Dielectric absorption of polar molecules in a few polymer matrices

Advances in Molecular Relaxation and Interaction Processes, 13 (1978) 287-298

287

0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

DIELECTRIC

ABSORPTION

A. LAKSHMI, Department

S. WALKER,

N.A. WEIR,

IN A FEW POLYMER

Lakehead

University,

of Salford,

Lancashire,

England

22 February

MATRICES

and J.H. CALDERWOOD*

of Chemistry,

*University (Received

OF POLAR MOLECULES

Thunder

Bay, Ontario,

Canada,

P7B 5El

1978)

ABSTRACT A detailed

study has been made of benzaldehyde

Eyring parameters lar (AHE=

have been obtained

kJ mol-1)

a polyethylene

relaxation

matrix.

been investigated

processes.

(AHE=

Benzaldehyde

in polyethylene,

polypropylene,

and polystyrene

Within

the experimental

little

influence

for group relaxation accuracy

on the enthalpy

observed

is to be contrasted

are virtually

with

hyde in polyethylene,

of activation

the molecular

polystyrene,

reported

carboxaldehyde matrices.

the medium

have

In a

and polypropylene

is

and

error,

for 2-fluorene

which

re-

has

group relaxation,

of the order of the experimental process

in

to that of benzaldehyde.

here,

for aldehyde

relaxation

and molecu-

for both group and molecular

was very similar

for the systems

and the

has also been examined

and 2-fluorene

have been obtained

matrix,

kJ mol-')

carboxaldehyde

the AHE value

the variations

for both the group

4-Biphenyl

few cases the Eyring parameters laxation;

in a polystyrene

definitely

This

carboxaldedependent

on the medium.

INTRODUCTION Dielectric

measurements

that dipolar molecules medium

of Frank et al [l] and Davies

dissolved

of very high viscosity.

loss factor occurs solution,

Further,

be more pronounced

in a polystyrene The frequency

is then considerably

at which

behave

somewhat

the maximum

as if in a

value of dielectric

lower than that in the case of a liquid

this effect of viscosity for molecular

matrix

et al [2,3] have indicated

rotation,

on relaxation

which

time may be expected

invo1ve.s the motion

to

of a species

of

288

than for the rotation

large volume,

of much smaller

substituent

groups within

the

molecule. The group rotational Ill01

-1

rotational

microwave

barrier,

and i.r. respectively,

while Grindley

siderably,

ranging between

and thus further

concentrations of directly tion.

to examine

equation

to dielectric

respectively

may be gained.

of the weight

(p1/n2)2 = (cot 0)

although

2

the weight

providing

2

=l.

the relaxation

-1

[6], and

differs

from the molecular

the value

our temperature

the process

should be good.

relaxa-

the Eyring

rate

if any, of the medium

Cl and C2 for molecular

subtends

magnitude

itself

from dipole moment with

and group re-

of the two processes data from the

the long axis of the molecule.

~1 = n cos 0, n2 = u sin 0, and Cl/C2 =

is greater

aldehydes

Mountain Thus,

than that for the

and in such circumstances

for the group and molecular

range,

exists

for the energy barrier

by applying

the latter is far from negligible,

within

con-

at low

the possibility

0 to be 38', and hence Cl is 0.62 for benzaldehyde.

appreciably

for

from an i.r. study,

From data on a few aromatic

time values

from

The energy barrier

where

contribution

factor for the molecularprocess

process,

for the

aldehydes.

of the molecule,

andCl+C

[ll] deduced

intramolecular

polymers

Both Cl and C2 may be estimated

If n is the dipole moment

[7], 28.1

and some related molecules

of the relative

dipole moment

-1

[9] gave 27.7 kJ mol-1

-1 .

the influence,

factors

an appreciation

24.8

to 20 kJ mol

as deduced

data and to examine

angle that the molecular

and Walker

in benzaldehyde

[6] kJ mol

by these procedures

to establish

and a few other aromatic

From consideration laxation

of this paper

group rotation

on benzaldehyde

of non-polar

[4] is 33 kJ

is merited.

