Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular Poly(Vinyl Chloride) Prepared by Urea Clathrate Polymerization at Low Temperatures

*Masatomo Minagawa, Jun Yatabe, Fumio Yoshii, Shin Hasegawa, Nobuhiro Sato and Tomochika Matsuyama*

## **Abstract**

Stereoregular poly(vinyl chloride) (PVC) was obtained by urea clathrate polymerization. The sample was a white crystalline powder. Its molecular structure was studied by appearance, FT-IR, WAXD, and NMR (solid) in comparison with those of ordinary free radical one. The sample was totally insoluble to polar solvent such as DMF in contrast with good solubility of free radical one. Prolonged heating at high temperatures ensured discoloration and elimination reaction permitted formation of trans-type double bond. This structural change was traced by FT-IR and solid-state NMR. Two non-compromise characteristics, stiff molecular chain and easy discoloration, in canal PVC are described.

**Keywords:** stereoregular PVC, analysis by WAXD/FT-IR/NMR/ESR, elimination reaction

## **1. Introduction**

Solid-state polymerization is a unique polymer synthetic method in Polymer Science. The most famous example is probably a urea clathrate polymerization of vinyl chloride (VC) as described here. That is, VC monomers are packed regularly in one-dimensional narrow urea canal under low temperatures (canal complex or inclusion complex). When strong γ-irradiation or electron beam one will be made, polymerization takes place, and highly stereoregular poly(vinyl chloride) (PVC) is obtained.

The first research in this area was carried out by Brown and White, researchers of GE company (USA) [1, 2]. They showed that urea canal-polymerized polymers have a remarkable difference in its physical properties. Particularly, not only ordinary urea but also thiourea does the canal complex at low temperature, and their difference is an inner diameter of cavity (5A or 6A). The structures and properties

**Figure 1.** *Krimm's data [3, 4].*

of the resulting polymers are well described by a limited number of instruments including solubility measurements, etc. Although the described time period is old, their valuable finding and observation have still a brilliant light in Polymer Science even at the present time.

Stereoregular PVC was investigated by Krimm et al. by using IR spectroscopy [3, 4]. Their first paper on stereoregular PVC was only one page, but its IR spectra were printed and published in all the textbooks and professional ones in the world (see **Figure 1**). In the IR spectra, structural difference appeared in the 700– 600 cm<sup>−</sup><sup>1</sup> region. One can notice that only two peaks are clearly seen in the urea canal PVC in contrast with three peaks in free radical one. Lack of the left-hand side band (690 cm<sup>−</sup><sup>1</sup> , assigned to be isotactic) strongly suggests that stereoregular PVC is highly syndiotactic.

In Japan, a detailed IR study of PVC including stereoregular one was carried out by Shimanouchi and Tasumi in the University of Tokyo [5, 6]. Their standpoint of view was purely scientific, and direct application to industrial field appeared to be relatively small. However, their effort was greatly helpful for the improvement of commercial PVC products in Japan. They synthesized various model compounds and confirmed IR assignment of PVC, for example, the effects of C-Cl position on IR spectra and related problems are typical examples. Their collaborative work has been summarized and published in Ref. [7].

## **2. Theory: principle of urea clathrate polymerization**

**Figure 2** shows the principle of urea canal polymerization [8–10]. When organic monomers are mixed with fine urea and the mixture is kept at low temperatures (−78°C), a canal complex is formed spontaneously. This is a typical inclusion phenomenon, and the resulting canal complex is called *inclusion complex*. It must be noted that such an inclusion is caused by *the phase transition* of urea, when

**109**

**Figure 3.**

*The shape and size of canal complex.*

**Figure 2.**

*Principle of urea canal polymerization.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

urea is mixed with organic molecules and then temperature is kept at such lower

The geometrical shape and size of the complex are quite different according to the type of monomers [9, 10]. An ideal complex is n-paraffin/urea system (**Figure 2**, right). A well-known fact is that started from ethylene/urea system,

In the case of polar vinyl monomers, inclusion structure is quite different according to the type of monomers, e.g., *monoclinic* (VC/urea) and *hexagonal* (AN/ urea) (**Figure 3**). That is, slurry of initial mixture (urea/liquid monomers) turned to be dry flake-like white substance eventually under such low temperatures. The γ-irradiation toward the canal complex must be carried out carefully under

*DOI: http://dx.doi.org/10.5772/intechopen.90784*

linear polyethylene with no branching is obtained.

temperatures.

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

urea is mixed with organic molecules and then temperature is kept at such lower temperatures.

