Physical characterization of blends of isotactic poly(butene-1) with ethylene-propylene copolymer

Eur. Po(vm. J. Vol. 23, No. 2, pp. 117-124, 1987 Printed in Great Britain

0014-3057/87 $3.00+0.00 Pergamon Journals Ltd

PHYSICAL CHARACTERIZATION OF BLENDS OF ISOTACTIC POLY(BUTENE-1) WITH ETHYLENEPROPYLENE COPOLYMER J. K. KALLITSlSand N. K. KALFOGLOU Department of Chemistry, University of Patras, 26110 Patras, Greece (Received 8 May 1986)

ANtraet--Melt-mixed blends of isotactic poly(butene-l) (PB) with an ethylene propylene copolymer (EPM) containing 60 wt% PP were studied over the complete composition range. Phase-contrast polarizing microscopy and dynamic mechanical spectroscopy revealed that the blend is heterogeneous. DSC studies of quenched and annealed blends for both PB modifications indicate that total blend crystallinity decreases linearly with the EPM content. Pure PB crystallinity is enhanced to a small degree in the presence of EPM. Tensile behaviour of the blends was good up to moderate EPM levels. It was also demonstrated that blends containing EPM with increased PP content showed synergism in tensile behaviour not exhibited by blends with EPM of lower PP content. Appropriate mechanical models tested over the complete composition and temperature range suggest that the rubbery phase adheres strongly to the PB matrix. Overall, the experimental results support the contention that the system is mechanically compatible, possibly a result of component miscibility at elevated temperatures as predicted on thermodynamic grounds. INTRODUCTION

Property diversification of polyolefins has been attained principally by blending [1-3]. Thus for example, increased stiffness to polypropylene (PP) was imparted by blending it with high density polyethylene (HDPE) and increased toughness by adding an ethylene propylene copolymer (EPM) rubber. Among the various polyolefins studied, very little has been published on isotactic poly (butene-l) (PB)/EPM blends. Patent information [3, 4] indicates that addition of EPM increases the stress crack resistance, toughness and tear resistance of films and also that these blends have an excellent combination of mechanical strength, heat resistance and transparency. In a previous paper [5] the compatibility behaviour of PB with chlorinated PE (CPE) was described. It was demonstrated that, though incompatible on a segmental level, this blend was mechanically compatible up to moderate levels of CPE. This report examines the physical and mechanical properties of PB/EPM blends for the complete composition range. Among the EPM's available, an amorphous copolymer with a high proportion (60 wt%) of PP monomer was chosen, since it is known [6, 7] that PB/PP blends are mechanically compatible. Polyolefin blends at ambient temperatures phase separate: this effect has been attributed [8] to their low energy of interaction. In this system however, based on the solubility parameter concept, miscibility cannot be excluded at elevated temperatures (ca 200C) where mixing is performed. At room temperature using Small's Scheme [9], ~SpB= 8.24 and 6EpM = 7.8[ (cal/cm~) J~2. Using the relationship [10] relating the temperature dependence of 8 with the thermal expansion coefficient ct, the solubility parameters of the two components approach each other at elevated temperatures. (A6 ~- 0.01 at 25OC), 117

since the coefficient of thermal expansion of PB is considerably larger [11] than that of EPM: :teB=8.04 x 10 -4 and 0~EpM=5.60 X 1 0 - 4 C ~. The same considerations apply to blends of PB or poly(pentene-1) with the lower members of the polyolefin family, lnterfacial tension is also predicted as low and this would favour compatibility. Using the harmonic equation [12] and assuming no polarity for both components, 7~2 at 200C is calculated to be 0.014 dyn/cm. Pure component data were taken from Ref. 11 and 12. Even for phase-separated systems at ambient temperatures, interface adhesion can be promoted [1] by wettability and segment interpenetration and give mechanically useful blends. The spreading coefficient, 2~2, which gives [12] a measure of wettability, is calculated to be 0.736 or -0.764 erg/cm 2 at 200C, depending whether PB spreads over EPM or vice versa. Though the predicted wettability is low, it is higher than that predicted [13] for the HDPE/EPM blend. With regard to segment interpenetration and/or branch entanglement, it is an important structural factor enhancing adhesion since. for kinetic reasons when samples are cooled, segments from dissimilar chains may not disentangle. Thus branched chains may favour phase "interlocking". There is experimental evidence [2] that blends from low density PE (LDPE)/EPDM at the same degree of crystallinity have higher tensile strength than for unbranched HDPE/EPDM. Starkweather has also demonstrated [141] the increased interaction of the amorphous phase of LDPE/EPDM compared to HDPE/EPDM blends. Another factor is that pendant branches seem to affect the tensile behaviour [15] restricting chain slippage under tension. This effect was not observed for HDPE. It could favour mechanical compatibility among polymer pairs which deform in a similar manner.

