Study of segmental orientation in poly (vinyl chloride)/poly (α-methyl-α-n-propyl-β-propiolactone) blends by fourier-transform infrared spectroscopy

Fourier-transform infrared (FTIR) spectroscopy has been used to investigate the segmental orientation of poly(vinyl chloride) (PVC)/poly (α-methyl-α-n-propyl-β-propiolactone) (PMPPL) blends in uniaxially stretched samples over a wide range of compositions and draw ratios. The results indicate that for pure PVC, syndiotactic segments reach a higher degree of orientation than isotactic segments and gauche conformations. Similarly, for pure PMPPL, crystalline segments orient more than amorphous segments at any given elongation. Thus, for both polymers, the higher orientation is obtained for the more rigid segments or those located in a more rigid (crystalline) phase. The addition of the macromolecular plasticizer PMPPL has no effect on the orientation of PVC syndiotactic segments, but it lowers the orientation of PVC gauche conformations, suggesting that the polyester is located in the amorphous regions of PVC. Finally, the PMPPL orientation function initially decreases with the addition of PVC and thereafter remains constant. The results are discussed in terms of interpenetrating networks and relaxation processes.     

Poly(vinyl chloride)‐based miscible blends: Changes induced in the structural characteristics and in dielectric α relaxation of pure poly(vinyl chloride)

In this work we investigate by means of dielectric relaxation spectroscopy how segmental motions occurring in poly(vinyl chloride) (PVC) are modified by blending of PVC with small amounts of two different homopolymers: crystalline poly(ϵ‐caprolactone) (PCL) and glassy syndiotactic poly(methylmethacrylate) (sPMMA). The dynamics of the α relaxation of PVC is severely changed by blending it with PCL or sPMMA becoming faster or slower, respectively. Simultaneously, the shape of the relaxation function is being importantly altered. It shows a stronger non‐Debye character being broader and strongly temperature‐dependent. This fact leads us to calculate distributions of relaxation times for the blends that are wider in comparison to the one obtained for pure PVC. Complementary X‐ray diffraction measurements have been performed in order to assure the absence of crystallinity in the blends, and some small variations can be deduced at the level of interchain structural correlations of PVC. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 234–247, 2000     

Synthetic thermally reversible gel systems. VIII. Poly(vinyl chloride)–dioxane

When interpreted by network theory, equilibrium swelling measurements on poly-(vinyl chloride) (PVC) film in dioxane and moduli measurements on the equilibrium swelled films yield values for the approximate molecular weight between thermally reversible crosslinks and for the number of these crosslinks per polymer chain. These values are in reasonable agreement with the thermodynamic analysis of PVC–dioxane gels by Takahashi, Nakamura, and Kagawa and with the premise that three-dimensional network formation in these gels occurs by crystallization of a very limited number of syndiotactic sequences per chain having a sequence length of between 8 and 10. Failure to observe fusion endotherms by DTA on PVC–dibutyl phthalate gels supports the view that PVC gels have a low crystalline crosslink density and a low heat of crosslinking. The heat of crosslinking obtained by the method of Eldridge and Ferry shows only moderate agreement with expectations based on the heat of fusion of PVC and the number of repeating units per PVC chain passing through a crystalline crosslink in a PVC–dioxane gel.     

A study of wet PVC gels by raman spectroscopy

Raman spectroscopy has been used to study PVC gels made in cyclohexanone in the wet state at concentrations from 21 to 93% by weight of PVC. Parallel and perpendicular spectra were obtained in the C-Cl stretching region, and after subtraction of the solvent spectrum they were analyzed into a set of overlapping peaks due to various structural components. The positions of the peaks found were in good agreement with those found earlier for PVC samples in the solid state. The fractional contribution of the areas of peaks assigned to crystalline material to the total area under the C-Cl stretching region was used to estimate the crystallinity of the gels, and changes in their depolarization ratios and relative intensities were interpretated as providing further evidence for the presence of two types of crystallites in PVC gels. From a determination of the crystallinity at the gel transition point and reasonable assumptions, the contributions of the two types of crystallites to the total crystallinity were estimated.     

NMR spectrum of poly(vinyl chloride)

The 100-MHz proton NMR spectra of commercial and laboratory-prepared poly(vinyl chloride) (PVC) have been measured in various solvents at high temperature (80–150°C). Tacticity in PVC was determined by the analysis of the β-proton spectrum. The spectrum was calculated assuming that the PVC chain consists of tetrad sequences of monomer units and that their distribution in the chain is described by a simple Bernoulli-sequence statistics with a P_m (the probability of isotactic placement) of 0.45 for commercial PVC polymerized at 50°C. Tacticity calibration curves based on measurements made for the polymer in pentachloroethane and β-dichlorobenzene were established, and they provide a simple method for the measurement of tacticity in PVC directly from the observed spectra. Excluding samples prepared in butyraldehyde solution, the formation of syndiotactic structures in PVC (prepared by free-radical polymerization) was found to be favored by lowering the polymerization temperature. This preference is due to an increase in the activation enthalpy of 510 cal/mole which is required for forming an isotactic placement in the chain during the propagation step.     

