Conformation transition and molecular mobility of isolated poly(ethylene oxide) chains confined in urea nanochannels

Inclusion compounds formed from host small molecules and guest polymers have provided a novel platform to study the behavior of isolated polymer chains confined in nanochannels. In this article, the PEO chain conformation in the metastable poly(ethylene oxide) (PEO)-urea inclusion compound (IC) and its transition was characterized via a combination of different analytical methods. Based on the FTIR and Raman spectroscopy results, PEO chains in the metastable tetragonal IC are tentatively assigned to the tgg′ conformation. The structural changes of the metastable tetragonal IC to the stable trigonal form were observed via in situ FTIR and ex situ WAXD. The transformation is a kinetic solid-solid process and can even occur at room temperature. The activation energy of about 222 kJ/mol indicates that the transition occurred via cooperative disruption of several hydrogen bonds. Measurement of the laboratory frame spin-lattice relaxation time T₁ (¹³C) shows that molecular motions of the nanoconfined PEO chains are more intensive than the neat crystalline PEO but weaker than those of the neat amorphous PEO. Second harmonic generation microscopy demonstrates that the trigonal IC exhibits stronger nonlinear optical activity than the tetragonal IC. The intermolecular hydrogen bonding is attributed to the driving force for the transformation of the metastable tetragonal IC into the stable trigonal form.     

Investigation of the structure of poly(vinyl alcohol)-iodine complex hydrogels prepared from the concentrated polymer solutions

The structure and dynamics of poly(vinyl alcohol) (PVA)-iodine complex hydrogels that were prepared from concentrated PVA solutions have been characterized by high-resolution solid-state ¹³C NMR spectroscopy. The fully relaxed dipolar decoupling (DD)/MAS ¹³C NMR spectrum indicates that the hydrogels contain at least two components, a highly mobile and broader components. The former is assigned to the soluble or well water-swollen PVA chains that are not closely associated with the PVA-iodine complexes, whereas the latter may be mainly ascribed to the aggregated PVA chains that are produced by the formation of the PVA-iodine complexes because no diffraction peaks due to the conventional PVA crystallites are observed by wide-angle X-ray diffractometry. Furthermore, ¹³C spin-lattice relaxation time (T_1C) analyses reveal that the broader component is composed of the highly restricted component probably assignable to PVA molecular chain aggregates containing the PVA-iodine complexes and the less mobile component. As for the former component, their CH resonance line measured by the T_1C-filtering method is successfully resolved into 7 constituent lines by the least-squares curve fitting. The statistical analysis of the integrated intensities of the constituent lines thus obtained also reveals that the probability f_a for the formation of intramolecular hydrogen bonding in the successive two OH groups along each chain and another probability f_t of the trans conformation are, respectively, as high as 0.86 and 0.88. This fact indicates that the PVA molecular chain aggregates containing the PVA-iodine complexes should be composed of PVA segments with the trans-rich conformation and the PVA-iodine complexes therein may also be formed with these several trans-rich segments surrounding the rod-like polyiodine cores in agreement with the so-called aggregation model. Moreover, several new diffraction peaks that should be interpreted in terms of the hexagonal structure are observed for the PVA-iodine complex hydrogels in the low 2θ region in the wide-angle X-ray diffraction (WAXD) profile measured by a strong X-ray source at SPring-8. This suggests the necessity of more detailed WAXD characterization to propose a new structure model, which should be referred to as the hexagonal aggregation model, for the PVA-iodine complexes.     

NMR determination of crystallinity for poly(?-l-lysine)

Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the ¹H spin-spin relaxation times (T₂^H), the ¹³C spin-lattice relaxation times (T₁^C), and the ¹³C NMR signal shapes between the crystalline and the non-crystalline phases. The observed ¹H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed ¹³C relaxation curves obtained from the Torchia method were double-exponential. The ¹³C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the ¹H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T₂^H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T₁^C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment.     

