Comparison of the Vibrational Spectra and Assignments for a-Syndiotactic,/ -Syndiotactic, Isotactic, and Atactic Polystyrene and Toluene

R. A. N Y Q U I S T , C. L. P U T Z I G , M. A. L E U G E R S , R. D. M c L A C H L A N , and B. T H I L L The Dow Chemical Company, Analytical Sciences Laboratory, 1897F Building, Midland, Michigan 48667 (R.A.N., C.L.P., M.A.L., R.D.M.); and The Dow Chemical Company, 433 Building, Midland, Michigan 48667 (B.T.)

Vibrational assignments for a-syndiotactic polystyrene are made with the use of parallel and perpendicular polarization of uniaxially oriented film, and by comparison of vibrational data and assignments for toluene and atactic and isotactic polystyrene. Vibrational assignments are given for a cast film of ~-syndiotactic polystyrene. These assignments are made by comparison with assignments for toluene and isotactic and atactic polystyrene and partial assignments for a- and ~-syndiotactic polysty- rene. Some of our assignments suggest that the crystal structure of a-SPS may not be isomorphous with C2, symmetry.

Index Headings: Infrared; Vibrational assignments: a-syndiotactic poly- styrene, ~-syndiotactic polystyrene, isotactic polystyrene, atactic poly- styrene; Molecular structure; Polystyrene, a-syndiotactic; Polystyrene, ~-syndiotactic; Polystyrene isotactic; Polystyrene, atactic; Raman spec- troscopy.

INTRODUCTION

We have previously studied temperature affects on styrene/acrylic acid copolymer and styrene/acrylamide copolymer, 1 atactic polystyrene, 2 styrene/acrylonitrile copolymer, 3 and syndiotactic polystyrene. 4 It was re- ported that films of syndiotactic polystyrene (SPS) cast from boiling 1,2-dichlorobenzene under an IR heat lamp existed in a crystalline low-temperature form after cool- ing to room temperature. 4 Heating the crystalline low- temperature form of SPS at a temperature of approxi- mately 180°C converts it to a high-temperature form of SPS. Kobayaski e t al. 5 reported that SPS exists in an a-crystalline form and a fl-crystalline form. They report that the a-form (which is formed by crystallizing from the melt) consists of molecules having the all-trans (TT) skeletal conformation. They also report that the ~-form (which is crystallized from solution or from holding glassy samples in an atmosphere of solvent vapor) exists in a crystalline form containing trans-trans-gauche-gauche (TTGG) skeletal conformation2 The/~-form of SPS cor- responds to the low-temperature form and the a-form corresponds to the high-temperature form of SPS re- ported by Nyquist. 4

Kobayaski e t al. report that the fiber identity periods of the a and/~ phases of SPS as determined by x-ray diffraction are 5.0 A and 7.5 A, respectively) Conti e t al. have examined the a-crystalline form of SPS. 6

Kobayaski e t al. suggest that the a-form takes an all- trans planar zigzag (TT) skeletal conformation and the ~-form a TTGG-type conformation, presumably forming

Received 13 January 1991. * Author to whom correspondence should be sent.

a twofold helical structure by analogy with syndiotactic polypropylene)

Since complete vibrational data and assignments have not been reported for a- and ~-SPS, we have attempted to make a complete vibrational assignment for a- and /~-SPS by comparing the spectral data with those for atactic (APS) and isotactic polystyrene (IPS) and for toluene. 7

EXPERIMENTAL

A film of the/~-form of SPS was prepared by casting a film onto a potassium bromide plate from 1,2-dichlo- robenzene and heating the film under an IR heat lamp until the solvent had evaporated and then allowing the film to cool to ambient temperature before recording the IR spectrum.

A sample of the a-form was prepared by gradually heating/~-SPS to 290°C and allowing it to cool to ambient temperature; this film was used to record the Raman spectrum and an IR spectrum that was shown in Ref. 4. Parallel- and perpendicular-polarization IR spectra and FT-Raman spectra were also recorded of a uniaxially oriented film of a-SPS with MW = 240 K. The film was stretched 150% at 135°C. A thin coat of mineral oil was placed on the film surface in order to eliminate inter- ference fringes.

IR spectra were recorded with a Perkin-Elmer 983 IR spectrometer equipped with a AgC1 polarizer, a Nicolet 60SX FT-IR, and a Bomem DA 3.02 FT-IR.

The sample of a-SPS used to obtain the Raman spectra consisted of a thin (~0.5 mm thick) sheet with cleavages along its long dimension. A 2-mm-wide strip was peeled off the KBr plate, and its end and sides were polished with 0.3-ttm alumina sheet.

This specimen was mounted on a goniometer head and oriented so that one of the specimen surfaces was per- pendicular to the spectrometer axis and another was per- pendicular to the incident laser beam. The specimen fluoresced when illuminated with 514 A light (from an argon-ion laser). It was found that the fluorescence in- tensity diminished with time under continuous illumi- nation. The sample was illuminated for approximately 16 h before the spectra were recorded. This process was repeated each time the sample was re-oriented.

