An NMR study of structure and dynamics of poly(fumarate)s in the solid state

Journal of Molecular Structure, 300 (1993) 303-311 0022-2860/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved

303

An NMR study of structure and dynamics of poly(fumarate)s in the solid state Hiromichi Kurosua, Takeyoshi Yamadaa’*, Isao Andoa, Kazuo Satob, Takayuki OtsuC aDepartment of Polymer Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, Japan ‘Idemitsu Petrochemical Co., Ltd., Ichihara, Chiba, Japan ‘Department of Applied Chemistry, Oosaka City University, Sugimoto, Sumiyoshi-ku, Oosaka, Japan

(Received 19 April 1993) Abstract 13C cross polarization/magic angle spinning (CP/MAS) NMR spectra and partially-relaxed 13C NMR spectra of poly(diisopropy1 fumarate) (PDiPF) and poly(dicyclohexy1 fumarate) (PDCHF) in the solid state were measured over a wide range of temperatures. On the basis of these experiments, 13C spin-lattice relaxation times (Tic) for the polymers were determined as a function of temperature. From these results, the molecular motion of the main chain and side chains of the polymers was clearly elucidated. In addition, ‘H spin-lattice relaxation times (TF) and ‘H spin-lattice relaxation times in the rotating frame (Z’tpH)of the polymers were measured by ‘H pulse NMR over a wide range of temperatures. From these results, dynamics of the main chain and side chains of these polymers was elucidated. The reorientation frequency of the main chain of PDiPF is about 43 kHz at 12O”C, while that of PDCHF at 120°C is less than this. These pulse NMR results do not conflict with the CP/MAS NMR results.

Introduction Poly(fumarate)s with bulky substituents on every main chain carbon have been systematically with radical polymerization by synthesized Bengough et al. [l] and Ostu and co-workers configuration of [2-71. The stereochemical poly(fumarate)s has been successfully determined by solution-state high-resolution 13C NMR [8,9]. The relationship between the bulkiness of the ester substituents and the stereochemical configuration of the polymers was elucidated. However, molecular motion of the polymers has been qualitatively deduced on the basis of their structural features, with great steric hindrance due to the bulky substituents. According to these studies, it has been suggested that the main chain adopts a rod-like structure and so is in the * Corresponding

author.

immobile state, with the side chains in the mobile state. However, real dynamical features of the polymers in the solid state have not been clarified. It is well known that solid-state NMR has provided useful information about the dymamics of polymers in the solid state, associated with structure. In particular, solid-state high-resolution 13C NMR is a powerful tool for determining structure and dynamics of polymers in the solid state [lo-121. For poly(fumarate) samples, it is effective to utilize the variable temperature (VT) 13C cross polarization/magic angle spinning (CP/MAS) NMR and ‘H pulse NMR experiments since one is able to elucidate exactly the structure and dynamics. From such a situation, the purpose of this work is to investigate the structure and dynamics of the main and side chains of poly(diisopropy1 fumarate) and poly(dicyclohexy1 fumarate) (Fig. 1) in the solid state as a function of temperature, by

H. Kurosu et al./J. Mol. Strut. 300 (1993) 303-311

PDiPF

I) Q

P c=o CH

II

PDCHF

Fig. 1. Structures of PDiPF and PDCHF.

observing the ‘H and 13C NMR relaxation times and high-resolution 13C NMR spectra obtained using VT solid-state NMR.

kindly supplied by the Japan Fats and Oils Co. Ltd. These samples were dissolved in acetone and were reprecipitated with ethanol. Figure 2 shows Fischer and planar zigzag projections of meso and racemic diads of poly(fumarate). By definition, in the meso (m) arrangement two consecutive substituents are located on opposite sides of the planar zigzag plane, and in the racemic (r) arrangement two consecutive substituents are located at the same side of the planar zigzag plane. The fractions of the triad configurations for the polymers were determined by solution-state highresolution 125 MHz 13CNMR [8] and are shown in Table 1 together with those determined by solidstate high-resolution 13CNMR as described below. From this Table, it is found that the fraction for the mr triad is somewhat larger than that for the mm triad, and the fraction for the rr triad is nearly zero. NMR

measurements

Experimental Materials Poly(diisopropy1 poly(dicyclohexy1

fumarate) (PDiPF) fumarate) (PDCHF) Fischer

and were

Solid-state high-resolution r3C NMR spectra were measured using a JEOL GSX-270 NMR spectrometer operating at 67.8 MHz, equipped with CP/MAS and VT accessories, over a wide range of temperatures from -90 to 125°C. The sample Planar zigzag

R meso R

*

racemlc

Fig. 2. Fischer and planar zigzag projections

of poly(fumarate).

