Thermodynamic study of solubility of graft copolymers of perchlorovinyl and polyvinylacetate obtained by the radiation method

(2) The structure of the oligomers has been confirmed by IR spectroscopy and by the reactions of bromination, hydration and iodomethylation. Translated by R. J. A. I-IENDB,Y

REFERENCES 1. A. W. JOHNSOI~, J. Chem. Soc. 1009, 1946

2. J. B. ARMITAGE, E. R. H. JONES and M. C. WHITING, J. Chem. Soc. 44, 1951 3. H. A. SZYMANSKI, Interpreted Infrared Spectra, vol. 2, 5, 1966; Plenum Press, New York 4. V. WOLF, Liebig's Arm. Chem. 592: 222, 1955 5. V. WEST (Ed.), Use of Spectroscopy in Chemistry, 1959 6. Yu. I. PORFIR'EVA, E. S. TURBANOVA and A. A. PETROV, Zh. organ, khim. 2: 772, 777, 1966 7. J. H. WOTIZ, F. A. MILLER and R. J. PALCHAK, J. Amer. Chem. Soe. 72: 5055, 1950 8. C. L. COOK, E. R. H. JONES and M. C. WHITING, J. Chem. Soc. 2888, 1952 9. H. A. STANSBURY and W. R. PROOPS, J. Organ. Chem. 27: 320, 1962

THERMODYNAMIC STUDY OF SOLUBILITY OF GRAFT COPOLYMERS OF PERCHLOROVINYL AND POLYVINYLACETATE OBTAINED BY THE RADIATION METHOD* S. A. TASHMUKHAMEDOV, K m U. Us~A~ov, R. S. TILLAYEV a n d L. L. KIS'VYAI~TSEVA V. I. Lenin State University, Tashkent

(Received 16 March 1967)

THERE is at present a definite lack of published information in connection with thermodynamic studies of the solubility of graft copolymers obtained by the radiation method. However investigations of this type are important as the method adopted for radiation initiation of the graft copolymerization reaction (irradiation dose and dose rate, presence or absence of air) determines the mechanical properties of the product obtained, including its solubility. In an earlier paper we showed that the reduced solubility of the graft copolymer compared with the initial polymer is due either to a reduction in the negative value of the enthalpy component (AH1) of the thermodynamic potential of the solvent (for the system cellulose acetate-polyvinylpyrrolidone [1]), or to a reduction in the * Vysokomol. soyed. AI0: No. 2, 379-383, 1968.

positive values of the entropy component (Tz~S1) of this potential (for the system polymethylmethacrylate-butyl rubber [2]) in addition changes in solubility were explained as a function of side processes of degradation or crosslinking taking place through the effect of ionizing radiation upon components of the graft copolymer while it is being synthesized. This report gives the results of a thermodynamic study of change in solubility for several graft copolymers of perchlorovinyl (PerCV) and polyvinylacetate (PVA) depending on t h e irradiation dose with which they were synthesized. EXPERIMENTAL