benzaldehyde

the group relaxation

It is the purpose

for aldehyde

estimated

of this molecule

in solid matrices

separating

[5] and 19.6

a value of 34 kJ mol

34 kJ mol-l by n.m.r,

examination

It seemed of interest

20.6

An -ab initio MO calculation

in benzaldehyde

studies

also has given estimates

and in the liquid phase,

et al [lo] reported

group rotation

from n.m.r.

spectroscopy

in the gas phase,

[8] from i.r. studies.

aldehyde

for benzaldehyde

Vibrational

in vinyl chloride.

Ph-CHO

28.6

barrier

the chance of detection

processes

differ

and separation

of

289 EXPERIMENTAL

RESULTS

The dielectric bridge

measurements

in the frequency

circular,

parallel

range 50 to lo5 Hz.

plate

purged with dry nitrogen ture to about 400K.

have been made on a General

capacitor gas.

mounted

measurements

Q-meter

with a temperature-controlled

1.5x10'

Hz.

viously.

chamber

from liquid nitrogen

tempera-

were made using a Hewlett-Packard

two-terminal

and measurement

cell was a three-terminal,

in a temperature-controlled

The cell may be operated

Additional

The apparatus

The measuring

Radio 1615A capacitance

cell in the range 2.5~10~

techniques

have been described

4342A to

pre-

[12,13]

The polystyrene

matrix

and we have adopted the relaxation

was prepared

their procedures

both experimentally

time and distribution

tion and the enthalpy

of activation

in the way described

parameter

by Davies

and Swain

[2],

and also in the evaluation

by means of the Fuoss-Kirkwood

from the Eyring equation,

of

equa-

The atactic polystyrene

had a zw value of 2.3~10~. When isotactic was used,

polystyrene,

the same procedure

was used as a solvent Benzaldehyde,

polypropylene was adopted

in the latter

salicylaldehyde,

dehyde have each been examined are presented

in Table r.

are given in Table

equation,

to obtain

activation

in a variety

The results

values

standard

statistical

for the relaxation

or less, in agreement

cases, since

carboxaldehyde, of polymer

of the Eyring

and 4-biphenylcarboxal-

matrices,

equation

The relaxation

analyses

intervals

(see Ostle

data

of these data

of the enthalpy along with

intervals

the work of Davies

intervals

typically

For this reason,

for each of

For the ASE term,

were of the order of ?50% of the nominal

(l/T) plot.

(ASE) of

?lO% of the nominal

et al. [2,3]

this term is often a small part of the intercept,

of the In (T r) versus

to the

of these two

(AHE) and entropy

confidence

on AHE were

of temperature

[14]) have been employed

of the line and the variances

values

with

time as a function

techniques

process

The 95% confidence

these confidence

that p-xylene

II.

These data yielded

these two.

except

(low density)

two cases.

L-fluorene

the slope and intercept

parameters.

or polyethylene

to make the sample,

In the fitting of the data of relaxation Eyring

(atactic)

values

in some

(In (h/kg) - ASE/R),

an extensive

study of the matrix

290 was undertaken higher

to obtain

a larger number

of points

on the Eyring

plot extending

to

temperatures.

DISCUSSION A sample of benzaldehyde

in atactic polystyrene

plot of log rT v l/T.

One of these straight

range 102-138K,

an enthalpy

yields

pared with a slightly which

larger

a similar

enthalpy

benzaldehyde higher

of activation

falls

bromobenzene

may be attributed

of 16 k.J mol-1.

to the molecular

temperature

This low temperature relaxation

process,

172-201K

yields

to the value of 29 k.J mol-'

obtained

for the group relaxation

in atactic polystyrene

both the AHE values correct magnitude Benzaldehyde similar mol

-1

for molecular

to that for the polystyrene

of data between

this yielded

on the bridge.