118

J . K . KALLITSISand N. K. KALFOGLOU

In this work the degree of compatibility was assessed using the dynamic mechanical analysis ( D M A ) technique over an extended temperature range. In our experience [16, 17] the technique is capable of detecting amorphous phase mixing even in semicrystalline polymers. Tensile testing was applied to determine ultimate properties useful for practical applications. It is also known [14, 18] that these tests provide information on the degree of mechanical compatibility, possible synergism etc. The effect on tensile properties of changing the PP content in the E P M at a single blend composition was also examined. Thermal properties (such as melting transitions, degree of crystallinity and the effect of annealing and of varying blend composition) were determined using the DSC technique. Morphological examination was performed with phase-contrast and polarized light microscopy. The results were analyzed using suitable models to obtain information on phase connectivity in the blends. EXPERIMENTAL

Materials and specimens preparation PB was obtained from Aldrich-Europe, Belgium. Specific gravity was 0.91 and /1~,, reported [19] to be 4.09× 105g/mol. DSC measurements gave 58 and 44% degree of crystallinity for modifications I and lI, respectively. The EPM rubber (trade name Vistalon 404) was donated by Essochem Europe and contained 40 wt% ethylene. Specific gravity was given as 0.86 and Mooney viscosity 35M5 (1 + 8' at 100"C). EPMs with higher ethylene content were also tested at one blend composition, viz. Vistalon 606 and 707 with 50 and 65 wt% ethylene, respectively. EPM 606 had a higher Mooney viscosity (55 70 at 12T'C). Solution viscosity in toluene [20] at 30'C gave 3~. as 1.0 x 10s. A high polydispersity index was reported for these products. Melt mixing was carried out at 190-200C as before [5, 16]. Films were prepared by melt-pressing at 10 MPa for 5 min at 190'~Cand they were annealed at 100C for 2 hr or else quenched at 0C. All samples except where indicated were stored for 1 week prior to measurements. Thus the transformation of PB to its stable modification I can be assumed as complete [21]. The following compositions were studied, 100PB/0, 90PB/10, 75PB/25, 50PB/50, 25PB/75, 10PB/90 and 0PB/100, where the first numeral denotes the percentage by weight of PB. Apparatus and procedures Thin films prepared by melt pressing were examined under a phase-contrast microscope (Orthoplan Leitz) with oil (n~3= 1.518) immersion in bright field. A polarizing microscope (Leitz Wetzlar) was also used. As before, samples were prepared by melting the blend on the microscope slide and slightly pressing with a cover glass to obtain a sufficiently thin layer. DSC measurements were carried out using a Du Pont 910 Calorimeter system coupled with a 990 programmer recorder. Calibration was made with Indium standard. Sample weight was ca 15 mg and heating rate 20°C/rain. The first heating cycle to 160cC was followed by holding for 60 sec, quenching at ca 50 C/min to - 100°C followed by a second cycle. Dynamic mechanical data, loss tangent tan6 and complex modulus IE*I were obtained between -100 and 120C at 1l0 Hz for quenched (0~'C) blends, using the direct reading viscoelastometer (Rheovibron DDV I1-C, Toyo-Baldwin) and the procedure described already [16].

Tensile properties were determined at room temperature using a J.J. machine type TS001. Two types of test specimens were used. Film strips with dimensions 0.6 x 12 × 60 mm 3 and microtensile test pieces according to ASTM D1708-66. For the latter an injection molding machine was used with barrel and mold temperatures at 230 and 70°C, respectively. Crosshead speeds were 30 mm/min and 420mm/min for the dumbell and film test-pieces, respectively.

