Production and properties of polyacenaphthylene—V dilute solution properties

Eur. Polym. J. Vol. 22, No. 12, pp. 943-948, 1986 Printed in Great Britain

0014-3057,86 $3.00+0.00 Pergamon Journals Ltd

PRODUCTION AND PROPERTIES OF POLYACENAPHTHYLENE--V DILUTE SOLUTION PROPERTIES* HENRY AGBAJE and JU-RGEN SPRINGERt Institut ffir Technische Chemie der Technischen Universit~it Berlin, Fachgebiet Makromolekulare Chemie, StraBe des 17. Juni 135, 1000 Berlin 12, Germany

(Received 12 May 1986)

Abstraet--Polyacenaphthylene was synthesized by thermal bulk polymerization, fractionated into I I fractions by fractional precipitation and characterized by gel permeation chromatography, light scattering and osmometry. Long chain branching was observed in polyacenaphthylenes with 3~tw> l × 106 g/mol. 0-temperatures of branched and linear polyacenaphthylenes were determined in 1,2-dichloroethane and are different in magnitude. Polyacenaphthylene undergoes chemical degradation in manufacturers' grade 1,2-dichloroethane. Intrinsic viscosities in benzene, toluene, tetrahydrofuran at 25~C, and in 1,2-dichloroethane at 41.I°C have been measured and the Mark-Houwink constants of the viscositymolar mass relationship evaluated.

INTRODUCTION

The molecular structure of polyacenaphthylene (PACE), I, is of interest as every alternate C - C bond

n

I

of the polymer main chain is bound to a bulky naphthalene substituent which, because of its size, restricts free molecular rotation around these bonds, The P A C E chain is therefore expected to exhibit considerable inflexibility and an expanded coil conformation in solution, Several studies on the dilute solution properties of P A C E have been reported [1-5] but the results of these hydrodynamic and thermodynamic investigations show considerable discrepancies. Whereas Moacanin et al. [1] gave the 0-temperature as 35~C in 1,2-dichloroethane, Barrales-Rienda and Pepper [2] reported a value of 20°C for the same solvent. Further differences are fourid in the values of the constants of the viscosity-molar mass relationships in various solvents as well as in values relating to the unperturbed dimensions of P A C E [1-5]. With regard to the rigidity of P A C E , Tsvetkov et al. [5] reported a rigidity which is approximately twice as large as that of macromolecules in which all the main chain segments have unrestricted rotations.

*Dedicated to Professor Dr Georg Manecke on his 70th birthday. tFourth communication: J. Schmelzer and J. Springer, Influence of Molecular Structures and End Groups on the Elution Volumes in Gel Permeation Chromatography, Chromatographia 20(6), 347 (1985). 943 EPJ

22 12

A

Barrales-Rienda and Pepper [3], on the other hand, found the polymer chains to be more flexible than expected, i.e. their segmental length was smaller than expected on the basis of dimensions of the m o n o m e r units. These discrepancies can possibly be attributed to the photodegradation of P A C E solutions by light as first reported by Springer et al. [6]. The photodegradation of P A C E was later investigated by Utracki et al. [7]. M o r e recently, a study on the thermodynamics, kinetics and mechanism of P A C E photodegradation in solution was reported by Stelter and Springer [8]. In their study, a certain proportion o f " w e a k links" in the polymer chains was detected. In view of the results of the latter investigations, interest at reinvestigating the thermodynamic and hydrodynamic solution properties of P A C E was developed. The aim of this paper is not only to investigate the reasons for the discrepancies in the reported molecular dimensions of P A C E in solution but also to elucidate the question of P A C E rigidity in solution. EXPERIMENTAL Materials