The spectra were measured with a Jobin-Yvon HG25 Raman spectrometer equipped with a Lexel 95-4 argon- ion laser. The resolution used was about 5 cm -1, the scan rate was 50 cm-1/min, and the amplifier time constant

Volume 46, Number 6, 1992 0003-7028/92/4606-098152.00/0 APPLIED SPECTROSCOPY 981 © 1992 Society for Applied Spectroscopy

03-,~ Z ,~: n." I--cd "~cd

o

FIG. 1.

S Y N D I O T R C T I C POLYSTYRENE ( P E R P E N D I C U L R R )

I00 3~B3 a~s6 a6oo t866 NRVENUHBER

L~ss 16oo 166

IR spectrum of syndiotactic polystyrene (perpendicular).

~ss

<E I -

z oE l--(o

S Y N O I O T R C T I C POLYSTYRENE ( P R R R L L E L )

~ss 20oo l~SS NRVENUHBER

1~s3 tSoo ~6

FIG. 2. IR spectrum of syndiotactic polystyrene (parallel).

3ss

was 2 s. The sample was illuminated with 200 mW of 5145/~ light, focused with a 40-mm-focal-length lens. A half-wave plate was used to rotate the plane of polariza- tion of the laser beam, and a polaroid film analyzer was used to select the polarization of the scattered light.

The raw spectra exhibited a positively sloping baseline between 200 and 1800 cm -1 from the laser line; thus all spectra were flattened with the use of baseline points at 700 and 1500 cm-L The flattened spectra were smoothed with the use of a 25-point Savitsky-Golay smoothing operation to remove additional noise.

Each of the four different possible polarized spectra was measured for four different orientations of the sam- ple. The spectra showed evidence of extensive depolar- ization of both the incident and scattered light, and thus each spectrum is an indeterminate mixture of four dif- ferent polarizations: the intended polarization, the one resulting from depolarization of the incident light, the one resulting from depolarization of the scattered light, and (to a lesser extent) the one resulting from depolar- ization of both the incident light and the scattered light. Because of this uncertainty, little useful information is available from the individual polarized spectra. By ad- di t ion, composi te spec t ra were created , which ap- proximate the isotropic and anisotropic parts of the po- lar izabi l i ty deviat ive tensor . These spect ra should approximate the parallel- and perpendicular-polarized spectra of a nonoriented sample. These two were also added together to form a composite spectrum which should approximate an unpolarized spectrum of a non- oriented sample.

The spectra added for the isotropic spectrum were y(xx)z, z(yy)x, and y(zz)x (where z is the long axis of

the polymer sheet, x is the shorter axis, and y is per- pendicular to the sheet; and, in the designation A(BC)D, A represents the illumination direction, B the polariza- tion of the incident light, C the polarization of the scat- tered light, and D the direction of observation). For the anisotropic spectrum, the y(zy)z, x(zx)z, and y(xy)x were added. The principal contaminants in each of these (re- sulting from depolarization of either the incident or scat- tered light) are the other off-diagonal elements, as the diagonal components can appear only as a result of de- polarization of both the incident and scattered light.

RESULTS AND DISCUSSION

Infrared spectra for uniaxially oriented a-SPS are giv- en in Figs. 1 and 2. Table I compares the number of normal modes and selection rules for a- and ~-SPS. Table I shows that there are 92 normal vibrations for a-SPS and 188 normal vibrations for B-SPS, and all are active in the Raman. Only 75 normal vibrations are IR active in a-SPS, while 141 normal vibrations are IR active in /~-SPS. Thus, one would expect that the IR spectrum for /3-SPS would be more complex than the IR spectrum for a-SPS. In the case of a-SPS the A and B1 modes should yield perpendicular-polarized IR bands, while the B2 modes should yield parallel-polarized IR bands. In t h e case of/3-SPS the B1 and B2 modes should yield perpen- dicular-polarized IR bands, while the B3 modes should yield parallel bands.

Some IR bands of a-SPS are present in the parallel- polarized spectra and others are present in the perpen- dicular-polarized spectrum, while other bands are pres- ent at nearly the same frequency in both the parallel and

TABLE I. The selection rules and the number of normal modes for a- and 0-syndiotactic polystyrene, a.b

a-SPS (TT, C2v) /~-SPS (TTGG, D2)

Species nl T, R IR Raman Species n~ T, R IR Raman

A1 29 T~ A(±) A A 47 F A A2 17 F A B1 47 Tx A(_L) A B, 29 Ty, R2 A(_L) A B2 47 Ty A(±) A B~ 17 T= ~ A B s 4__ ! Tz, R2 ~ A

92 75A 92A 188 141A 188A

a Note: A = allowed; F = forbidden; T = pure translation; R = pure rotation around the chain axis; x = parallel to the chain axis;y and z = perpendicular to the chain axis.

b The a-SPS form has two styrene molecules in the repeat unit with C2v symmetry and the ~-SPS form has four styrene molecules in the repeat unit with D2 symmetry.

