PII: 0014-3057(94)90299-2Perg,mo. Eur. Polym. J. Vol. 30, No. 3, pp. 353 360, 1994
Elsevier Science Ltd Printed in Great Britain.
0014-3057/94 $6.00 + 0.00
SYNTHESIS AND APPLICATION OF POLY- ARYLATE-POLY(METHYL METHACRYLATE)
BLOCK COPOLYMER AS COMPATIBILIZER FOR POLYARYLATE/POLY(VINYLIDENE FLUORIDE) BLEND
TAE OAN AHN, ~ JONGCHAN LEE, 1 HAN MO JEONG 2. and KILWON CHO 3 ~Department of Chemical Technology, Seoul National University, Seoul 151-742, Korea
2Department of Chemistry, University of Ulsan, Ulsan 680-749, Korea 3Department of Chemical Engineering, Pohang Institute of Science & Technology,
Pohang 790-600, Korea
(Received I0 November 1992; accepted 28 May 1993)
Abstract--Polyarylate (PAR)-poly(methyl methacrylate) (PMMA) block copolymers were synthesized via radical polymerization of methyl methacrylate using a macroinitiator. The compatibilizing effect of this block copolymer in PAR/poly(vinylidene fluoride) (PVDF) blends was investigated by examining thermal properties, morphology and surface characteristics. The depression of melting point of PVDF and the increase in Tg of PAR with increasing PAR content in PAR/PVDF/PAR PMMA block copolymer ternary blends were accentuated by the addition of the PAR-PMMA block copolymer. Furthermore, a rather finer dispersion was obtained by the addition of block copolymer, which is evidenced also by contact angle measurements, showing that the contact angle of blend is greatly influenced by the presence of block copolymer. These experimental results clearly demonstrate the compatibilizing effect of PAR-PMMA block copolymer in PAR/PVDF blends.
INTRODUCTION
Polymer blending is a simple and efficient method for developing new higher performance materials, start- ing from easily available polymers. Most of the polymer blends, however, are immiscible polymer systems with unsatisfactory properties because of poor interfacial adhesion between the phases [1-3].
The use of block or graft copolymers as compatibi- lizers for controlling the morphology and mechanical performances of incompatible polymer blends is be- coming an important approach in the field of polymer alloys [4--6]. The constituent blocks in the copolymer are expected to diffuse into the homopolymer phases of identical chemical structure and form associations between the homopolymer phases. Therefore, a higher compatibilizing effect is expected when the penetration of each block into the respective homo- polymer phase is easier. When a phase-separated block copolymer, having a block chemically identical with homopolymer, is used as compatibilizer, it has been shown that the miscibility is sensitive to the molecular weight ratio of the homopolymer and the corresponding block of the copolymer, i.e. when the molecular weight ratio exceeds unity the entropy change becomes unfavorable for mixing [7,8]. However, when compatibilizers with chemically different, but thermodynamically miscible blocks are used, the exothermic enthalpy of mixing the homo- polymer with the corresponding copolymer block
To whom all correspondence should be addressed.
gives an additional thermodynamic driving force for solubilization [9-11].
Macroinitiators containing azo or peroxy groups have been reported to be effective for synthesizing multiblocks copolymers having blocks of both condensation and addition type polymers [12-14]. However, only a few studies on the utilization of block copolymers from a macroinitiator in polymer blends are reported [15].
Since poly(methyl methacrylate) (PMMA) is thermodynamically miscible with poly(vinylidene fluoride) (PVDF) [16, 17], copolymers containing PMMA blocks are expected to be useful as compat- ibilizers in blends with PVDF [18-20].
In this study, a PMMA-polyarylate (PAR) multi- block copolymer was synthesized using a macro- intiator and the compatibilizing effect of the block copolymer in PAR/PVDF blend was accessed by examining the morphology, thermal properties and surface characteristics.
EXPERIMENTAL PROCEDURES
Terephthaloyl chloride (Fluka A.G.), isophthaloyl chloride (Fluka A.G.), 4,4'-azobiscyanopentanoic acid (ACPA, Fluka A.G.), bisphenol-A (BPA, Junsei Chemical), triethylamine (Junsei Chemical), and thionyl chloride (Junsei Chemical) were used without further purification.
Methyl methacrylate (MMA) from Junsei Chemical was purified by the usual procedure [21]. Solvents were dried and fractionally distilled before use in a routine manner, PVDF and PAR were purchased from Aldrich and Unitika Co.,
353
b i s p h e n o l - A
+ n
C I - C ~ C - C 1
i s o p h t h a l o y l c h l o r i d e / t e r e p h t a l o y l
c h l o r i d e
( m o l e r a t i o :
1 / 1 )
~H 3
C H 3
C H 3
h y d r o x y - t e r m i n a t e d P A R
I
o ? ~
?.~ o
II tl
H O C C H ~ C H ~ C - N = N - C - C H 4 C H ~ C O H
C N
C N
4 , 4 ' - a z o b i s c y a n o p e n t a n o i c
a c i d
I O C I
-~-cH 2cH
C N
4 , 4 ' - a z o b i s c y a n o p e n t a n o y l
c h l o r i d e
O
~ H 3
2 m
m a c r o a z o i n i t i a t o r
l° C H .