305

H. Kurosu et al.lJ. Mol. Struct. 300 (1993) 303-311 Table 1 Probabilities of triad configurations for PDiPF and PDCHF solid-state high-resolution 13C NMR Polymer

Probability

by solution-state

high-resolution

13C NMR and

of triad configuration

Solution-state

PDiPF PDCHF

as determined

Solid-state NMR

NMR

mm

mr

rr

mm

mr

rr

0.42 0.36

0.58 0.64

0 0

0.45 0.36

0.55 0.64

0 0

was contained in a cylindrical rotor made of ceramic materials and spun at about 4 kHz. The contact time was 2 ms, and the repetition time 5 s. The spectral width and number of data points were 27 kHz and 8 K, respectively. The ‘H field strength was 1.5 mT for the decoupling processes. The number of accumulations was 100-400 to achieve a reasonable signal-to-noise ratio. 13C chemical shifts were calibrated indirectly through external adamantane (29.5ppm relative to TMS). t3C spin-latice relaxation times TIC were measured using the Torchia sequence [13] with a contact time of 2ms during the CP, and the repetition time was 4 s. The 90” pulse widths for proton and carbon nuclei were 4.0 ps. The ‘H spin-lattice relaxation time ( TtH) and ‘H spin-lattice relaxation time in the rotating frame (Tt p”) were measured by a Bruker CXP-90 NMR spectrometer operating at 90 MHz with a VT accessory over a wide range of temperatures from -90 to was 1 mT 125°C. The ‘H field strength (=42.6 kHz).

data in ref. 8. As shown in Fig. 3, the peak intensities of the carbonyl, main chain CH and side chain CH carbons decreased with an increase in temperature. When the frequency of molecular motion becomes close to the decoupling frequency, the decoupling becomes inefficient and so the signal intensity becomes very weak. Therefore, from the experimental findings, it can be shown that the

Results and discussion Variation of I-% CPIMAS temperature

NMR spectra with

c=o 13C CP/MAS spectra of PDiPF in the solid state were measured over a wide range of temperatures from -30 to 115°C as shown in Fig. 3. The assignments of these peaks for the main chain CH carbon and side chain carbonyl, CH and CH3 carbons were performed straightforwardly using reference

\CH I

7 -CH-

-CH3

Fig. 3. 13C CP/MAS NMR spectra of PDiPF in the solid state at increasing temperatures.

306

H. Kurosu et al./J. Mol. Struct. 300 (1993) 303-311

Fig. 4. 13C CP/MAS NMR spectra of PDCHF in the solid state at increasing temperatures.

frequency of molecular motion for the main chain at 115°C is close to the decoupling frequency (63 kHz). This also shows that the main chain CH carbon and side chain carbonyl and CH carbons are undergoing reorientation at frequencies below 63 kHz and temperatures below 90°C. The peak intensities of the methyl carbons are almost independent of temperature. This shows that the methyl carbon is undergoing fast rotation around the CsV axis and the molecular motion of the methyl carbon is in the extreme-narrowing region of the Bloembergen-Purcell-Pound (BPP) theory 1141. From these experimental findings, it can be said that the molecular motion of the main chain CH carbon and side chain carbonyl and CH carbons is in the slow motion region. If we look carefully at the 13C CP/MAS spectra at temperatures below 3o”C, it is found that the main chain CH carbon signal splits into two

peaks, one upfield and one downfield, which are assignable to the mr and mm triad configurations, respectively, on the basis of solution-state highresolution 13C NMR results reported previously. The fractions of these triads determined are shown in Table 1. These values agree well with those determined by solution-state high-resolution 13C NMR as seen in Table 1. Also, it is found that in the 13C CP/MAS spectra above 30°C the carbonyl carbon signal consists of two overlapping peaks (similar to the case of the main chain CH carbon signal), the upfield and downfield peaks of which are assignable to the mr and mm triad configurations, with the peak intensity ratio of the mr and mm triads being very close to those obtained from the main chain CH carbon signal. 13C NMR CP/MAS spectra of PDCHF in the solid state are shown as a function of temperature in Fig. 4. The assignment of the peaks arising from