982 Volume 46, Number 6, 1992

T A B L E II. Infrared and Raman data for a-syndiotactic polystyrene. ~

Inf ra red da ta

Pe rpen- Para l l e l d icular 90o--0 ° 0 ° (cm- ' ) 90 ° (cm -1) Acm -~

R a m a n da ta

(cm-O R.I. D.R. Ass ignment

3976.29 3646.17 3619.62

3161.78 3161.97 0.19

3103.14 3103.47 0.33 3082.36 3083.04 0.68 3060.18 3060.63 0.50 3026.54 3027.22 0.68 3001.08 3001.51 0.43

2935.48 2923 2920.89 2.11 2846 2805.39 2716.87 2712.49 4.38

2675.9 2669.60 6.30

2631.4 2630.69 0.71

2602.89 2603.07 0.18

2581.67 2581.37 0.30

± , II

± , II

_L, II ± , II ± , II _L, II ± , II

± , II ± , II ± , II ± , II

2547.23 2549.26 2.03 ±, l l

2508.71 2502.60 6.11 ± , l l ±,ll

2336.81 2336.38 0.43 ± , ] ] 2311.31 2312.15 0.84 ± , ] ]

1986.34 II

1955 1960.00 5.00 2 ,

1941.74 1943.63 1.89 ± ,

1869.06 1871.25 2.19 ± ,

1800.92 1802.84 1.92 ± ,

1775.21 1775.02 0.19 ± ,

1744.18 1746.31 2.13 ± ,

1704.41 IJ 1673.21 1675.29 2.08 ±,11

1601.65 1601.94 0.29 ± , l ] 1582.95 1582.99 0.04 ±,11 1540.98 1542.20 1.22 ±,11 1493.36 1494.00 0.64 ±,11 1452.02 1448.51 3.51 ±,11 1376.69 1375.16 1.53 ± , l l 1348.69 U

1333.35 1279.1 1277.10 2.00 Z ,U 1245 1247.75 2.75 ±

1221.85 0.87 II

1181.48 1182.32 0.84 Z, ] [ 1154.7 1155.24 0.54 ± , l l 1141.41 1111.00 ± , l l

1093.00 1069.54 1069.55 0.01 ±,11 1029.68 1029.42 0.26 ±,ll 1004.23 1004.03 0.20 ± , l l 977.5 980.00 ±,If

1603.9 24.6 0.28 1583.9 9.6 0.27

1452.8 8.5 0.18

1319.8 5.4 0.67

1204.7 17.7 0.02 1182.7 13.1 0.19 1156.7 8.5 0.22

1071.6 3.9 0.38 1029.6 26.3 0.02 1002.6 100.0 0.05

3083 + 904.8 = 3987.8 3027.2 + 621.2 = 3648.4

3060.6 + 569 = 3629.6 2(1582.95) = 3165.90 2(1582.99) = 3165.98

vTB(B,) V~oB(B,) V'so(A,)

v'2(A,)

v , ~ C H ~ ~.~CH~

1582.95 + 1222.72 = 2805.67 1493.36 + 1222.72 = 2716.08

1494.0 + 1221.85 = 2715.85 1333.35 + 1348.69 = 2682 1221.85 + 1448.51 = 2670.4 1601.65 + 1029.68 = 2631.33 1601.94 + 1029.42 = 2631.36 1601.65 + 1004.23 = 2605.88 1601.94 + 1004.03 = 2605.97 1582.95 + 1004.23 = 2587.18 1582.99 + 1004.03 = 2587.02

1601.7 + 976.9 = 2578.6 1582.95 + 964.43 = 2547.38

1582.95 + 964 = 2547 1601.94 + 904.8 = 2506.7 1601.65 + 903.0 = 2504.7 1182.3 + 1155.2 = 2337.5

2(1155.2) = 2310.4 2(1154.7) = 2309.4

1029.4 + 964.0 = 1993.4 1029.7 + 964.4 = 1994.1

2(977.5) = 1955; 2 I 2(980) = 1960

977.5 + 964.43 = 1941.93;I + II 980 + 964 = 1944

964.43 + 903.03 = 1867.46;II + I I I 964 + 904.8 = 1869

964.43 + 840.99 = 1805.42;II + IV 964 + 840.73 = 1805

1029.68 + 752.36 = 1782.04 1029.42 + 750.97 = 1780.39

903.03 + 840.99 = 1744.02;III + IV 904.80 + 840.73 = 1745.53

2(852.75) = 1705.50;2 IV 977.5 + 695.30 = 1672.80;I + VI

980 + 695.94 = 1676 BgB(B,) vgA(A,)

rigA(A,) VlaB(B,) and 5CH2 5CH ~'(CH2)-A P'3(B~)

%(CH2)-A

840.73 + 405.91 = 1246.64

(B2) vsA(A,) d15(B1)

1781 + 315.3 + 621.3 = 1114.7 skeletal vCC v'lsB(B,) v,sA(A,) vx(A,) vs(B2)-A; I

APPLIED SPECTROSCOPY 983

TABLE II. Continued.