The geometrical shape and size of the complex are quite different according to the type of monomers [9, 10]. An ideal complex is n-paraffin/urea system (**Figure 2**, right). A well-known fact is that started from ethylene/urea system, linear polyethylene with no branching is obtained.

In the case of polar vinyl monomers, inclusion structure is quite different according to the type of monomers, e.g., *monoclinic* (VC/urea) and *hexagonal* (AN/ urea) (**Figure 3**). That is, slurry of initial mixture (urea/liquid monomers) turned to be dry flake-like white substance eventually under such low temperatures. The γ-irradiation toward the canal complex must be carried out carefully under

**Figure 2.**

*Nuclear Magnetic Resonance*

even at the present time.

side band (690 cm<sup>−</sup><sup>1</sup>

PVC is highly syndiotactic.

been summarized and published in Ref. [7].

**2. Theory: principle of urea clathrate polymerization**

600 cm<sup>−</sup><sup>1</sup>

**Figure 1.** *Krimm's data [3, 4].*

of the resulting polymers are well described by a limited number of instruments including solubility measurements, etc. Although the described time period is old, their valuable finding and observation have still a brilliant light in Polymer Science

Stereoregular PVC was investigated by Krimm et al. by using IR spectroscopy [3, 4]. Their first paper on stereoregular PVC was only one page, but its IR spectra were printed and published in all the textbooks and professional ones in the world (see **Figure 1**). In the IR spectra, structural difference appeared in the 700–

canal PVC in contrast with three peaks in free radical one. Lack of the left-hand

region. One can notice that only two peaks are clearly seen in the urea

In Japan, a detailed IR study of PVC including stereoregular one was carried out by Shimanouchi and Tasumi in the University of Tokyo [5, 6]. Their standpoint of view was purely scientific, and direct application to industrial field appeared to be relatively small. However, their effort was greatly helpful for the improvement of commercial PVC products in Japan. They synthesized various model compounds and confirmed IR assignment of PVC, for example, the effects of C-Cl position on IR spectra and related problems are typical examples. Their collaborative work has

**Figure 2** shows the principle of urea canal polymerization [8–10]. When organic monomers are mixed with fine urea and the mixture is kept at low temperatures (−78°C), a canal complex is formed spontaneously. This is a typical inclusion phenomenon, and the resulting canal complex is called *inclusion complex*. It must be noted that such an inclusion is caused by *the phase transition* of urea, when

, assigned to be isotactic) strongly suggests that stereoregular

**108**

*Principle of urea canal polymerization.*

**Figure 3.** *The shape and size of canal complex.*

sufficiently cooled conditions (below −78°C). This is because if temperature is increased, the canal complex is destroyed, then unreacted monomers will be liberated from the inclusion matrix. The liberated free monomers can be detected by broad line NMR through free rotation of liberated monomers [11, 12]. In spite of the fact that these monomers (VC/AN) are typical electronegative polar monomers equally, quite different configuration is attained (*syndiotactic/VC* and *isotactic/AN*, respectively). The reason why such different microtacticity is attained has neither been clarified experimentally nor theoretically.

## **3. Experimental**

Canal PVC was a white powder and was totally insoluble to organic solvent such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). *Characterization* is given in **Table 1**. It is important to notice that *sample A* means urea canal PVC prepared as described here while *sample B* does free radical one (commercial PVC: Zeon 103, EP-8, straight type/homopolymer). *Sample C* was a standard polymer taken from 100 kinds of standard polymers (Scientific Polymer Products, Inc., USA).


*1 Prepared in JAERI, Takasaki by urea canal polymerization as described in the text. 2 Supplied from production company, Japan Zeon Co. Ltd. This polymer was a homopolymer. 3 Supplied from the Scientific Polymer Products (USA). This was a high molecular weight homopolymer. 4 Solubility into DMF at room temperature. (0), soluble, (x) insoluble.*

#### **Table 1.**

*Characterization of PVC samples.*

Various measurements were carried out by using instrumental analyses such as solid-state NMR, FT-IR (KBr method), WAXD, TG, solid-state ESR, etc. under carefully controlled conditions. For example, typical NMR conditions in **Figure 7** were as follows: spectrometer, JEOL JNM GX-270; nucleus, 13C; PW2 contact time, 8 ms; PW1 pulse width (90° pulse), 4.5 μs; PD repetition time, 5000 s; number of scans, 150,000; probe, Doty's ceramic probe (7 mm⏀); and external reference, secondary peak of adamantane.

