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7 Fourier Transform Infrared Spectroscopy as a Probe of Phase Behavior in Copolymer Blends A Comparison of Theoretical Predictions to Experimental Data Michael M . Coleman, Hongxi Zhang, Yun Xu, and Paul C . Painter Polymer Science Program, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802

Results of theoretical and experimental studies of poly(4-vinyl phenol) (PVPh) blends with styrene-co-methyl acrylate (STMA) copolymers are reported. The calculated solubility parameters of STMA copolymers are practically independent of copolymer composition, so that the unfavorable contribution to the free energy of mixing from the "physical" intermolecular interactions remains essentially constant in all PVPh-STMA blends. PVPh is miscible with poly(methyl acrylate), but as the concentration of styrene in the STMA copolymer is increased, the contribution from the favorable hydrogen bonding interactions must decrease. Eventually a point is reached when there is an insufficient contribution to the free energy from favorable specific interactions to overwhelm the unfavorable contribution from the physical forces. Miscibility windows and maps for STMA blends with PVPh and styrene-co-vinyl phenol copolymers are readily calculated and compare favorably with experimental results performed in our laboratories.

EXPRESSION

g e n - b o n d (1-16)

F O R T H E F R E E E N E R G Y O F MIXING O F POLYMERS that h y d r o -

c a n b e obtained f r o m a F l o r y - t y p e lattice m o d e l that w e 0065-2393/93/0236-0221$06.50/0 © 1993 American Chemical Society

Urban and Craver; Structure-Property Relations in Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1993.

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have developed a n d tested over the past f e w years. A s a result o f this treatment w e obtained a separation o f the unfavorable " p h y s i c a l " c o n t r i b u tions to the free energy o f mixing, e m b o d i e d i n a F l o r y χ parameter, f r o m the favorable " c h e m i c a l " contributions emanating f r o m the changing distribu t i o n o f h y d r o g e n bonds, àG /RT; A G is change i n free energy resulting f r o m hydrogen b o n d i n g , R is the gas constant, a n d Τ is temperature. T h e free energy o f m i x i n g ( A G ) c a n b e w r i t t e n as H

B

m

AG — ^ RT

m

Φ = — I nΦ Α

M

A

Φ + — I nΦ

A G

Β

Α

M

Β

+ Φ Φ χ + Α

Α

B

Β

Β Λ

H

J^J,

(1) ν )

where Φ , Φ a n d M , M are the v o l u m e fractions a n d degrees o f p o l y m e r ization o f polymers A a n d B , respectively. Α

Β

A

B

M i s e i b i l i t y w i n d o w s a n d maps are a convenient w a y o f displaying the phase behavior o f c o p o l y m e r blends as a f u n c t i o n o f c o p o l y m e r composition at a given temperature (8, 10-13, 16). I n this chapter w e consider the case o f blends c o m p o s e d o f polymers that contain v i n y l p h e n o l , m e t h y l acrylate, and styrene segments. These studies c o m p l e m e n t recently reported studies o f styrene-co-vinyl p h e n o l ( S T V P h ) copolymer blends w i t h p o l y ( n - a l k y l methacrylates) (10-12), p o l y ( e t h y l e n e - c o - m e t h y l acrylates) (13), a n d poly(ethylene-co-vinyl acetates) (13). E a c h o f these p r i o r studies e m p h a s i z e d experimental testing o f one o f the major hypotheses o f o u r association m o d e l . T h i s theme is c o n t i n u e d here. T h e motivation f o r the present study comes f r o m the recognition that the calculated solubility parameters o f p o l y (methyl acrylate) ( P M A ) and polystyrene ( P S ) are almost identical (14), w h i c h infers that the average solubility parameters o f p o l y (styrene-co-methyl acrylate) ( S T M A ) copolymers are essentially independent o f composition (16). T h i s , i n turn, implies that i n a h o m o p o l y m e r - c o p o l y m e r system o f S T M A blends the " p h y s i c a l " c o n t r i b u t i o n to the free energy o f mixing is also essentially independent o f c o p o l y m e r composition. A c c o r d i n g l y , as w e dilute P M A w i t h styrene, w e are effectively only r e d u c i n g the A G / K T t e r m i n e q 1. Because w e k n o w f r o m previous studies that P V P h is miscible w i t h P M A (7) at 25 °C, an interesting question c a n b e posed: H o w m u c h styrene c a n b e incorporated into P M A before the system becomes i m m i s c i b l e ? W e addressed a similar question previously w h e n w e successfully p r e d i c t e d the miseibility w i n d o w s for S T V P h blends w i t h the p o l y (methyl, ethyl, a n d b u t y l methacrylates) ( J O ) ; the difference here is that w e w i l l b e " d i l u t i n g " the non-self-associating p o l y m e r P M A b y copolymerization w i t h styrene. Finally, w e w i l l t u r n o u r attention to the m o r e c o m p l i c a t e d case o f blends containing two copolymers, S T V P h a n d S T M A , w h e r e b o t h the self-associating ( V P h ) a n d non-self-associ ating ( M A ) segments are " d i l u t e d " b y copolymerization w i t h an inert ( n o n hydrogen-bonding) diluent ( S T ) . H