Infrared data

Perpen- Parallel dicular 0 ° (cm-0 90 ° (cm-0

900-0 ° Acm-~

Raman data

(cm-0 R.I. D.R. Assignment

978.77 976.87 964.43 964.00 940 940.00

1.90 II ±, II ±, II

903.03 904.80 1.77 L,l[ 852.75 II 840.99 840.73 0.26 L,[[

763 752.36 750.97 1.39 ±,[[ 695.3 695.94 0.64 ±,[[ 670 670.00 ±

630.0 620.55 621.15 0.60 2,[[ 569 579.00 ± 544.17 538.43 5.74 L,[I

473.6 462.73 445.77 435.66 415.09 405.91

v6(B2)-B 1/17(A2); II

544.17 + 415.09 = 959.26 538.43 + 405.91 = 944.34

905.0 1.3 0.34 v~7B(B2)-B~ and A2; III v~o(A2)-A

839.9 1.3 0.24 V~o(A2)-B; IV 796.4 5.4 0.08 B~ 773.4 15.8 0.03 A~

V~os(B2) -E V~os(B2)-A; V ~,,(B~)

232.1 + 435.66 = 667.76 232.1 + 445.77 = 677.87

v6~(B~) 621.3 12.9 0.27 ves(B~)

v4(B~)-A v.(B~)

526.5 2.3 0.18 (B~) SK DEF

~CCC 402.2 4.6 0.14 P16A(A2) 315.3 ~CCC 232.1 13.0 0.71 v~6B(B2) 178.1 4.6 0.03 SK DEF

"Note: For uniaxially oriented syndiotactic polystyrene, the A~ and B, fundamentals should yield perpendicular polarized IR bands and the B2 modes should yield parallel polarized IR bands. R.I. is relative intensity; D.R. is depolarization ratio. II is parallel polarization; ± is perpendicular polarization. SK DEF is skeletal deformation.

polarized spectrum, and these bands have different in- tensities. These IR bands, which differ by ~0.2 cm -~ or more (but less than ~2 cm-0, we believe result from similar but different molecular vibrations, since the fre- quency accuracy of the FT-IR system is within 0.1 cm -~. We suggest that the corresponding IR bands at approx- imately the same frequency are the result of molecular vibration involving the same molecular vibrations of each styrene unit in the dimer repeat unit, but differ in that one normal mode of the dimer repeat unit is an in-phase vibration while the other normal mode of the dimer unit is an out-of-phase vibration.

Tentative assignments for a-SPS and fl-SPS are given in Tables II and III, respectively, and a comparison of the assignments for a- and fl-SPS with IPS, APS, and toluene are give in Table IV.

A~ and B~ Fundamentals. The aliphatic and aromatic CH and CH2 stretching modes occur above 2800 cm -~ and are assigned in the tables. No discussion of these modes will be given. Only the IR modes that are con- formationally sensitive and reasonably assigned to AI and B~ fundamentals will be discussed.

A medium-intensity perpendicular-polarized IR band for a-SPS occurs at 1375.3 cm -~, and a weak to medium- intensity IR band occurs at 1376.3 cm -1 in the parallel- polarized spectrum. An IR band at 1375 cm -~ for APS has been assigned as 5CH, and for IPS the 1365-cm -1 band has been assigned as ~CH or as a complex mode involving both 5CH and oJCH2 .5,s The 1375.3-cm -~ per- pendicular IR band for a-SPS is assigned as a complex mode involving ~CH and o~CH2 .5

IR bands at 1327.4, 1348.8, and 1351.4 cm -~ have been assigned to a complex mode involving a skeletal mode

with c0CH2 and 5CH for IPS, a-SPS, and/~-SPS, respec- tively2 The 1348.8-cm -1 IR band for a-SPS is a parallel band.

The perpendicular IR band at 1333.5 cm -1 for a-SPS, the 1318-cm -1 IR bands for B-SPS, and the 1314-cm -1 IR band for IPS have been assigned to a complex mode involving ~0CH2 and 5CH. 5

A parallel IR band at 1221.9 cm -~ for a-SPS has been assigned to a complex skeletal mode including 5CH2 The comparable mode for/3-SPS is assigned at 1275.3 cm -1, and for IPS it is assigned at 1197.1 cm-13

A perpendicular IR band at 1069.7 cm -~ for a-SPS has been assigned as an in-plane ring mode2 For APS, v'l~B (B~) is assigned to an out-of-phase in-plane ring hydrogen bending mode. This mode is assigned at 1089 cm -~ for toluene, at 1082.5 cm -1 for IPS, and at 1069.1 cm -1 for fl-SPS.