Technical acenaphthylene (ACE) (Chemische Fabrik Weyl AG, Mannheim) was purified by double sublimation in vacuum followed by multiple recrystallization from ethanol. The yellow crystalline ACE m.p. 92.5°C was preserved in dark bottles to prevent photo reactions. Benzene and toluene "p.A." (Merck, Darmstadt) were used as received and not subjected to further purification. Dioxane, tetrahydrofuran (THF) "p.A." and 1,2-dichloroethane "reinst" ~Merck, Darmstadt) were dried over molecular sieves (4 A) and purified by passing through an activated alumina column followed by distillation under N 2, Polymerization

PACE was prepared by thermal bulk polymerization of ACE with 2.5 × 1 0 - 2 wt% benzoyl peroxide for 18 hr at 100-'Cunder vacuum. The polymer was dissolved in benzene, precipitated in excess methanol, twice reprecipitated and dried in vacuum at 40"C (yield 65%) to constant weight.

944

HENRY AGBAJE a n d JORGEN SPRINGER Table I. Osmotic pressure and light scattering data for P A C E in benzene at 25°C. = radius of gyration Fraction

h4. x 10 3 (g mol i)

A 2 x 104 (cm 3 mol g - : )

Unfractioned 1 3 4 5 6 7 8 9 10 11

337 --865 733 506 423 317 205 133 92

1.12 --1.30 1.49 1.39 1.49 2.08 1.91 2.08 3.26

/Q'wx 10 3 (g r e e l - t ) 842 2130 1700 1040 828 607 490 383 263 185 161

A 2 x 104 (cm 3 mol g - : )

(nm)

1.06 0.66 0.71 1.20 1.29 1.44 1.48 1.69 1.73 1.86 --

45 63 55 38 34 33 32 27 27 26 --

Fractionation The polymer was fractionated by fractional precipitation from a 0.8% benzene solution with methanol into 11 fractions,

mined from zero angle and zero concentration extrapolation of the Zimm plots. Figure 1 shows a typical Zimm plot for PACE in benzene. Zimm plots of almost all fractions showed good linearity. Slight curvatures were detected for low molecular fractions Viscosity which were supposedly caused by photodegradation Solution viscositiesin benzene, THF and toluene at 25°C of the polymer solutions during measurement. The and in 1,2-dichloroethane at the 0-temperature were deter- results of the light scattering experiments are summined with an automated Ubbelohde viscometer (FICA, Le marized in Table 1. Molecular weight determinations, Mesnil-Saint Denis). for example of fraction 1 in THF, toluene dioxane, Molecular weight show good agreement (see Table 3). No solventOsmotic pressure molecular weight determinations were dependent effect such as association, microgel forcarried out in benzene at 25°C using a High-Speed Os- mation etc. which could account for the discrepancies mometer (Model 503, Hewlett Packard) with regenerated reported in the introduction was observed. The radii cellulose membranes (Sartorius, G6ttingen). of gyration in THF, toluene and dioxane were apThe light scattering measurements were performed on a proximately equal, benzene with the greater radius of FICA light scattering photometer (PGD 42000, Le gyration and larger A2 proving to be a particularly Mesnil-Saint Denis). Solvents and solutions were clarified good solvent. by direct filtration through a 0.45/~ regenerated cellulose filter (Sartorius, G6ttingen) into the optical cells. The GPC refractive index increments were determined in an already described differential refractometer [9] calibrated with KCI Figure 2 shows the elution volumes V, of PACE in solutions. The refractive indices of the solvents and their T H F as a function of ~Q'w. In accordance with the temperature dependencies were taken from the literature theory for homologues under identical experimental [10]. All light scattering measurements were made with green conditions, a linear relationship is found between the (Hg-line, 546 nm) unpolarized light to exclude possible elution volume and the logarithm of molar mass. errors due to fluorescence by PACE [11, 12]. To minimize However, deviations from this linearity are observed photodegradation, the solutions were only exposed to irra- for the fractions 1 and 3. Their elution volumes are diation during measurements, larger than expected for their molar masses, indiRESULTS AND DISCUSSION Osmotic pressure measurements The number-average molar mass h~tn and second osmotic virial coefficient A2 of the fractions were derived from osmotic pressure measurements. Linear plots of the reduced osmotic pressure (n/C) vs the concentration (C) were obtained in all cases and no drifts were observed during the measurements. Resuits of measurements made on fractions with higher molar mass (Fractions 1-3), proved unreliable in this polymer-solvent system. The number-average molar mass (~Q'n) and the second virial coefficient (A2) for PACE in benzene are given in Table 1.

