Initial Crystallization Mechanism of Isotactic Polystyrene from Different

Mar 2, 2005 - Department of Chemistry, School of Science and Technology, ... Chinese Academy of Sciences, Beijing 100080, P. R. China, and The Procter...
0 downloads 0 Views 115KB Size
Download PDF
5586

J. Phys. Chem. B 2005, 109, 5586-5591

Initial Crystallization Mechanism of Isotactic Polystyrene from Different States Jianming Zhang,† Yongxin Duan,‡ Harumi Sato,† Deyan Shen,‡ Shouke Yan,*,‡ Isao Noda,§ and Yukihiro Ozaki*,† Department of Chemistry, School of Science and Technology, Research Center for EnVironment Friendly Polymers, Kwansei-Gakuin UniVersity, Gakuen, Sanda 669-1337, Japan, State Key Laboratory of Polymer Physics & Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China, and The Procter & Gamble Company, 8611 Beckett Road, West Chester, Ohio 45069 ReceiVed: NoVember 7, 2004; In Final Form: January 28, 2005

The isothermal crystallization processes of isotactic polystyrene at 160 °C from different initial states (quenched glassy state and melt state), i.e., cold- and melt-crystallization processes, have been investigated by infrared (IR) and generalized two-dimensional (2D) IR correlation spectroscopy. It has been found that not only the crystallization kinetics and crystallinity but also the sequential changes of the amorphous and crystalline sensitive bands are quite different for the cold- and melt-crystallization processes. This leads to the conclusion that the physical origins for spinodal decomposition prior to polymer crystallization may be different for different crystallization processes.

1. Introduction The crystallization process of polymers is extremely complex and has long been a matter of hot debate. Its molecular mechanism is not completely understood, despite numerous theoretical and experimental studies over the past 60 years. The classical theory of polymer crystallization is the HoffmannLauritzen theory proposed in 1959.1 This theory combined with its modifications and extensions have been dominating the discussion in this field since the beginning of 1960s.2-4 The classic Hoffman-Lauritzen theory of crystallization has been founded on a description of polymer single-crystal growth and it has been used with great success to describe the nucleation and growth of polymer spherulites. In this context, however, nucleation is not the primary nucleation event from the entangled melt or another amorphous state that gives rise to the critical nucleus. It is, rather, a description of subsequent chains adding to a crystalline growth front. Thus, the H-L theory does not address the time period before a growing crystal is formed. Now, it is generally accepted that the induction period of polymer crystallization is not well-understand. Therefore, the induction period, and perhaps its extension into the earliest growth stage of the polymer spherulite, has been under intensive investigations. Recently, a number of experimental results on the structure evolution at larger length scale in the very early stage of both cold- and melt-crystallization processes suggest a multistep process from the entangled melt via different metastable structures to the final polymer crystal.4-13 The most important evidence for that rests on the fact that a small-angle X-ray scattering (SAXS) peak appears before wide-angle X-ray diffraction (WAXD) crystalline peaks.14-22 It was thought that the SAXS peak results from density fluctuations on the order of 5-30 nm, while the WAXD crystalline peaks originate from * To whom all correspondence should be addressed. Fax: +81-79-5659077. E-mail: [email protected]. † Kwansei-Gakuin University. ‡ Chinese Academy of Sciences. § The Procter & Gamble Co.

