16

Kolloid.Zeitschrift und Zeitsehrifl fiir Polymere, Band 193 9 Heft I

From the IHrd Institute o/Physics, University, G6ttingen Specific Y o l n m e o f P o l y m e r s a s a F u n c t i o n o f T e m p e r a t u r e a n d P r e s s u r e

By P. H e y d e m a n n and H. D. G u i c k i n g With 18 figures and 1 table (Received August 5, 1963)

A new field of p o l y m e r research developed more r e c e n t l y is t h e investigation of the d e p e n d e n c e of various properties on h y d r o static pressure. T h e e v a l u a t i o n of d y n a m i c mechanical or dielectric m e a s u r e m e n t s in t e r m s of free v o l u m e requires d e p e n d a b l e d a t a of t h e specific v o l u m e as f u n c t i o n of t e m p e r a t u r e a n d pressure. I t is - a m o n g o t h e r reasons - t h e lack of such d a t a t h a t initiated t h e present s t u d y . According to _Ferry (1) the free v o l u m e is the difference b e t w e e n t o t a l v o l u m e a n d t h e v o l u m e of the molecules (equilibrium v o l u m e of t h e material a t 0 ~ K ) t o g e t h e r w i t h the space occupied b y t h e t h e r m a l vibrations of the molecules; it is assumed t h a t t h e l a t t e r v o l u m e fraction is n o t available for segmental jumps. I f more mechanisms freezing-in a t t e m p e r a t u r e s below Tg a d d to t h e t h e r m a l expansion, the v o l u m e occupied b y these motions is c o n s e q u e n t l y n o t a d d e d to t h a t free volume, which is available for segmental r o t a t i o n a b o v e Tg a n d assumes a c o n s t a n t value below T_. Since e x t e r n a l pressure will essentially reduce t h e inter-molecular distances a n d n o t so m u c h t h e shape o f the molecules (the degree of disorder is only slightly affected b y pressure), it is e x p e c t e d t h a t s e c o n d a r y t r a n s i t i o n ranges will often be less affected b y the change of t h e h y d r o s t a t i c pressure t h a n the dielectric m e a s u r e m e n t s of Koppelmann a n d Gielessen (2). T h e pressure d e p e n d e n c e of a t r a n s i t i o n t e m p e r a t u r e t h e r e f o r e renders some useful i n f o r m a t i o n on t h e t y p e of molecular m o t i o n i n v o l v e d in the specific t r a n s i t i o n : if the molecular m o t i o n is hindered b y neighbouring chains t h e influence of pressure will be large; if the h i n d r a n c e originates f r o m neighbours on t h e same chain, t h e influence of pressure will be smaller. I. Design and Calibration of the Dilatometer

W i t h isotropie bodies v o l u m e changes m a y be d e t e r m i n e d f r o m t h e change o f the length of a r o d - s h a p e d sample. I n the work in h a n d

linear t h e r m a l e x p a n s i v i t y was m e a s u r e d as f u n c t i o n of the h y d r o s t a t i c pressure. The materials investigated were polyvinylchloride (PVC), p u r e a n d plasticized, and polym e t h y l m e t h a c r y l a t e (PMMA). Also isothermal compressibility m e a s u r e m e n t s were m a d e a t various t e m p e r a t u r e s . T h e available a p p a r a t u s allowed m e a s u r e m e n t s in the t e m p e r a t u r e range - - 8 0 to + 150 ~ and in the pressure range 1 to 1000 a t m . A cross-section of the pressure vessel and the d i l a t o m e t e r is p r e s e n t e d in fig. 1.