The method used to produce the graft copolymers involved simultaneous irradiation of polymer and monomer in the absence of air. The grafting of vinylacetate to perehlorovinyls (chlorinated polyvinylchloride) with m.w. 51,600, chlorine content 61.2%) was carried out by means of e°Co y-irradiation with a dose range of 0.25-1.5 Mrad, at rates of 50 and 200 rad/scc. The method of experiment and the results of synthesis may be found in reference [3]. The integral heats of swelling and dissolution were determined by means of a Sehottka type microcalorimeter [4] and the values of At/l, by the method suggested by Taher [5]. The isotherms of sorption were recorded with a sorption apparatus [6] suitable for work with organic solvents. The density of the graft copolymers was found by the hydrostatic weighing method based on determination of the apparent loss of weight of a sample when immersed in a liquid [7J. PerCV-PVA graft copolymers synthesized over the dose range 0.25-1.5 Mrad at the rate of 200 tad/see are soluble in acetone and dichloroethane which are solvents for the initial components of the graft copolymers under review. Consequently grafting under these conditions caused no marked change in solubility. However the heats of interaction for the graft copolymers containing acetone changed markedly compared with the initial PerCV, as was evident from the reduction in the positive heat from 7.2 cal/g for PerCV to 2-4 cal/g for the graft copolymers (Fig. la). It was found that PVA dissolves in acetone with a small positive heat close to zero--0.3 cal/g. Therefore the reduced thermal effect of interaction for the PerCV-PVA graft copolymer containing acetone, compared with PerCV indicates that the structure of PerCV becomes denser as a result of crosslinking. Certainly as Fig. lb, shows the experimental data for determination of the density of the graft copolymers confirms this assumption. In addition in a number of graft copolymers the reduction in heats with increase in grafted PVA accords with the rise in density. This mechanism is observed for all the irradiation doses used to synthesize the graft copolymers. Moreover as m a y be seen from Fig. 1, with increase in irradiation dose (0.25-1.5 Mrad) the heats are reduced, while the density is increased, apparently on account of crosslinking of chains of the graft copolymer accompanying increase in the irradiation dose, since PerCV according to determination of [~/] for the solutions over the dose range indicated undergoes crosslinking and the PVA polymer being grafted is also classed under crosslinking polymers [8].

DeSermination of the heats of dissolution for PerCV-PVA graft copolymers in dichloroethane showed the absence of appreciable changes in these heats in the series of copolymers. Thus PerOV dissolves in dichloroethane with heat evolution of 4.5 cal/g; the heat of dissolution of PVA in dichloroethane is 3.0 cal/g. For the

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FIG. I. Integral heats of swelling (a) and density (b) of PerCV-PVA graft copolymers obtained with doses of: 1--0.25; 2--0.5; 3--0.75; 4--1.0; 5--1.5 Mrad. FIG. 2. Curve of for systems: 1--diehloroethane-PerCV; 2--dichloroethanePerCV-PVA graft copolymer containing 67.1% PVA.

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graft copolymers the heat of dissolution varied in the series of copolymers in which the content of grafted PVA varied from 18.3 to 67.1% within limits o£ 3.6-4.2 cal/g. This small difference in the heats of dissolution is evidently due to the good interaction of diehloroethane with both components of the graft, eopolymer. The reduction in heats of dissolution for the graft copolymersin dichloroethane compared with the initial PerCV is shown by the data in Fig. 2 indicating t h a t the curve of ,4H=f(w2) for the graft copolymer is below the curve for PerCV. However calculation of losses in ztZ1 from the isotherm of dichloroethane sorption by the graft copolymer containing 67.1% PVA and for the eopolymer produced with a dose of 1.5 Mrad (Fig. 3) showed that the affinity of dichloroethane for the graft eopolymer had increased compared with the initial polymer. It can be seen from the data in Table 1 that this increased affinity of the solvent in relation to the graft copolymer is due to an increase in the entropy component,

of the thermodynamic potential of the solvent, since the negative energy-producing component AH1 of this potential was reduced in terms of absolute value compared with the initial PerCV. The increase in the entropy component TA~I rJ:ABLE ] .

C H A N G E I N THERMODY]qAMIC F U N C T I O N S OF D I C H L O R O E T H A N E I N I T S R E A C T I O N ~VIT:I~

PERCY

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Craft copolymer containing 67.1% PVA

Weight fraction of polymer

0'99 0"97 0"95 0"93 0"90

COPOLYMER

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TA~

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TAS1

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--31.3 --31.3 --28.9 --25.4 --19.8

--26.5 --27-9 --25-8 --22.5 --17.0

--19-2 --12"2

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8"8

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6.8

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apparently indicates the increased flexibility of the PerCV chains owing to the flexible-chained PVA being grafted to it. It should be noted at this point that the glass temperature of PerCV-PVA graft copolymers (Fig. 4) is also lower than Tg for PerCV; with increase in the PVA content of the series of copolymers this