## **4. Results and discussion**

#### **4.1 Characterization of PVC powder**

**Figure 4** shows IR spectra [12]. There was a distinct difference in the band below 700 cm<sup>−</sup><sup>1</sup> region. Only two peeks are clearly observed in sample A. Lack of the left-hand side band (690 cm<sup>−</sup><sup>1</sup> : assigned to be isotactic in amorphous region) suggests that the urea canal PVC has syndiotactic configuration. It is apparent that Krimm's novel finding was confirmed in this way.

A small difference was also observed in 2900 cm<sup>−</sup><sup>1</sup> region. A new band (2933 cm<sup>−</sup><sup>1</sup> ) appeared especially in the urea canal PVC (**Figure 5**). This band may

**111**

section).

**Figure 5.**

**Figure 4.**

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

be correlated with some stereochemical structural factors including *Fermi resonance* and the like, which appears in highly symmetric molecules with very strong intermolecular interaction (enhanced intermolecular hydrogen bonding). The existence of such IR characteristic band has already been pointed out by Tasumi [13]. In fact, this band is directly related to the structurally well-ordered region in PVC sample, since in WAXD results, many Debye-Scherrer rings are clearly observed (see next

**Figure 6** shows the WAXD results. The existence of many coaxial Debye-Scherrer rings in the sample A is apparent. Careful observation revealed sixth diffraction rings can be counted. With regard to WAXD measurements,

*DOI: http://dx.doi.org/10.5772/intechopen.90784*

*Comparison of IR spectra of two kinds of PVC.*

*FT-IR spectra of νCH2 region (diffuse reflection, KBr).*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 4.** *Comparison of IR spectra of two kinds of PVC.*

*Nuclear Magnetic Resonance*

**3. Experimental**

Products, Inc., USA).

*1*

*2*

*3*

*4*

**Table 1.**

secondary peak of adamantane.

*Characterization of PVC samples.*

**4. Results and discussion**

below 700 cm<sup>−</sup><sup>1</sup>

(2933 cm<sup>−</sup><sup>1</sup>

**4.1 Characterization of PVC powder**

the left-hand side band (690 cm<sup>−</sup><sup>1</sup>

Krimm's novel finding was confirmed in this way. A small difference was also observed in 2900 cm<sup>−</sup><sup>1</sup>

been clarified experimentally nor theoretically.

sufficiently cooled conditions (below −78°C). This is because if temperature is increased, the canal complex is destroyed, then unreacted monomers will be liberated from the inclusion matrix. The liberated free monomers can be detected by broad line NMR through free rotation of liberated monomers [11, 12]. In spite of the fact that these monomers (VC/AN) are typical electronegative polar monomers equally, quite different configuration is attained (*syndiotactic/VC* and *isotactic/AN*, respectively). The reason why such different microtacticity is attained has neither

Canal PVC was a white powder and was totally insoluble to organic solvent such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). *Characterization* is given in **Table 1**. It is important to notice that *sample A* means urea canal PVC prepared as described here while *sample B* does free radical one (commercial PVC: Zeon 103, EP-8, straight type/homopolymer). *Sample C* was a standard polymer taken from 100 kinds of standard polymers (Scientific Polymer

**Type Symbol Code Form Color Solubility4**

Canal1 *A* γ-Ray Powder White × Radical2 *B* Zeon 103 Particle White ○ Radical3 *C* #038 Powder White ○

*Supplied from the Scientific Polymer Products (USA). This was a high molecular weight homopolymer.*

*Prepared in JAERI, Takasaki by urea canal polymerization as described in the text.*

*Solubility into DMF at room temperature. (0), soluble, (x) insoluble.*

*Supplied from production company, Japan Zeon Co. Ltd. This polymer was a homopolymer.*

Various measurements were carried out by using instrumental analyses such as solid-state NMR, FT-IR (KBr method), WAXD, TG, solid-state ESR, etc. under carefully controlled conditions. For example, typical NMR conditions in **Figure 7** were as follows: spectrometer, JEOL JNM GX-270; nucleus, 13C; PW2 contact time, 8 ms; PW1 pulse width (90° pulse), 4.5 μs; PD repetition time, 5000 s; number of scans, 150,000; probe, Doty's ceramic probe (7 mm⏀); and external reference,

**Figure 4** shows IR spectra [12]. There was a distinct difference in the band

suggests that the urea canal PVC has syndiotactic configuration. It is apparent that

region. Only two peeks are clearly observed in sample A. Lack of

) appeared especially in the urea canal PVC (**Figure 5**). This band may

: assigned to be isotactic in amorphous region)

region. A new band

**110**

**Figure 5.** *FT-IR spectra of νCH2 region (diffuse reflection, KBr).*

be correlated with some stereochemical structural factors including *Fermi resonance* and the like, which appears in highly symmetric molecules with very strong intermolecular interaction (enhanced intermolecular hydrogen bonding). The existence of such IR characteristic band has already been pointed out by Tasumi [13]. In fact, this band is directly related to the structurally well-ordered region in PVC sample, since in WAXD results, many Debye-Scherrer rings are clearly observed (see next section).