three-dimensional crystalline ordering on the order of 0.2-1 nm. Therefore, the SAXS and WAXD results imply the occurrence of density fluctuation before polymer crystallization. On the basis of the fact that the SAXS peak intensity grew exponentially with time whereas its position remained unchanged, the density fluctuation was argued to be consistent with the Cahn-Hilliard theory for spinodal decomposition.23,24 Consequently, the density fluctuation, consistent with the spinodal decomposition, was considered as the precursor of polymer crystallization in both solid and molten states. The presence of spinodal decomposition can be rationalized for the quenched glassy polymer in that the quenched liquid may retain a large degree of “frozen” nonequilibrium structure due to its long relaxation times. It has, nevertheless, provoked significant challenges to the conventional theories for crystallization from the polymer melt. Olmsted et al.25 proposed that the spinodal decomposition prior to polymer crystallization is due to the coupling of density and chain conformation in the supercooled melt. There is, however, no direct experimental evidence at the molecular level. Moreover, little research has been performed to answer the question concerning whether polymer crystallization from different initial states can be described by different crystallization theories. To completely understand the chain arrangement process of polymers from random coils to regular crystals, it is important to clarify the complicated crystallization mechanism at the molecular level. Fourier transform infrared spectroscopy (FTIR) is very useful in investigating the conformations and local molecular environments of polymers.26-28 Especially since the introduction of generalized two-dimensional (2D) correlation spectroscopy by Noda in 1993,29,30 IR spectroscopy has become an even more powerful and versatile tool for elucidating subtle structural changes in polymers induced by an external perturbation. The 2D IR correlation spectroscopy enhances apparent spectral resolution by deconvoluting highly overlapping bands into individual component bands and probes the specific order of certain events taking place under the influence of a controlled physical variable. Recently, by using the 2D IR, we have

10.1021/jp0449004 CCC: $30.25 © 2005 American Chemical Society Published on Web 03/02/2005

Initial Crystallization Mechanism of iPS

J. Phys. Chem. B, Vol. 109, No. 12, 2005 5587

Figure 1. Temporal changes in IR spectra in the region of 800-1100 cm-1 during the cold (a) and melt (b) crystallization of iPS at 160 °C.

successfully investigated the structural changes of isotactic polystyrene (iPS) in the induction period during the coldcrystallization process.31 It was found that the ordering of the phenyl ring and formation of 31 helix chains of iPS occurred already in the induction period. The structural evolution of poly(L-lactide) during the isothermal cold-crystallization process was also explored by using 2D IR spectroscopy.32 One may suggest that 2D IR correlation spectroscopy can also shed additional light on advancing the polymer crystallization theory that usually heavily relies on the SAXS, WAXD, and morphology data, such as atomic force microscopy and transmission electron microscopy. Therefore, in the present study, the isothermal crystallization processes of iPS at 160 °C from different initial states (quenched glassy state and molten state), i.e., cold- and meltcrystallization processes, are investigated by IR and generalized 2D IR correlation spectroscopy. 2. Experimental Section 2.1. Material and Sample Preparation Procedures. Powder iPS sample (Mw = 400 000, with the isotacticity of 90%) was purchased from Scientific Polymer Products, Inc. Its glass transition temperature and melting temperature are ca. 100 °C and 230 °C, respectively, and some detailed calorimetric data regarding its crystallization and melt behavior can be found in our previous paper.33 Amorphous thin films of about 10 µm in thickness were prepared by compressing the iPS powder at 250 °C with a pressure of 75 kg/cm2 and subsequently quenching quickly into ice water at 0 °C. The amorphous thin films thus prepared were dried in a vacuum oven at room temperature for 24 h. 2.2. FTIR Spectroscopy. The amorphous film prepared was put between two round KBr plates with a spacer of polyimide (ca. 20 µm) for IR measurements. The pair of plates was set on a Bruker P/N 21525 series variable temperature cell, which was placed in the sample compartment of a Bruker EQUINOX 55 spectrometer equipped with a DTGS detector. iPS is a semicrystalline polymer characterized by very slow crystallization rate and low crystallinity (about 30%). Therefore, it is suitable to investigate its crystallization process by using real time IR measurement. For the experiment of the cold-crystallization process, the sample was then heated at 10 °C/min up to 160 °C. By real time IR measurement during the heating process, we noticed that there was almost no change when the sample was heated at 10 °C/min to 160 °C. This means that we can get