the bridge

range of 4.7~10~

a.virtually

associated

with

process

the isotactic

range to that for benzaldehyde

swiftly solely

from the matrix, to molecular

centration

of the

This is similar

process

in p-OHC-C6[16]

Thus,

are of the

respectively.

polystyrene

in a temperature of activation

the work was extended

AHE=29.5

polymer.

range

of 29 kJ

kJ mol-'.

influenced

range 169-193K,

by the relative temperature

Benzaldehyde

the solute

tended

molecules

-1

and

imply order

and frequency

was also

to be exuded

the AHB value of 19 kJ mol

of benzaldehyde

frequency

These figures would

This was a similar

However,

to a higher

in the temperature

in atactic polystyrene.

and whether

relaxation

Analysis

for

In order to check this result and the continuity

is not greatly

medium.

process

in polystyrene

and an enthalpy

Hz on the Q-meter

identical

in a polyethylene

matrix,

and Q-meter

to 5.2~10~

that the intramolecular

studied

in isotactic

[15]

range and has

may be observed.

for benzaldehyde

and group relaxation

was also examined

was obtained

a AHB of 27 kJ mol-'.

when only group relaxation

of 13 and 27 kJ mol-'

This is to be com-

in atactic polystyrene

betweeen

H4-CHO

lines from a

in the temperature

of 13 kJ mol-'.

range also falls in a similar

of activation

temperature

two straight

lines, which

rigid molecule,

for the given frequency

yielded

quite

may be attributed

dispersed

in very low con-

is not established.

In order to ensure

that the two AHB values

styrene had been assigned molecule,which

is somewhat

correctly, bigger

for benzaldehyde

we also examined

than benzaldehyde,

in isotactic

salicylaldehyde. a chelated

poly-

In this

ring is formed held

291 together

by a very strong

McClellan

[17]).

intramolecular

If group relaxation

AHK (e.g., ~40 kJ mol

-1

Hence,

).

may look upon this molecule atactic

polystyrene,

the molecular somewhat

smaller

process

molecule.

lower AHK of benzaldehyde

-1

absorption

in these media

process

In

polystyrene, was similar.

the molecular

relaxa-

[18] has more recently

of benzotrichloride

de-

in

, and this again sets an upper limit for

of benzaldehyde

in polystyrene

All these data thus support

in isotactic

by a high

of comparison.

and in isotactic

a co-worker

relaxation

[17] to be 21 kJ mol

relaxation

for the purposes -1

and

region of the bridge we

range of dielectric

Further,

the AHg for the molecular

atactic polystyrene

a

-1 ,

(see Pimentel

it would be accompanied

a AHK of 23 kJ mol

that for benzaldehyde

tion AHK is less than 24 kJ mol

bond 0-H"'OCH

in the low temperature

the temperature

We may, in fact, conclude

termined

occurred,

as a rigid molecule

we obtained

In both,

24 kJ mol-1.

hydrogen

polystyrene

since benzaldehyde

the interpretation

is

of the

in terms of the molecular

relaxa-

tion process. For dielectric is abundant variation

absorption

evidence

volume

to demonstrate

in relaxation

change in viscosity

or molecular

such as relaxation

changes

for a solute

variations

aldehyde

such behaviour

-4

a AHE=

kJ mol

laxation

times and the enthalpies

being

the process

in polymer

and a relaxation

responsible

higher

rigid molecule,

for the higher

where

the

4-biphenyl

Both 4-biphenyl

temperature

processes

carbox-

with

and have identical

of activation

relaxa-

are of the same

4-nitrobiphenyl

[15], which has

Thus, both the re-

favour a molecular

temperature

of such

In order to

we examined

time at 300K of 4.6x10 -4 s. of activation

to the effective

independent

matrices,

respectively

These enthalpies

considerable

(owing to substantial

in a few media,

yielded

there

that an intramolecular

could be considerable,

of 72 and 76 kJ mol-'

s at 300K.

also reveal

solvents

exhibits

of a non polar solvent.