1. Mechanical apparatus The cylindrical pressure vessel A (fig. 1) is connected with the high pressure pump by means of a steel capillary at P. The bottom plate B is made pressure tight with a soft copper gasket. Four insulated electrical

outlets are built into the bottom plate. The extenso-

meter is screwed to the bottom plate. During temperature and pressure runs the sample is not directly accessible and the volume has to be measured with a transmitting-type gauge. Inductive measurement of the length of the sample rod is made with a sensitive differential transformer. For isotropic samples volume changes are easily calculated from the change in length. The sample S, a cylindrical rod of approximately 90 mm length and 10 to 15 mm diameter is screwed to the base plate with a short stud bolt. This was the most successful of several methods tried. Feeler and probe coil are pressed to the upper end of the rod by their own small weight. The feeler slides in two guide sleeves G. The exciting coils EC are connected in series but wound in opposite sense. A 50 cps-current through the coils excites an inhomogeneous alternating magnetic field inside the coils. This field in turn induces a position dependent signal voltage in the probe coil. The changes of this signal voltage are a measure for the variation of the length of the sample rod. Thermal expansion of the apparatus itself was reduced to a minimum by the use of fuzed quartz tubes Qu as spacers between base plate and bobbin.

2. Pressure and temperature control The complete pressure vessel is placed inside an air thermostat with forced air flow. In some measurements (+ 100 to + 150 ~ a liquid filled thermostat was used. The available temperature range thus extends from --90 to + 150~ Temperature can be changed at constant rate by driving the nominal value setting means in the electronic thermometer with a synchronous

motor. The pressure vessel is connected through the wall of the thermostat with a positive-displacement pump. Silicon oil (DC 200/10) is used to transmit the

Heydemann and Guicking, Specific Volume of Polymers as a Function of Temperature and Pressure hydrostatic pressure. This type of oil permits measurements down to --80 ~ at 1 arm and to --50 ~ at 1000 arm without disturbing solidification. Swelling experiments showed that the polymers investigated are not noticeably affected by the silicon oil. Swelling of the polymers would also lead to a systematic increase of the measured volume. No such effects were observed. The pressure was measured with a calibrated pressure gauge with an accuracy of 0.6O/o. Temperature inside the pressure vessel was measured with Ptresistance thermometers. Air-free filling of the apparatus was accomplished by evacuating the apparatus through an oil-filled receiver.

17

the same time the phase is reversed by 180 ~ In order to obtain an output voltage which is a linear function of the feeler position, the signal voltage from the probe coil is demodulated in a phase sensitive rectifier circuit proposed by Morton (3). The rectified output voltage is very sensitive to variations of the supply voltage. The latter was therefore stabilized with a commercial electronic-magnetic stabilizer.

4. Calibration o/ the apparatus The Pt-resistance thermometer was calibrated with freezing and boiling point of water as fixed points. Between these points the variation of the resistance with temperature was taken from the tables of LandoltBSrnstein (4). The bridge is designed to minimize the non-linearity of the relation between resistance and diagonal voltage. The dilatometer was calibrated by means of a micrometer gauge.

5. Corrections o / t h e experimental data Several corrections had to be applied to account for the following effects of temperature and pressure on the apparatus : a) temperature dependence of the exciting current due to the variation of the resistance of the exciting coils (reduced to a small correction by the high-ohmic series resistor), b) non-linearity of the differential transformer (correction derived from the calibration with the micrometer gauge), c) compressibility of the apparatus. The correction was calculated from tabulated values; it is essentially based on the compressibility of the fuzed quartz spacers which is very well known (5). d) a small pressure dependence of the temperature indication, which was determined experimentally with measurements at constant temperature and variable pressure. The immeasurably small pressure dependence of the exciting current and the thermal expansion of the apparatus, which amounts to less than 0.50/0 of the expansion of the samples, were neglected. To check the validity of the corrections and the reliability of the results measurements were made at various temperatures and pressures with sample rods of fuzed quartz and Jenaer Thermometerglas 16lII. The data of these materials are precisely known and tabulated (6); within the accuracy of measurement no deviation of the experimental values from the tabulated ones was observed. Fig. 1. Pressure vessel and dilatometer. A: pressure vessel; B: bottom plate; Cu: copper gasket; I : insulators; Pl: coaxial plugs; S: sample; Qu: quartz glass tubes; F : feeler; PC: probe coil; EC: exciting coil; G: guide sleeves; P : to pressure generator

3. Electronic apparatus The expansion was directly plotted as function of the temperature on an X- ]Z-recorder. A Pt-thermometer is placed in a d.c.-bridge. The diagonal voltage of the bridge is supplied to the recorder. The differential transformer is supplied from the mains transformer through a highohmic resistor for current stabilization. When the feeler is moved through its central position the signal voltage at the probe coil runs through a minimum, since at this point the opposing magnetic fields from the two exciting coils cancel each other. At