An A~ fundamental for toluene is assigned to a polar- ized strong Raman band at 788 cm-~. 7 This AI funda- mental has ~30% potential energy contribution from phenyl-C stretching; therefore, the corresponding mode in other mono-substituted benzenes is expected to be sensitive to the nature of the alkyl group. Thus, the corresponding A~ fundamental has been assigned to a polarized strong Raman band at 760 cm -1 for ethylben- zene, at 740 cm -1 for isopropy!benzene, and at 705 cm -~ for tert-butylbenzene, s In the case of a-SPS we assign the polarized Raman band at 773 cm -1 to the A~ fun- damental, which includes significant potential energy contribution from phenyl-C stretching. The polarized Raman band at 796.4 cm -~ may be due to the corre- sponding B1 fundamental in the dimeric repeat unit.

A B~ fundamental for toluene is assigned at 622 cm -1,

984 Volume 46, Number 6, 1992

T A B L E I I I . Infrared data for B-synd io tae t i e po lys ty rene .

I R d a t a ( c m - 0 A s s i g n m e n t

3646.O 3618.0 3200.0 3160.0 3102.9 3082.5 3060.4 3026.4 3001.7 2924.3 2846.0 2810.0

2718.0

2681.0

2630.0

2603.0 2580.0 2544.0 2504.0

2336.0 2258.0 2184.0 1984.0

1961.0 1946.3 1872.6 1805.4

1775.0 1746.0

1670.0 1601.1 1583.2 1543.0 1543.0 1493.8 1452.3 1438.8 1377.7 1351.4 1335.0 1318.8 1302.0 1275.3 1248.0 1232.0

1223.0 1180.8 1166.0 1154.3 1127.0

1113.0

1090.0 1069.1 1029.7 1002.6

977.3 966.0 945.3 932.3 908.5

1 II

1

1

±, II

3026.4 + 621.1 = 3647.5 3060.4 + 572.1 = 3632.5

2(1601.1) = 3202.2 2(1583.2) = 3166.4 v7(B,) V2oB(B,) V'2oA(A,) v'2(A~) d2(A,)?

v,:,.~.CH2 1351.4 + 1452.3 = 2803.7 1583.2 + 1223.0 = 2806.2 1583.2 + 1232.0 = 2715.2 1452.3 + 1275.3 = 2727.6 1377.7 + 1318.8 = 2696.5

1351.4 + 698.7 + 621.1 = 2671.2 1318.8 + 1377.7 = 2696.5 1601.1 + 1029.7 = 2630.8

2(1318.8) = 2637.6 1601.1 + 1002.6 = 2603.7

(980) + 1601.1 = 2581.1 1583.2 + 966.0 = 2549.2 1601.1 + 908.5 = 2509.6

1002.6 + 1493.8 = 2496.4 1180.8 + 1154.3 = 2335.1

2(1127) = 2254 1154.3 + 1029.7 = 2184

977.3 + 1002.6 = 1979.9 1030.0 + 966.3 = 1996

2(980) = 1960 2 I (980) + 966.0 = 1946 I + I I 966.0 + 908.5 = 1874.5 I I + I I I 966.0 ÷ 841.2 = 1807 2 I I + I I I 966.0 + 856.0 = 1822 I I + IV

1029.7 + 748.6 = 1778.3 908.5 + 856.0 = 1764.5 I I I + IV 908.5 + 841.2 = 1749.7 (980) + 698.7 = 1678.7 I + VI

v~(A~) v~(B,)

698.7 + 856.0 = 1554.7 689.7 + 841.2 = 1539.9

v,~B(B0 6(CH2) 5CH a n d wCH2 B2

572.1 + 768.0 = 1340.1 ~'~(BJ

768.0 + 539.9 = 1308 B~

547.7 + 698.7 = 1246.4 2(621.1) = 1242.2

538.9 + 698,7 = 1237.6 598.6 + 621.1 = 1219.7

vCC h e l i x 547.7 + 621.1 = 1168.8

v',5(B1) 538.9 + 598.6 = 1137.9 698.7 + 440.0 = 1138.7 538.9 + 572.1 = 1111 547.7 + 572.1 = 1119.8 538.9 + 547.7 = 1086.6

v',~(B,) v~aa(A,) v,(A1) vs(B2); I v,~A(A2); I I

406 + 538.9 = 944.9 v,7s(B2) V,vs(B2); III

T A B L E I I I . Continued.