0 C, H3
~ H 3
C N
C ~ = O
J r
P A R - P M M A m u l t i b l o c k c o p o l y m e r
S ch
em e
Synthesis and application of PAR-PMMA block copolymer 355
respectively. The molecular weight of PAR was measured by gel permeation chromatography (GPC) in THF, giving ~/n = 18,000, Klw = 41,100. The viscosity average molecular weight (K-/V) of PVDF was measured in dimethylacetamide (DMAc) at 20°C according to the procedure described in Ref. [22], giving a value of 230,000.
Synthesis and characterization of the PAR-PMMA block copolymer
The overall reaction scheme for the preparation of the PAR-PMMA multiblock copolymer is illustrated in Scheme 1.4,4'-Azobiscyanopentanoylchloride (ACPC) was synthesized from ACPA and thionyl chloride according to a reported procedure [23]. The half-life of ACPA at 65°C was reported to be 36,000 sec [24]. Hydroxy terminated PAR was prepared in chloroform through the use of stoichiometric unbalance of reactants, i.e. using excess amount of BPA [25]. "~/n and '('/v of the hydroxy terminated PAR were determined by the end group analysis [25] and viscosity measurement in dichloroethane at 25°C using the following equation (1) [26]. The values obtained were • / , = 4800, ~V/v = 8100.
[q] = 1.17 × 10 3/~v'576 (1)
Macroazoinitiator was synthesized from equimolecular mixture of hydroxy terminated PAR and ACPC. Larger [r/] value of macroazoinitiator compared with that of hydroxy terminated PAR, i.e. 0.546 dl/g compared with 0.209 dl/g, showed some degree of coupling between hydroxy termi- nated PAR and ACPC.
PAR-PMMA block copolymer was synthesized by the radical polymerization of 0.150mol MMA using 17.1 g (3.39 × 10 3 mol ofazo group) of the above macroazoinitia- tor in 570.0 ml chloroform in a round-bottom flask with a stirrer. Stirring was continued for 24 hr at 60°C under a continuous flow of nitrogen. The reaction mixture was poured into 10-fold of methanol, and the precipitated polymer was filtered and dried under reduced pressure.
Block copolymer was dissolved in CDCI 3 and ~H-NMR spectrum was taken on a Bruker AC-80 FT-NMR spectrometer.
The molecular weight of the block copolymer relative to PS standard was measured by GPC with THF as solvent, giving A~° = 31,000, At~ = 105,900.
Fractional precipitation
Fractional precipitation curves were obtained from the 5% (w/v) polymer solution of chloroform at 25°C. Methanol was used as a nonsolvent to precipitate polymers [27, 281.
Thermal analysis
Blends used for differential scanning calorimetry (DSC) were prepared by a solution/precipitation method. Polymer mixtures dissolved in THF were poured into 10-fold of methanol and the precipitates were dried at 60°C for 72 hr in vacuum.
Glass transition temperature (Ts), melting temperature (Tin), crystallization temperature (T¢), heat of fusion (AH m ), and heat of crystallization (AHc) were determined on a Perkin-Elmer DSC-4 under nitrogen atmosphere. The samples were conditioned in DSC at 230°C for 10 min before scanning to erase the previous thermal histories. T c and AH c were measured on cooling from 230°C at the rate of 20°C/rain. Tg, Tm and AH m were measured on heating at the rate of 20°C/min for the samples quenched at 320°C/min from 230°C to 0°C in the DSC.
Morphological analysis
The morphology was investigated by transmission elec- tron microscopy (TEM, Hitachi H-300) and scanning elec- tron microscopy (SEM, Jeol JSM-35CF).
Thin films for TEM observation were obtained on glass slide by drawing it out slowly from 1% (w/v) polymer solution of THF. After drying, the films were annealed at 230°C for 10 min, and stained with RuO4 vapor for 3 hr at room temperature [29, 30].
The films for SEM observation were obtained by the slow removal of solvent from 3% (w/v) solution of polymer in THF. After drying and annealing at 230°C for 10min, fracture surfaces prepared at liquid-nitrogen temperature were examined by SEM.
Measurement of contact angle
Films were prepared by the same method as in SEM analysis except that of PVDF which was obtained from 3% (w/v) solution of DMAc. Contact angles of films with water were measured on the NRL contact angle goniometer (Rame Hart). About 1 #1 of distilled water was used for each measurement.