carboxaldehyde

order as that of the similar-sized -1

process

group is reasonably

is paralleled

carboxaldehyde

of activation

tion times of 1.7x10

solution

viscosity

and 2-fluorene

and Z-fluorene

enthalpies

in non polar

and is also sensitive

such studies

of an aldehyde

in a dilute

in macroscopic

carboxaldehyde

that a molecular

interaction)

However,

process

whether

of polar molecules

time by a change in local environment

of the molecule.

determine

studies

absorption.

relaxation It can

as

292 thus be seen

(Table II) that there is a reasonable

for the high temperature molecule,

process

Such behaviour

from a group relaxation. AHS values

differ

volume

parameter

29 kJ mol

-1

4-biphenyl

,

from that of the high

styrene

which

and group processes

matrices,

which

factor is enormously

for 4-biphenylcarboxaldehyde

larger

as molecular

time and

since the corresoccurs,

has been achieved

the relaxation

is

for

to identify

times for

lo6 in the poly-

than is usually

relaxation

as distinct

In fact, it may be noted

rod-shaped,

seem reasonable

process

only group relaxation

carboxaldehyde.

are roughly

to 2-fluorene

one, and its

differ by a factor of approximately

Thus, it would

phase studies.

temperature

of the two processes

and 2-fluorene

of the

the relaxation

group relaxation

[16] where

Thus, a clear separation

that in these two aldehydes, molecular

to aldehyde

for terephthaldehyde

carboxaldehyde

from a molecular process

AHS values

volume

from benzaldehyde

would be expected

AH=27 kJ mol-1 is to be attributed ponding

increasing

For the low temperature

appreciably

between

(atactic PS) and the effective

both AHP and molecular

carboxaldehyde.

correlation

found in liquid

the longer

and the shorter

relaxation one as group

relaxation. In polyethylene observed

in 4-biphenyl

considerably

carboxaldehyde,

measurements

of the matrices.

similar

In all three atactic polymer

polypropylene parameters

reflect

environments. sequentially transition

falling

bound bulky phenyl temperatures).

relaxation

parameters

in the various

is probably

to a rigid chain

in in

These polymeric

the result of the (at sub-glass

these effects would be less noticeable

there is a considerably

of the degree of random branching

in this

was observed

and polystyrene.

relaxation

attached

in which

Under

of the large scale deformation

the activation

for polystyrene

On the other hand,

in the low density polyethylene, on account

also molecular

of molecular

groups

at temperatures

of these polymers.

those in polyethylene

AHE value

it occurs

was not

parameters.

above room temperature,

the difficulty

process

group rotation was observed

activation

media

in between

The higher

because

temperatures

aldehyde

In all three media,

carboxaldehyde

relaxation

cannot be made on account

near 200K, yielding

2-fluorene

possibly

above the glass transition

such conditions

aldehyde

the molecular

and polypropylene,

of the chains.

higher

free volume

In polystyrene

and

293 polypropylene,

aldehyde

group rotation

with AHK of 27 and 30 kJ mol molecular

peaks overlap

respectively.

and extend

rendering

group rotation,

-1

was also observed

in this molecule

In polyethylene,

out into the absorption

a clear cut determination

near ZOOK,

the tail of the

peaks owing to aldehyde

of AHK for the group process

not

feasible.

CONCLUSIOHS Altogether

our experimental

the molecular

and group processes

In 2-fluorene molecular

carboxaldehyde

and group processes

now been detected carboxaldehyde

absorption

peaksextends

ing it not feasible

aldehyde

to the chemical

that free volumes required

listed

when

A change in medium

fluorene tion. shown

has caused

whilst

absorption

is small.