**Figure 6** shows the WAXD results. The existence of many coaxial Debye-Scherrer rings in the sample A is apparent. Careful observation revealed sixth diffraction rings can be counted. With regard to WAXD measurements,

Sakurada et al. already observed sixth diffraction rings in γ-ray PVC (consists of three components indicating partial dissolution into DMF solvent) [14], but they didn't show a WAXD photograph. Even in our experiments, it was very difficult to show rings by ordinary WAXD photograph technically; therefore, we preferred to the direct observation of negative film. By this method, the number of higher order of reflected rings can be counted. Further, very thin but distinct coaxial rings in sample B (commercial one) are obvious.

**Figure 7** shows the solid-state NMR spectra. (Since this polymer didn't dissolve in any organic solvent, high-resolution NMR spectra couldn't be obtained.) In comparison with that of free radical PVC (sample B), there was a distinct difference in the NMR spectra. PVC shows two 13C NMR peaks deriving from CH and CH2 groups on a polymer backbone. Their relative height was almost equal in *sample B*, but it was quite different in *sample A*. The peak area of CH and CH2 signals in each sample was almost equal, however. From the broadness of NMR spectra, it is possible to consider that three peaks (mm, mr, rr) are separated to some extent toward

**Figure 6.** *Comparison of WAXD of three kinds of PVC (negative film).*

**113**

**Figure 9.**

*FT-IR of PVC suspension heated in DMF 1080 cm<sup>−</sup><sup>1</sup>*

 *at 120 °C: a: original, b: 1 h, and c: 19 h.*

**Figure 8.**

*Solubility of PVC in DMF solvent.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

*DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 7.** *Comparison of solid-state 13C NMR spectra of two kinds of PVC.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 8.** *Solubility of PVC in DMF solvent.*

*Nuclear Magnetic Resonance*

sample B (commercial one) are obvious.

*Comparison of WAXD of three kinds of PVC (negative film).*

*Comparison of solid-state 13C NMR spectra of two kinds of PVC.*

Sakurada et al. already observed sixth diffraction rings in γ-ray PVC (consists of three components indicating partial dissolution into DMF solvent) [14], but they didn't show a WAXD photograph. Even in our experiments, it was very difficult to show rings by ordinary WAXD photograph technically; therefore, we preferred to the direct observation of negative film. By this method, the number of higher order of reflected rings can be counted. Further, very thin but distinct coaxial rings in

**Figure 7** shows the solid-state NMR spectra. (Since this polymer didn't dissolve

in any organic solvent, high-resolution NMR spectra couldn't be obtained.) In comparison with that of free radical PVC (sample B), there was a distinct difference in the NMR spectra. PVC shows two 13C NMR peaks deriving from CH and CH2 groups on a polymer backbone. Their relative height was almost equal in *sample B*, but it was quite different in *sample A*. The peak area of CH and CH2 signals in each sample was almost equal, however. From the broadness of NMR spectra, it is possible to consider that three peaks (mm, mr, rr) are separated to some extent toward

**112**

**Figure 7.**

**Figure 6.**

**Figure 9.** *FT-IR of PVC suspension heated in DMF 1080 cm<sup>−</sup><sup>1</sup> at 120 °C: a: original, b: 1 h, and c: 19 h.*

the outer direction and CH peak appeared as a broad single peak with the whole envelope of these peaks [15].

Microtacticity of γ-ray PVC couldn't be determined by solid-state NMR in this way, although quite different NMR peak shape was obtained.

### **4.2 Solubility in DMF solvent**

**Figure 8** shows the solubility results of PVC. Free radical PVC (*sample B*) dissolved in DMF completely at room temperature and provided apparently transparent solution. Urea canal PVC (*sample A*), however, didn't. It did a suspension; PVC powder was dispersed in the solvent. Continuous heating up to a high temperature caused a slightly discoloration from white to pale yellow, red, brown, and black. The heated samples were recovered and FT-IR spectra were taken.

Results are given in **Figures 9** and **10**. In *sample A*, change in IR spectra is very little. Polymer backbone is retained even after heating of 19 hours. This is related to the fact that the sample is insoluble and is heated in a suspension state.