amorphous sample at 160 °C by such heating rate. Moreover, such a heating rate is more stable and controllable than a faster heating rate. Thus, we did not use a more rapid heating rate. However, the melt-crystallization rate at 160 °C is more rapid than that of cold-crystallization. Therefore, for the experiment of the melt-crystallization process, the sample was melted at 250 °C for 5 min and subsequently cooled as fast as possible (ca. 30 °C/min) to 160 °C to try to get the “perfect” amorphous sample. IR spectra of the specimens were collected at a 4 cm-1 resolution with a 2 min interval during the annealing process. The spectra were obtained by coadding 32 scans, and it took about 30s to measure each spectrum. 2.3. 2D IR Correlation Analysis. Before performing the 2D correlation analysis, the IR spectra were preprocessed to minimize the effect of baseline instabilities and other nonselective effects. The frequency regions of interest were truncated first and subjected to a linear baseline correction, followed by offsetting to the zero absorbance value. The spectra recorded at an equal time interval in a certain wavenumber range were selected for the 2D correlation analysis (30 and 10 spectra were used for calculating the 2D maps of cold- and melt-crystallization processes, respectively), which was carried out by using the software “2D Pocha” composed by D. Adachi (Kwansei Gakuin University). The time-averaged 1D reference spectra are shown at the side and top of the 2D correlation maps for reference. In the 2D correlation maps, regions without dots indicate positive correlation intensities, while those with dots indicate negative correlation intensities. 3. Results and Discussion 3.1. Comparison of the Crystallization Kinetics. Parts a and b of Figure 1 show spectral variations in the region of 1100-800 cm-1 during the isothermal cold- and melt-crystallization processes of iPS at 160 °C, respectively. Many crystalline-sensitive bands, which have been assigned previously,34-37 are located in this region. It was well-established that, in the crystalline phase, iPS possesses a 31 helix conformation consisting of a regular repetition of trans (T) and gauche (G) conformations of the skeletal C-C bonds.34 Bands located at 899, 920, 1052, and 1083 cm-1 arise from the intramolecular conformation changes (i.e. the formation of 31 helix chains). Usually the band at 981 cm-1 is attributed to a crystallization band. However, in a previous study,32 it was found that the band at 981 cm-1 is ascribed to the ordering of phenyl rings rather

5588 J. Phys. Chem. B, Vol. 109, No. 12, 2005

Figure 2. The crystallization curves for the cold (9) and melt (b) crystallization of iPS at 160 °C obtained by monitoring the intensity ratio (A981/A840) of the crystalline sensitive band at 981 cm-1 and the amorphous band at 840 cm-1.

than a true crystalline band reflecting the regular packing of polymer chains in the crystal lattice. In fact, in this region of 1100-800 cm-1, only crystalline-sensitive bands exist and no true crystalline band can be identified. Nevertheless, bands at 840 and 906 cm-1 are well-assigned to the amorphous phase of iPS. A band at 1026 cm-1 is due to the localized vibrational mode associated with the C-H in-plane bending of the phenyl ring. Kimura et al. found that both the peak height and shape of this band change during the crystallization of iPS.38 Therefore, this band could not strictly be regarded as an internal standard, although its intensity changes little with its crystalline status. Interestingly, this band appears to change significantly in the melt-crystallization process than that in the cold-crystallization process. For the melt- and cold-crystallization processes, our measurement conditions were the same. Thus, such a difference should not be solely caused by thickness variation as a function of time. Maybe it is induced by different conformation changes of the phenyl ring during the crystallization of iPS from different initial states (glassy state and melt state). From Figure 1a,b, it can be clearly seen that the spectral evolutions for the cold- and melt-crystallization processes of iPS are similar to each other. In both cases, the intensities of bands at 981, 899, 920, 1052, and 1083 cm-1 associated with the crystalline and 31 helix chains of iPS increase with time, while those at 840 and 906 cm-1 due to its amorphous counterpart decrease. Although the 981 cm-1 band is not a “true crystalline band”, it is still a crystalline-sensitive band and its intensity is in proportion to the crystallinity of iPS, as shown in Figure 1. Meanwhile, this crystalline-sensitive band and the amorphous band at 840 cm-1 are well-separated in the original spectra. Therefore, the intensity ratio of these two bands is used to depict the crystallization curves for the cold and melt crystallization of iPS at 160 °C, as shown in Figure 2. It is found that, even at the same crystallization temperature, the crystallization rates are clearly different between the melt- and cold-crystallization processes. The melt crystallization of iPS proceeds much faster than the glassy state crystallization. Moreover, since the intensity ratio of the crystalline-sensitive and amorphous bands is in direct proportion to the relative