II. Performance of the Measurements The samples were cut from plate material. They were carefully annealed at for example 120 ~ f o r p u r e P V C a n d 150 ~ f o r P M M A , cooled down very slowly to obtain samples free from stress and were then turned on a lathe to cylindrical shape. A short tapped b l i n d h o l e ( M 2,6) w a s s c r e w e d i n t o o n e e n d . Two types of measurements were carried out: the expansivity was measured at various constant pressures and constant rates of temperatures change (heating or cooling), and the compressibility was measur-

18

Kolloid-Zeitschrifl and Zeitschrift f l i t Polymere, Band 193 9 Heft I

ed at various constant temperatures with increasing and decreasing pressure. Since below Tg the material is not in thermodynamic equilibrium, different results are obtained from the two types of measurements; at given temperature T and pressure ~o the lengths of the sample rods may also depend on the previous history. For the evaluation of the continuously recorded isobaric curves of the length of the samples as function of the temperature first of all small statistical fluctuations were smoothed out. Then the experimental data were read from the diagrams at intervals of 5 ~ from an arbitrary starting point. These data were corrected for the above mentioned effects. The resulting data for the relative sample lengths are estimated to be correct to • 2 x 10 -a mm. The specific volume V is calculated according to

between the secondary freezing points T 1 of 5 ~ is somewhat larger; b u t here the uncertainty in the determination of T 1 rises to + 2 ~ For these reasons all curves were measured with falling temperature only instead of using mean values obtained from measurements with rising and falling temperature for the evaluation. The temperature shift of the curves caused b y pressure and plasticizer is thereby not affected but the absolute values of the critical temperatures might be slightly higher than indicated here for the given rate of temperature change. The curves no. 1 in fig. 2 were started at + 105 ~ with temperature falling down to --70 ~ and then up again. Obviously the two branches separate only in the secondary transition range at about --30 ~ and continue as parallels until an additional separation occurs at the glass transition. At higher temperatures the two branches are A12 V (A1) = Vo + 3 V o ~ + 3Vo 10-~-, [1] again parallel. We assume that this separation is not caused by volume aftereffects with Vo specific volume at 1 at and 20 ~ as (these should level out along the parallel determined from mass and volume measure- sections), b u t b y a nonuniformity of the ments, l0 length of the sample under the temperature variation caused b y a change of same conditions, zJl measured difference the temperature conductivity 2 in the between the length 1 at ~o and T, and 10. In transition ranges. This is in agreement with most cases the third term on the right side other measurements: the heat conductivity of equation [1] is negligible. The relative z of PVC does not change in the transition accuracy of the resulting specific volume is range (7), the specific heat c_ of PVC in+ 10 -4 cm3/g. This corresponds to the width creases by about 40% at the glass transition of the lines in the V @)-diagrams (figs. 2 (8), in the same interval the specific volume V to 6). The accuracy of the determination of changes only b y about 1%, so that the Vo and 10 is better than _+ 1%. This vahie temperature conductivity 2 = ~. V/c v determines also the absolute accuracy. should drop noticeably with temperature A number of preliminary experiments will rising through the glass transition. With the now be discussed the results of which are heat conductivity ~ = 4- 10 -4 cal/~ 9cm. sec of significance for the performance of the (7) and c v = 0,36 and 0,25 cal/g ~ (8) above actual measurements. and below T a the calculated temperature difference between the center of the rod and 1. I s o b a r i c m e a s u r e m e n t s its surface is 0,7 ~ below and 1,1 ~ above The results of isobaric measurements m a y Tg, if the temperature is changed at a rate If the V(T)-curves are displaced well depend on the direction of the tempera- of 25 ~ ture change. The curves no. 1 in fig. 2 were b y 0,4 ~ the temperatures obtained at the measured with pure I~VC with temperature breaks will differ b y about 0,65 ~ Obviously rising and falling at a rate of 25 ~ The the difference of the glass temperatures is specific volume is plotted as function of the satisfactorily explained b y the change of the temperature. The glass temperatures Tg are specific heat at Tg. The step of c v at the found at 75 ~ with falling and at 76 ~ with secondary transition is not known. rising temperature. Also in other similar The small separation of the curves for measurements with different samples and at rising and falling temperature indicates that various pressures the differences between the the heat transfer from the steel cylinder glass temperatures did never exceed 2 ~ It through the silicone oil to the sample is has furthermore to be kept in mind that the satisfactory and that the Pt-thermometer glass temperatures are obtained from the indicates almost the sample temperature intersection of two tangents with an accuracy although it is placed a few millimeters apart of not better than + 0,5 ~ The difference from the sample in the silicone oil. An

