Course). p. 52, Izd. "Vysshaya Shkola", 1969 14. Ye. FETTES (Ed.), Khimicheskie reaktsii polimerov (Chemical Reactions of Polymers). Vo]. 1, p. 462, Izd. "Mir", 1967
THE MECHANICAL PROPERTIES AND MORPHOLOGY OF BUTADIENE-STYRENE BLOCK-COPOLYMERS OF DIFFERENT COMPOSITIONS* N. S. SURKOVA,G. T. TKACHE~TKO, YE. A. SIDOROVICH,G. M. TOLSTOPYATOV, A. I. M_A~E~and YE. V. KUVSHI~SKII S. V. Lebedev All-Union Synthetic Rubber Research Institute (Received 28 J u n e 1972)
A dynamic mechanical method and electron microscopy have been used to study butadicne-styrene (BDST) thermoplastic elastomers of different compositions. The effect of the n u m b e r of blocks present in the polymer chains at a fixed composition and molecular weight on the properties of these block copolymers has been established. The minimal block dimensions at which the polymers would behave like random eopolymers have been estimated. Three-block copolymers with 40~o styrene were found to have decreasing elasticity and loss moduli when the molecular weight increased * Vysokomol. soyed. A16: No. 6, 1241-1249, 1974.
1427
4. O. Ya. FEDOTOVA, M. L. KERBER and 1. P. LOSEV, Vysokomol. soyed. 2: 1020, 1960 (Not translated in Polymer Sei. U.S.S.R.) 5. L. B. SOKOLOV and T. V. KUDI1K, Vysokomol. soyed. 9: 698, 1960 (Not translated in Polymer Sei. U.S.S.R.) 6. G. I. KUDRYAVTSEV, L. F. BALAKLEITSEVA, A. M. SHCHETININr and L. V. CHIKURINA, Vysokomol. soyed. A10: 2205, 1970 (Not translated in Polymer Sei. U.S.S.I~.) 7. V. K. BELYAKOV, A. A. KOSOBUTSKAYA, V. M. SAVINOV, L. B. SOKOLOV, S. S. GITIS and V. M. IVANOVA, Vysokomol. soyed. A12: 610, 1970 (Translated in Polymer Sci. U.S.S.R. 3: 684, 1970) 8. S. NISHIZAKI and A. FUKAM[, J. Chem. Soc. Japan, Ind. Chem. Sec. 66: 383, 1963; 67: 474, 1964 9. Yu. A. SHLYAPNIKOV, V. B. MILLER and M. B. NEIMAN, Vysokomol. soyed. 2:1409 1960 (Not translated in Polymer Sci. U.S.S.R.) 10. O. Ya. FEDOTOVA, M. L. KERBER and B. M. KOVARSKAYA, Plast. massy, No. l, 14, 1967 11. L. H. LADY, J. J.KESSE and R. E. ADAMS, J. Appl. Polymer Sci. 3: 71, 1960 12. N. N. SEMENOV, Razvitie tcorii tsepnykh reaktsii i teplovogo vosplameneniya (Development of the Chain l~eaction Theory and of Thermal Ignition). Izd. "Znanie", 1969 13. J. MAYO, Polymer Preprints 8: 11, 1967 14. M. B. NEIMAN (Ed.), Sb.: Starenie i stabilizatsiya polimerov (The Ageing and Stabilization of Polymers). p. 11, Izd. " N a u k a " , 1964 15. V. V. KORSHAK, Sb.: Kinetika i mekhanizm obrazovaniya makromolekul (In: The Kinetics and Mechanism of Macromolecular Synthesis), p. 127, Izd. "Nauka", 1968 16. K. INGOL'D, Uspekhi khim. 33: 1107, 1964 17. T. NARAGAN, ZAKSHMI and C. MARVEL, J. Polymer Sci. 5, A - l : 1113, 1967 18. S. NISHIZAKI and A. FUKAMI, J. Chem. Soe. Japan, Ind. Chem. Sec. 68: 383, 1965
THE MOLECULAR WEIGHT DISTRIBUTION (MWD) OF OLIGOCAPROLACTONES AND THE EXCHANGE REACTIONS BETWEEN CHAINS* A. A. GURYLEVA, R . A. SHLYAKHTER a n d B. YA. TEITEL'BAUM A. ¥ c . Arbuzov I n s t i t u t e of Organic and Physical Chemistry, U.S.S.R. Academy of Sciences S. V. Lebedev All-Union Synthetic R u b b e r Research Institute (Received 26 J u n e 1972)
Turbidimetric titration was used on oligocaprolactones (OCL) with ~r n = 660-4500 to arrive at a solubility equation; the MWD and/~r values were calculated and found to agree well with the fractionation data. The M w / M n ratio was found to depend on the possibility of exchange reactions between chains and to increase with growing 7~., u n t i l approaching the value of 2. The 21~w changes, when a mixture of two artificial * Vysokomol. soyed. A16: No. 6, 1235-1240, 1974.