Mechanical behavior of double-C60-end-capped poly(ethylene oxide)

Double-C₆₀-end-capped poly(ethylene oxide) (PEO) possesses good mechanical properties arising from a network-like structure due to the aggregation of C₆₀. The tensile strength is about 20 MPa, the elongation at break exceeds 640% and the fracture toughness is more than 110 MJ/m³. The material also possesses shape recovery ability. In contrast, single-C₆₀-end-capped PEO does not possess good mechanical properties.     

Role of boric acid in the formation of poly(vinyl alcohol)-iodine complexes in undrawn films

The role of boric acid in the formation of poly(vinyl alcohol) (PVA)-iodine complexes in undrawn films has been investigated by using wide-angle X-ray diffraction (WAXD) and high-resolution solid-state ¹³C NMR spectroscopy. From UV-vis absorption spectroscopy, it is confirmed that boric acid is necessary for the formation of the complexes in films that are treated with I₂/KI aqueous solutions at relatively low I₂ concentrations. The WAXD profiles indicate that, irrespective of the presence of iodine, crystallite sizes perpendicular to the chain axis become smaller by the addition of boric acid in the swelling media. Moreover, small crystallites and surficial parts of larger crystallites may be partially dissolved in the swelling process with water and boric acid suppresses the re-crystallization in the drying process with or without iodine. The ¹³C spin-lattice relaxation time analysis reveals that there exist two components called the mobile and the less mobile components in the films and the latter component, which contains the complexes and the crystalline component, is increased in the fraction by the presence of boric acid. The evaluation of the CH resonance line shows that some of the intermolecular hydrogen bonds are broken by boric acid, which increases the intramolecular hydrogen bonds. The CH₂ lineshape analysis also reveals that the gauche fraction is appreciably increased in the less mobile component by the addition of boric acid. These facts suggest that boric acid may promote the formation of PVA-iodine complexes particularly in the surficial areas of the crystallites probably by reducing the molecular mobility of the PVA chains by causing cross-linking among them.     

Solid-state C NMR investigation of the structure and hydrogen bonding for stereoregular poly(vinyl alcohol) films in the hydrated state

The structure and hydrogen bonding of the hydrated stereoregular poly(vinyl alcohol) (PVA) films have been investigated by high-resolution solid-state ¹³C NMR spectroscopy. It is found by the ¹³C spin-lattice relaxation analysis that there exist three components with different T_1C values assigned to the crystalline, less mobile and mobile components for the hydrated syndiotactic PVA (S-PVA) and highly isotactic PVA (HI-PVA) films. The line shape analysis indicates that the probability of intramolecular hydrogen bonding is appreciably increased in the crystalline region for the S-PVA films by the hydration but a slightly helical structure, which is probably allowed by the formation of the successive intramolecular hydrogen bondings along the chains in the crystalline region, seems not to undergo any significant change by the hydration for HI-PVA. This fact indicates that intramolecular hydrogen bonding is more stable in the hydrated state in the crystalline region. As for the less mobile component, the line shape of the CH resonance line for the hydrated S-PVA or HI-PVA films is found to be very similar to that of the corresponding crystalline component, probably being due to the successive formation of intermolecular or intramolecular hydrogen bonding in the interfacial region, which mainly contributes to the less mobile component, for the S-PVA or HI-PVA films even in the hydrated state. The mole fractions of the mm, mr and rr sequences are also estimated for the mobile component that is produced in each stereoregular PVA sample by swelling with water and it is concluded that no prominent preferential partitioning of the mm, mr and rr sequences occurs in the crystalline and noncrystalline regions for the PVA films with different tacticities.     