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Phase Behavior in Copolymer Blends

Experimental Details T h e copolymer compositions, molecular weights ( M ) , a n d glass transition n

temperatures ( T ) o f the polymers used i n this study are s u m m a r i z e d i n Table g

I. T h e P V P h , S T V P h , a n d P M A polymers have b e e n described previously (13).

R a n d o m S T M A copolymers were synthesized b y direct free-radical

polymerization o f styrene w i t h m e t h y l acrylate i n toluene at 70 °C using azobisisobutyronitrile ( A I B N ) as the initiator. P r i o r to polymerization, the monomers were passed through a short c o l u m n o f neutral a l u m i n a a n d vacuum-distilled over c a l c i u m hydride. T o l u e n e was redistilled over c a l c i u m hydride u n d e r nitrogen a n d the A I B N

initiator was recrystallized f r o m

acetone before use. C o p o l y m e r compositions were d e t e r m i n e d b y p r o t o n N M R spectroscopy i n C D C 1

3

f r o m the relative areas o f the peaks assigned to

the m e t h y l protons o f the M A repeat unit a n d the aromatic protons o f the S T repeat unit. Solutions ( 1 % w t / v o l ) o f the polymers were p r e p a r e d i n m e t h y l isobutyl ketone. Blends o f various compositions were then made b y mixing a p p r o p r i ate

amounts

o f these solutions. Samples

f o r F o u r i e r transform infrared

( F T I R ) spectroscopy a n d differential scanning calorimetry ( D S C ) studies were obtained b y solution casting at r o o m temperature. T h e solvent was r e m o v e d slowly u n d e r ambient conditions f o r a m i n i m u m o f 24 h . T h e samples were then d r i e d i n a v a c u u m desiccator f o r a n additional day before placement i n a v a c u u m oven at 120 °C f o r 4 h to completely remove the residual solvent. T o m i n i m i z e water absorption, samples were stored u n d e r v a c u u m desiccation. T h e problems associated w i t h p o l y m e r b l e n d sample preparation a n d the experimental determination o f the miseibility o f a particular b l e n d have b e e n discussed previously (11, 13). H e r e w e only reiterate that w e have b e e n very careful to study the i n f r a r e d spectra o f the b l e n d samples first, at ambient temperature after preparation, t h e n at a n elevated temperature o f 150 °C

Table I. Polymers Employed in This Study Copolymer Styrene-co-methyl acrylate (11.2 wt%) Styrene-co-methyl acrylate (24.8 wt%) Styrene-co-methyl acrylate (38.3 wt%) Styrene-co-methyl acrylate (72.4 wt%) Styrene-co-methyl acrylate (91.2 wt%) Poly (methyl acrylate) Styrene-co-4-vinyl phenol (10 wt%) Styrene-co-4-vinyl phenol (25 w t % ) Styrene-co-4-vinyl phenol (43 wt%) Styrene-co-4-vinyl phenol (75 wt%) Poly(4-vinyl phenol)

Symbol STMA[11] STMA[25] STMA[38] STMA[72] STMA[91] PMA STVPh[10l STVPh[25] STVPh[43] STVPh[75] PVPh

M

n

(GPC)

10,700 14,500 8,600 10,900 11,100 44,000 14,000 11,000 15,000 14,000 1500-7000


T

g

(°c) 94 87 74 45 27 5 109 133 145 166 140

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(above the T o f all components) after an annealing p e r i o d o f approximately 15 m i n , a n d again at ambient temperature u p o n cooling, to ensure that every attempt has b e e n made to approach a state o f t h e r m o d y n a m i c e q u i h b r i u m . g