However,

In contrast

tion time when

of the aldehyde.

considerable relaxation

matrix

occurs,

render-

for the latter process. -1

appears

indicative

AHK value being

Further, is varied,

polymers

of the

relatively

this value does not possibly

considerably

studies

on polar

process,

indicating

exceed

the variation

the volume

is changed

is much

time acti-

as seen in the case of Zfor aldehyde

in non polar

to macroscopic

in enthalpy

studies

in the relaxation

change

solutes

is sensitive

the variation

the matrix

the polymer

variation

causing very little

relaxation

for small molecules

Debye equation,

parameters

in atactic polystyrene,

the various

for a molecular

that the molecular

although

with

the group process

group rotation.

carboxaldehyde,

Dielectric

nature

has been

the tail of the molecular

II a AHK ~30 k.J mol

the type of polymer

associated

for aldehyde

vation parameters

in Table

have

For 4-biphenyl

only the group process

out into the region where

both

and both processes

in polypropylene,

in polyethylene,

the relaxation

of both

in polystyrene,

observed,

and polyethylene,

group relaxation

alter significantly

carboxaldehyde

carboxaldehyde

carboxaldehyde

of activation

in atactic polystyrene.

have been previously

to measure

For the molecules

insensitive

and 4-biphenyl

in polypropylene

In 2-fluorene

enthalpies

for benzaldehyde

for 2-fluorene

detected.

aromatic

data have yielded

group

solvents

viscosity

reveal vast changes

and the molecular

by the

for such systems

in molecular

enthalpy

have

changes

less than that predicted of activation

relaxa-

relaxa-

of activation

alters

294

appreciably. This difference in behaviour of the molecular and small relaxing segment of a molecule is the very basis on which separation of the group and molecular motions may be achieved in the matrix and eliminates the complicationswhich can sometimes ensue with a Budo analysis of the dielectric data of polar solutions in the liquid phase. [19] Clearly, much more work is necessary on the dielectric absorption of flexible molecules in various types of polymer matrices where, from that reported here, it follows that one polymer matrix may better facilitate the separation of particular molecular and intramolecularprocesses more readily than another.

ACKNOWLEDGEMENTS We are grateful to the National Research Council of Canada for support and to Mr. B. K. Morgan for invaluable technical help.

TABLE I Fuoss-Kirkwood Analysis Parameters for Four Solutes in Polymer Matrices (Solute Concentrations are in parenthesis)

T (0

106,(s)

103c"max

Bensaldehvde in atactic uolvstvrene (0.232Mj 102

107 113 118 123 128 133 138

362 173 92.6 44.6 25.9 14.3 8.3 5.3

0.17 0.16 0.17 0.17 0.18 0.17 0.16 0.17

9.65 10.20 10.70 11,oo 11.30 11.60 11.80 12.00

2.64 2.63 2.63 2.62 2.62 2.60 2.60 2.59

Benzaldehyde in atactic polystyrene (0.655Ml 172 178 184 193 201

1.03 0.44 0.33 0.20 0.04

0.24 0.23 0.22 0.21 0.18

18.82 14.59 15.12 15.70 16.81

Benzaldehvde in isotactic uolvstvrene (0.633M 139.1 141.2 143.9

96.3 65.9

49.3

0.15 0.17 0.15

0.19 0.19 0.20

2.62 2.62 2.62

295

T(K)

10%(6) Benzaldehyde in isotactic polystyrene (0.633M) can't

145.8 148.2 151.7 178 182.9 188.2 193

38.0 23.3 12.9 0.527 0.277 0.185 0.0724

0.15 0.16 0.15 0.20 0.21 0.22 0.49

0.20 0.20 0.21 0.17 0.17 0.18 0.19

2.62 2.62 2.62 2.62 2.62 2.62 2.62

Benzaldehyde in polyethylene (0.897M) 214.6 224.9 235.1 254.1 273.4 297.3

259 185 108 53.8 27.0 9.99

0.39 0.34 0.32 0.27 0.24 0.22

53.57 54.51 54.31 51.85 46.34 35.58

2.88 2.85 2.83 2.78 2.74 2.67

Salicylaldehydein polystyrene (0.52lM) 114.2 118.8 125.4 128.8 132.5 140.8

363 129 50.2 22.1 11.7 3.05

0.14 0.14 0.13 0.13 0.14 0.14

16.35 17.28 18.46 19.16 19.81 21.48

2.68 2.68 2.66 2.66 2.66 2.64

Salicylaldehydein isotactic polystyrene (0.63M) 122.5 124.9 129.2 133.3 138.4 142.3 145.2