1428
A. A. G ~ v A
et al.
OCL fractions w i t h d i f f e r i n g / ~ r was h e a t e d at a n u m b e r of t e m p e r a t u r e s , were u s e d to e s t i m a t e t h e a c t i v a t i o n energies of t h e e x c h a n g e processes; this was f o u n d to b e 14 keal/mole in t h e presence of 0-1 °/o tin d i b u t y l diIaurate as catalyst, and 24 k e a l / m o l e w i t h o u t i~. A similar result was found b y analysing t h e p r i m a r y t u r b i d i m e t r i c d a t a 7 , - - v o l u m e fraction of p r e c i p i t a n t producing t h e p r e c i p i t a t i o n of h a l f t h e OCL p r e s e n t in t h e solution.
I~ THE synthesis of high molecular weight (mol.wt.) products from oligomers-it is important to know the average mol.wt, and of the mol.wt, distribution (MWD) of the oligomers used, and also of the possibility of controlling these values by mixing samples of different Mn while considering the exchange reactions which occur between chains. The frequent uses of oligomers in industry present this investigation with the problem of finding a rapid and sufficiently accurate method of determining the polydispersity. The turbidimetric titration used to study polymers with large mol.wt, is one of the rapid methods giving such information. Recent publications [1-3] describe the possibility of selecting conditions in which the turbidimetric method will give results which are in good agreement with those of fractionation when oligomers of different origins are used. Oligomers with hydroxyl end groups which are used to synthesize methane elastomers are of special interest. OCL produced by cationic polymerization from e-caprolactone in the presence of a diol [4] belong to this groups. The mechanism of OCL synthesis is by living chain propagation which ensures a narrow MWD. The composition of the OCL macromolecules with ester groups in the main chain, and with hydroxyl end groups will facilitate the exchange reactions between chains, which is typical of hetero-chain polymers regardless of the synthesis used. These exchange reactions must naturally alter the MWD. If they progress to an equilibrium, the polymer will possess the most probable distribution at which the Mw/Mn will equal 2. Polyester type oligomers will have a much lower ratio, but it will approach 2 when ~rn increases [5]. This report describes the results of a study of the MWD of OCL (with Mn ~660A4500) and the exchange reaction between chains. EXPERIMENTAL F r a c t i o n a t i o n and t u r b i d i m e t r i c t i t r a t i o n methods were used in the study. The l a t t e r h a d t h e curves a u t o m a t i c a l l y r e c o r d e d [6]. T h e initial v o l u m e of t h e solution was 10 ml, t h e m e t e r i n g r a t e of t h e preci~oitant 0.32 m l / m i n , and m i x i n g was a t 240 r.p.m. Benzeno was used as t h e solvent, petrole~um ether as t h e precipitant; b o t h were purified as described b y Weissberger and co-authors [7], and t h e t i t r a t i o n was carried o u t at 25°C. T h e OCL crystallized at a lower t e m p e r a t u r e , which u p s e t the m a i n condition for t h e fractionation, i.e. t h e p o l y m e r s e p a r a t i o n in t h e liquid phase [8] b u t it was difficult to precipitate it a t a higher t e m p e r a t u r e .