Infrared spectra were obtained o n a F o u r i e r transform infrared ( F T I R ) spectrometer ( D i g i l a b F T S - 6 0 ) using a m i n i m u m o f 64 co-added scans at a resolution o f 2 c m . Spectra recorded at elevated temperatures w e r e obtained using a heating c e l l m o u n t e d inside the sample chamber. P r o t o n N M R spectra were r e c o r d e d o n F T - N M R spectrometers ( B r u c k e r W P - 2 0 0 or A M - 3 0 0 ) . M o l e c u l a r weights and molecular weight distributions based u p o n polystyrene standards w e r e d e t e r m i n e d using a size exclusion chromatograph (Waters 150C). T h e r m a l analysis was c o n d u c t e d o n a differential scanning calorimeter ( P e r k i n - E l m e r D S C - 7 ) c o u p l e d to a c o m p u t e r i z e d data station. A heating rate o f 20 ° C / m i n was used i n all experiments, a n d the glass transition temperature was taken as the m i d p o i n t o f the heat capacity change. - 1

Results and Discussion Poly (4-vinyl phenol) Blends with Styrene-co-Methyl Acrylate Copolymers. Theoretical Calculations. T h e p o l y m e r b l e n d system that w e describe here was deliberately chosen because the calculated solubility parameters o f P S a n d P M A are almost identical [9.5 a n d 9.6 ( c a l / c m ) , respectively] (14, 16), w h i c h infers that the solubility parameters o f S T M A copolymers are essentially independent o f composition. T h i s independence is illustrated schematically i n F i g u r e 1, w h i c h shows a plot o f S T M A solubility parameters as a f u n c t i o n o f c o p o l y m e r composition. T h e solubility parameter o f the h o m o p o l y m e r P V P h is also shown as a straight line parallel to the χ axis. 3

0 5

Because w e estimate the magnitude o f χ b y the difference i n the n o n - h y d r o g e n - b o n d e d solubility parameters ( Δ δ ) o f S T M A a n d P V P h a n d the value o f the reference v o l u m e , V (a constant i n this case because we use the P V P h c h e m i c a l repeat to define this quantity), it follows that χ is also practically independent o f the c o p o l y m e r composition ( 3 , 9, 16). A c c o r d ingly, dilution o f P M A w i t h styrene effectively reduces only the AG /RT t e r m i n e q 1. T h e methodology for the calculation o f the free energy o f mixing, phase diagrams, miseibility windows, a n d maps for p o l y m e r - p o l y m e r b l e n d systems w i l l be m e n t i o n e d only briefly here because it has b e e n described i n p r i o r publications (1-15) a n d is presented i n detail, together w i t h appropriate c o m p u t e r software, i n o u r recently c o m p l e t e d b o o k (16). T h e previously obtained parameters (13) r e q u i r e d for this calculation are s u m m a r i z e d i n T a b l e II. These parameters can be used w i t h no adjustments to calculate explicitly the relative contributions f r o m the Φ Φ χ a n d AG /RT terms o f e q 1 to the total free energy AG /RT. T h e s e contributions are B

H

Α

Β

m


H

7.

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COLEMAN ET AL.

11 PVPh Δδ

91

STMA

f

ι

I

>\

0.0

0.5

1.0

^

Volume Fraction Styrene in Copolymer

^

PMA

PS

Figure 1. Schematic diagram showing the variation in solubility parameters of STMA copolymers.

Table II. Parameters Employed in This Study

Segment

Solubility Parameter (cal/cm )

K

69.8 93.9 100

9.6 9.5 10.6

21.0

3

MA Styrene(ST) VPh

Equilibrium Constant at 25 °C

Molar Volume (cm /mol)

3

05

Enthalpy of hydrogen bond formation, h = 5.6, h

NOTE:

2

B

K

2

B

66.8

K

A

47.5

= 5.2, and h = 4.0 kcal/mol A

presented graphically i n F i g u r e 2 for 50:50 ( w t % ) P V P h - S T M A blends as a function of S T M A copolymer composition at 150 °C (a temperature

above

the T s of b o t h components of the blends, w h i c h were selected to facilitate g

e q u i h b r i u m conditions). [ F o r h i g h molecular weight polymers, the c o n t r i b u tion f r o m combinatorial entropy (the first two terms o n the right-hand side o f e q 1) is negligible a n d is left out of F i g u r e 2 for the sake of clarity.] F i g u r e 2 quantitatively describes the trends suggested i n the schematic diagram i n F i g u r e 1. T o calculate a miseibility w i n d o w , the second derivative o f the

free

energy of m i x i n g of a b l e n d o f the two homopolymers, P V P h and P M A , is


226

STRUCTURE-PROPERTY

RELATIONS IN

POLYMERS

0.2

initially calculated over the entire blend composition range at the d e s i r e d temperature (150 °C, i n this case). F o r P V P h - P M A blends the calculated second derivative curve is positive over the entire composition range for temperatures i n the experimentally accessible range o f —100 to + 2 5 0 °G, a n d this b l e n d is p r e d i c t e d to be miscible (single phase) (7, 13). Styrene is simply considered to be an inert diluent a n d this calculation process is n o w repeated for P V P h a n d a S T M A c o p o l y m e r containing 9 9 % m e t h y l acrylate ( S T M A [ 9 9 ] ) a n d t h e n repeated at 1 % c o m p o s i t i o n intervals d o w n to S T M A [ 1 ] . T h e two phase region o f the phase diagram (spinodal) is defined b y the area where the calculated second derivatives o f the free energy assume values < 0, w h i c h , i n t u r n , sets the limits o f the miseibility w i n d o w . T h e results o f such a computation are s h o w n for the P V P h - S T M A b l e n d system at 150 °C i n F i g u r e 3. A s s u m i n g e q u i h b r i u m conditions are attained, P M A a n d S T M A copolymers that contain u p to about 65 w t % styrene are p r e d i c t e d to be miscible w i t h P V P h . A t concentrations above 6 5 % styrene at 150 °C, the contribution f r o m the AG /RT t e r m (eq 1) is not sufficient to o v e r w h e l m the unfavorable χ Φ Φ t e r m . n

Α

Β


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227

Figure 3. Theoretical miseibility window.

Experimental Results. A c o m b i n a t i o n o f F T I R spectroscopy a n d ther m a l analysis was e m p l o y e d to test t h e foregoing predictions. T h e p r o b e size o f the F T I R technique (individual c h e m i c a l functional groups) is smaller than the probe size o f the t h e r m a l analysis; thus the F T I R is m o r e sensitive to mixing at the molecular level. It is important to reiterate that even the presence o f a p r o m i n e n t i n f r a r e d b a n d attributed to a n intermolecular interaction between groups o f dissimilar polymers does not necessarily m e a n that the mixture is miscible (single phase): W h a t is r e q u i r e d is that the measured fraction o f h y d r o g e n - b o n d e d groups b e equal to the e q u i h b r i u m distribution at that temperature. H o w e v e r , i f w e have accurate knowledge o f the e q u i h b r i u m constants that describe self- a n d interassociation, w e are able to establish w h e t h e r o r not the system exhibits this e q u i h b r i u m distribution a n d is therefore single phase ( I I , 16). F o r the P V P h - S T M A p o l y m e r b l e n d systems considered here w e have such i n f o r m a t i o n f r o m previous studies a n d w e c a n readily calculate t h e fraction o f h y d r o g e n - b o n d e d carbonyl groups that s h o u l d b e present i n a specific b l e n d o f a particular composition at a


228

STRUCTURE-PROPERTY

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IN

POLYMERS

given temperature assuming that the mixture is a single phase. W e can then compare the theoretical fraction of the various intermolecular interactions w i t h the values observed experimentally b y F T I R spectroscopy. If the theo retical values equal, w i t h i n error, the experimentally d e t e r m i n e d values, a miscible (single-phase) b l e n d can be confidently inferred. Conversely, i f the theoretical values deviate significantly f r o m the experimentally d e t e r m i n e d values, an i m m i s c i b l e (two-phase) mixture is indicated. A t the extreme, w h e n the two phases resemble essentially p u r e components, the theoretical values w i l l approach the values originally present i n the pure materials. I f the p o l y m e r b l e n d is truly miscible, the theoretical fraction o f hydro gen-bonded ( H B ) carbonyl groups ( f § ° ) for P V P h blends w i t h the S T M A copolymers as a function o f b l e n d composition at 25 °C may be calculated from B