Grafting of poly(ethylene oxide) onto C60 fullerene using macroazo initiators

In order to improve the solubility of C₆₀ fullerene in conventional solvents, grafting of hydrophilic poly(ethylene oxide) (PEO) by utilizing the radical-trapping nature of C₆₀ fullerene was investigated. Macroazo initiators containing a poly(ethylene oxide) unit, known as Azo-PEO, were prepared at various molecular weights by the reaction of 4,4′-azobis(4-cyanopentanoyl chloride) with poly(ethylene glycol) methyl ether. PEO radicals formed by thermal decomposition of Azo-PEO were successfully trapped by C₆₀ fullerene to give PEO-grafted C₆₀ fullerene. Their structures were confirmed by FT-IR spectroscopy, size exclusion chromatography, UV-vis spectroscopy, and differential scanning calorimetry. When Azo-PEO with low-molecular weight was reacted with C₆₀ fullerene, a bis-adduct, C₆₀-(PEO)₂, and a tetrakis-adduct, C₆₀-(PEO)₄, were formed. In contrast, in reactions with Azo-PEO of higher molecular weight, only the bis-adduct was formed, and no formation of the tetrakis-adduct was observed. The structure of bis-adduct was found to be 1,4-type. The solubility of C₆₀ fullerene in water, THF, methanol, and other conventional organic solvents was remarkably improved by grafting of PEO. In addition, the thermal stability of PEO was dramatically increased by grafting onto C₆₀ fullerene.     

Effect of nano-porous Al2O3 on thermal, dielectric and transport properties of the (PEO)9LiTFSI polymer electrolyte system

Thermal, electrical conductivity and dielectric relaxation measurements have been performed on (PEO)₉LiTFSI+10 wt.% Al₂O₃ nano-porous polymer electrolyte system. It is observed that the conductivity enhances substantially due to the presence of the filler particles with different surface groups. The highest enhancement is found for the filler particles with acidic groups followed by basic, neutral, and weakly acidic. The results reveal that the filler particles do not interact directly with poly(ethelene) oxide (PEO) chains indicating that the main chain dynamics governing the ionic transport has not significantly affected due to the filler. The results are consistent with the idea that the conductivity enhancement is due to the creation of additional sites and favourable conduction pathways for ionic transport through Lewis acid-base type interactions between the filler surface groups and the ionic species. This is reflected as an increase in the mobility rather than an increase in the number of charge carriers. A qualitative model has been proposed to explain the results.     

Structural characterization of maleic anhydride grafted polyethylene by C NMR spectroscopy

Maleic anhydride grafted polyethylene, [2,3-¹³C₂] MA-g-PE, which was synthesized with ¹³C labeled maleic anhydride [2,3-¹³C₂] MA in solution, was characterized by ¹³C NMR spectroscopy in order to make clear the structure of graft groups. The results reveal that [2,3-¹³C₂] MA-g-PE has succinic anhydride oligomeric grafts with a terminal unsaturated MA ring in addition to well-known saturated succinic anhydride oligomeric grafts and that the former grafts are longer but fewer than the latter.     

NMR study of temperature-induced phase separation and polymer-solvent interactions in poly(vinyl methyl ether)/D2O/ethanol solutions

The changes in the dynamic structure during temperature-induced phase transition in D₂O/ethanol solutions of poly(vinyl methyl ether) (PVME) were studied using NMR methods. The effect of polymer concentration and ethanol (EtOH) content in D₂O/EtOH mixtures on the appearance and extent of the phase separation was determined. Measurements of ¹H and ¹³C spin-spin and spin-lattice relaxations showed the presence of two kinds of EtOH molecules: besides the free EtOH expelled from the PVME mesoglobules there are also EtOH molecules bound in PVME mesoglobules. The existence of two different types of EtOH molecules at temperatures above the phase transition was in solutions with polymer concentration 20 wt% manifested by two well-resolved NMR signals (corresponding to free and bound EtOH) in ¹³C and ¹H NMR spectra. With time the originally bound EtOH is slowly released from globular-like structures. From the point of view of polymer-solvent interactions in the phase-separated PVME solutions both EtOH and water (HDO) molecules show a similar behaviour so indicating that the decisive factor in this behaviour is a polar character of these molecules and hydrogen bonding.     