RESULTS
The large changes in solubility of OCL when the M~ changes ensured easy fractionation of the sample in the selected titration conditions (Fig. 1). To establish that the turbidimetric characteristics were independent of M we titrated
Molecular weight distribution of oligoeaprolactones
1429
separate fractions (or narrow M W D samples) at several concentrations (from 0.01 to 0.15 g/dl). A solubility equation connecting volume fraction 7 of the precipitant at any point of the titration curve with the solution concentration and the mol.wt. M was produced from the experimental curve processed according to [9]. 7----1.15--0-35 log c--0"19 log M~-0"08 log c log M The calculated value of M, equivalent to the experimental 7, was found for any OCL sample according to this equation and the distribution curve was plotted. The reliability of the turbidimetric titration data was assessed b y comparing the latter with the results of column fractionation. D 2-
e
z/
g.65
075
0.85/
FIG. 1. The OCL turbidimetric titration curves for/~r n of: 1 -- 660; 2-- 1560; 3-- 1900; 4--2300; c=0.05 g/dl. OCL samples with ~ / n ~ 2 3 0 0 and 660 were fractionated b y extraction from a thin film at 30°C [5] using the same solvent-precipitant system as for the titration. The mol.wt, of the isolated fractions were determined b y ebullioscopy in benzene. Figure 2 shows the integral MWD curves of the sample with ~rn ~ 2300 which were plotted from the fractionation and turbidimetrie data; they demons'trate the good agreement of the results from the two methods. The objectivity of the data was verified b y the frdetionation method and the results from samples under identical conditions in methylethylketone (MEK)n-hexane confirmed it. The latter system is less "severe" and gives better separation as it provides a broader range of volume fractions of the precipitant in which precipitation (or solubflization) of OCL will take place. Complete precipitation is produced b y such large volume fractions of the precipitant that a turbidimetric titration would be impossible in a vessel of limited volume. The system benzene-petroleum ether was therefore chosen for the titration. Comparison of the results from both the systems shows at the same time the full agreement of mol.wt, characteristics (Table 1). One can therefore regard the calculated MWD as reliable and also their changes based on turbidimetric titrations.
1430
A.A.
GURYLEVA et al.
The results given in Table 1 comply with the dependence of polydispersity coefficients on the mol.wt., which is generally similar to that found for polyethylene-, polydiethylene- and polytriethyleneglycol adipates [5]. These results W 1"0o2
0.80"80"40"20
I #
2
I 6~bT~/O"3
:FIG. 2. The M W D integral curves for OCL and .3~rn=2300 using: 1 - - f r a e t i o n a t i o n ; 2 - - t u r b i d i m e t r i c titration. ( W - - w e i g h t f r a c t i o n integral).
indicate the existence of an exchange reaction between chains during the syntheses of OCL (cyclic products can be present here, as in the majority of oligomeric polyesters; these must broaden the MWD, but this problem is not being discussed here). T A B L E i . T H E AVERAGE
mol.wt.
AND P O L Y D I S P E R S I T I E S OF O C L
E x p e r i m e n t a l results
Calculated f r o m f r a c t i o n a t i o n in s y s t e m
Sample, No.
.Z~n × 10 -2 (ebulliometry)
/]S/wX 10 -a (lightscattering)
MEK-n-hexane
_#s: ~ I ,
2 3 4*
6-0 15 19 23
5 6175
45 18 18.5
1
1200 2550 3000 4900
5
780 1560 1900 2600
3
4300 8600 2190 2300 2400 2550
Mn
benzene-petroleum ether
t u r b i d i m e t r y in benzene-petroleum ether
iw
1.54 720 108 1.63 1-58 1.88 2470 452 2200 406 2.00 1.05 1.06
* Fraetionated twice in system benzene-petroleum ethcr. t Produced at 60°C without catalyst. $ Produced at the same temperature with 0"1% tin dibutyl dilaurate as catalyst.
150
1.83
1.84
75£ 1470 1790 2200
1160 2300 2690 4070
1.55 1.56 1.50 1.85
143l
Molecular weight distribution of oligoeaprolaetones
The fairly large differences in 21~ values, according to ebullioscopic measurements and fractionation of samples 6 and 7 (Table 1), seem to be explained b y the presence of some original lactone in the samples. The unusually narrow MWD in these (Mw/M~=I'05 and 1.06) led to the assumption of exchange reactions between chains not taking place during their synthesis. This fact can be associated with the low temperature used (60°C for these two, 150°C for the others). As one of the samples (No. 7) was synthesized over a catalyst, and No. 6 without, one can conclude that the catalyst (tin dibutyl dilaurate) will hardly affect the inter-chain exchange reaction. W
l.ol
0~8 O#
0.4 t2# 0"2 0
~3
2
I
I
4
I
I
#
I
H~lO-8
I
8
FiG. 3. The effect of inter-chain exchange reaction~ on the MWI). 1--OCL with 71~, 4860; 2--OCL with M~ 730; 3-8--mixture of OCL 1 and 2 at 1 : 2 ratio (_71~n-~1090) after heating to 100°(3 for (hr): 3--15; 4--31; 5--50; 6--76; 7--100; 8--150. The inter-chain exchange reactions were investigated on the Jlw of specially prepared OCL mixtures, using samples 1 and 4 fractions with/]]rn-~ 750 and 5000 (Table 1; the correct figures were 730 and 4860 during the study of the uncatalyzed exchange, and 780 and 5260 during that catalyzed b y 0.1 ~/o w/w tin dibutyl dilaurate). The fractions were mixed at a 1 : 2 ratio b y weight, the mixtures sealed in ampoules under less than 6 x 10 -8 m m H g vacuum, and were then heated at 100, 120, 150 and 180°C in the case of uncatalyzed, 60, 90, 120 and 150°C in that of catalyzed exchange. Samples were taken at regular intervals and solutions prepared of the required concentrations. The latter were titrated as described above and the titration curves, together with the given equation, used to calculate the MWD of each sample. As Fig. 3 shows, the distribution curve for the mixture heated at 100°C without catalyst shifts towards the low mol.wt, component as the temperature rises,