I R d a t a (era -1) A s s i g n m e n t

856.0 841.2 777.2

768.0 748.6 698.7 674.0 630.0 621.1 609.0 598.6

572.1 547.7 538.9 501.1 452.0 440.0 406.0 346.0 310.0 260.0 231.0 176.5 131.5 108.0

vlo(A~) rio(A2); V

231 + 547.7 = 778.7 231 + 538.9 = 769.9

175.5 + 598.6 = 774.1 Vlo(B2) V~o(B2); V vn(B2); VI

231.0 + 440.0 = 671.0 231.0 + 406.0 = 637.1

~6~(B,) 175.5 + 440.0 = 615.5

2(175.5) + 2(131.5) = 614 231.0 + 2(175.5) = 584.0

v6(B~) v4(B2) ~4(B~) v6(A1)

2(231) = 462 ~CCC V,6A(A2)

2(176.5) = 353 ~°CCC 2(131.5) = 263 v16B(B~) S K D E F " ? ?

S K D E F is s k e l e t a l d e f o r m a t i o n .

and a corresponding band of atactic PS is assigned at 620 cm -1, Vs,(B0, and for isotactic PS v6B (B0 is assigned at 619.6 cm -1. For ~-SPS, a Raman band occurs at 621.3 cm -1 and a parallel IR band occurs at 620.6 cm -1, and a perpendicular IR band occurs at ~630 cm-L The band at ~630 cm -~ we suggest results from VeB(B0-B2 and the 620.6-cm -1 band we suggest results from v68(B~)-A~ (also, see below).

Raman spectra-structure correlations have been de- veloped for mono-substituted benzenes? ° The Raman spectra-structure correlation developed for mono-sub- stituted benzenes involves three in-plane vibrations whose frequencies and relative band intensities are relatively constant regardless of the substituent atom or group joined to the phenyl group. In the case of APS these bands are assigned as Vlsa(A~) at 1031 cm -1 with medium intensity, v~(A~) at 999 cm -~ with very strong intensity, and v6B(B~) at 621 cm -~ with medium intensity? ~ For e-SPS the corresponding assignments for these Raman bands are: 1029.6 cm -1, relative intensity of 26.3; 1002.6 cm -~, relative intensity of 100; and 621.3 cm -~, relative intensity of 12.9. The corresponding IR bands for a-SPS occur at 1029.4, 1004.0, and 621.2 cm -~, and these inten- sities are medium, weak, and weak, respectively. Com- parable assignments for ~-SPS are given in Tables III and IV.

A 2 and B 2 Fundamentals . It is helpful in the assignment of the out-of-plane deformations that their combination and overtones apply to group frequency correlations de- veloped for substituted benzenes? 2 For a mono-substi- tuted benzene derivative the five out-of-plane hydrogen deformations are numbered I-V in order of decreasing frequency, and the out-of-plane ring deformation is num- bered VI. Thus, IR bands for atactic, isotactic and a-

APPLIED SPECTROSCOPY 985

TABLE IV. Comparison of vibrational modes for a- and O-syndiotactic polystyrene, toluene, isotactic and atactic polystyrene."

Toluene 7 IPS (cm -~) /~-SPS (cm -1) a-SPS, H (cm-~) a-SPS, _L (cm -~) APS (cm -~) Assignments ~

3103.4 3102.9 3103.20 3103.7 3099.0 ~7s(B~) 3083.0 3082.5 3082.80 3082.5 3080.8 ~2oB(B1) 3060.1 3064.4 3060.80 3059.4 3058.5 ~'=oa(A~) 3025.3 3026.4 3026.60 3023.9 3025.0 ~'2(A~) 3000.1 3001.7 3001.60 3001.9 3000.0 2926.0 2924.0 2923.11 2920.9 2923.0 v~.CH2 2845.0 2846.0 2847.00 2945.9 2851.0 v,~ CH2

1606, A~ 1601.3 1601.1 1601.80 1601.9 1601.0 ~gs(B1) 1587, B~ 1582.9 1583.2 1583.50 1583.0 1582.3 VgA(A1) 1497, A~ 1493.2 1493.8 1493.60 1494.0 1492.0 v~gA(A~) 1468, B1 1452.4 1452.3 1452.10 1453.5 1452.0 v~gB(B1) 1445, B1 1439.0 1438.8 1453.5 1452.0 5(CH2)

1385.0 1377.7 1376.30 1375.3 1369.7 &(CH) 1327.4 1351.4 1348.80 1350.2 1349.0 B2 1314.0 1318.8 1333.5 1327.0 ~'~(B1) 1314.0 1335.0 1311.0 1310.0 ~4(B~) 1303.6 1302.0 1304.0 1290.0

1286, B~ 1297.5 1275.3 1279.00 1277.2 1280.0 %(CH2)-A 1211, A1 1197.1 1275.3 1222.90 1221.2 1179.0 ~(A~) 1211, A~ 1187.6 1194.0 1182, A~ 1180.8 1180.8 1181.50 1182.3 1181.0 1157, B~ 1155.3 1154.3 1154.70 1155.2 1155.0 ~'~5(B1)