H. Kurosu et al./J. Mol. Struct. MO (1993) 303-311

the main chain CH and side chain carbonyl and cyclohexyl carbons are also done by reference data in the previous work by Wang et al. [8] as well as the case of PDiPF except for the assignment of cyclohexyl carbons in the side chains. If we look carefully at the main chain CH signal, it is found that the main chain CH signal at temperatures below -25°C consists of the overlapping of two peaks, upfield and downfield, which are assignable to the mr and mm triad configurations on the basis of solution-state high-resolution “C NMR results reported previously. The fractions of the mr and mm triad configurations determined are shown in Table 1. These values agree well with those determined by solution-state high-resolution 13CNMR as seen from Table 1. The peak intensity for the main chain CH carbon and side chain carbonyl carbon is almost independent of temperature. Such a situation is different from the case of PDiPF. This shows that the molecular motion of PDCHF is more restrained compared with that of PDiPF. The cyclohexyl carbon signal which appears at 15-40 ppm and at 75 ppm is assigned using reference data for cyclohexane derivatives [15]. The chemical shift values are shown in Fig. 5 as stick spectra. The signal of cyclohexyl carbons in the polymer can be assigned as follows. The peak at 32.2ppm is assigned to the C/3 carbon in the equatorial form. The peak at 25Sppm comes from the overlapping of the Cy and C6 carbon peaks in the equatorial form. Another peak at 21.2ppm appears in the spectrum at -90°C. This peak can be assigned to the Cy carbon in the axial form. Therefore, the cyclohexyl ring of PDCHF at -90°C takes both equatorial and axial forms. The fraction of the equatorial and axial forms can be determined by the line shape analysis of the peak intensity of the Co carbon at about 70 ppm to be 74 : 26. Table 2 shows the fraction for the equatorial and axial forms as a function of temperature. This shows that the fraction of the equatorial conformation increases as the temperature is increased. As shown in Fig. 4, the intensity of the main chain CH carbon signal of PDCHF

Equatorial Form

13.6

32.6

Axial Form

CU

CP

H,C-T=O 0 Ca

25.6

fj/ppm

$ Cb

dll

Cb

CCt

Q

Cb

69.6

30.6 27.6

21.6

b/wm

Fig. 5. Stick 13C NMR spectra of cyclohexane derivatives with the equatorial and axial forms (ref. 13). is almost independent of temperature measurement temperature range.

within

the

13C spin-lattice relaxation In order to obtain information about dynamics for PDiPF and PDCHF, 13C Ti (Ty) at temperatures from -30 to 115°C was measured using the Torchia sequence. The obtained Ti values for PDiPF and PDCHF are plotted against temperature in Figs. 6 and 7, respectively. The Ty values of the main chain carbon, carbonyl carbon Table 2 Fraction of the equatorial and axial forms in PDCHF at various temperatures Temperature (deg C) 125 78.5 40 -25 -90

Fraction Equatorial

Axial

0.87 0.85 0.80 0.76 0.74

0.13 0.15 0.20 0.24 0.26

308

H. Kurosu et al./J. Mol. Strut. 300 (1993) 303-311

and CH carbon in the side-chain of PDiPF decrease within the measurement temperature range as the temperature is increased. This shows that molecular motion of these carbons is in the slow-motion region and is below 67.8 MHz. However, the Ty values of the CHs carbon increase as the temperature is increased. This shows that molecular motion of the CHs carbon is in the extreme narrowing region and is over 67.8MHz. The obtained Tf values of all of the carbons for PDCHF decrease within the measurement temperature range as the temperature is increased. This means that molecular motion of all of the carbons is in the slow motion region and is below 67.8 MHz. It is possible to obtain more detailed information about the mobility of the main chain CH carbon for the mm and mr triad configurations on the basis of the line shape analysis of partially-relaxed spectra. Figure 8 shows partially-relaxed 13C NMR spectra of PDCHF at 30 and 110°C obtained -by the Torchia pulse sequence with different recovery time. As can be seen from this figure, there is no line shape difference between the main chain CH carbons for the mr and mm triads in the partially relaxed spectra measured at 30°C. From the line shape analysis of the partially relaxed spectra, the Ty values for the mr and mm triads are determined to be 36.6 s and are very long. Therefore, it can be said that their molecular

.

m

vF

--LCh.CYeq

.,.‘,..‘...‘...‘...‘...

0.1 20

40

60

80

Temperature Fig. 7. Plots of the Ty of PDCHF temperature.