A small band appeared at 1080 cm<sup>−</sup><sup>1</sup> , which can be assigned to be trans-type of double bond [16]. In *sample B*, spectral change was large. New band appeared at 1080 cm<sup>−</sup><sup>1</sup> and became progressively large. The decrease of C-Cl band (700– 600 cm<sup>−</sup><sup>1</sup> ) is obvious. It is known that elimination reaction (HCl) accompanies the formation of trans-type of double bond. This mechanism was common in both samples. Results are summarized in **Figure 11**.

**Figure 12** shows the solid-state NMR spectra [17]. In sample A, spectral change was small. In contrast, in sample B, it was large. The appearance of broad peak at about 125–130 ppm is probably due to the formation of double bond, –(CH=CH)n −. In fact, various rubberlike materials having double bond in its molecular structure

**115**

**Figure 12.**

**Figure 11.**

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

have strong peak in this region [18]. NMR results were as a whole in good agreement

**Figure 13** shows a photograph of heated PVC samples [12]. Canal PVC turns in its color from white (RT) to pale purple (160°C), deep purple (200°C), and then black (~280°C). It is very easy in discoloration. In contrast, free radical one is very hard in its discoloration. One can understand this when compared with the color of two PVC specimens heated up to 200°C (indicated by an arrow). Canal PVC is very deep purple (left), whereas free radical one is only slightly pale orange (right side). Easy discoloration of sample A is probably inherent characteristics of urea canal

with those of FT-IR (**Figures 9** and **10**).

*Comparison of solid-state 13C NMR spectra of heated PVC.*

**4.3 Discoloration by heat treatment**

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*Variation of IR intensity of trans-type double bond.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 11.**

*Nuclear Magnetic Resonance*

envelope of these peaks [15].

**4.2 Solubility in DMF solvent**

the outer direction and CH peak appeared as a broad single peak with the whole

way, although quite different NMR peak shape was obtained.

heated samples were recovered and FT-IR spectra were taken.

A small band appeared at 1080 cm<sup>−</sup><sup>1</sup>

samples. Results are summarized in **Figure 11**.

at 1080 cm<sup>−</sup><sup>1</sup>

600 cm<sup>−</sup><sup>1</sup>

the fact that the sample is insoluble and is heated in a suspension state.

Microtacticity of γ-ray PVC couldn't be determined by solid-state NMR in this

**Figure 8** shows the solubility results of PVC. Free radical PVC (*sample B*) dissolved in DMF completely at room temperature and provided apparently transparent solution. Urea canal PVC (*sample A*), however, didn't. It did a suspension; PVC powder was dispersed in the solvent. Continuous heating up to a high temperature caused a slightly discoloration from white to pale yellow, red, brown, and black. The

Results are given in **Figures 9** and **10**. In *sample A*, change in IR spectra is very little. Polymer backbone is retained even after heating of 19 hours. This is related to

of double bond [16]. In *sample B*, spectral change was large. New band appeared

and became progressively large. The decrease of C-Cl band (700–

) is obvious. It is known that elimination reaction (HCl) accompanies the formation of trans-type of double bond. This mechanism was common in both

**Figure 12** shows the solid-state NMR spectra [17]. In sample A, spectral change was small. In contrast, in sample B, it was large. The appearance of broad peak at about 125–130 ppm is probably due to the formation of double bond, –(CH=CH)n

In fact, various rubberlike materials having double bond in its molecular structure

, which can be assigned to be trans-type

 *at 120°C: d, 1 hour; e, 10 hours; and f, 19 hours.*

−.

**114**

**Figure 10.**

*FT-IR of PVC solution heated in DMF 1080 cm<sup>−</sup><sup>1</sup>*

*Variation of IR intensity of trans-type double bond.*

**Figure 12.**

*Comparison of solid-state 13C NMR spectra of heated PVC.*

have strong peak in this region [18]. NMR results were as a whole in good agreement with those of FT-IR (**Figures 9** and **10**).

#### **4.3 Discoloration by heat treatment**

**Figure 13** shows a photograph of heated PVC samples [12]. Canal PVC turns in its color from white (RT) to pale purple (160°C), deep purple (200°C), and then black (~280°C). It is very easy in discoloration. In contrast, free radical one is very hard in its discoloration. One can understand this when compared with the color of two PVC specimens heated up to 200°C (indicated by an arrow). Canal PVC is very deep purple (left), whereas free radical one is only slightly pale orange (right side). Easy discoloration of sample A is probably inherent characteristics of urea canal

polymer due to the absence of termination reaction. Because of these characteristics, end radicals are generally living, which would act as a trigger of an elimination reaction (HCl) via a well-known β-elimination mechanism at higher temperatures.