cating that polymers of these fractions differ from the others in their configuration. The polydispersity Mw/Mn of the fractions have been calculated from elution curves with the help of a calibrating plot [13] using peak maxima and the corresponding Atw values. The results are tabulated with those calculated from osmotic and light scattering measurements in Table 4. Polydispersity estimates from osmotic pressure and light scattering measurements show comparative narrowness to those calculated from GPC measurements.

Table 2. Refractive index increment dn/dC

Light scattering m e a s u r e m e n t s The refractive index increments (dn/dC) of PACE in various solvents are given in Table 2. The refractive index increment for PACE in 1,2-dichloroethane showed no measurable temperature dependence between 24°C and 40°C. The weight-average molar mass (h~n) and second virial coefficients were deter-

Solvent Benzene

P A C E 2 = 546 nm, T = 25~C dn/dC

Toluene Dioxane THF 1,2-Dichloroethane

(cm3g-') 0.209

0.216 0.267 0.281 0.250

of

Dilute solution properties

945

18

16 .,X

?

14--

O

¥ 12--

~ ~o X 08

~

0=0

O6

o4 oo

I 02

I 04

I 06

I 08

I 10

I 12

Sin (Theto/2)~2+

I 14

I 16

I 18

I 20

I 22

B~C

Fig. l. Zimm plot of PACE, fraction 3 in benzene at 25°C: Concentration x 10-3 (g/cm3); /~ 0.738, + 1.111, x 1.579, ~ 1.873.

Viscosity measurements The results of viscosity measurements in benzene, toluene, T H F and 1,2-dichloroethane are given in Table 4. Intrinsic viscosities [q] were derived using the Huggins equation [14]. The PACE solutions exhibited Newtonian flow, i.e. no dependence of [q] on shear rate was observed. The Huggins plots for all fractions for concentrations 2-12 x 10 -3 (g/cm 3) are linear and the [r/l-values in Table 4 are obtained from extrapolation to zero concentration,

Viscosity-molar mass relationship From the M a r k - H o u w i n k equation, [q] = K . M a, the relationship between-~'w, viscosity-average molar mass ~Q', and the intrinsic viscosity [q] can be expressed by the equation [ r l ] = K w . M ~ = K , . M ~. The different molar mass averages are related by the equation [15]

polymer by shear stress or the presence of a different molecular structure in these polymers. No change in [q] was observed when measurements were made at different shear gradients. By shear degradation, lower values of [~] should have been found, with [~/] decreasing and the degradation being enhanced by higher capillary flow rates. Since no change in [r/] was observed, shear degradation can be ruled out. The deviation from linearity of the log [q] - log h4~ plot can be attributed to long chain branching in these PACE samples. The coil density of a branched molecule is higher than that of a linear molecule. Hence, under similar experimental conditions, the intrinsic viscosity of a branched chain is comparatively lower than that of a linear chain with the same molar mass. The higher molecular weight PACE fractions (fractions 1 and 3) are obviously highly branched so that differences in their solution behav-

A4",= 0.5(a + 1)Mw - 0.5(a -- 1)M,, which enables the viscosity-average molar mass to be calculated from the Mw, ~¢, and a values, Figure 3 shows a double logarithmic plot of [q] as a function of 3~tWfor PACE in benzene at 25°C. Again fractions 1 and 3 deviate from linearity. Similarly, deviations are observed in the log [~/]- log AT"wand log ~ t plots for PACE in T H F and toluene. Possible reasons for this deviance are either degradation of the

ol o3 I 1°6

Table 3. Light scattering data for PACE (fraction 1) in various solvents at 25'C Solvent