Heydemann and Guicking, gpecific Volume of Polymers as a Function of Temperature and Pressure

eventual discontinuity of the temperature conductivity of the silicone oil could therefore not have any signifiant influence on the experimental results. The density of the silicone oil was measured in the entire temperature range resulting in a perfectly smooth Q(T)-curve. Discontinuities of the temperature conductivity are therefore quite improbable. The position of the transition on the temperature scale depends also on the rate of temperature change. The slower the

19

as compared with the 25 ~ Measurements with temperature rising and falling at a rate of 7 ~ (not reproduced here) show also a smaller separation of the two branches. Since the measurements with the slower rate of temperature change do not seem to lead to significantly better or different results, all measurements were made with 25 ~ The reason for performing the measurements with falling temperature only is illustrated in fig. 2, curve no. 3. The cycle was started at +105 ~ and atmospheric pressure. It is obvious from the diagram t h a t only the sections A and C are reversible.

2. Isothermal measurements 0,73 V

For isothermal measurements the temperature was kept constant and the pressure was varied between 1 and lO00 at in steps of 200 at. After each pressure change about l0 min. were necessary for attaining temperture equilibrium, and more time was allowed for the volume to balance. The length of the sample was measured 20 rain. after each pressure change. No further volume changes were observed within the next 20 min. With rising and falling pressure the temperature reached after 20 rain. differed by about 0,2 ~ and volume differences were observed which were slightly higher than those corresponding to this temperature difference. The volume differences could however hardly be resolved. They are not much larger t h a n the width of the lines in the figs. 2 to 6.

T 0,7~

|

0,71

0,70

0,69 - 60

-~0

-20

0

20

hO

60

80

I00 ~

.T Fig. 2. Preliminary measurements with PVC

samples are cooled, the lower the temperatures at which equilibrium is still attained and the lower the transition temperatures. It is however well known from many measurements with polymers t h a t the time constants for the a t t a i n m e n t of equilibrium are strongly dependent (about exponentially) on temperature. With the technically possible variation of the cooling rates the transition temperatures can therefore only be shifted by a few degrees (9, 10). Curves no. 2 in fig. 2 illustrate the influence of different cooling rates. The upper curve was measured with 25 ~ and the lower one with 7 ~ With the 7 ~ T~ and T z are shifted by about 3 ~ towards lower temperatures

III. Experimental Results 1. PolyvinylchIoride a) Transition temperatures The specific volumina of pure and plasticized polyvinylchloride are plotted as function of the temperature for 1, 200, 400, 600, 800 and 1000 at [-= kp/cm 2] in figs. 3 to 6. The solid lines indicate the results of isobaric, the dotted lines those of isothermal measurements. Tangents are drawn at the curves. Their intersections indicate the transition temperatures. Hellwege and co-workers (21) published results of isothermal compressibilit y measurements. Their values of the specific volume of PVC have also been entered into fig. 3 (solid points). According to their performance of measurements the data were fitted to ours for the 200 at-curve. With pure PVC and PVC with 10% DOP a secondary transition is clearly seen beside the main glass transition. With increasing 2*

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21

Heydemaurt and Guicking, Npeeific Volume of Polymers as a Function of Temperature and Pressure

pressure both the glass transition and the secondary transition are shifted towards higher temperatures by about 13 to 15 ~ per 1000 atmospheres. Within the limits of the measuring accuracy the temperature shift is a linear function of the pressure.