**Figure 14** shows solid-state ESR results for sample A under the dynamic heating conditions. Pay attention to the central signal indicated by an asterisk (\*), which is derived from the PVC power. Outer several peaks are due to the one from MnO+2 inserted as an ESR marker. One can notice that peak intensity increased with the elevation of temperature.

As summarized in **Figure 15**, signal intensification is started at about 160°C, which corresponds to the onset of color changing from white to pale purple (see a

**Figure 13.** *Comparison of a photograph of heated PVC.*

**117**

**Figure 16.**

*Comparison of solid-state 13C NMR spectra.*

**Figure 15.**

*ESR intensity and TG derivative curve.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

photograph in **Figure 13**). Smooth increase of signal intensity means that elimination reaction proceeds zipper-like (autocatalytically), but its intensity stopped apparently in two regions (*symbols 1 and 2*). An ideal zipper-like reaction started from chain ends in amorphous region was stopped due to *resonance stabilization*

*DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 14.** *Solid-state ESR spectra under dynamic heating conditions.*

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

**Figure 15.** *ESR intensity and TG derivative curve.*

*Nuclear Magnetic Resonance*

elevation of temperature.

polymer due to the absence of termination reaction. Because of these characteristics, end radicals are generally living, which would act as a trigger of an elimination reaction (HCl) via a well-known β-elimination mechanism at higher temperatures. **Figure 14** shows solid-state ESR results for sample A under the dynamic heating conditions. Pay attention to the central signal indicated by an asterisk (\*), which is derived from the PVC power. Outer several peaks are due to the one from MnO+2 inserted as an ESR marker. One can notice that peak intensity increased with the

As summarized in **Figure 15**, signal intensification is started at about 160°C, which corresponds to the onset of color changing from white to pale purple (see a

**116**

**Figure 14.**

**Figure 13.**

*Comparison of a photograph of heated PVC.*

*Solid-state ESR spectra under dynamic heating conditions.*

**Figure 16.** *Comparison of solid-state 13C NMR spectra.*

photograph in **Figure 13**). Smooth increase of signal intensity means that elimination reaction proceeds zipper-like (autocatalytically), but its intensity stopped apparently in two regions (*symbols 1 and 2*). An ideal zipper-like reaction started from chain ends in amorphous region was stopped due to *resonance stabilization*

and the like, and subsequent reaction may proceed in an irregular form such as interchain elimination or at random fashion type of elimination in unreacted rigid stereoregular sequence.

It is worth while noting that *step 2* in ESR signal agrees with the higher temperature peak of the double peak (306°C–319°C) in TG derivative curve, which were measured in other independent experiments. At any rate, the presence of non-propagating stopping mechanism is obvious. There may be some fine structure and the like in both steps, but these features could not be detected experimentally.

**Figure 16** shows solid-state NMR spectra. The original structure has retained considerably in sample A, since CH2 and CH peaks are clearly present. In contrast, in sample B, the original structural peaks have lost and new broad peak appeared at 130 ppm region. This spectral change in NMR is basically very close to those of FT-IR spectra in **Figures 9** and **10** (heat treatment in the solution or suspension state). In NMR measurements, it should be noted that the peak area is directly proportional to the concentration of functional groups in question; therefore, from both the position (chemical shift) and the peak shape (area), one can understand the mechanism wholly or intuitively.

## **5. Conclusion**


**119**

**Author details**

Nobuhiro Sato4

Masatomo Minagawa1

\*, Jun Yatabe2

1 NPO: Dream-Create-Laboratories, Yonezawa, Japan

2 Teikyo University of Science, Uenohara, Japan

provided the original work is properly cited.

and Tomochika Matsuyama4

4 Research Reactor Institute Kyoto University, Kumatori, Japan

\*Address all correspondence to: gakusai-minagawa@memoad.jp

, Fumio Yoshii3

3 Takasaki-Establishment, Japan Atomic Energy Research Institute, Takasaki, Japan

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

, Shin Hasegawa<sup>3</sup>

,

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular…*

We wish to express our hearty thanks to Mr. H. Sugisawa (JEOL), Prof. Y. Nozawa (Tohoku University), and Mr. T. Katoh (Yamagata University) for NMR measurements. Thanks are also expressed to Prof. M. Matsuda, Prof. T. Miyashita, and Dr. F. Bae (Tohoku University) for many conveniences in solid-state ESR measurements. The valuable discussion on IR spectroscopic data with Prof. M. Tasumi

*DOI: http://dx.doi.org/10.5772/intechopen.90784*

(University of Tokyo) is also greatly acknowledged.