/Q. x I0 3

A 2 x 104

~r 2

(gmol ')

(cm3molg 2)

(nm)

Benzene

2130

0.66

63

THF Toluene Dioxane

2190 2070 2140

0.58 0.44 0.54

58 57 53

10 m

2'7 2'8 2'9 30

3'I 3'2 2'3 3/* 35

36

Ve[ml]

Fig. 2. GPC elution volume (lie) as a function of molar mass (Mw): Column set/~-styragel 103, 104, 105 and 106/~; THF flow rate 2 cm3/min.

946

HENRY AGBAJE a n d JORGEN SPRINGER Table 4. Polydispersity and viscosity data for PACE [r/]

(cm 3 g-i)

Fraction

ATw/.~" .

Mw/M*

Benzene**

Toluene**

THF**

1,2-Dichloroethane** *

1 3 4 5 6 7 8 9 10 11

--1.20 I. 13 1.20 1.17 1.21 1.28 1.39 1.61

1.62 1.30 1.20 1.33 1.39 1.32 1.39 1.29 1.31 1.62

121.5 113.3 87.4 75.2 62.0 52.5 42.2 32.3 27.9 23.2

108.5 95.6 74.8 63.7 54.3 44.2 37.4 29.6 23.8 21.3

113.6 106.8 87.6 72,4 60.0 51.0 41.0 33.1 26.1 22.2

63.2 57.9 44.4 40.7 36.5 33.0 30.0 22.5 19.8 18.1

• GPC measurements; **T = 25°C; ***T = 41.1°C.

iour compared with that of lower molecular weight homologs are observed. For these reasons, in the elevation of the constants K and a of the viscositymolar mass relationship, these fractions (fractions 1 and 3) were excluded. The log [r/] - log AS¢,plots for PACE in benzene as well as similar plots in toluene and T H F at 25°C show good internal consistency and linearity. In the 0-solvent, 1,2-dichloroethane at 41.1°C (Fig. 4) the plot of log [q] vs log -~w was linear, giving a slope of 0.5 in good agreement with theory. The constants were derived by least square analysis and are valid for 105> M , > 106 (g/mol). The results and those previously published are compiled in Table 5. The evaluated values of the exponent a of the Mark-Houwink equation for PACE in benzene, toluene and T H F (Table 5) confirm previous reports [1, 2] that PACE in dilute solutions behaves in a manner similar to that of flexible coils. The extreme deviations found in the constants reported by BarralesRienda and Pepper [2] are due to their very low dn/dC (0.190 cm3/g) for PACE in toluene resulting in higher )1,7, values. Subsequently their plots gave lines with lower intercepts K and higher exponents a. Another possible contributing factor to the discrepancies in the reported K and a values is the effect of chain branching which became apparent in fractions of very high molar mass. The proportion of branching in the lower molecular weight fractions is

100

100

/

.~

w

10 -ttl~)5

....... M [g/tool]

1~)6 :

Fig. 4. Viscosity-molar mass relationship for PACE in 1,2-dichloroethane at 41.1°C.

unknown but assumed to be negligible. However, the deviations from linearity of the Mark-Houwink relationship observed in this work show that for PACE with ASt,> 1.1 x 106 (g/mol) chain branching is evident and therefore cannot be neglected. Theta temperature determination The 0-temperature was determined from light scattering measurements. The second osmotic virial coefficient A2 was measured at temperatures close to 0 and evaluated by extra-respectively interpolation of Table 5. Mark-Houwink constants K and a for PACE in various solvents Solvent 1,2-Dichloroethane

Kw x 103

a(+0.02)

42.7

0.50

K, x 103 --

45.6

0.50

--

l

Benzene T = 25°C

10

-111,05

1,1 [g/rno(l

.....

--=

lb 6

Fig. 3. Double logarithmic plot intrinsic viscosity [r/] vs molar mass (5.3,) of PACE in benzene at 25°C.