Zhang et al. crystallinity of semicrystalline polymer, Figure 2 clearly shows that the crystallinity of the melt-crystallized iPS is higher than its cold-crystallized counterpart. With the data in Figure 2, the Avrami plots for the cold- and melt-crystallization processes can be constructed. The results are shown in Fgiure 3. The values of the Avrami exponent n, which is related to the nature of nucleation and to the geometry of the growing crystals,39 derived from these data are 2.12 and 1.10 for the cold and melt crystallization of iPS at 160 °C, respectively. The Avrami exponent for polymers is typically in the range of 2-4, reflecting crystal growth in two or three dimensions from isolated nuclei.40 First-order crystallization kinetics with n ≈ 1 is highly unusual. Polymers stretched at extremely high rates have shown first-order kinetics, presumably because alignment of the chains induces massive nucleation.41 However, our materials are quiescent during the crystallization of iPS at 160 °C. Lotz and Kovacs42 and Loo et al.43 once obtained unusual Avrami exponents (n ≈ 0.5 and 1) for block copolymers with a glassy matrix and a minority crystallizable component. They suggested that the extremely small value of the Avrami exponent reflects the confinement imposed by the glassy matrix. In our case, the iPS is quiescent during crystallization. The large difference in the Avrami exponents suggests that primary nucleation or the geometry of the growing crystals is very much different for the cold- and melt-crystallization processes of iPS. Another notable point in Figure 3 is that, for the cold-crystallization, the Avrami plot deviates distinctly from linearity in the later stages of crystallization, which may result from the secondary crystallization caused by the spherulite impingement in the later stage. However, such kind of deviation is not obvious for the melt crystallization of iPS at 160 °C. 3.2. 2D Correlation Analysis. Parts a and b of Figure 4show the synchronous 2D IR correlation spectra Φ(ν1,ν2) in the range of 1100-800 cm-1 generated from the time-dependent spectra in Figure 1 for the cold and melt crystallization of iPS at 160 °C, respectively. The patterns of the synchronous spectra in Figure 4a,b are similar to each other. In both 2D spectra, it can be seen that highly overlapping peaks in the ranges of 950870 and 1100-1040 cm-1 are deconvoluted effectively by spreading the peaks along the second spectral dimension. In the range of 950-870 cm-1, three autopeaks can be detected unambiguously. The appearance of these peaks is consistent with the assignments mentioned above; the 899 and 920 cm-1 bands are due to the 31 helix structure, and the 906 cm-1 band is associated with the amorphous state of iPS. In the range of 1100-1040 cm-1, two autopeaks associated with the appearance of the 31 helix structure are developed at 1052 and 1083 cm-1. In this way, compared with the 1D spectra in Figure 1, the changes in the bands at 899, 920, 1052, and 1083 cm-1 due to the 31 helical chain structure can be detected clearly in the synchronous 2D spectra of iPS during the cold- and meltcrystallization processes. According to the sign of cross-peaks in Figure 4a, the intensities of bands at 899, 920, 1052, and 1083 cm-1 due to the 31 helix structure and that of the band at 981 cm-1 due to the ordered orientation of phenyl ring of iPS increase during the crystallization process, while those of the bands at 906 and 840 cm-1 associated with the amorphous state decrease. These observations are consistent with those in the original 1D spectra in Figure 1. Figure 5a,b shows the corresponding asynchronous spectra Ψ(ν1,ν2) of iPS. An asynchronous spectrum represents sequential or successive changes of spectral intensities measured at ν1 and ν2. According to Noda’s rules,29,30 the sign of an asynchronous cross-peak becomes positive if the intensity change at ν1

Initial Crystallization Mechanism of iPS

J. Phys. Chem. B, Vol. 109, No. 12, 2005 5589

Figure 3. Avrami plots generated from the data in Figure 2 for the cold-crystallization (a) and melt-crystallization (b) process of iPS at 160 °C.