RESULTS AND DISCUSSION

Morphology In general, the state of blend dispersion should depend on the melt viscosities of the two components and their concentration in the blend [22]. The melt viscosity of PB is essentially similar to that o f i P P [23] and is lower than that of EPM. Thus it is expected that the rubber will be coarsely dispersed when it is the minor component while, at the other extreme of compositions, PB will be finely dispersed [22]. Figures 1, 2 and 3 summarize the morphological study using phase contrast and polarized microscopy. Figure 1 indicates the heterogeneous nature of blends at small E P M contents. Given the refractive index values of E P M and PB calculated [24] to be nEpM 1.498 and neB = 1.457, at positive phase contrast dark and light areas represent the EPM and PB phases, respectively. Comparison of quenched (la,b) with annealed (lc,d) specimens indicates the coarsening of blend morphology by annealing at 100"C. More revealing are the results obtained with the polarizing microscope for annealed (Fig. 2) and quenched (Fig. 3) blends. Figure 2 shows that at all compositions when blends are annealed below the Tc of PB (at 100°C), the rubbery component is segregated in the form of spherical globules. In certain areas, deformation of the EPM particles is also observed. There is no evidence that the rubbery material concentrates into the interspherulitic regions. At increased rubber levels, 50PB/50 and 25PB/75, a more uniform dispersion seems to be attained. Quenched samples (Fig. 3) show a considerable decrease of spherulitic size. Increase in rubber content leads to the destruction of the crystalline order at the median composition range. N o essential difference is observed when EPM with a higher ethylene content (65 wt%) was used (compare Fig. 3b and 3f). The morphology results resemble those reported by Martuscelli and coworkers [25] for an analogous system (iPP/EPDM). They suggest that the appearance of small particles of EPM may indicate partial miscibility in the molten state. =

Thermal properties Data obtained with DSC are summarized in Fig. 4 and Table 1. Figure 4 shows that, for both quenched and annealed blends and for both modifications I and II, the overall blend crystallinity decreases almost linearly with EPM content extrapolating to zero crystallinity. This is expected when the rubber acts merely as a diluent to the crystalline phase and when specific interactions associated with component miscibility are absent [26]. The PB crystallinity is somewhat increased with addition of EPM. This has been observed [25] in similar polyolefin blends and has

~i

i ~ ~i~i ¸¸ i~ii!i ~ i

i ~ i i i ~,i,~!!~!i~i~i~i ¸

,!!i!!i!!! ¸iiii~i,lii~i ~,~iiiii!!!!il .......~" !!~"ill? ~i ~i '+¸¸¸~'~¸~¸~

.....

%

Fig. 1. Phase contrast micrographs of blends; (a,b) annealed; (c,d) quenched (a,c) 90PB/10: (b,d) 75PB/25.

Fig. 2. Optical micrographs with crossed polarizers of annealed blends; (a) 100PB/0; (b) 90PB/10: (c) 75PB,'25: (d) 50PB/50: (e) 25PB/75. 119

120

J . K . KALLITSISand N. K. KALFOGLOU

Fig. 3. Optical micrographs with crossed polarizers of quenched blends; (a) 100PB/0; (b) 90PB/10; (c) 75PB/25; (d) 50PB/50; (e) 25PB/75; (f) 90PB/10, EPM with 65% ethylene.

/ 701

~ •-

~

o

",\

r]

\

\ \ \

\

\ \ \.A,\6\

\

o 30

"-u

\x<,

-%

10

\

I 40 EPM Wt %

I 80

Fig. 4. C o m p o s i t i o n dependence o f crystallinity; filled symbols indicate total blend crystallinity and open symbols the

PB crystallinity. (U],.) annealed at 10OC; (O,O) quenched at 0'C; (z~,A) PB modification II.