REStJLTS Ar~I~ mSCtJSSlON
Characterization of PAR-PMM,4 block copolymers
Figure 1 shows the N M R spectrum of the P A R - P M M A block copolymer giving signals at 0.9 and 3.6ppm (aliphatic hydrogens of MMA), 1.7 ppm (aliphatic hydrogen of bisphenol-A), 7.2 ppm (aromatic hydrogen of bisphenol-A), 7.7, 8.5 and 9.0 ppm (aromatic hydrogens of isophthaloyl chloride), 8.3 ppm (aromatic hydrogen of tereph- thaloyl chloride) [25].
The contents of the PAR and P M M A blocks in the block copolymer calculated from this N M R spec- trum, by comparing the area of aromatic protons and aliphatic protons, were about 40 and 60 wt%, respectively. In multiblock copolymers the M n of constituent block is proportional to the content of each block. So, from the M, of PAR block and composition calculated from N M R spectrum, we can estimate the M, of the P M M A block to be roughly about 7200.
Fractional precipitation methods were used to confirm the formation of a block copolymer. The percentage of precipitated amounts for PAR/PMMA(50/50) blend and P A R - P M M A block copolymer from polymer solutions plotted against r values, i.e. the volume ratio of nonsolvent (methanol)/solvent (chloroform), are shown in Fig. 2. In the case of P A R / P M M A blend, most of the PAR precipitates at r value around 0.8, whereas the re- maining P M M A precipitates at r value around 2.8. The precipitation curve of the P A R - P M M A block copolymer is located exactly midway between the r values of PAR and P M M A and has a smooth shape without any abrupt inflection. This may be con- sidered as conclusive evidence for the formation of a block copolymer with the macroazoinitiator.
The morphology of the block copolymer was examined using transmission electron microscopy (TEM). RuO 4 is more effective in the staining PAR phase than P M M A phase [30]. One can observe clearly the phase separated morphology from the T E M micrograph of P A R - P M M A block copolymer stained by RuO 4 (Fig. 3). This phase separated morphology of the block copolymer was also re- vealed in the DSC thermogram, i.e. two separate Tgs of PAR phase (194°C) and P M M A phase (133°C). This high Tg value of P M M A phase shows some
e C
H 3
10C
8c
r
Fig. 2. Fractional precipitations of PAR/PMMA (50/50) blend (O) and PAR-PMMA block copolymer (O).
dissolution of PAR segment into PMMA phase due to partial miscibility [31, 32].
Morphologies of blends The compatibilizing effect of the PAR-PMMA
block copolymer in PAR/PVDF blends is clearly shown in Fig. 4. The unmodified blend exhibits large
Fig. 3. TEM micrograph of PAR-PMMA block copolymer.
<.
c ci
Fig. 4. TEM micrographs of PAR/PVDF/PAR-PMMA block copolymer ternary blends: (A) 70/30/0 (B) 70/30/3, (C) 70/30/7, (D) 70/30/40 by weight.
358 TAE OAN AnN et aL
Fig. 5. SEM micrographs of PAR/PVDF/PAR-PMMA block copolymer ternary blends: (A) 70/30/0, (B) 70/30/7 by
weight.
block copolymer (40 phr) is added, the morphology is prone to resemble that of block copolymer shown in Fig. 3.
In Fig. 5(A), the scanning electron micrograph of the fractured surface prepared at liquid nitrogen temperature indicates a lack of interfacial adhesion in the unmodified blend. However, the addition of a small amount of the block copolymer (7 phr) remark- ably changes the topology of the fractured surface, i.e. PVDF particle size is decreased and the particles seem to be firmly adhered to the matrix as shown in Fig. 5(B).
175
170
~0 0.2 0.4 0.6 0.8
Weight fraction of PVDF
Fig. 6. T m of PVDF in PAR/PVDF/PAR-PMMA block copolymer ternary blend with 0phr (©), 5 phr (0) and
7 phr (11) of PAR-PMMA block copolymer.
Thermal properties of blends
Figure 6 shows the Tm of PVDF in PAR/PVDF/PAR-PMMA block copolymer ternary blends with different amounts of block copolymer. Melting of crystalline PVDF is discernible even at low PVDF concentration. In the unmodified blends, the Tm of PVDF decreases after an initial increase as the content of PAR increases. The initial increase in Tm at low PAR concentrations is likely due to selective dissolution of defective PVDF molecules such as those of low molecular weights into PAR domains. The depression of T~ at higher PAR content suggests that some amounts of PAR molecules are solubilized in the PVDF phase [33-35].