Solid-state C NMR investigation of the structure and dynamics of highly drawn polyethylene—detection of the oriented non-crystalline component

The structure and dynamics of highly drawn polyethylene samples were studied by solid-state ¹³C NMR spectroscopy. The analyses of the ¹³C spin-lattice relaxation time (T_1C) and the ¹³C spin-spin relaxation time (T_2C) have revealed that at least three components with different T_1C and T_2C values, which correspond to the crystalline, less mobile non-crystalline, and rubbery amorphous components, exist for these materials, as in the case of isothermally crystallized samples. However, another component with a mass fraction of 0.13-0.18 exists which has a ¹³C chemical shift very close to that of the orthorhombic crystalline phase but has an extremely small T_1C. Since this component is believed to have the all-trans conformation, it is termed fast all-trans. The chemical shift anisotropy (CSA) spectra for various samples that have small T_1C values have been recorded and resolved into those of the non-crystalline and fast all-trans components. As expected, the CSA spectra of the less mobile non-crystalline and rubbery amorphous components that have the smallest T_1C values display only a slight asymmetry. In contrast, the CSA spectrum of the fast all-trans component displays higher asymmetry. However, the spectrum is still much narrower than that of the normal orthorhombic crystalline phase, indicating a high degree of motional averaging. It is proposed that this component should be a highly oriented non-crystalline component, which may exist as taut tie-molecules traversing the non-crystalline region. To account for the narrow CSA, this component must undergo rapid fluctuation with large amplitudes at the torsional potential minimum in each C-C bond and possibly an additional random jump or diffusional rotation around the chain axis. Additional measurements obtained by aligning the draw axis of the sample parallel or perpendicular to the static magnetic field indicate that the fast all-trans component is oriented along the drawing direction and subjected to rapid motion around the chain axis.     

Use of 13C nuclear magnetic resonance distortionless enhancement by polarization transfer pulse sequence and multivariate analysis to discriminate olive oil cultivars

Distortionless enhancement by polarization transfer (DEPT) pulse sequence was used to set up a quantitative high-resolution ¹³C nuclear magnetic resonance (NMR) method to discriminate olive oils by cultivars and geographical origin. DEPT pulse sequence enhances the intensity of NMR signals from nuclei of low magnetogyric ratio. The nuclear spin polarization is transferred from spins with large Boltzmann population differences (usually protons) to nuclear species characterized by low Boltzmann factors, e.g., ¹³C. The signal enhancement of ¹³C spectra ensures the accuracy of resonance integration, which is a major task when the resonance intensities of different spectra must be compared. The resonances of triglyceride acyl chains C _n:0, C_18:1, C_18:2, and C_18:3, were also assigned. Multivariate analysis was carried out on the 35 carbon signals obtained. By using variable reduction techniques, coupled with standard statistical methods—partial least squares and principal components analysis—it was largely possible to separate the samples according to their variety and region of origin. With one problem variety removed, 100% prediction of the three remaining varieties was achieved. Similarly, by using the three regions with greatest representation in the data, all but one of a test set of 34 samples were correctly predicted. Thus, the composition of olive oils from different cultivars and of different geographical origin were compared and successfully studied by multivariate analysis. These considerations in conjunction with the structural elucidations of triglyceride molecules demonstrated that ¹³C NMR is among the most powerful techniques yet described for analysis of olive oils.     

Strain-Relief Patterns and Kagome Lattice in Self-Assembled C60 Thin Films Grown on Cd(0001)

We report an ultra-high vacuum low-temperature scanning tunneling microscopy (STM) study of the C₆₀ monolayer grown on Cd(0001). Individual C₆₀ molecules adsorbed on Cd(0001) may exhibit a bright or dim contrast in STM images. When deposited at low temperatures close to 100 K, C₆₀ thin films present a curved structure to release strain due to dominant molecule–substrate interactions. Moreover, edge dislocation appears when two different wavy structures encounter each other, which has seldomly been observed in molecular self-assembly. When growth temperature rose, we found two forms of symmetric kagome lattice superstructures, 2 × 2 and 4 × 4, at room temperature (RT) and 310 K, respectively. The results provide new insight into the growth behavior of C₆₀ films.     