ο =_ 1 -

1 + Κ Φ Α

κ,

1 -

Β Ι

KJ B

+

Ko

K

\ (1 - Κ Φ

B

Β

Β Ι

)

(2) using the stoichiometric equations ( I I ,

Φ

= ΦΒι

Β

κ,

+

Β/ ΦΑ = Φ Α ι + Κ Α Φ Α ι Φ Β ι

16)

Κ Φ

Ko

Α

Α Ι

(3)

1 +

Μ _ ( Ι

Κ Β

Κρ

Φ )^ Β Ι

+

κ,

κ

\ Ι-Κ

Β

Β

Φ

(4) Β

Ι

where Φ and Φ are the v o l u m e fractions of the totally "free m o n o m e r s " of the self-associating species Β a n d the non-self-associating species A . K a n d K are e q u i h b r i u m constants describing the self-association of Β whereas K corresponds to the e q u i h b r i u m constant describing the interassociation of Β w i t h A a n d r is the ratio of the molar volumes V / V ( 1 - 3 , 10, 16). Β ι

Λ ]

2

B

A

A

B

T h e results o f such theoretical calculations for the P V P h blends w i t h the S T M A copolymers synthesized for this study (Table I) are shown i n F i g u r e 4. These theoretical curves illustrate an important point. C o n s i d e r the vertical b r o k e n fine passing through the curves at a b l e n d composition of 5 0 % P V P h . I n a miscible b l e n d of P V P h a n d S T M A [ 9 1 ] , about 4 2 % of the carbonyl groups are calculated to be hydrogen-bonded, whereas corresponding values for miscible 50:50 blends o f P V P h and S T M A [ 7 2 ] , S T M A [ 3 8 ] , S T M A [ 2 5 ] , and S T M A f l l ] are approximately 45, 52, 54, a n d 5 7 % , respectively. I n other words, as we dilute P M A b y copolymerization w i t h styrene, the relative proportion of p h e n o l i c hydroxyl groups to M A carbonyl groups increases for a constant blend composition. This, i n turn, leads to an increase i n the fraction


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229

o f h y d r o g e n - b o n d e d carbonyl groups i n a miscible system, as dictated b y the e q u i l i b r i u m constants. Infrared spectra r e c o r d e d at 150 °C i n the carbonyl stretching region, f r o m 1650 to 1800 c m " , o f P V P h blends w i t h four different S T M A copoly mers are displayed i n Figures 5 a n d 6. F o r clarity, a l l spectra are scale expanded a n d p l o t t e d w i t h respect to a relative absorbance scale, b u t w e emphasize that all the spectra were r e c o r d e d f r o m films that were sufficiently t h i n to ensure that m a x i m u m absorbances d i d not exceed 0.6 absorbance units. T h e interpretation o f i n f r a r e d spectra o f P V P h blends w i t h carbonylcontaining polymers, such as polyesters, polyacrylates, and polymethacrylates, has b e e n discussed i n detail previously (7-13, 16) a n d only the essential features w i l l b e restated here. P u r e amorphous S T M A copolymers (denoted Ε i n Figures 5 a n d 6) are characterized b y carbonyl stretching vibration at approximately 1 7 3 5 - 1 7 3 9 c m " . W h e n there is appreciable mixing at the molecular level i n the P V P h - S T M A b l e n d system, an additional b a n d is observed at approximately 1715 c m " a n d is attributed to h y d r o g e n - b o n d e d carbonyl groups (see, f o r example, the large contribution i n the spectra denoted A i n F i g u r e 5). T h e large difference i n the spectra recorded f o r P V P h blends w i t h S T M A [ 3 8 ] a n d S T M A [ 2 5 ] is significant. A l t h o u g h the S T M A [ 3 8 ] cannot definitively b e p r o n o u n c e d a miscible system before an 1

1

1


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STRUCTURE-PROPERTY


Figure 5. Scale-expanded FTIR spectra recorded at 150 °C in the carbonyl stretching region for PVPh blends with STMAÎ91] (top) and STMA[72] (bottom): 80:20, A; 60:40, B; 40:60, C; 20:80, D; pure STMA, E.