In Fig. 6, the addition of the PAR-PMMA block copolymer has a clear effect on the melting behavior of PVDF. In ternary blends, as the content of PAR increases Tm increases initially and then decreases as in unmodified blends. However, in ternary blend the change of Tm is more pronounced than in the un- modified blend. This evident change seems to be due to the enhanced miscibility of PVDF and PAR by the addition of the PAR-PMMA block copolymer, i.e. enhanced dissolution of defective PVDF molecules into PAR phase and enhanced dissolution of PAR molecules into amorphous PVDF phase. In Fig. 7, AHm of PVDF decreases more pronouncedly in modified blends as the content of PAR increases. These results may be ascribed to the increased inter- ference on PYDF crystallization by the increased amount of solubilized PAR molecules.
The Tg of PVDF ( -30°C) [16] is much lower than that of PAR (192°C). Therefore, when PVDF mol- ecules are solubilized in the PAR phase, Tg of PAR phase is expected to decrease considerably. In Fig. 8, the Tg of the PAR phase is lower than that of PAR when the content of PVDF in the unmodified blends is high. By the addition of block copolymer the decrease of Tg of the PAR phase is more pronounced than that of unmodified blends (Fig. 8). This also shows the compatibilizing effect of the PAR-PMMA block copolymer, i.e. enhanced dissolution of PVDF molecules into the PAR phase.
In PVDF/PAR-PMMA block copolymer binary blends, the values of T m, T c, AHm, AH c of the PVDF
60
A
LL
Weight fraction of PVDF
Fig. 7. AH m of PVDF in PAR/PVDF/PAR-PMMA block copolymer ternary blends with 0 phr (©), 5 phr (O) and
7 phr/(B) of PAR-PMMA block copolymer.
Synthesis and application of PAR-PMMA block copolymer 359
phase decrease drastically (Figs 9 and 10), demon- strating the intimate molecular mixing of P V D F and the P M M A block of the copolymer.
In P A R / P A R - P M M A block copolymer binary blends, the Tg of P A R phase varies linearly with composit ion (Fig. 11). Although the two Tgs are too close to discuss the miscibility of the P A R homopoly-
205
_ o j
1 9 5 i i i t 0 0 . 2 0 . 4 0 . 6 0 . 8
Weight fract ion of PAR
Fig. 8. Tg of PAR phase in PAR/PVDF/PAR PMMA block copolymer ternary blend with 0phr (©), 5 phr (O), and
7 phr (11) of PAR-PMMA block copolymer.
1813
0 0.2 0.4 0.6 0.8 Weight fraction of PVDF
210
200
Weight fraction of PAR
Tg of PAR phase in PAR/PAR PMMA block copolymer binary blend.
mer and the PAR block, the miscibility of the PAR homopolymer and the PAR block can be presumed from the previously discussed compatibilizing effect of the P A R - P M M A block copolymer in the P A R / P V D F blend.
Surface characteristics
The surface and bulk characteristics of multi- component polymer systems are not identical because of the significant differences in the solid-state surface tension of each component [36]. The contact angles of water on P A R / P V D F binary blends are larger than the values calculated from simple additive rules (Table 1). These suggest that the surface is predomi- nated by the PVDF phase which has a lower surface energy than the P A R phase.
The contact angles of the P A R / P V D F / P A R - P M M A block copolymer ternary blends decrease as the content of the P A R - P M M A block copoly- mer increases and the value approaches that of PAR above 7phr block copolymer (Table 2), suggesting that with a sufficient amount of block copolymer the dispersed PVDF phase is embedded in the bulk.
Fig. 9. T m (O) and T c (O) of PVDF in PVDF/PAR-PMMA block copolymer binary blend.
6 0 , i i ,
10
Weight fraction of PVDF
Fig. 10. AH~ (©) and AH c (Q) of PVDF PVDF/PAR-PMMA block copolymer binary blend.
in
Table I. Contact angles of water on the surface of PAR/PVDF blends
PAR/PVDF Contact angle weight ratio (degree)
0/100 98.5 10/90 98.5 30/70 98.3 50/50 95.7 70/30 89.6 90/I 0 87.2
100/0 82.4
Table 2. Contact angles of water on the surface of PAR/PVDF (70/30) blends compatibilized by means of PAR-PMMA block
copolymer PAR PMMA block Contact angle
copolymer (phr) (degree) 0 89.6 3 89.5 5 88.2 7 84.2
10 83.4
360 TAE OAN AnN et al.
CONCLUSIONS
A P A R - P M M A block copolymer was effectively synthesized using a macroazoini t ia tor . F r o m the measurements of thermal property, the enhanced mutua l dissolut ion of two homopolymers was ob- served when the P A R - P M M A block copolymer was used as a compatibi l izer in P A R / P V D F blends. The compatibi l iz ing effect of the P A R - P M M A block copolymer was also confirmed from the investigation of morphology and surface characteristics.
Acknowledgement--This work was financially supported by a Research Grant (901-1005-027-2) from the Korea Science and Engineering Foundation.
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