been attributed to the EPM serving as a nucleating agent for PB crystallization. T m for both modifications is slightly depressed (see Table 1) with increasing EPM. This may be attributed to morphological factors (less perfect crystallites) since no mixing between the amorphous phases of the two components was detected by the D M A technique (see below). This is also in line with morphology findings on quenched blends (see Fig. 3). However, no definite conclusions can be drawn in this respect since no thermodynamic analysis of melting data was performed according to the Hoffman-Weeks procedure [27]. In an analogous system (iPP/PIB), such an analysis gave evidence [25] for miscibility in the melt. Ultimate properties Ultimate strength and elongation as a function of composition are shown in Fig. 5. It is significant that the addition of 10 wt% E P M acts synergistically for both properties. This increase can be attributed to the crystallinity enhancement of PB at low rubber levels (see Table 1). This was not the case for the PB/CPE blend [5] where no crystallinity increase was observed. Weynant et al. [28] reported that an

Physical characterization o f blends o f PB with E P M

121

Table 1. Thermal properties of polyblends Modification I

Modification II Quenched

Polyblend sample

Tm (~C)

AHf (J/g)

PB Cryst. (%)

Blend Cryst. (%)

Tm ("C)

AHr (J/g)

PB Cryst. (%)

Blend Cryst. (%)

BP100/0 PB90/10 PB75/25 PB50/50 PB25/75 PB10/90 PB90/10* PB90/10+

129 129 128 126 125 125 128 128

72.8 78.5 77.8 80.3 79.9 83.9 73.5 74.3

58.2 62.8 62.2 64.0 63.9 67.0 58.8 59.5

58.2 56.5 46.7 32.0 16.0 6.7 53.0 53.6

I 15 115 115 113 113 113 115 115

33.4 36.6 33.5 36.7 37.0 40.5 34.7 36.0

44.4 48.7 44.5 48.8 49.2 53.8 46.1 47.9

44.4 43.8 33.9 24.4 12.3 5.4 41.6 43.2

PBI00/0 PBg0/10 PB75/25 PB50/50 PB25/75

135 135 134 132 131

87.5 91.4 86.0 90.4 88.5

70.0 73.1 68.8 72.3 70.8

Annealed 70,0 65.8 51.6 36.2 17.7

*EPM rubber with 50% ethylene, "tEPM rubber with 65% ethylene.

increase in crystallinity and spherulite diameter of pure PB produces a reinforcement and embrittlement of the material. It is pertinent to note that, at low rubber levels, blend dynamic modulus (characterizing material stiffness) is also higher than for pure PB (see below). Further EPM increase causes a reduction of these properties since the decreased strength and stiffness of the rubbery phase cannot be offset by the small increase of PB crystallinity. What is of practical importance is also that the ultimate elongation of PB films is not seriously impaired by the addition of EPM. This is an indication of good interphase adhesion [26, 29]. Tensile testing with EPM copolymers containing a higher ethylene content was also performed at the 90PB/10 composition. No synergism and no crystallinity enhancement was observed. Thus

the cause for synergism should indirectly at least be attributed to the increased PP content of the EPM rubber used making it a more effective nucleating agent, or by providing more entanglements across the interface [30]. As before [5] the small elongation and increased strength of the injection molded specimens (see Fig. 5) can be attributed [31] to the molecular orientation of the pure PB component at the skin of the specimens leading to reinforcement but brittle behaviour.

Dynamic mechanical properties Thermomechanical spectra are shown in Fig. 6 and the main relaxation maxima reported in Table 2. At

~°~ E :" " - % ' ~ \

s~..:

o% •.<

//t\{ 46

k.. .,

\

\%.

,o. mo

i

•I

~

~ Oo°

I

"

,

o°o o oo co qo

I0 ~ o o

•

o

o,,\-o

oo/

/~\\

~ / \ ,~ ~'~\

oo •

\_

~, l o "~

o °Oo°

-~

LLI

I

I

40

80

(b)

\

E o

__

_ " ~_ . \

• • •

~

\\\\-~.~_~

".0 o

°o• •

~

~

__ I -~20

___

40

t 40

____L 120

EPM Wt % Fig. 5. Composition dependence of ultimate strength and strain of btends; ( - - ) strength; ( - - ) strain; ( ..... ) strength of injection molded test pieces at 20% strain; ( A ) strength of 90PB/10 blends containing E P M with 50 and 6 5 % ethylene.