Figure 4. Comparison of the synchronous correlation spectra of iPS, in the region of 1100-800 cm-1, calculated from the spectra obtained during the cold (a) and melt (b) crystallization of iPS at 160 °C.

Figure 5. Comparison of the asynchronous correlation spectra of iPS, in the region of 1100-800 cm-1, calculated from the spectra obtained during the cold (a) and melt (b) crystallization of iPS at 160 °C.

occurs predominantly before ν2 in the sequential order of t. It becomes negative, on the other hand, if the change occurs after ν2. This rule is, however, reversed if the corresponding synchronous intensity becomes negative, i.e., Φ(ν1,ν2) < 0. Unexpectedly, the signs in the maps of Figure 5a,b are surprisingly different than each other. Especially, the signs of the asynchronous cross-peaks shared between the amorphous band at 840 cm-1 and these crystalline-sensitive bands at 920, 981, 1052, and 1083 cm-1 are reversed in parts a and b of Figure 5. In the asynchronous spectra, Ψ(920,840), Ψ(981,840), Ψ(1052,840), and Ψ(1083,840) are positive for the coldcrystallization (Figure 5a) but negative for the melt crystallization (Figure 5b), although for both cases they are negative in the corresponding synchronous spectra (Figure 4). These observations indicate that, in the cold-crystallization process of iPS, the amorphous phase changes prior to the structural ordering

of the local molecular chain and phenyl rings. However, for the melt crystallization, the situation is totally different. The structural ordering of the molecular chain and phenyl rings of iPS occurs prior to the changes of the amorphous phases. The sequential changes of the amorphous and crystallinesensitive bands in the cold crystallization of iPS at 160 °C are the same as those in the previously reported cold crystallization of iPS at 130 °C both in the induction period and the subsequent crystallization period.32 Therefore, it seems that, for crystallization of iPS from quenched glassy state, the change in amorphous phase occurs prior to the formation of the ordered structure, such as the ordering of phenyl rings and the 31 helical conformation. The physical origin for the change of amorphous phase prior to the structural ordering of iPS is not quite clear yet. It may be induced by the spinodal decomposition like density fluctuation in the quenched glassy state. One thing we

5590 J. Phys. Chem. B, Vol. 109, No. 12, 2005 can ensure is that the structural ordering of the local chains is not the initial driving force for the change in the amorphous phase during the cold-crystallization process of iPS. In contrast, for the melt crystallization of iPS at 160 °C, 2D correlation analysis indicates that the ordered structures of iPS are formed prior to the changes of the amorphous phases. Following the two-phase models of semicrystalline polymers,44 the changes in the amorphous bands and crystalline bands should be synchronous. This means that the formation of ordered structures (31 helix conformation) should also occur prior to the formation of crystal in the melt-crystallization process of iPS. This observation strongly supports the idea of preordering in the polymer melt before the formation of crystal and is also consistent with the theory of spinodal decomposition, which was explained recently by Olmested et al.25 as being a consequence of the conformation-density coupling in polymer melts. They suggested that the conformation-density coupling could induce a liquid-liquid phase transition. The two liquids differ in their distributions of conformations, with the denser liquid adopting a distribution closer to that needed for crystalline packing. However, for the case of the cold-crystallization process, the density fluctuation, consistent with the conventional spinodal decomposition behavior, may act as a main driving force for the iPS crystallization from quenched glass states. It is commonly assumed that conformational (the formation of helix chains by intramolecular interaction) and crystalline (helix chains packing by intermolecular interaction) ordering occurs simultaneously during the crystallization of polymer. However, it is noted that, for both the cold- and meltcrystallization processes of iPS at 160 °C, changes in the conformational sensitive bands and the amorphous band occur sequentially. This means that the conformational ordering and the three-dimensional ordering of the crystal unit appear sequentially. Our recent studies on PHB44 also indicated that there are sequential changes for the bands, which are sensitive to the structural formation of chain segment conformations, helical chain conformations, and chain packing. Moreover, even for the various functional groups in a polymer chain, sequential changes can also be observed. For example, in our previous study on the cold crystallization of PLLA,33 the sequential change for the methyl and ester groups was monitored. These observations indicate that not only the “cooperativity” but also the “sequence” is one of the important characteristics for the structural adjustment of polymer chains in the crystallization process of polymer. 4. Conclusions The isothermal crystallization processes of iPS at 160 °C from the different initial states (quenched glassy state and melt state) have been investigated by IR and generalized 2D IR correlation spectroscopy. It has been found that there are significant differences in the crystallization rate, degree of crystallinity, and Avrami plot between the cold and melt crystallization. These results indicate that the initial states of polymer play an important role on affecting the crystallization behaviors. Moreover, the detailed analysis of the 2D IR spectra has revealed that the sequential changes of the amorphous band and the crystalline-sensitive bands are totally reversed for the cold and melt crystallization. That is, the change of the amorphous phases occurs prior to the structural ordering of the local chain conformations and the phenyl rings of iPS during the coldcrystallization process, whereas in the melt-crystallization process, the ordered structure, such as the 31 helix chains of