Toluene

T =25°C THF

T=25oc

[I]

20.0

0.54

21.2

T = 35"C [2] T = 20"C

5.81 5.43 5.30 2.82

0.69 0.69 0.68 0.74

5,96 --2.94

This work [16] [l] [2] This work

E

o -"

Source This work T = 41.1 °C

8.38

0.65

8.64

6.76

0.66

6.83

[2]

5.24

0.70

5.32

This work

Dilute solution properties

947

14

2

~oo °

10

=

2 \ U ,

08

÷

06

04

X

=

1 0.2

oo

$

I 04

I 06

] 08

I ~0

] ~2

I 14

I 16

Sin ( T h e t c l / 2 ) ~ e 2 + B~C Fig. 5. Zimm

plot of PACE, fraction I, in manufacturers' grade 1,2-dichloroethane at 3 3 . 4 C : Concentration x 10 3 (g/cm3); /X 0.201, + 0.438, x 0.626, ~ 0.818, T 1.032.

the relationship between A 2 and the corresponding temperatures to A 2 = 0. The 0-solvent used was 1,2-dichloroethane. It was observed that use of this solvent, as supplied by the manufacturer without purification, resulted in distorted Zimm plots, inconsistent results and the evaluated molar mass being considerably lower than expected. A typically distorted Zimm plot of PACE in manufacturers' grade 1,2-dichloroethane is shown in Fig. 5. At first, these distortions were assumed to have

been caused by the instability of PACE towards irradiation. However, the sharp decrease in molar mass indicated extensive degradation of the polymer. In purified 1,2-dichloroethane, light scattering measurements gave "normal" Zimm plots (Fig. 6), consistent results and the expected molar mass. Gas chromatographic investigations showed the unpurified and the purified solvents were 97% and 99% purity respectively. It can be assumed that the polymer degradation was initiated by this small amount of impurity which is possibly of a

75-

65

o o

6O ~0

o

I--

55

Y

5O

o

45

40

O0

02

04

06 08 10 Sin ( T h e t o / 2 ) ~ - 2 + B~C

12

14

16

Fig. 6. Zimm plot of PACE, fraction 1, in purified 1,2-dichloroethane at 37.5('C: Concentration x 10 -2 (g/cm3); /X 0.252, + 0.397, x 0.619, ~ 0.824, T 1.069.

948

~-

HENRY AGBAJE and JORGEN SPRINGER

40

~" E %~ 30 2-" 20 "~ 10 0 "zO . -T0

o Fr 1 ~ Fr 6

. .2's

) .

/ .

' .

l . t'~]

- 20

-30 -~0

Fig. 7. Temperature dependence of the second osmotic virial coefi~cient A2 for PACE in 1,2-dichloroethane.

halogen-carbon radical character. The degradation is statistical and independent of the solution concentration. The molar mass distribution in the polymer solutions is therefore diversely affected during dissolution and storage. Each solution subsequently has a different molar mass distribution, so accounting for the distortion of the Zimm-diagrams. The degradation of PACE in unpurified 1,2-dichloroethane was also observed to occur in the dark. According to storage time, decreases up to 50% in molar mass were observed with the distortion of the Zimm diagrams steadily increasing. Although no further investigation regarding the chemistry of the impurity was conducted, traces of this impurity with a radical character are to be held responsible for this specific type of degradation. The

removal by purification proves that it is a constituent of manufacturers' grade 1,2-dichloroethane. The normal Zimm plots obtained when measurements were performed in purified solvent confirms that the polymer degradation had been initiated by these substances. Experiments were performed to determine the 0-temperature of a branched (fraction 1) and a linear PACE sample (fraction 6). The second osmotic virial coefficient decreases as expected with increasing temperature. Within the measured temperature range, temperature dependency of both the branched and linear polymer is linear (see Fig. 7). It is interesting to note that, even at temperatures up to 15° below 0, no phase separation or precipitation of the polymer from solution was observed. Least square analysis of the plot yields an intercept (A2 = 0) for the branched PACE sample at T = 0 -- 39.2 _+ 1.5°C and for the linear PACE sampie at T = 0 = 41.1 __. 1.5°C. The slopes of the lines are 2.1 x 10 -6 and 2.0 x 10 -6 (cm 3mol/g2 degree) for the branched and linear samples respectively.