Temp (°C) Fig. 6. Temperature dependence o f storage (a) and loss (b) moduli o f blends; ( - - ) 100PB/0; ( - - - ) 9 0 P B / 1 0 ; ( . . . . . ) 7 5 P B / 2 5 ; ( - - . - - ) 50PB/50; ( O ) 2 5 P B / 7 5 ; ( © ) 10PB/90; ( B ) 0PB/100.

122

Polyblend

sample

J.K. KALLITSISand N. K. KALFOGLOU Table 2. Glass transitions of the polyblends Emax tan6~ ct fl ~ fl

PB 100/0

-

4

PB90/10 PB75/25 PB50/50 PB25/75 PBI0/90 PB0/100 S= Shoulder.

-2 -4 -5 ----

--

5

-48s -48 -48 -46 -47 -48

6 4 4 2 ---

--

-48 -48 -46 -40 -37 -34

DSC # --60 -61 -61 -61 -60

low rubber contents, an increase in stiffness is observed (compare 90PB/10 with 100PB/0 in Fig. 6a). This stiffening has also been observed [5] in PB/CPE and was attributed to polarity. In the present system, increased crystallinity is likely to be the cause. No such stiffening was observed in blends of H D P E / E P M [13] and H D P E / E P D M [16] while for blends of iPP/EPM modulus enhancement was observed [17] at the 90iPP/10EPM composition. Little crystallinity increase was observed at this composition. In Fig. 6b the loss modulus spectra show that the system is immiscible. The main relaxation [31] ~ of PB at - 4 ° C and fl of EPM [17] at - 4 8 ° C , do not merge nor do they shift to each other with changing blend composition. Thus D M A does not indicate any miscibility at the segmental level and at low temperatures where the major relaxations are observed. The heterophase nature of blends and the good adhesion between the components, as established by the tensile testing, induced us to test suitable models [32, 33] proposed to predict properties of blends using pure component data. In previous studies [13, 16, 17] it was shown that, for blends of H D P E / E P M , H D P E / E P D M and iPP/EPM, a parallel phase connectivity over-estimated the modulus of the composite. In the present system, this simple model seems to be satisfactory (see insert in Fig. 7). This modulus synergism may be due to the changing phase properties of PB in the blends. Indeed, as shown in Fig. 4 and Table 1, the crystallinity of PB increases with the EPM content. Both the Kerner model [33] and an equivalent model described by Dickie [34] were applied to predict dynamic and loss moduli, respectively, for the complete composition and temperature range (See Figs 7 and 8). The models assume perfect adhesion between soft, randomly dispersed spherical inclusions with a hard matrix, a real viscoelastic Poisson ratio v and also that properties of the constituents in the blend are the same as in bulk. Kerner's model can be expressed as, I Ec = E m (7

[

-

(I)iEi 5 vm)Em q'- (8

--

~LtA hi

--

(1)m 1 10 Vrn)gi -~ 15(f•Vrn)

10 101°

u o o

o o o

"t

ILl ld °

oo

--

°Oo

\

xo

L

~

°

o

o

,'

° o o

'\

-~

109

08

04

o o o

\

o o

108

\ o \ i

1

-100

-40 Temp

I

i

20

80

(°C)

Fig. 7. Dynamic modulus prediction using Kerner's model; (©) experimental values; ( ) calculated with PB matrix; ( - - - ) calculated with EPM matrix; (--. ) pure PB values corrected only for crystallinity increase. Numbers next to curves denote weight percentage of EPM. Insert; prediction of relative values of blend modulus using the parallel and series model at 40~C.

109 ~

000o

1

1o

.2"<°o

oj~OoO°O

/

oo

°°o°

108

oo

"o

108

T°°o

°°

-

o

o

k'<~o 4 \o o

o

Oo \

o

o

(I)i g m

i7 - 5 Vm)Em + (8 -- 10 Vm)E~

(1) where E is the dynamic modulus and indices c, m and i indicate a property of the composite (blend), the matrix and of the inclusion at volume fraction ~, respectively. The Poisson ratio of the composite vc

I

I -100

I -40

I 20

] ~ 80

Temp (°C I

Fig. 8. Loss modulus prediction using Dickie's equation; (©) experimental values; ( ) model prediction. Numbers next to curves denote weight percentage of EPM.