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Figure 6. Scale-expanded FTIR spectra recorded at 150 °C in the carbonyl stretching region for PVPh blends with STMAÎ38] (top) and STMAÎ25] (bottom): 80:20, A; 60:40, B; 40:60, C; 20:80, D; pure STMA, E.


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POLYMERS

analysis o f quantitative results, the S T M A [ 2 5 ] is most certainly i m m i s c i b l e b y inspection, because i f it w e r e miscible there w o u l d be an even greater fraction o f h y d r o g e n - b o n d e d carbonyl groups present than i n the P V P h S T M A [ 3 8 ] system. T h e fraction o f h y d r o g e n - b o n d e d carbonyl groups can b e quantitatively d e t e r m i n e d b y measuring the relative areas o f these two bands, after due consideration is given to differences i n the respective absorptivity coefficients (7, 10, 16). T h e results o f curve fitting the carbonyl stretching region o f the blends are s u m m a r i z e d i n T a b l e III a n d the experimental and theoretical values o f the fraction o f h y d r o g e n - b o n d e d carbonyl groups are c o m p a r e d i n F i g u r e 7. W i t h i n error, the experimental values match the theoretical values for the three P V P h blends w i t h S T M A copolymers containing 91, 72, a n d 3 8 % M A , w h i c h is consistent w i t h these mixtures b e i n g miscible. I n m a r k e d contrast, the P V P h - S T M A [ 2 5 ] b l e n d (and the corresponding S T M A [ 1 1 ] system, w h i c h is not shown) is obviously grossly phase separated (immiscible) because the experimentally d e t e r m i n e d fraction o f h y d r o g e n - b o n d e d carbonyl groups is significantly less than theoretically calculated for a single phase. C o r r o b o r a t i n g evidence was obtained f r o m t h e r m a l analysis a n d T a b l e I V lists the results obtained for the P V P h - S T M A blends. T w o T s at tempera tures close to those o f the p u r e components were observed for the P V P h blends w i t h S T M A [ 2 5 ] a n d S T M A [ 1 1 ] . Conversely, single T s close to those estimated f r o m the F o x equation were observed for the corresponding blends w i t h S T M A [ 9 1 ] , S T M A [ 7 2 ] , a n d S T M A [ 3 8 ] . These results are entirely consis tent w i t h the F T I R analysis described previously. g

g

F i g u r e 8 shows a final comparison between the theoretically calculated miseibility w i n d o w for P V P h - S T M A copolymer blends at 150 °C a n d the experimentally determine miseibility behavior o f these blends at the same temperature. T h e u n f i l l e d a n d filled circles represent miscible a n d i m m i s c i b l e blends, respectively. T h i s encouraging comparison leads us to believe that the assumptions inherent i n o u r association m o d e l are reasonable.

Styrene-eo-Vinyl Phenol Copolymer Blends with Styrene-coMethyl Acrylate. W e n o w consider the case o f blends c o m p o s e d o f t w o copolymers. H e r e w e calculate miseibility maps at a particular temperature a n d vary the composition o f b o t h copolymers. F o r example, w e might w i s h to consider simultaneously the effect o f d i l u t i n g b o t h v i n y l p h e n o l a n d m e t h y l acrylate b y copolymerization w i t h styrene. T h e calculated solubility parameters o f P V P h a n d P S are 10.6 a n d 9.5 ( c a l / c m ) , respectively, w h i c h sets the limits o f the average solubility parameter range for S T V P h copolymers. A s already m e n t i o n e d , the calculated solubility parameters o f P M A a n d P S are very similar a n d there is practically no dependence o f the average solubility parameter o n c o p o l y m e r composi tion. T h i s behavior is illustrated graphically i n F i g u r e 9. C o m p a r i s o n o f F i g u r e s 9 a n d 1 reveals that, i n addition to the unfavorable (to mixing) t r e n d 3

0 5


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are a l l the other blends o f the S T V P h a n d S T M A copolymers, located according to c o p o l y m e r compositions. T h e wedge-shaped two-phase region shown i n F i g u r e 10 predicts that as P V P h is d i l u t e d w i t h styrene, the range o f miseibility w i t h S T M A copolymers steadily increases.


7.

COLEMAN ET AL.


237

Figure 8. Comparison of theoretical miseibility window to experimental data. Filled and unfilled circles denote immiscible and miscible blends, respectively.