Zhang et al. iPS, appears first. These observations suggest that the meltcrystallization process of polymer can be explained by the theory of spinodal decomposition recently proposed by Olmested et al. However, density fluctuation, consistent with the conventional spinodal decomposition behavior, may act as a precursor for polymer crystallization from glass states. Acknowledgment. Jianming Zhang thanks the Japan Society for the Promotion of Science (JSPS) for financial support. The financial support of the National Natural Science Foundation of China (No. 20425414, 20304018 and 20374056) is also gratefully acknowledged. References and Notes (1) Lauritzen, J. H.; Hoffmann, J. D. Nat. Bur. Stand. 1959, 31, 1680. (2) Sadler, D. M. Polymer 1983, 24, 1401. (3) Albrecht, T.; Strobl, G. Macromolecules 1996, 29, 783. (4) Hoffman, J. D.; Miller, R. L. Polymer 1997, 38, 3151. (5) Gedde, U. W. Polymer Physics; Chapman and Hall: London, 1995; pp 169-198. (6) Pogodina, N. V.; Winter, H. H.; Macromolecules 1998, 31, 8164. (7) Pogodina, N. V.; Siddiquee, S. K.; van Egmond, J. W.; Winter, H. H.; Macromolecules 1999, 32, 1167. (8) Acierno, S.; Grizzuti, N.; Winter, H. H. Macromolecules 2002, 35, 5043. (9) Samon, J. M.; Schultz, J. M.; Hsiao, B. S. Polymer 2002, 43, 1873. (10) Kumaraswamy, G.; Verma, R. K.; Issaian, A. M.; Wang, P.; Kornfield, J. A.; Yeh, F.; Hsiao, B. S.; Olley, R. H. Polymer 2002, 43, 8931. (11) Wang, Z. H.; Hsiao, B. S.; Sirota, E. B.; Agarwal, P.; Srinivas, S. Macromolecules 2000, 33, 978. (12) Strobl, G. Eur. Phys. J. E 2000, 3, 165. (13) Cheng, S. Z. D.; Li, C. Y.; Zhu, L. Eur. Phys. J. E 2000, 3, 195. (14) Imai, M.; Mori, K.; Mizukami, T.; Kaji, K.; Kanaya, T. Polymer 1992, 33, 4451. (15) Imai, M.; Kaji, K.; Kanaya, T.; Sakai, Y. Phys. ReV. B 1995, 52, 12696. (16) Imai, M.; Kaji, K.; Kanaya, T. Macromolecules 1994, 27, 7103. (17) Lee, C. H.; Saito, H.; Inoue, T.; Nojima, S. Macromolecules 1996, 29, 7034. (18) Ezquerra, T. A.; Lop _ez-Cabarcos, E.; Hsiao, B. S.; Balta`-Calleja, F. J. Phys. ReV. E 1996, 54, 989. (19) Matsuba, G.; Kanaya, T.; Saito, M.; Kaji, K.; Nishida, K. Phys. ReV. E 2000, 62, 1497. (20) Wang, Z. H.; Hsiao, B. S.; Sauer, B. B.; Kampert, W. G. Polymer 1999, 40, 4615. (21) Schultz, J. M.; Hsiao, B. S.; Samon, J. M. Polymer 2000, 41, 8887. (22) Matsuba, G.; Kaji, K.; Kanaya, T.; Nishida, K. Phys. ReV. E 