100

120

140

/ “c in the solid state vs.

motions are strongly restrained in the same degree. However, there is a clear line shape difference between the mr and mm triads in the partially relaxed spectra measured at 110°C. The fi values for the mr and mm triads were determined to be 9.8 and 13.8 s, respectively, by the line shape analysis of partially relaxed spectra as shown in Fig. 9. As the main chain CH carbon is in the slow motion region, the mobility for the mr triad is higher than that for the mm triad at 110°C. The Ty values of the main chain CH carbon for the mr and mm triads of PDiPF were determined to be almost the same within the measurement temperature range. ‘H spin-lattice relaxation

\

m

”

E” 1

:

“11 -60

’

I

’

-20

20

N1

Temperature Fig. 6. Plots of the Ty of PDiPF temperature.

’ I(x)

’

140

/ “c in the solid state vs.

According to the BPP theory, elevation of temperature leads to an increase in molecular motion of the polymers in the solid state (the decrease of the correlation time (7J in molecular motion) and so T, decreases, reaching a minimum at ~7, = 1, where w is the resonance frequency, after which Tl again increases. From the Tl minimum, we can obtain the correlation time TV for molecular motion at MHz frequencies. On the other hand, T,p shows Tt-like behaviour versus temperature, but a minimum in T,p is reached at wtrc = 1, w1/27r = yH,/2r = 42.6 kHz (for this experi-

H. Kurom et d/3.

Mol. Strue:. 300 (1993) 303-311

Fig. 8. Partially-relaxed

‘k CP/MAS NMR spectra of PDCHF in the solid state at (a) 30°C and (b) 110°C.

n

Fig. 9. Line shape analysis of the main chain CH carbon for the mm and mr triad configurations by the Torchia pulse sequence.

in PDCHF, observed at I 10°C

H. Kurosuet al.lJ. Mol. Struct. 300 (1993) 303-311

experimental trend of the Ty curve at higher temperature, there may also be another minimum above 180°C due to the reorientation of the main chain. From these results, it can be said that the main chain of PDiPF is in a more mobile state than that of PDCHF, since the reorientation rate of the main chain of PDiPF is about 43 kHz at 12O”C, while a similar rate for PDCHF is not reached even at 180°C. References 1 W.I. Bengough, G.A. Park and R.A. Yough, Eur. Polym. J., 11 (1975) 305. 2 T. Otsu, 0. Ito, N. Toyoda and S. Mori, Makromol. Chem., Rapid Commun., 2 (1981) 725. 3 N. Toyota and T. Otsu, J. Macromol. Sci., Chem., 19 (1983) 1011. 4 T. Otsu and N. Toyota, Polym. Bull., 11 (1984) 453. 5 T. Otsu, T. Yasuhara, K. Shiraishi and S. Mori, Polym. Bull., 12 (1984) 449.

311

6 T. Otsu, T. Yasuhara and T. Matsumoto, J. Macromol. Sci., Chem., 25 (1988) 537. 7 T. Otsu, A. Matsumoto, T. Kubota and S. Mori, Polym. Bull., 23 (1990) 43. 8 X. Wang, T. Komoto, I. Ando and T. Otsu, Makromol. Chem., 189 (1988) 1845. 9 M. Yoshioka, A. Matsumoto, T. Otsu and I. Ando, Polymer, 32 (1991) 2741. 10 R.A. Komoroski (Ed.), High Resolution NMR Spectroscopy of Synthetic Polymers in Bulk, VCH, Deerfield Beach, FL, 1986. 11 (a) H. Saito and I. Ando, in G.A. Webb (Ed.), Annual Reports on NMR Spectroscopy, Vol. 21, Academic Press, London, 1989, p. 209. (b) I. Ando, T. Yamanobe and T. Asakura, Prog. Nucl. Magn. Reson. Spectrosc., 22 (1990) 349. 12 J. Schaefer and E.O. Stejskal, in G.C. Levy (Ed.), Topics in Carbon-13 NMR Spectroscopy, Vol. 3, Wiley-Interscience, New York, 1979, p. 284. 13 D.A. Torchia, J. Magn. Reson., 30 (1978) 613. 14 N. Bloembergen, E.M. Purcell and R.V. Pound, Phys. Rev., 73 (1948) 6. 15 E. Breitmaier and W. Voelter, 13C NMR Spectroscopy, Verlag Chemie Weinheim, New York, NY 1978. 16 D.C. Douglass and G.P. Jones, J. Chem. Phys., 45 (1966) 956.