to-.~._O~ r (3 ~

PVC

~.~.-

/ 3

b) Isothermal compressibility Above the glass transition isothermal and isobaric measurements lead to the same specific volumina except at temperatures near to Tg. In each transition range the isothermal curves show an S-shaped course with rising separation from the isobaric curve corresponding to the same pressure. With the isothermal V(T)-eurves the transitions are marked by the inflection of the curves of equal pressure. The temperatures corresponding to the points of inflection are below the respective transition temperatures. It is quite interesting to note that in some eases the isothermal curves approximate the isobaric curves only at temperatures well above the glass temperature measured at the respective pressure. This observation indicates that the time constant for isobaric contraction or expansion due to a temperature change is different from that for isothermal compression. A certain dependence of the shape of the relaxation spectrum on the type of stress or strain was also observed in other studies of this laboratory (ll, 12) and by Koppelmann (13) The isothermal compressibilities calculated from these curves according to 1

1 0 -so

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-20

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40

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Fig. 7 ,~II Cm 2

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with V mean value of the specific volume within the interval Ap, are plotted as functions of the temperature in figs 7 to 10. Here the transition ranges are marked b y a stepwise increase of the compressibility The height of the steps decreases and the point of inflection is shifted towards higher temperatures as the pressure is raised. With pure PVC and PVC with 10% D O P there are obviously two separate transitions while with PVC with 20 % D O P and 30% DOP there is only one rather broad transition range The course of the thermal expansivity as function of the temperature for these latter samples indicates that here the secondary transition and the glass transition overlap. With PVC with 20% and 30% D O P another secondary transition is indicated at very low temperatures, which has not been studied in greater detail.

[ -40

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-40

-20

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20

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Fig. 10 Fig. 7-10. Isothermal compressibility of PVC, pure and plasticized, as flmetion of temperature and hydrostatic pressure

22

Kolloid-Zeitschrift und Ze~tschrift fi~r Polymere, Band 193 9 Heft 1

.,o c ! I

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Fig. 14

Fig. 11-14. Thermalexpansivityof PVC, pure and plasticizedas funetion of temperature and hydrostatic pressure

Above the glass transition the compressibility increases as a linear function of the temperature. The slope of this line decreases with increasing pressure. c) T h e r m a l e x p a n s i v i t y

The thermal cubical expansivity was calculated from isobaric measurements according to 1 LIV v AT The results for pure and plasticized PVC are plotted in figs. l l to 14 as functions of the temperature with the hydrostatic pressure as a parameter. The transition ranges are marked by the stepwise increase of the thermal cxpansitivity. These steps are shifted towards higher temperatures as the pressure is raised and simultaneously the height of the steps is reduced. With pure PVC the specific volume was measured only in a very small temperature range above the glass transition. This leads to an increased uncertainty in

the determination of the slopes. The wide gap between the curves for 200 and 400 at in fig. 15 is certainly due to this fact. The curves for pure PVC and PVC with 10% DOP again show two distinctly separate transition ranges. The curves in fig. 13 are easily explained as the superposition of one large and one small step. The position of the secondary transition is essentially unaffected by the increase of the plasticizer content from 10 to 20%, while the glass transition temperature is reduced by about 40 ~ No trace of the secondary transition is seen in fig. 14. d) Influence of the plasticizer concentration on the transition temperatures

The values of the thermal expansivity of the PVC samples in equivalent temperature ranges, i . e . between corresponding transitions are about the same for all plasticizer concentrations except a slight reduction of at T ~ Tg and a similar increase at very

Heydemann and Guicking, gpecific Volume of Polymers as a Function of Temperature and Pressure

low temperatures with increasing plasticizer concentration. The transition temperatures taken from the isobaric volume-temperature curves are plotted for 1 and 1000 at in fig. 15. oC T

80

l-

,\

6O

lot ~

OOaf"

,~o 20

23

transition range towards higher temperatures is probably smaller at higher plasticizer concentrations. If glass transition and secondary transition are really overlapping in PVC with 20 and 30% DOP, then the transition temperatures determined in figs. 5 and 6 are incorrect. The increase of the thermal expansivity of PVC and PVC with 10% DOP around T1 is d~ = 3 9 10-5/~ The same value is assumed to hold for PVC with 20 and 30% DOP. The glass temperatures would then be found 7 ~ higher, if the secondary transition was placed below the glass transition. The glass temperatures of pure PVC and PVC with 10~ D O P should therefore not be compared with those of I~VC with 20 and 30% DOP without paying attention to these facts.

