Noncrystalline component

On the other hand, the analysis results in respect of the noncrystalline components are greatly changed with drawing. A significant increase in is recog-... 

To elucidate the phase structure in detail it is necessary to characterize the molecular chain conformation and dynamics in each phase. However, it is rather difficult to obtain such molecular information, particularly of the noncrystalline component, because it is substantially amorphous. In early research in this field, broad-line H NMR analysis showed that linear polyethylene crystallized from the melt comprises three components with different molecular mobilities solid, liquid-like and intermediate molecular mobility [13-16]. The solid component was attributed to molecules in the crystalline region, the liquid component to... 

Rather recently, we have studied the solid-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],and amylose [31] with solid-state high-resolution X3C NMR with supplementary use of other methods, such as X-ray diffraction and IR spectroscopy. Through these studies, the high resolution solid-state X3C NMR has proved very powerful for elucidating the solid-state structure of polymers in order of molecules, that is, in terms of molecular chain conformation and dynamics, not only on the crystalline component but also on the noncrystalline components via the chemical shift and magnetic relaxation. In this chapter we will review briefly these studies, focusing particular attention on the molecular chain conformation and dynamics in the crystalline-amorphous interfacial region. 

This suggests that the broad component includes some contribution from a rigid noncrystalline component. 

Spin-Spin Relaxation. In order to determine the content of these two noncrystalline components, we next examined the transverse relaxation by a pulse sequence shown schematically in Fig. 1—III. The partially recovered magnetization in the z direction for a T of 3.5 s was followed by transverse relaxation for varying time xf, and the FID was observed under JH DD. The spectra at different steps of transverse relaxation were thus obtained, and the result is shown in Fig. 6. The spectrum at xf = 0.5 ps (a dead time in this pulse sequence) is assumed... 

It is evident that the noncrystalline component is distributed in two phases that are associated with the same Tic but different T2C values. What does this mean In order to understand this phenomenon we have to refer to the theory of the relaxation reviewed in Section 2.2 [43]. Provided the internuclear vector between carbon and hydrogen nuclei involves only a single motion, that is, if each term of the correlation function of the dipole-dipole interaction between 13C and H spins evolves exponentially with one correlation time ic (relaxation time of... 

To this end, we emphasize that the two phases assumed for the noncrystalline component are well-defined by the differences in T2c. In the crystalline-amorphous interphase, a long-ranged molecular motion accompanying the conformational change of ca. 10-20 carbon atoms is very slow or almost inhibited. In this phase the trans-trans conformation may be somewhat abundant but generally all permitted conformations are widely distributed. 

Spin-Lattice and Spin-Spin Relaxation. In order to examine the content of these crystalline and noncrystalline components, we examined the spin relaxation of each resonance line. Firstly it was found that the line due to the orthorhombic crystalline component at 33 ppm involves plural Tic s for all samples, as summarized in Table 4. In relation to the T1C for each sample, very long Tic values are recognized for three higher molecular weight samples. These values are expected... 

Fig. 15. 13C spin-spin relaxation behavior of the noncrystalline component of Hifax... 

DD/MAS13C NMR Spectra. Figure 16 shows the equilibrium 13C NMR spectra of those samples that were obtained by the pulse sequence (7t/4-FIDdd-3Tic)ii at room temperature. Here the sample A is the undrawn dried gel, B is the sample obtained from A by annealing at 145 °C for 4 minutes, and C, D, and E are samples drawn 50,100, and 50 times, respectively For most spectra there is a recognized downfield resonance at ca. 33 ppm assignable to the orthorhombic crystalline component and an upfield resonance at ca. 31 ppm assignable to the noncrystalline component. 

Spin-Lattice and Spin-Spin Relaxations. In order to determine the content of these crystalline and noncrystalline resonances, the longitudinal and transverse relaxations were examined in detail. It was first confirmed that the noncrystalline resonance of all samples is associated with Tic in an order of 0.45-0.57 s. Hence, the noncrystalline component of all samples comprises a monophase, in as much as judged only by Tic. However, it was found that the noncrystalline component of drawn samples generally comprises two phases with different T2C values amorphous and crystalline-amorphous interphases. The dried gel sample does not include rubbery amorphous material it comprises the crystalline and rigid noncrystalline components. However, the rubbery amorphous phase with T2C of 5.5 ms appears by annealing at 145 °C for 4 minutes. For the orthorhombic crystalline component, three different Tic values, that suggest the distribution of crystallite size, were recognized for each sample, as normal for crystalline polymers [17,54, 55]. The Tic and T2C of all samples examined are summerized in Table 6. 

The resonance lines at 72.9 and 28.3 ppm are assigned to the crystalline components of a- and 3-methylene carbons because of their longer Tic values. These crystalline resonance lines are associated with two T1C values of ca. 209 and 9-10 s. This shows that both methylene carbons possess two components with different Tic >s> but this will not be discussed further, since the existence of plural TiC s is a normal finding for crystalline polymers as discussed in previous sections. On the other hand, the resonance lines at 70.9 and 27.0 ppm recognized for a-and (3-methylene carbons are assignable to the noncrystalline component, because these chemical shifts are very close to those in the solution. These lines are associated with only one Tic of 0.15 or 0-14 s and two T2c values of 7.95 s and 0.099 ms, or 8.22 s and 0.099 ms, respectively for the a- and (3 -methylene carbons. This suggests that the noncrystalline component involves two components, both associated with a same Tic and different T2c Js. The noncrystalline component with a T2c of 7.95 or 8.22 ms is thought to form an amorphous phase and that with a T2C of 0.099 ms comprises a crystalline-amorphous interphase. In order to confirm this, we examined the elementary line shapes of each component and performed the line shape decomposition analysis of the equilibrium spectrum. 

Spectrum (a) shows the DD/MAS 13C NMR spectrum of the a-methylene carbon that was obtained by a single pulse sequence with a repetition time of 0.8 s. This is 0.8 s is longer than 5 times the Tic of the noncrystalline component and much shorter than Tic of the crystalline component (cf. Table 10). Hence, this spectrum represents the contribution from the noncrystalline component that consists of amorphous and crystalline-amorphous interphases. Spectrum (b) is a partially relaxed spectrum transversely for 600 ps. Since 600 ps is much longer... 

When a melt-miscible polymer system is analyzed at temperatures lower than the crystallization temperature of one constituent, a phase-separated or single crystalline phase structure might result. When the T% of the noncrystalline component is lower than the crystallization temperature, the component phase separates as it is rejected from the crystal structure. The extent of phase separation may be easily visualized... 

In a similar manner, the ethylene-octene copolymer crystallized directly via the orthorhombic phase without the intervention of the anticipated hexagonal phase as would be anticipated in linear polyethylenes at these high pressures and temperatures (at approximately 3.8 kbar and around 200 °C). At 100 °C, see Fig. 15, the d values for (110) and (200) orthorhombic reflections are 4.08 A and 3.71 A. When the sample is cooled below 100 °C, a new reflection adjacent to the (110) orthorhombic peak appears at 80 °C. The position of the new reflection is found to be 4.19 A and so corresponds to a new phase. No change in the intensity of the existing (110) and (200) reflections is observed, however the intensity of the amorphous halo decreases, which suggests that the appearance of the new reflection (d = 4.19 A) is solely due to the crystallization of a noncrystalline component. On cooling further as the new reflection intensifies, the (110) and (200) orthorhombic reflections shift gradually. However, at 50 °C, the (100) monoclinic reflection appears with a concomitant decrease in the intensity of the (110) orthorhombic reflec-... 

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