1432
A. A. GURYLEVA et al.
until the state of equilibrium is reached. The same result was typical also for the other heat treatment temperatures. The MWD curves were used to calculate the ~r w and the kinetic curves then plotted as shown in Fig. 4a. The catalyzed exchange data were produced b y the same method.
Z
O
.q..~ l vO
.
a
Z
I
~
F
/0
1.0 0.0 o
.
I
I
/00 "/'/me,/lp Fro.4
1
I
/dO
e.o~
3.o
-0~t
-/'0
Fro. 5
Fla. 4. The kinetic curves of a: the Mw, b: the 7, changes in OCL mixture at (°C): 1--100; 2--120; 3--150; 4--180. FIC. 5. The dependence of log ~ on 1/T for kinetic curves of the type contained in Fig. 4. I - - U n c a t a l y z e d exchange; / / - - e x c h a n g e in the presence of 0.1% tin dibutyl dilaurate assessed on 1 - - M w, 2--~,~.
The inter-chain exchange reactions can also be traced in the OCL from a primary turbidimetric characteristic such as y~ (Fig. 4b). The ~÷ will become larger as heating is continued while ~r w will decrease to a limit which is identical for all the studied temperatures. This fact alone is already evidence for the changes of these values not being connected with decomposition or hydrolytic processes, although they cannot be excluded at the higher temperatures [12]. These conclusions were confirmed in special control experiments, i.e. b y heating the original components before the ebullioseopie M , determination (Table 2), and also b y turbidimetric analysis, as described above. Table 2 shows t h a t the l])n of the high and low mol.wt, components remain the same within the ebulliometric determination limits, or for that matter of the turbidimetric ones. The results lead to the conclusion that no decomposition, nor any secondary reactions, take place which would result in ~r w changes under the test conditions, and would also affect solubility. The kinetic curves contained in Fig. 4 demonstrate the strong temperature dependence of the rate of change of Mw (or ~t). It should be noted that the Mw values drop at 120 and 150°C to slightly below the equilibrium value and rise later to it. The curves for 7, are similar in shape. The minimum obviously
1433
Molecular weight distribution of oligocaprolactones
corresponds with the state of transition to a non-equilibrium MWD [8]. This phenomenon can be associated with a fairly large rate of inter-chain exchange reactions (which will result in the production of short molecules) when compared with the average rate at which the distribution equilibrium forms. The same course is also highly probable at 180°C, but its rapidity (equilibrium reached in 1 hr) did not make it possible to spot the minimum on this curve. T A B L E 2. T H E M n
OF T H E O R I G I N A L C O M P O N E N T S AND OF T H E I R M I X T U R E S A F T E R H E A T I N G
Sample High mol.wt, component Low mol.wt, component Component mixture (1 : 2)
T,°C 150 150 180
20 4860 730 1090
4950 740 1070
Heating time, hr 30 50 100
150
250
4940 4860 5000 4900 720 780 760 740 1060 1080 1100 980
1070
The exchange reaction progresses more easily when a catalyst is present at any temperature. The kinetic curves do not show a minimum in such a c a s e and this could be due to the rapidity with which the equilibrium is reached in the system. No reaction occurs at 60°C however, even when the catalyst is present, and a 200 hr heating did not produce any MWD change. This confirms the earlier conclusion t h a t the very narrow MWD of samples 6 and 7 is due to the absence of exchange reactions between chains under their synthesis conditions. I t is possible on the basis of the kinetic curves for -~w and 7½ to get an idea about the activation energy of the exchange reaction from the transformation method [13]. Such an evaluation does not require any detailed knowledge of the mechanism, or kinetic order, of the reaction. By leaving out the characteristics of curves 2 and 3 in Fig. 4 one can say t h a t d a t a processing would be fully justified by this method. As a matter of fact we got good constancy of the transformation coefficient K, by e.g. selecting the 120°C data mark isotherm. The activation energies calculated from Fig. 5 were 14 and 22 kcal/mole for the catalyzed and uncatalyzed exchange reaction respectively. These values are close to those got for an exchange between a polyester and a low mol.wt. alcohol or acid [14]. The authors express their gratitude to Ye. Ye. Sidirova for assistance with the ebullioscopic determinations, T. V. Stupalova for participation in the catalyzed exchange reaction studies, and Yu. P. Vauchski for the supply of samples. Translated by K. A. Ar.~EN REFERENCES