0 / i/

-20

10

20

3O % DOP

Fig. 15. Transition temperatures of PVC as function of the plasticizer concentration for 1 a n d 1000 at

The influence of small plasticizer concentrations on the glass transition of linear polymers with polar repeating units (for example PVC) is small, since masking of a few active centers can hardly reduce the number of cross-links because of the mobility of the chains and the great number of polar groups. Only plasticizer concentrations exceeding a certain threshold become fully effective (14). Therefore the glass temperature decreases monotonously with increasing plasticizer concentration except for very small concentrations the additive becomes less efficient again (15). The secondary transition temperature of pure PVC at 1 at is found at --26 ~ and with PVC with 10% DOP at --8 ~ If the transition is caused b y the same molecular process in both cases, it is obviously hindered b y the plasticizer molecules. The type of molecular process involved is not completely elucidated yet (16, 17). With PVC with 20% I)OP the transition is certainly found between 0 and - - 1 0 ~ at 1 at (fig. 13). With PVC with 30~o D O P the secondary transition is no longer detected. It might be situated at the beginning of the glass transition or could also have disappeared completely as is indicated b y dynamic measurements (11, 12). The shifting of the secondary

2. Polymethylmethacrylate The isothermal and isobaric V(T)-curves of PMMA are plotted in fig. 16 as function of the temperature. There are weak breaks in the isobaric curves at --7 ~ and + 62 ~ and a marked break at + 103 ~ A transition at 67 ~ was reported b y Becker (18), and one at 0 ~ is also known from literature (19). crr?Ig

0,8; v t ! 0,86

0,ss

~8~ ~8:

~s2 ~81

0,8_6 O0 -1,0 -20

0

20

~0

60

80 100 t20 1~0 ~ -T

Fig. 16. Specific volume of PMMA as function of temperature and hydrostatic pressure. Solid lines: isobaric measurements; dotted lines: isothermal measurements

24

Kolloid-Zeitschrifl u n d Zeitschrift fi~r Polymere, B a n d 193 9 Heft 1 Table 1

zlfl (1 at, Tv) Acr (1 at, Tg) Afl/Aa dTg/dp

PVC pure

PVC + 10% DOP

PVC + 20% DOP

PVC + 30% DOP

PMMA

1.75 3.71 4.6 1.4

1.52 3.15 4.7 1.4

1.10 2,96 3,6 1.3

0.65 3.07 2.1 1.5

2.2 3.1 7.1 1.8

The glass transition at about +103 ~ is known from various publications. It is quite interesting to note that neither the transition at -- 7~ nor that at + 62 ~ are affected b y hydrostatic pressure while the glass transition is shifted b y about 0,018 ~ These phenomena were also confirmed b y dielectric measurements of one of the authors (P. Heydemann) and b y Koppelmann and Gielessen (20). Values of Hellwege and co-workers of the specific volume of PMMA were entered into fig. 16 in the same manner as the values for PVC in fig. 3. They agree rather well with our data.

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5

/

T4 2

f ---J I"-'-"

-~

0

20

~0

x • • •

l0 - n cm2/dyn 10-4/~ 10 2 ~ 10 -~ ~

The thermal cubical expansivity of PMMA calculated from isobaric measurements is plotted in fig. 17. There distinct steps mark the transition ranges. The corresponding steps of the compressibility are less marked and only the glass transition adds significantly to the isothermal compressibility (fig. 18).

3. Ehren/est's law The complete compressibility changes Aft and expansitivity changes As at the glass transition are used to check Ehren/est's law: dTg _ J f l dp A or "

All pertinent data are collected in table 1 showing very poor agreement between the calculated and the measured shifting factors. Hellwege and co-workers found satisfactory agreement for their experimental values, while disagreement was found b y various other authors with different substances. The authors wish to thank Prof. Dr. Dr.