1110.0 1113.0 1111.5 1109.0 1090.0 1093.3 ~'~s(B~)

1085.0 1089, B~ 1082.5 1069.1 1069.70 1069.7 1069.3 ~'~s~(B~)

1052.9 1030, A1 1026.8 1029.7 1029.70 1029.5 1028.2 ~A(A1) 1005, A~ 1002.4 1002.6 1004.70 1004.7 1002.3 ~(A~) 991, B2 982.7 977.3 978.90 977.0 980.1 ~(B2) (975), A~* 964.5 966.0 964.40 964.0 965.0 ~7~(A2)

940.0 945.3 940.00 940.0 941.0 See text 921.3 932.3 ~7~(B2)

898, B2 907.1 908.5 902.80 904.8 907.0 ~,vs(B2) 899.5 ~lvs(B2)

856.0 852.60 ~lo(A2) 841, A~ 839.0 841.2 841.10 840.8 842.2 ~o(A2)-E 788, A~ 785.0 773.40 773.4

764.0 ~os(B2) 732, B2 762.2 768.0 752.10 751.7 757.8 ~lo~(B~)-A

748.6 698, B2 701.9 702.0 ~(B=)

696.9 698.7 695.30 696.2 700.0 ~H(B2) 630.00 630.0 ~(B~)

622, B1 619.6 621.1 620.60 621.2 622.0 ~s(B~) 586.0 572.1 569.0 558.0 ~A(A1)

522, A~ 565.8 547.7 569.00 579.0 ~4(B2)-E 467, B~ 544.9 638.9 544.17 538.4 542.0 ~4(B2)

498.0 501.1 513.00 513.0 ~(A,)-E 427.7 440.0 445.80 435.7 446.0 5CCC

407, A2 409.0 406.0 406.00 405.7 410.0 ~,~(A2) 348, B1 365.0 346.0

314.0 310.0 315.30 220, B2 221.0 231.0 232.10

169.5 176.5 178.10 131.0 131.5

108.0

315.3 325.0 5CCC 232.1 216.0 v~(B2) 178.1 196.0 ~'8~(Bl)

152.0

See text

a Note: (*) Expression is calculated. IPS is isotactic polystyrene. APS is atactic polystyrene; a-SPS is a-syndiotactic polystyrene. /~-SPS is /3-syndiotactic polystyrene. [[ is parallel polarization; _L is perpendicular polarization. For uniaxially stretched a-SPS, A1 and B1 fundamentals should yield perpendicular polarized IR bands and the B2 modes should yield parallel polarized IR bands.

and/3-syndiotac t ic polystyrene near 975, 960, 910, 840, 750, and 700 cm -1 are assigned as I-VI, respectively. 4 Moreover , combinat ion and overtone assignments are also assigned according to the same system. These are: 2 I near 1960 cm -~, I + II near 1940 cm -1, I ÷ I I I near 1870 cm -1, II + IV near 1800 cm -1, and III + IV near 1750 cm-L 4

In the assignment of A2 and B2 fundamenta ls for ~- and/~-syndiotact ic polystyrene (~- and/~-SPS) it is help-

ful to compare their vibrat ional da ta with vibrat ional da ta and assignments for isotactic polys tyrene (IPS), atact ic polys tyrene (APS), and toluene.

Mode I, B~ or B , The mode I, B2 fundamenta l is as- signed at 991 cm -1 for toluene, 7 at 980.1 cm -1 for APS, and at 982.7 cm -1 for IPS. ~ In APS it is assigned as ~5(B2). In the case of a -SPS, mode I, vs(B2) is assigned to the medium-in tense perpendicular IR band at 977 cm -~, and for /~-SPS mode I, ~5(B1), it is assigned at 977.3 cm-L

986 Volume 46, Number 6, 1992

Mode II, A2 or BI. An A2 ring mode for toluene is assigned at 975 cm-1, 7 at 965 cm -1 for APS, and at 964.5 cm -~ for IPS and is assigned as v17(A2) 11 With two phenyl groups in the repeat unit , and if a -SPS has (TT,C2v) s tructure, then the two normal modes corresponding to the A2 mode in toluene or APS would be Vlo(A2)-B~ and V~o(A2)-A 2. The B~ fundamenta l should be IR active and be perpendicular ly polarized, while the A2 mode should be IR inactive in the case of a -SPS. In the case of/~-SPS, the two normal modes should be B~ and B2 modes and both should be IR active and perpendicular ly polarized. A peak shoulder is observed at 964 cm -~ in the perpen- dicularly polarized IR spec t rum of a -SPS and an IR band is observed at 964.4 cm -1 in its parallel-polarized IR spec- t rum. Assignment of the 964-cm -1 band for a -SPS as Vl0(A2)-B~ is reasonable on the basis of the above theo- retical data; however, assignment of the 964.4-cm -~ IR band to vlo(A2)-A2 is not plausible. If the 964.4-cm -~ IR band for a -SPS indeed does result from a v~0(A2) type of fundamenta l , the crystal s t ructure for a -SPS cannot be isomorphous with C2v point groups. Mode II is assigned at 966 CE -1 for ~ -SPS .