174 165 46.2 24.1 11.7 6.02 4.38

0.14 0.12 0.14 0.15 0.14 0.14 0.14

14.25 14.58 15.31 16.02 16.86 17.56 18.12

2.66 2.64 2.65 2.65 2.64 2.64 2.64

4-Biuhenvlcarboxaldehydein polyethylene (0.296Ml 181.6 190.1 198.8 207.5 216.5 249.2

389 154 72.5 54.3 28.7 0.4

0.39 0.36 0.35 0.28 0.31 0.36

6.14 6.47 6.99 8.00 4.44 51.2

2.36 2.36 2.36 2.36 2.37

4-Biphenyl carboxaldehyde in polypropylene (0.254M) 185.4 192.7 197.5

202 207.6 212.7 217.8 224

390 149 93.8 42.0 31.0 19.7 12.5 9.5

0.39 0.42 0.43 0.42 0.42 0.41 0.39 0.36

6.94 7.33 7.49

7.84 7.86 8.25 8.83 9.88

2.26 2.25 2.25 2.24 2.24 2.27 2.23 2.23

296

T(K)

10%(s)

B

103Pmax

EC.2

2-Fluorene carboxaldehyde in,polystYrene (0.33M) 294.7 303.4 311.9 317.3 322 326.7

1126 446 293 231 178 LO9

0.57 0.60 0.58 0.57 0.55 0.57

38.03 37.78 34.76 33.79 32.86 31.00

2.57 2.56 2.55 2.53 2.51 2.49

2-Fluorene carboxaldehyde in polypropylene (0.216M) 295.2 306 310.7 314.9 320.9 325.4 330

1766 500 414 281 208 143 120

0.49 0.53 0.52 0.53 0.51 0.52 0.50

71.65 73.09 75.04 75.39 74.76 75.03 74.87

2.52 2.51 2.51 2.51 2.50 2.49 2.49

2-Fluorene carboxaldehvde in polv~ro~vlene (0.216M) 202.4 206.7 210.6 213 217.5 220.6 223.9 230.5

406 226 185 127 95.4 65.7 59.4 42.2

0.41 0.45 0.42 0.43 0.44 0.43 0.40 0.41

4.62 4.88 5.05 5.26 5.34 5.79 6.02 7.07

2.39 2.39 2.39 2.39 2.39 2.39 2.38 2.38

297

TABLE II Eyring Analysis

Results

for Several Molecules

Type of Relaxation Molecule

Benzaldehyde

AHE (kJ_l al01 )

AsE (J-K-’

mol

-1

)

in Polymer

Matrices

AGElOo

AGE200

CkJ_l

(kJ_1

mol

)

mol

Temperature Range (K)

)

in

a) atactic polystyrene

mol

13

-45

18

27

102-138

group

27

31

24

18

172-201

group

29

35

26

19

163-193

c) polyethylene

mol

19

-88

27

45

215-297

a) atactic styrene

mol

23

28

20

15

114-141

mol

24

31

21

15

122-145

group

34

10

33

31

182-249

group mol

32 72

-2 67

32 65

32 52

185-224 295-330

grow

27

-19

29

33

176-223

a) atactic polystyrene

mol

76

79

68

52

296-330

b) polyethylene

mol

51

-15

53

56

295-327

c) atactic polypropylene

mol

59

8

58

57

295-330

d) atactic polystyrene*

group

27

-34

30

37

200-230

e) atactic polypropylene

group

30

-29

33

39

202-231

polystyrene b) isotactic styrene

poly-

poly-

b) isotactic styrene

poly-

4-Biphenyl carboxaldehyde in a) polyethylene b) atactic polypropylene c) atactic polystyrene 2-Fluorene carboxaldehyde in

*In process

of publication

(see ref. 16)

298

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