E. h. E. Meyer for his great interest in this

I 0 -60 -~0 -20

_

units

60

80

,I

100 120 7~0 ~ -T

Fig. 17. Thermal cubical expansivity of PMMA as function of temperature and hydrostatic pressure

work. We are also very much obliged to Prof. Dr. K. A. Wol/of the BASF, Ludwigshafen, for providing the samples and to the Deutsche Forschungsgemeinschaft for part of the apparatus. The investigation was carried out as part of one item of a research contract with the Department of Physical Research, Admirality, London.

15: Summary

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-20

0

20

tO

60

80

100

t20 1t0 ~ -I

Fig, 18. Isothermal compressibility of PMMA as function of temperature and hydrostatic pressure

The specific volume of pure and plasticized polyvinylchloride and of polymethylmethacrylate was studied with a dilatometer as function of temperature (--80 to +150~ and hydrostatic pressure (1 to 1000 at.). Beside the glass transition also two types of secondary transitions are observed with PVC and PMMA which correspond to dynamic secondary dispersion ranges. Below the glass transition the specific volumina depend on how they were reached. The transition temperatures of the samples were determined at elevated pressures with decreasing temperatures. Glass transition and secondary transitions cause stepwise increases of the thermal expansivities and the isothermal compressibilities. Above the glass transition the compressibilities are rising in proportion to the temperature.

Germar, Absolutbestimmung der Taxie des Polyvinylchlorid8 aus dem Ultrarotsl)e]ctru~*~ With PVC all transition temperatures are shifted by about 0,013 to 0,015 ~ as the pressure is raised. With PMMA the transitions at --7 ~ and at + 62 ~ are not affected by hydrostatic pressure while the glass transition is shifted by 0,018 ~ Addition of plasticizer to PVC shifts the glass transition to lower and the secondary transition to higher temperatures. There is no agreement between the measured shifting factors dT~/dp and those calculated according to Ehren/est's law :lfl/,l~ dT~/'dp.

Zusamm en/assung Das spezifisehe Volumen yon reinem and weiehgemachtem Polyvinylchlorid und yon Polymethylmethacrylat wurde mit Hi]fe eines Dilatometers als Funktion der Temperatur (--80 bis + 150 ~ und des hydrostatisehen Drucks (1 bis 1000 at) gemessen. AuI~er dem Glasiibergang wurden bei PVC und PMMA noch weitere sekund~tre Obergangsbereiche gefunden, die dynamischenNcbendispersionsgebietenentsprechen. Untcrhalb der Glastemperatur hgngen die spezifischen Volumina stark yon dem Wege ab, auf dcm sie erreicht wurdcn. Die l~bergangstemperaturen der Proben wurden bei erh6htem Druck mit fallender Tcmperatur bestimmt. Der Glasfibergang und die sekundaren Oberggnge sind yon stufenweisen Jmderungen der thermischen Ausdehnungskoeffizienten and der isothermen Kompressibilitgten begleitet. Oberha]b des Glasiibergangs steigen die Kompressibilitgten proportional zur Temperatur an. Bei PVC werden alle (~bergangstemperaturen dutch steigenden Druck um etwa 0,013 bis 0,015 ~ verschoben. Bei PMMA werden die Ubergangsgebiete bei --7 ~ und bei +62 ~ durch hydrostatischcn Druck nicht beeinflul]t, wghrend der Glasiibergang um etwa 0,018 ~ verschoben wird. Der Zusatz yon Weichmacher zu PVC verschiebt den Glasiibergang zu ticferen und den sekundgren l~bergang zu hSheren Temperaturen. Die gemessenen Verschiebungsfaktoren dTa/d p stimmen nicht mit den nach der Ehren/estschen Beziehung berechneten iiberein.