Physical characterization of blends of PB with EPM was assumed to be equal to the arithmetic m e a n of its c o m p o n e n t s weighted as their volume fraction. Values for v used in the calculation were, VEpM = 0.33, VpB= 0.40 below Tg a n d VEpM = VpB = 0.49 above Tg. The basic e q u a t i o n used by Dickie [34] from which an expression for storage a n d loss m o d u l u s was derived (see A p p e n d i x 1 in Ref. 34) is given by, E* (I - q))Em*+ fl(u + ~ ) E * E-- = 7 (l + ~ * ) E * + ~fl(l - * ) E *

(2)

where, = 2(4 - 5 Vm)/(7 -- 5 Vm) fl = (I + Vm)/(1 + vi) 7 = (1 + v~)/(l + Vm) In Figs 7 a n d 8 d y n a m i c m o d u l u s a n d loss m o d u l u s predictions using K e r n e r ' s a n d Dickie's models, respectively, are c o m p a r e d with experimental results. The d y n a m i c m o d u l u s prediction for b o t h models is the same. The same Figures show that, taking into account the change o f PB properties (increased modulus due to crystallinity), improves model predictions. This " c o r r e c t i o n " for PB was performed by extrapolating blend moduli values to ~i = 0, a n d for the E P M c o m p o n e n t to ~ = 1.0. M o d e l predictions for the t e m p e r a t u r e dependence of E " (see Fig. 8) are fairly accurate in view of the fact that in the experim e n t the loss m o d u l u s is indirectly measured. The d y n a m i c m o d u l u s prediction does n o t indicate any matrix reversal up to ca 50PB/50 composition. At higher E P M contents, b o t h matrices are unsatisfactory and a better correlation with the experimental data is provided at the 10PB/90 composition, when E P M is the matrix. This was not observed [17] for the system i P P / E P M blend where matrix reversal was clearly indicated by model prediction. As pointed out before [5], PB m a y form a super-molecular crystalline network persisting at high r u b b e r concentrations. Based on morphological evidence, Kresge reported [2] a PP i n t e r p e n e t r a t i n g network in an atactic P P / E P M blend even down to 1 5 w t % PP component. CONCLUSIONS Both m o r p h o l o g y e x a m i n a t i o n a n d d y n a m i c viscoelastic b e h a v i o u r s u p p o r t the view t h a t P B / E P M blends are incompatible at the segmental level at a m b i e n t temperatures. This does n o t exclude blend miscibility in the melt a n d indeed this is plausible on t h e r m o d y n a m i c a n d kinetic grounds; e.g. similar values, low rate o f phase separation of b r a n c h e d components. G o o d interphase adhesion, manifested by the good tensile properties and by the successful application of mechanical models, supports the view that the b r a n c h e d structure of PB a n d possibly its high M.W. [30] stabilize the system, again for kinetic reasons, and at r o o m t e m p e r a t u r e it behaves as a mechanically compatible blend.

Acknowh, dgements--The assistance of Dr A. Zacharopoulou, and Dr C. Katagas in obtaining the optical micrographs, is greatly appreciated. Thanks are also due to Professor A. Dondos for providing the tensile testing facility and to Essochem Europe for the EPM. The partial support

123

of the Ministry of Industry, Energy and Technology, the General Secretariat of Research and Technology is also acknowledged. REFERENCES