2002, 65, 61801. (23) Cahn, J. W.; Hilliard, J. E. J. Chem. Phys. 1958, 28, 258. (24) Cahn, J. W. J. Chem. Phys. 1965, 42, 93. (25) Olmsted, P. D.; Poon, W. C. K.; Mcleish, T. C. B.; Terrill, N. J.; Ryan, A. J. Phys. ReV. Lett. 1998, 81, 373. (26) Chalmers, J. M.; Hannah, R. W.; Mayo, D. W. Spectra-structure correlations: Polymer spectra. In Handbook of Vibrational Spectroscopy; Chalmers, J. M., Griffiths, P. R., Eds.; John Wiley & Sons: Chichester, UK, 2002; Vol. 4, pp 2389-2547. (27) Koenig, J. L. Spectroscopy of Polymers, American Chemical Society, Washington, DC, 1992. (28) Mallapragada, S. K.; Narasimhan, B. Infrared Spectroscopy in Analysis of Polymer Crystallinity. In Encyclopedia of Analytical Chemistry; Meyers, R. A., Eds.; John Wiley & Sons: Chichester, UK, 2000; pp 76447658. (29) Noda, I. Appl. Spectrosc. 1993, 47, 1329. (30) Noda, I.; Ozaki, Y. Two-Dimensional Correlation Spectroscopys Applications in Vibrational and Optical Spectroscopy; John Wiley & Sons: Chichester, UK, 2004. (31) Zhang, J. M.; Duan, Y. X.; Shen, D. Y.; Yan, S. K.; Noda, I.; Ozaki, Y. Macromolecules 2004, 37, 3292. (32) Zhang, J. M.; Tsuji, H.; Noda, I.; Ozaki, Y. Macromolecules 2004, 37, 6433. (33) Kobayashi, M.; Tsumura, K.; Tadokoro, H. J. Polym. Sci. 1968, 6, 1493. (34) Duan, Y. X.; Zhang, J. M.; Shen, D. Y.; Yan, S. K. Macromolecules 2003, 36, 4847 (35) Painter, P. C.; Koenig, J. L. J. Polym. Sci., Part B: Polym. Phys. 1982, 2, 2277. (36) Kobayashi, M.; Nakaoki, T.; Ishihara, N. Macromolecules 1990, 23, 78.

Initial Crystallization Mechanism of iPS (37) Nakaoki, T.; Katagiri, C.; Kobayashi, M. Macromolecules 2002, 35, 7708. (38) Kimura, T.; Ezure, H.; Tanaka, S.; Ito, E. J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 1227. (39) Qin, Z. B.; Mo, Z. S.; Zhang, H. F.; Sheng, S. R.; Song, C. S. J. Polym. Sci., Part B: Polym. Phys. 1993, 31, 371. (40) Hay, J. N. Br. Polym. J. 1971, 3, 74.

J. Phys. Chem. B, Vol. 109, No. 12, 2005 5591 (41) Blundell, D. J.; MacKerron, D. H.; Fuller, W.; Mahendrasingam, A.; Martin, C.; Oldman, R. J.; Rule, R. J.; Riekel, C. Polymer 1996, 37, 15. (42) Lotz, B.; Kovacs, A. J. ACS Polym. Prepr. 1969, 10, 820. (43) Loo, Y. L.; Register, R. A.; Ryan, A. J. Phys. ReV. Lett. 2000, 84, 4120. (44) Zhang, J. M.; Sato, H.; Noda, I.; Ozaki, Y. To be published.