25

l~e[erenc~8 l) Ferry, J. D., Viscoelastic Properties of Polymers, p. 220 (New York 1961). 2) Koppel~rtann, J. and J. Gielessen, Z. Elektrochemie 65, 689 (1961). 3) Morton, C., Trans. Far. Soc. 33, 474 (1937). 4) Landolt-BSrnstein, Zahlenwerte u. Funktioncn, 6. Aufl., 4. Bd., 3. Tell, S. 21 (Berlin 1957). 5) Reitzel, J., J. Simon and J. A. Walker, Rev. Sci. Instr. 28, 828 (1957). 6) Landolt-BSrnstein, Zahlenwerte u. Funktionen, 5. Aufl., HW I, 82; Eg I, 30, 678; Eg II, 1158; Eg Ilia, 70 (Berlin 1923). 7) Eiermann, K., K.-H. Hellwege und W. K~tappe, Kolloid-Z. 174, 134 (1961). 8) Dole, M., Kolloid-Z. 165, 40 (1959). 9) Fox, T. G. and J. Flory, J. Appl. Phys. 21, 581 (1950). 10) Aljrey, T., G. (;oldfinger and H. Mar]c, J. Appl. Phys. 14, 700 (1943). ll) Heydemann, P. and A. Zosel, Acustica 12, 360 (1962). 12) Heydemann, P. and H. N/igerl, to be published in Acustica 14 (1964). 13) Koppelmann, J., Kolloid-Z. 144, 12 (1955). 14) Mellan, I., The Behavior of Plasticizers, p. 16 (Oxford 1961). 15) Stuart, H. A., Die Physik der Hoehpolymeren, Bd. IV, w74 (Berlin-G6ttingen-Heidelberg 1952-1956). 16) Illers, K. H., H. G. Kilian and R. Kos/eld, Ann. Rev. Phys. Chem. 12, 49 (1961). 17) Wol[, K. A., Z. Elektroehemie 65, 604 (1961). 18) Becket, G. W., Kolloid-Z. 140, 1 (1955}. 19) :Vitsche, R. ,~nd K. A. Wol/, Kunststoffe, Bd. 1, S. 186 (Berlin 1962). 20) Koppeln~ann, J. and J. (;ielessen, Kolloid-Z. 175, 97 (1961). 21) Hellwege, K. H., W. Knappe and P. Lehmann, Kolloid-Z. u. Z. Polymerc 183, 110 (1962). Authors' address : Dr. t'. lleydemann and H. D. Guicking, I[[. Physikalischeslnstitut tier Universiti~tG6ttingen, 3400 G6ttingen, Biirgerstrafae.42/44

Aus dem Deutschen Kunststo/~-Institut, Darm,~tadt

Absolutbestimmung der Taxie des Polyvinylchlorids aus dem Uhrarotspektrum Von H. G e r m a r Mit 6 Abbildungen in 10 Einzeltlarstellungeu tt~M 2 Tabellen (Eingegangen am 8. August 1963)

1. Einleitung Die m a k r o s k o p i s c h e n E i g e n s c h a f t e n y o n H o c h p o l y m e r e n w e r d e n d u r c h die M i k r o s t r u k t u r d e r K e t t e n m o l e k e l n b e s t i m m t . Bei t a k t i s c h e n P o l y m e r e n ist es y o n g r o B e m I n t e r e s s e z u w i s s e n , i n w e l c h e m M a g e stereor e g u l g r e S e q u e n z e n i n n e r h a l b de,' K e t t e n vorkommen. Die K r i s t a l l i s a t i o n s f g h i g k e i t h g n g t z. B. e n g m i t d e r L S n g e d e r s t e r e o r e g u l g r e n K e t t e n b e r e i c h e z u s a m m e n . E s ist

b e k a n n t , dal~ die K r i s t M l i n i t / i t i m P V C mit zunehmendem syndiotaktischen Anteil w~i.chst (1-5). A b e r a u c h die K o n f o r m a t i o n einer isolierten K e t t e in v e r d i i n n t e r LSsung, d. h. die m 6 g l i c h e n R o t a t i o n s i s o m e r c n , s i n d d u r c h die K o n f i g u r a t i o n d e r K e t t c festgelegt. So w e r d e n sicher die e n e r g e t i s c h g i i n s t i g s t e n K o n f o r m ~ t i o n e n , wie sie i m K r i s t a l l v o r l i e g e n - b e i m s y n d i o t a k t i s c h e n P V C die ges t r e c k t e K e t t e *nit e b e n e n l K o h l e n s t o f f -