1. S. Newman. In Polymer Blends, (Edited by D. R. Paul and S. Newman), Voi. 2, Chap. 13. Academic Press, New York (1978). 2. E. N. Kresge. In Polymer Blends, (Edited by D. R. Paul and S. Newman), Vol. 2, Chap. 20. Academic Press, New York (1978). 3. A. P. Plochocki. In Polymer Blend~, (Edited by D. R. Paul and S. Newman), Vol. 2, Chap. 21. Academic Press, New York (1978). 4. D.J. Doentremont (Grace W. R. and Co.). US 3972964, Aug. 3 (1976); Mobil Oil Corp. Brit. 1,149,704, Apr. 23 (1969). 5. J. K. Kallitsis and N. K. Kalfoglou. 3. appl. Polym. Sei. In press. 6. A. J. Foglia. Appl. Polym. Syrup. It, l (1969). 7. A. Siegmann. J. appl. Polym. Sci. 24, 2333 (]979) and 27, 1053 (1982). 8. J. W. Barlow and D. R. Paul. A. Rev. Mater'. Sci. II, 299 (1981). 9. S. Krause. In Polymer Blends', (Edited by D. R. Paul and S. Newman), Vol. 1, Chap. 2. Academic Press, New York (1978). 10. I. C. Sanchez. In Polymer Blends, (Edited by D. R. Paul and S. Newman), Vol. 1, Chap. 3. Academic Press, New York (1978). 11. D. W. Krevelen. Properties of Polymers', p. 61). American Elsevier, New York (1972). 12. S. Wu. In Polymer Blends, (Edited by D. R. Paul and S. Newman), Vol. 1, Chap. 6. Academic Press, New York (1978). 13. N. K. Kalfoglou. J. Macromolec. Sci. Phys. B22, 343 (1983). 14. H. W. Starkweather, Jr. J. appl. Polym. Sei. 25, 139 (1980). 15. J. P. Rakus, C. D. Mason and R. J. Schaffhauser. J. Polvm. Sci. Polym. Lett. 7, 591 (1969). 16. N. K. Kalfoglou. J. Macromolec. Sei. Phys. B22, 363 (1983). 17. N. K. Kalfoglou. Angew. Makromolee. Chem. 129, 103 (1985). 18. See for example, G. A. Lindsay, C. J. Singleton, C. J. Carman and R. W. Smith. In Multiphase Polymers, (Edited by S. L. Cooper and G. M. Estes), p. 367. Adv. Chem. Ser. No 176, ACS Washington D. C. (1979): D. W. Bartlett, J. W. Barlow and D. R. Paul. J. appl. Polym. Sci. 27, 2351 (1982). 19. M. Cortazar and G. M. Guzman. Makromoh,e. Chem. 183, 721 (1982). 20. G. Delmas, V. Daviet and D. Filtrault. J. Polvm. Sci. Polym. Phys. Edn 14, 1629 (1976). 21. J. Haase, R. Hoseman and S. K6hler. Polymer 19, 1358 (1978). 22. S. Danesi and R. S. Porter. Polymer 19, 448 (1978). 23. R. Genillon, F. Deri and J.-F. May. Angew. Makromolec. Chem. 65, 71 (1977). 24. D. W. Krevelen. Properties of Polymers, p. 201. American Elsevier, New York (1972). 25. E. Martuscelli. Polym. Engng Sci. 24, 563 (1984); E. Martuscelli, C. Silvestre and G. Abate. Polymer 23, 229 (1982). 26. W. J. Macknight, F. E. Karasz and J. R. Fried. In Polymer Blends, (Edited by D. R. Paul and S. Newman), Vol. 1, Chap. 5. Academic Press, New York (1978). 27. J. D. Hoffman and J. J. Weeks. J. Res. nam. Bur. Stand. 66A, 13 (1961). 28. E. Weynant, J. M. Haudin and C. G'Se11. J. Mater. Sei. 15, 2677 (1980).

124

J . K . KALLITSISand N. K. KALFOGLOU

29. R. D. Deanin, S. B. Driscoll and J. T. Krowchun, Jr. Org. Coat. Plast. Chem. 40, 664 (1979). 30. A. Rudin. J. Macromolec. Sci. Rev. Macromolec. Chem. C19, 267 (1980). 31. M. Guo and J. Bowman. J. appl. Polym. Sci. 28, 2341 (1983).

32. R. A. Dickie. In Polymer Blends (Edited by D. R. Paul and S. Newman), Vot. 1, Chap. 8. Academic Press, New York (1978). 33. L. E. Nielsen. Mechanical Properties of Polymers and Composites, Vol. 2, Chap. 7. Marcel Dekker, New York (1974). 34. R. A. Dickie. J. appl. Polym. Sci. 17, 45 (1973).