1. A. Ire. TAVRIN and A. A. GURYI2EVA, Izd. Akad.
Nauk
SSSR, Ser. khim., 1300, 196~
2. A. A. GURYLEVA, B. Ya. TEITEL'BAD'M, R. A. SHLYAKHTER and L. P. MOSKEVICH, Vysokomol. soyed. A14: 1221, 1972 (Translated in Polymer Sei. U.S.S.R. 5:~
1370, 1972)
1434
N. S. SURKOVA et al.
3. N. G. MAL'TSEVA, I. F. TIBANOV and E. M. EIZENSHTEIN, Khim. volokna, No. 1, 26, 1971 4. N. P. APUKHTINA, L. V. MOZZHUKHINA and Yu. L. MOROZOV, Proizvodstvo i primenenie uretanovykh elastomerov (The Production and Uses of Uerthane Elastomers). Tsentral. nauch, issled, inst. tekhnol, neftekhim., 1969 5. V. I. VALUYEV, R. A. SHLYAKHTER and N. P. APUKHTINA, Vysokomol. soyed. B10: 147, 1968 (Not translated in Polymer Sci. U.S.S.R.) 6. B. Ya. TEITEL'BAUM and IV[. P. DIANOV., Zavod. labor. 30: 235, 1964 7. A. WEISSBERGER, E. PROSKAUER, J. RIDDICK and E. TUPPS, Organicheskie rastvoriteli (Organic Solvents). Izd. inostr, lit., 1958 8. S. Ya. FRENKEL, Vvedenic v statisticheskuyu teoriyu polimerizatsii (Introduction the Statistics Theory of Polymerization). p. 181, Izd "Nauka", 1965 9. A. I. SHATENSHTEIN, Yu. P. VIRSKII, N. h . PRAVIKOVA, P. P. ALIKHANOV, K. I. ZHDANOV and A. L. IZYUM~IKOV, Prakticheskoye rukovodstvo po opredeleniyu molekulyarnykh vesov i molekulyarno-vesovogo raspredeleniya polimerov (Practical Manual to Molecular Weight and Molecular Weight Distribution Determinations on Polymers). Izd. " K h i m i y a " , 1964 10. J. GOODMAN and B. F. NESBITT, Polymer 1: 394, 1960 11. J. GOODMAN and B. F. NESBITT, J. Polymer Sci. 48: 423, 1960 12. V. V. KORSHAK, G. I. TARASOVA and S. A. PAVLOVA, Vysokomol. soyed. A13: 1047, 1971 (Not translated in Polymer Sci U.S.S.R.) 13. N. M. EMA_NUEL and D. G. KNORRE, Kurs khimicheskoi kinetiki (Chemical Kinetics Course). p. 52, Izd. "Vysshaya Shkola", 1969 14. Ye. FETTES (Ed.), Khimicheskie reaktsii polimerov (Chemical Reactions of Polymers). Vo]. 1, p. 462, Izd. "Mir", 1967
THE MECHANICAL PROPERTIES AND MORPHOLOGY OF BUTADIENE-STYRENE BLOCK-COPOLYMERS OF DIFFERENT COMPOSITIONS* N. S. SURKOVA,G. T. TKACHE~TKO, YE. A. SIDOROVICH,G. M. TOLSTOPYATOV, A. I. M_A~E~and YE. V. KUVSHI~SKII S. V. Lebedev All-Union Synthetic Rubber Research Institute (Received 28 J u n e 1972)
A dynamic mechanical method and electron microscopy have been used to study butadicne-styrene (BDST) thermoplastic elastomers of different compositions. The effect of the n u m b e r of blocks present in the polymer chains at a fixed composition and molecular weight on the properties of these block copolymers has been established. The minimal block dimensions at which the polymers would behave like random eopolymers have been estimated. Three-block copolymers with 40~o styrene were found to have decreasing elasticity and loss moduli when the molecular weight increased * Vysokomol. soyed. A16: No. 6, 1241-1249, 1974.