Dielectric relaxation of poly(n-hexyl isocyanate) in concentrated solutions of polybutadiene

We report the dielectric relaxation in a ternary system in which a trace amount of poly(n-hexyl isocyanate) (PHIC) is dissolved in concentrated toluene solutions of polybutadiene (PB). The dielectric response is due to the rod-like PHIC molecules having high dipole moment along its chain contour. Solutions of PB form entanglement networks which retard the reorientation of the PHIC molecules. With increasing concentration (C_PB) of PB from 0 to 40 wt% the relaxation behaviour changed at a crossover concentration C_PB⁺. In the range below C_PB⁺, the relaxation time τ for reorientation of the PHIC molecules increased on account of the effect of entanglement. However above C_PB⁺, τ decreased and at the same time the relaxation strength decreased with increasing C_PB. The crossover concentration C_PB⁺ depended on the molecular weight M of the PHIC, i.e. C⁺_PB=0.13 at M=29,000, and C_PB⁺=0.25 at M=20,000. The decrease of the relaxation strength can be attributed to the reduction of the effective dipole moment due to the restriction of motions of the PHIC chains in entanglement networks of PB chains.     

CP/MAS C NMR analysis of the structure and hydrogen bonding of melt-crystallized poly(vinyl alcohol) films

The structure and hydrogen bonding of the melt-crystallized atactic poly(vinyl alcohol) (A-PVA) films, which were carefully prepared without significant thermal degradation, have been characterized by CP/MAS ¹³C NMR spectroscopy. The ¹³C spin-lattice relaxation analysis has revealed that there exist three components with different T_1C values, the crystalline, less mobile noncrystalline and mobile noncrystalline components, in good accord with the results for different PVA samples previously reported. It should be noted that the T_1C values of the crystalline and noncrystalline components are appreciably smaller for the melt-crystallized films than those for the un-annealed and annealed samples prepared by casting from the aqueous solution. The ¹³C NMR spectra of the crystalline and noncrystalline components are separately recorded by using the difference in T_1C and their CH lines are successfully resolved into three and seven constituent lines by the least-squares curve fitting, respectively. Moreover, the statistical analysis of the integrated intensities of the constituent lines thus obtained enables to determine the probability f_a for the formation of intramolecular hydrogen bonding in the successive two OH groups along each chain and another probability f_t of the trans conformation for the crystalline and noncrystalline components. It is found that the f_a value is relatively larger for the melt-crystallized films than those for the un-annealed and annealed samples. On the basis of these results, the features of the melt-crystallization and the resulting crystalline-noncrystalline structure are discussed by particularly considering effects of intra- and inter-molecular hydrogen bonding on the crystallization.     

Preparation and properties of C60-containing poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) was reacted with strong base NaH to yield pendant oxy anions, followed with nucleophilic addition to C₆₀. The resulted PVA(C₆₀-Na⁺)_n products were then converted to PVA(C₆₀H)_n by stirring with a strong acid cation exchanger of H⁺-form. Extraction of the C₆₀-containing PVAs by toluene, which is a good solvent for C₆₀, exhibits no color transfer to the toluene phase. The C₆₀-containing PVAs were identified by the characteristic IR and UV-Vis absorptions of C₆₀. The electrochemical behaviors in solution or in film state were investigated by cyclic voltammetric methods. The cyclic voltammogram of 4a shows a reduction peak at −2.30 V which should be due to the bonded C₆₀ chromophores. In the film state, obtained by coating C₆₀-containing PVA solution on graphite electrode, PVA(C₆₀-Na⁺)_n is much easily reduced and oxidized than PVA(C₆₀H)_n. Furthermore, the difference in this reduction and oxidation feasibility is enhanced with increasing C₆₀ content. However, coating with PVA(C₆₀H)_n or PVA(C₆₀-Na⁺)_n reduces the redox ability of the graphite electrode.     