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T h e PerCV-PVA graft copolymers obtained with a dose of 1.0 Mrad at the rate of 50 rad/see proved to be insoluble in acetone and diehloroethane. Consequently the dissolving power of these solvents was impaired in regard to the graft copolymers compared with the initial PerCV, as is indicated b y the marked

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FIG. 4. Plots of glass temperature of PerCV-PVA graft copolymers (Tg) vs. content of grafted PVA (A). FIG. 5. Intrinsic viscosity of solutions of PerCV-PVA graft eopolymers (in diehloroethane) obtained with doses of 0-5 (a) and 1"5 Mrad (b). change in the heats of swelling for the graft copolymers in acetone compared with the initial PerCV. Thus the positive heat of dissolution of PerCV in acetone, 7.2 cal/g is reduced to a negative heat of --0.9 cal/g for the graft eopolymer containing 45.8% PVA (Table 2). This sharp change in the heats of swelling, TABLE DENSITY

2.

INTEGRAL OF

I~EATS OF

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S W E L L I N G AND

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COPOLYMERS

OBTAI1WED W I T H A DOSE OF 1 . 0 M r a d ,

AT T H E RATE

OF 50 rad/see Amount of PVA in graft copolymer, Q, cal/g in % acetone 0 41.2 45.8 50"4 100

7.2 0 --0"9 --0.9 0.3

d, g/cm8 0.8158 1.2868 1.3163 1-2833 1.2027

and the insolubility of the PerCV-PVA graft copolymers obtained under these conditions are apparently the result of the higher degree of crosslinking of their chains in contrast to the graft copolymers obtained at the higher dose rate.

CONCLUSIONS

(1) I t has been shown t h a t if a graft copolymer consists of a combination of polymers in which irradiation gives rise to crosslinking, a rise in the irradiation dose with which the graft copolymers are synthesized results in higher specific weights and lower positive heats, while under certain conditions there is even a transition to a negative heat, despite the fact t h a t their initial components are dissolved with the evolution of heat. (2) With graft copolymers of perchlorovinyl and polyvinylacetate obtained at the rate of 200 rad/sec, the dissolving power of the solvent (dichloroethane) is found to increase; this is the result of increase in the e n t r o p y component of t he t h e r m o d y n a m i c potential, since the negative energy-producing component of this potential is reduced in absolute value compared with the initial polymer. The insolubility of graft copolymers s~ulthesized at the rate of 50 rad/sec is due to the crosslinking of their chains, as is shown by their negative heats of swelling in acetone. (3) I t has been shown t h a t the intrinsic viscosity of solutions of graft copolymers obtained at the rate of 200 rad/sec is reduced with increase in the content of grafted PVA in the series of copolymers; a rise in the irradiation dose with which t h e y are synthesized increased the viscosity of the solutions. Translated by R. J. A. I-IENDR¥ REFERENCES

1. I~Lh. U. USMANOV, R. S. TILLAYEV and S. A. TASHMUKHAMEDOV, Trans. Second Interaat. Symposium for Radiation Chemistry, Hungary, p. 699, 1966 2. S. A. TASHMUKHAMEDOV, R. S. TILLAYEV and Kh. U. USMANOV, Trans. Tash. State University, 302, 1966 3. Kh. U. USMANOV, R. S. TILLAYEV and S. A. TASHMUKHAMEDOV, Trans. Tash. State Univ. No. 257, 1964 4. A. A. YUL'CHIBAYEV, Thesis, 1958 5. A. A. TAHER and Zh. DOMBEK, Koll. zh. 15: 69, 1953 6. A. A. TAHER and V. A. KARGIN, Koll. zh. 10: 455, 1948 7. A. BAISBERGER, Physical Methods in Organic Chem. Vol. I, p. 108, 1950 8. A. CHARLESBY, Nuclear Radiations and Polymers, p. 445, 1962