**Acknowledgements**

*Solubility, Discoloration, and Solid-State 13C NMR Spectra of Stereoregular… DOI: http://dx.doi.org/10.5772/intechopen.90784*

## **Acknowledgements**

*Nuclear Magnetic Resonance*

stereoregular sequence.

the mechanism wholly or intuitively.

the canal complex were described.

gested by FT-IR characteristic band (2933 cm<sup>−</sup><sup>1</sup>

bond. The reaction rate of sample A was small.

will be attributed to the stiffness of molecular chain.

extent of the progress of degradation is greatly of help.

spectra of 700–600 cm<sup>−</sup><sup>1</sup>

experimentally.

**5. Conclusion**

NMR.

and the like, and subsequent reaction may proceed in an irregular form such as interchain elimination or at random fashion type of elimination in unreacted rigid

It is worth while noting that *step 2* in ESR signal agrees with the higher temperature peak of the double peak (306°C–319°C) in TG derivative curve, which were measured in other independent experiments. At any rate, the presence of non-propagating stopping mechanism is obvious. There may be some fine structure and the like in both steps, but these features could not be detected

**Figure 16** shows solid-state NMR spectra. The original structure has retained considerably in sample A, since CH2 and CH peaks are clearly present. In contrast, in sample B, the original structural peaks have lost and new broad peak appeared at 130 ppm region. This spectral change in NMR is basically very close to those of FT-IR spectra in **Figures 9** and **10** (heat treatment in the solution or suspension state). In NMR measurements, it should be noted that the peak area is directly proportional to the concentration of functional groups in question; therefore, from both the position (chemical shift) and the peak shape (area), one can understand

1.The principle of urea clathrate polymerization at low temperatures was described from a purely experimental point of view. The basis lies on the canal complex formation of urea at low temperatures. Geometrical shape and size of

2.Characterization of bulk PVC sample was carried out by using FT-IR, WAXD, and solid-state NMR spectra. Lack of isotactic sequence was confirmed by IR

3.Solubility into DMF was studied. Free radical sample showed perfect solubility in DMF, while canal sample didn't. Suspension was obtained. Heat treatment caused an elimination reaction followed by formation of trans-type of double

4.Discoloration by heat treatment was described. Canal PVC showed easy discoloration but rather delay in the TG degradation. The lack of termination reaction is related to the easy discoloration (β-elimination). Slow degradation

5.Solid-state ESR measurements were made. Signal intensity increased exponentially with temperature, but two abrupt stopping regions appeared. The existence of some modification of the mechanism (zipper-like autocatalytic

6.Solid-state NMR was used in various steps such as the characterization of original PVC and thermally degraded samples. Structural change can be visually understood by the appearance of a new peak. Since the peak area is directly proportional to the amount of functional group, a whole understanding of the

elimination) under uniform heating conditions became apparent.

region. Presence of well-ordered region was sug-

), WAXD rings, and solid-state

**118**

We wish to express our hearty thanks to Mr. H. Sugisawa (JEOL), Prof. Y. Nozawa (Tohoku University), and Mr. T. Katoh (Yamagata University) for NMR measurements. Thanks are also expressed to Prof. M. Matsuda, Prof. T. Miyashita, and Dr. F. Bae (Tohoku University) for many conveniences in solid-state ESR measurements. The valuable discussion on IR spectroscopic data with Prof. M. Tasumi (University of Tokyo) is also greatly acknowledged.

## **Author details**


\*Address all correspondence to: gakusai-minagawa@memoad.jp

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References Chapter 7**

[1] Brown JF Jr, White DM. Stereospecific polymerization in thiourea canal complexes. Journal of the American Chemical Society. 1960;**82**:5671-5678

[2] White DM. Stereospecific polymerization in urea canal complexes. Journal of the American Chemical Society. 1960;**82**:5678-5683

[3] Krimm S, Berens AR, Folt VL, Shipman JJ. Assignment of C-Cl stretching modes of polyvinyl chloride. Indian Journal of Chemistry. 1958;**1512**:1513

[4] Krimm S, Berens AR, Folt VL, Shipman JJ. Carbon-chlorine stretching modes of polyvinyl chloride. Chemistry & Industry. 1959;**433**

[5] Shimanouchi T, Tasumu M. Normal coordinate treatment and assignment of IR absorption bands of polyvinyl chloride. Bulletin of the Chemical Society of Japan. 1961;**34**:359-365

[6] Tasumi M, Shimanouchi T. Polarized IR studies on polyvinyl chloride film-Effect of drawing. Spectrochimica Acta. 1961;**17**:731-754