Direct evidence of intramolecular rearrangement in skeletal isomerization of n-butane over bifunctional catalysts

Mechanisms of skeletal isomerization of n-butane over bifunctional catalysts, Pt–Cs_2.5H_0.5PW₁₂O₄₀ and Pt-sulfated ZrO₂, as well as the corresponding solid acids were studied using 1,4-¹³C₂-n-butane. The isotopic distributions of the reactant and product were analyzed with field ionization mass spectrometry, by which the parent peak patterns were obtained. It was found that 1,4-¹³C₂-n-butane was selectively isomerized to ¹³C₂-isobutane over these catalysts in the presence of H₂ at 423–523 K, while the corresponding solid acids gave isobutane with binomial distributions of ¹³C. These results clearly demonstrate that the skeletal isomerization of n-butane proceeded mainly via a monomolecular path with intramolecular rearrangement on both the bifunctional catalysts, while it occurred through a bimolecular path with intermolecular rearrangement on the solid acids. This difference in reaction mechanism is reflected on that in the selectivity to isobutane.     

Initial stages of Pt deposition on Au(111) and Au(100)

The deposition of Pt onto unreconstructed Au(111) and Au(100) was studied with cyclic voltammetry and in-situ STM. The latter revealed that in [PtCl₄]²⁻ containing electrolytes, both surfaces are covered by an ordered adlayer of the complex. For the adsorbed [PtCl₄]²⁻ a slightly compressed (√7×√7) R19.1°-structure was assumed for Au(111) and a (3×√10) for Au(100). In both cases, a rather high overpotential for Pt deposition was observed, most probably due to the high stability of the [PtCl₄]²⁻ complex. Nucleation of Pt starts mainly at defects like step edges for low deposition rates and three-dimensional clusters are formed. Due to the high overpotential, some nuclei appear also on terraces at random sites. Higher coverages of Pt lead to a cauliflower like appearance. It is not possible to dissolve the platinum clusters at positive potentials without severely roughening the gold surface. The [PtCl₄]²⁻ complex is oxidized to the [PtCl₆]²⁻ complex at about 0.7 V, when metallic Pt is on the surface.     

Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

Highly isotactic poly(vinyl alcohol) derived from tert-butyl vinyl ether. Part IV. Some physical properties, structure and hydrogen bonding of highly isotactic poly(vinyl alcohol) films

Some basic physical properties, structure and hydrogen bonding have been characterized for different stereoregular PVA films including highly isotactic PVAs (HI-PVAs), which were recently succeeded in synthesis, as functions of the mm fraction by using different analytical methods. The melting temperature, degree of crystallinity, and ¹³C spin-lattice relaxation time of the crystalline component are found to have their own clear minima at the mm fraction of about 0.4-0.5. This fact suggests that structural disordering associated with the decrease in crystallinity may be most strongly induced at this mm fraction. The formation of the new crystal form of PVA has been reconfirmed for HI-PVAs with the mm fractions higher than about 0.55 by FTIR spectroscopy and the structure and hydrogen bonding have been investigated in detail by solid-state ¹³C NMR spectroscopy. It is found that all OH groups are allowed to form successive intramolecular hydrogen bonding along the respective chains in the crystalline region for HI-PVAs with the mm fractions higher than about 0.7. Since these chains should contain some amount of r units even in the crystalline region, a slightly helical structure with a considerably long period may be adopted by them as an energetically stable state. On the basis of the line shape analysis of the CP/MAS ¹³C NMR spectra of the crystalline components, structural causes of the appearance of the minima of the physical values described above are also discussed in relation to the introduction of disordered units mainly associated with hydrogen bonding to the syndiotactic or isotactic sequences forming successive intermolecular or intramolecular hydrogen bonding, respectively.