Mode III, B~. Mode III is assigned at 898 cm -~ for toluene, 7 at 907.1 cm -~ for APS, and at 921.3 and 899.5 cm -1 for IPS. ~ The medium-intense parallel-polarized IR band at 902.7 cm -1 for a -SPS is assigned to mode III, B2. Mode III is assigned at 908.5 cm -1 for f i-SPS.

Mode IV, A2 or BI. Mode IV is assigned at 841 cm -1 for toluene, at 842.4 cm -~ for APS, and at 839 cm -1 for IPSY ,H In the perpendicular-polar ized IR spect rum of a -SPS, an IR band occurs at 840.9 cm -~, while in the parallel-polarized IR spectrum, IR bands occur at 852.6 and 841.1 cm -1. As in the case for mode II, mode IV for a -SPS has A2 and B 1 modes. Only mode IV, B1 should be IR active, and the band should be perpendicular ly polarized. Thus , we assign the IR band at 840.9 cm -~ as mode IV, B~ for a -SPS. The 852.6-cm -~ band is only IR active in the parallel-polarized IR spectrum, and if this mode also is of mode IV type, the crystal s t ructure cannot be isomorphous with the C2v point group. Comparable IR bands occur at 841.2 and 856 cm -1 for f~-SPS, and at least one of these two bands is assigned as mode IV for ~-SPS.

Mode V, B2. The mode V, B 2 fundamenta l for toluene is assigned at 732 cm-1, 7 a t 760 cm -1 for APS, 11 and at 762.2 cm -1 for IPS. 8 The strong IR band at 751 cm -~ is assigned as mode V, B2 for a -SPS and at 748.6 cm -1 for fl-SPS. IR spectra of a- and/~-SPS show an IR band at 764 and 768 cm -~, respectively. These bands may be as- sociated with CH2 rocking, as suggested for the 785-cm -1 IR band for IPS. 8

Mode VI, B2. A B2 mode for toluene is assigned at 689 cm -~, at 700 cm -~ for APS, and at 702 cm -~ for IPS. 8 The corresponding mode VI for a- and/~-SPS we assign at 692.2 and 698.7 cm -1, respectively.

The 538.4-cm -~ IR band for APS is assigned as v4(B2), and is an out-of-plane ring deformation. 11 The corre- sponding mode is assigned to the parallel IR band at 544.2 cm -1 for a -SPS and at 538.9 cm -~ for /%SPS.

Combination and Overtones Involving Modes I-VI. Krimm has assigned several combinat ion tones in Ref. 11. The combinat ion and over tone assignments are given in Tables II and III according to the method developed by Nyquis t for mono through pentasubs t i tu ted ben- zenes. 12 These are 2 I, II + I I I ; II + IV, I I I + IV, 2 IV, and I + VI for all of the polystyrenes included in this report .

1. R. A. Nyquist, A. E. Platt, and D. B. Priddy, Appl. Spectrosc. 36, 417 (1982).

2. R. A. Nyquist, Appl. Spectrosc. 38, 264 (1984). 3. R. A. Nyquist, Appl. Spectrosc. 41, 797 (1987). 4. R. A. Nyquist, Appl. Spectrosc. 43, 440 (1989). 5. M. Kobayashi, T. Nakooki, and N. Isihara, Macromolecules 22,

4377 (1989). 6. G. Conti, E. Santoro, L. Resconi, and G. Zerbi, Mikrochim. Acta

I, 297 (1988). 7. C. L. Lau and R. G. Snyder, Spectrochim. Acta 27A, 2073 (1971). 8. P. C. Painter and J. L. Koenig, J. Polym. Sci. 15, 1885 (1977). 9. R. A. Nyquist, Appl. Spectroc. 42, 1314 (1988).

10. R.A. Nyquist and R. O. Kagel, "Infrared and Raman Spectroscopy of Organic Materials," in Practical Spectroscopy, Vol. 1, Infrared and Raman Spectroscopy, E. G. Brame, Jr., and J. S. Grasselli, Eds. (Marcel Dekker, New York, 1977), Part B, Chap. 6, p. 441.

11. S. Krim, Fortschr. Hochpolm.-Forsch., Bd. 2, 141 (1960). 12. R.A. Nyquist, The Interpretation of Vapor-Phase Infrared Spec-

tra: Group Frequency Data (Sadtler Research Laboratories, Phil- adelphia, 1984), Vol. 1, A-I-A-228.

APPLIED SPECTROSCOPY 987