The difference found in 0-temperature is in accordance with similar reports on branched and linear polystyrene in cyclohexane by Candau et al. [17-19]. Casassa [20], modifying a theory on the configuration of polymer molecules in solution due to Vrij [21], and Candau et al. [19], using two entirely different theoretical approaches, independently derived that the 0-temperature of a branched polymer must be lower than that measured for a linear homologue in the same solvent. Quantitative assessment of the degree of branching was not possible due to lack of experimental data on a linear sample of the same molar mass. However, the magnitude of the difference between the 0-temperatures of the linear and the branched PACE samples, even after allowing for experimental errors, is significant enough to show evidence of a relatively high degree of long chain branching. In spite of the expected stiffness due to the bulky substituent in PACE, the results of this paper have shown that theories relating to flexible coils are likewise applicable in elucidating the dilute solution properties of this polymer. The unperturbed dimensions and the question of PACE rigidity will be discussed in a subsequent communication. Acknowledgements~ne of us (Henry Agbaje) acknowledgesfinancial support by the German Academic Exchange Service(DAAD) and we both thank the Chemische Fabrik WeylAG for the gift of acenaphthylene.

REFERENCES I.J. Moacanin, A. Rembaum, R. K. Laudenslager and R. Adler, J. Maeromolee. Sei. Chem. AI 8, 1497 (1967). 2. J. M. Barrales-Rienda and D. C. Pepper, Polymer 8, 337 (1967). 3. J. M. Barrales-Rienda and D. C. Pepper, Polymer 8, 351 (1967). 4. J. Springer, K. Ueberreiter and R. Wenzel, Makromolek. Chem. 96, 122 (1966). 5. V. N. Tsvetkov, M. G. Vitovskaya, P. N. Lavrenko, E.N. Zakharova, I. F. Gavrilenko and N. N. Stefanovskaya, V~skomolek. Soedin. (Ser A) 13, 2532 (1971). 6. J. Springer, K. Ueberreiter and R. Wenzel, Makromolek. Chem. 96, 134 (1966). 7. L. Utracki, N. Eliezer and R. Shima, J. Polym. Sci. BS, 137 (1967). 8. Th. Stelter and J. Springer, Makromolek. Chem. 185, 1719 (1984). 9. F. Assmussen and J. Springer, Mebtechnik 3, 77 (1972). I0. M. B. Huglin, Light Scattering from Polymer Solutions, Chap. 2, pp. 29-33. Academic Press, New York (1972). 1I. J. Springer and F. Schneider, Makromolek. Chem. 146, 181 (1971). 12. C. David, M. Lempereur and G. Geuskens, Eur. Polym. J. 8, 417 (1972). 13. J. Springer, J. Schmelzer and T. Zeplichal, Chromatographia 13, 164 (1980). 14. M. L. Huggins, J. Am. chem. Soc. 64, 2716 (1942). 15. G. Meyerhoff, Adv. Polym. Sci. 3, 59 (1961). 16. J. C. Miiller, J. Chim. phys. 65, 567 (1968). 17. F. Candau and F. Franta, Makromolek. Chem. 149, 41 (1971). 18. F. Candau and P. Remmp, Eur. Polym. J. g, 757 (1972). 19. F. Candau, H. Strazielle and H. Benoit, Makromolek. Chem. 170, 165 (1973). 20. E. F. Casassa, J. Polym. Sci. A2 8, 1651 (1970). 21. A. Vrij, J. Polym. Sci. A2 7, 1627 (1969).