T o test the predictions experimentally F T I R spectroscopy was again e m p l o y e d . F i g u r e 11 shows typical infrared spectra o f a series o f 80:20 w t % S T V P h blends w i t h S T M A [ 2 5 ] a n d STMA[11] r e c o r d e d at 150 °C. Quantita tive results f r o m curve fitting together w i t h theoretical calculations o f the fraction o f h y d r o g e n - b o n d e d carbonyl groups (see p r e c e d i n g text) are s u m m a r i z e d i n T a b l e V . E x a m i n a t i o n o f these results leads to the following conclusions. S T M A [ 1 1 ] blends are miscible w i t h S T V P h copolymers contain i n g 10 a n d 2 5 % V P h , b u t i m m i s c i b l e w i t h the corresponding copolymers containing 43 a n d 7 5 % V P h . O n the other hand, S T M A [ 2 5 ] blends are miscible w i t h S T V P h copolymers containing 10, 25, a n d 4 3 % V P h , but i m m i s c i b l e w i t h the copolymer containing 7 5 % V P h . F i g u r e 12 presents a comparison between the theoretically calculated miseibility map (scale ex p a n d e d for clarity) a n d the experimental results. It is important to reiterate that this map was calculated f r o m transferable e q u i l i b r i u m constants obtained experimentally f r o m the two homopolymers, P M A a n d P V P h , and there are


238

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no adjustable parameters involved. T h e r e is excellent agreement

between

theoretical p r e d i c t i o n and experimental measurement.

Acknowledgments T h e authors acknowledge the financial support o f the N a t i o n a l Science F o u n d a t i o n , Polymers P r o g r a m , the D e p a r t m e n t o f E n e r g y u n d e r grant D E F G 0 2 - 8 6 E R 1 3 5 3 7 , and the E . I . d u P o n t d e N e m o u r s C o m p a n y .

References 1. Painter, P. C.; Park, Y.; Coleman, M . M . Macromolecules 1988, 21, 66. 2. Painter, P. C.; Park, Y.; Coleman, M . M . Macromolecules 1989, 22, 570; 1989, 22, 580. 3. Painter, P. C.; Graf, J. F.; Coleman, M . M . J. Chem. Phys. 1990, 92, 6166. 4. Coleman, M . M . ; Hu, J.; Park, Y.; Painter, P. C. Polymer 1988, 29, 1659.


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STRUCTURE-PROPERTY RELATIONS IN POLYMERS

5. Coleman, M . M.; Lee, J. Y.; Serman, C. J.; Wang, Z.; Painter, P. C. Polymer 1989, 30, 1298. 6. Hu, J.; Painter, P. C.; Coleman, M . M.; Krizan, T. D. J. Polym. Sci., Polym. Phys. Ed. 1990, 28, 149. 7. Coleman, M . M.; Lichkus, A. M.; Painter, P. C. Macromolecules 1989, 22, 586. 8. Serman, C. J.; Xu, Y.; Painter, P. C.; Coleman, M . M . Polymer 1991, 32, 516. 9. Serman, C. J.; Painter, P. C.; Coleman, M . M . Polymer 1991, 32, 1049. 10. Serman, C. J.; Xu, Y.; Painter, P. C.; Coleman, M . M. Macromolecules 1989, 22, 2015. 11. Xu, Y.; Graf, J. F.; Painter, P. C.; Coleman, M . M. Polymer 1991, 32, 3103. 12. Xu, Y.; Painter, P. C.; Coleman, M . M . Makromol. Chem. Macromol. Symp. 1991, 51, 61. 13. Coleman, M . M.; Xu, Y.; Painter, P. C.; Harrell, J. R. Makromol. Chem. Macromol. Symp. 1991, 52, 75. 14. Coleman, M. M.; Serman, C. J.; Bhagwagar, D. E.; Painter, P. C. Polymer 1990, 31, 1187. 15. Bhagwagar, D. E.; Serman, C. J.; Painter, P. C.; Coleman, M . M . Macromolecules 1989, 22, 4654. 16. Coleman, M . M . ; Graf, J. F.; Painter, P. C. Specific Interactions and the Miscibility of Polymer Blends; Technomic Publishing, Inc.: Lancaster, PA, 1991. RECEIVED for review May 14, 1991. ACCEPTED revised manuscript May 1, 1992.


Structure-Property Relations in Polymers - ACS Publications

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