[7] Shimanouchi T. "Vibrational Spectroscopy–Historical Basis and its Chemical Applications", by Memorial Event Group for Celebration of 60 Years Old of Prof. Shimanouchi, T. Tokyo: University of Tokyo; 1977

[8] Tsuruta T. Polymer Synthetic Reactions. Rev. ed. Tokyo: Nikkan Kogyo Shinbun; 1959

[9] Chatani Y. In: Ohtsu T, Takayanagi M, editors. In Progress in Polymer Science, Japan. Tokyo: Kodansha; 1977

[10] Minagawa M, Yamada H, Yamaguchi K, Yoshii F. γ-Ray irradiation canal polymerization conditions

ensuring highly stereoregular (>80%) poly(acrylonitrile). Macromolecules. 1980;**25**:503-510

Aliasing Compromises

*Jürgen M. Schmidt*

analysis referring to experimental <sup>3</sup>

attempt to resolve the bimodal <sup>3</sup>

aminoacid sidechain, protein structure

benefits from the measurement of <sup>3</sup>

**1. Introduction**

(**Figure 1**).

**121**

**Abstract**

Staggered-Rotamer Analysis of

Polypeptide Sidechain Torsions

Circular undersampling and the ensuing aliasing effect are demonstrated to compromise nuclear magnetic resonance (NMR)-based molecular torsion-angle

staggered-rotamer model, also known as Pachler model. This popular model is flawed insofar as it systematically produces counterintuitive probabilities for the two minor constituents out of the total three rotamers, to the effect that the apparent circular mean direction of the molecular bond conformation is inflected about its main rotamer angle, a situation that apparently went unnoticed for more than 50 years. The principal reason for systematic errors lay in the model's ill-conceived

crete points on the circle, thereby conflicting with the Nyquist-Shannon sampling theorem. An anti-aliasing approach is being offered that helps improve the results.

**Keywords:** circular distribution, directional data, probability density, torsion angle

Atom-atom bonds in a molecule often give rise to rotational degrees of freedom,

Finding out how two parts on either side of a rotatable bond relate to each other,

of a few Hertz, these are magnetic interaction parameters between atoms X and Y in

also known as torsion angles. A torsion angle, also known as dihedral angle, is formed by three consecutive bonds in a molecule and defined by the angle between the two outer bonds projected onto a plane perpendicular to the central bond

that is, assigning a value to the torsion angle, presents one of the challenges in molecular structure determination. A molecule adopting different geometric arrangements—without breaking or making bonds—is said to exhibit distinguishable conformers. Nuclear magnetic resonance (NMR) spectroscopy [2] is uniquely positioned to help characterize not only static molecular structure, but also dynamical processes that involve interconversion between conformers on a short, typically nanosecond timescale. Studying torsion-angle geometry and dynamics by NMR

conformation, staggered-rotamer equilibria, discrete Fourier transform, sampling theorem, undersampling, anti-aliasing, vicinal coupling constants, <sup>3</sup>

*J*-coupling constants when employing the

*J*-coupling-angle dependency by a mere three dis-

*J* coupling constants [3]. Typically on the order

*J*,

[11] Yoshii F, Abe T, Hayakawa N. Radiation-induced polymerization of vinyl chloride in urea canal complex as studied by broad line NMR. Kobunshi Ronbunshu. 1975;**32**:429-432

[12] Minagawa M, Narisawa I, Sugisawa H, Hasegawa S, Yoshii F. Solid state characterization and the thermal properties of stereoregular poly(vinyl chloride) prepared by urea clathrate polymerization. Journal of Applied Polymer Science. 1999;**74**:2820-2825

[13] Tasumi M. Private Communication

[14] Sakurada I, Nanbu K. On the polymerization by γ–irradiation on VC/urea inclusion compound. Kogyo Kagaku Zasshi. 1960;**81**:1011-1012

[15] Bovey F. Chain Structure and Conformations of Macromolecules. NY: Academic Press; 1982. p. 84

[16] Bellamy LJ. Infrared Spectra of Complex Molecules. 3rd ed. Vol. 1. London: Chapman and Hall; 1975. pp. 38-50

[17] Minagawa M, Katoh T, Yatabe J, Sato N, Matsuyama T. Solubility, discoloration, and 13C NMR spectra of stereoregular poly(vinyl chloride) prepared by urea clathrate polymerization at low temperatures. Preprints of Annual Meeting of the Fiber Society, Shanghai, May 25-27, 2015

[18] Bovey F. Chain Structure and Conformations of Macromolecules. NY: Academic Press; 1982. pp. 115-118

## **References Chapter 7**