X-ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)

X-ray diffraction scans and infrared absorption spectra for the C-CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x-ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C-CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.     

Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm^?1, while a crystalline Raman band is found at 1147 cm^?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.     

Non-resonance micro-Raman spectroscopic studies on crystalline domoic acid and its aqueous solutions

Domoic acid (DA) is a neurotoxin naturally present in the marine ecosystem. Since DA's toxicity has been explained by its molecular structure and particularly because of its ethylenic double bond, spectroscopic investigation of this molecule is of importance. We carried out Raman spectroscopy on crystalline DA and on DA in aqueous solutions (28,000-25 ng DA/mL) and assigned Raman modes in comparison with the Raman spectra of its substructures. Noise-free, clear Raman signal from the solutions containing low concentrations of DA were obtained by applying the drop coating deposition Raman (DCDR) technique. Raman spectra reveal that crystalline DA exists in the zwitterionic form. The Raman spectra of the DA aqueous solutions were analysed in the light of their pH whereas the variation in the spectra was attributed to the hydration, the degree of protonation and crystallinity of the solid film. We show that DCDR can be applied for the rapid detection of domoic acid down to 25 ng DA/mL (0.025 ppm).     

Experimental and DFT generated Raman study of two bent-core monomeric liquid crystalline compounds

The temperature dependence Raman spectra of two liquid crystalline compounds defined by the chemical formula of 3,5-difluoro-4?-(4-pentylcyclohexyl)-(1,1?-biphenyl)-4-carbonitrile and 3,4,5-trifluoro-4?-(4-pentylcyclohexyl)-1,1?-biphenyl is being first reported in this study. These compounds are bent-core monomers and their bent nature has been verified by the Density Functional Theory (DFT). The temperature-dependent Raman spectroscopy has been widely used in understanding the effects of temperature-based phase transitions on the molecular vibrations. The same spectroscopic technique; helps to understand various phase transitions temperature in the liquid crystalline compounds (LC) and also their molecular arrangements during the phase transitions. This study has successfully revealed the nature of intermolecular interactions between the investigated compounds during the phase transitions and the correlation between the observed Raman spectra and the measurement temperature. The contributions of different types of chemical bonds in the investigated LC compounds to their recorded Raman spectra have also been discussed in detail. In predicting the observed Raman spectra, the theoretical Raman spectra obtained from the DFT calculation was used as a reliable tool. In the light of the calculated data, the peak position, line width, and integral intensity data for each band in the observed Raman spectra were reported.     

Vibrational assignments for the CCL stretching region of the Raman spectrum of poly(vinyl chloride)

It is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm^–1. Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation.     

Conformation and vibrational spectra of 1,5-hexadiyne (bipropargyl)

The infrared spectra of 1,5-hexadiyne (bipropargyl) as a vapour, liquid and crystalline solid and in several solvents have been recorded. Raman spectra were obtained for the liquid (including polarization measurements), the crystal and for several solutions.The data were interpreted in terms of two conformers, trans and gauche, in the vapour and liquid states and one, the trans, in the crystalline form. Interpretation of the spectra in terms of the conformational equilibria was not straightforward, and firm conclusions could not be drawn from the spectra alone. Vibrational assignments were made, supported by normal coordinate calculations.     

Vibrational spectra and rotational isomerism of fluoroacetone

Infrared spectra have been redetermined for fluoroacetone in the vapor, liquid, and solid states, and Raman spectra have been obtained for the liquid. There are two rotational isomers present in the liquid, but only the more polar form is present in the crystalline solid and only the less polar form is present in the vapor. Vibrational assignments were made for the two rotamers with the aid of normal coordinate calculations that utilized a twenty-five parameter valence force field.     

Conformational behaviour and vibrational spectra of cyclopropyl methyl ketone and methyl cyclopropyl-carboxylate

Infrared spectra in the vapour, liquid, and crystalline states and Raman spectra in the liquid and crystalline states have been obtained for cyclopropyl methyl ketone and for methyl cyclopropylcarboxylate. In cyclopropyl methyl ketone, the dominant conformer in the liquid and vapour states, the cis, has been shown to exist exclusively in the crystal. In methyl cyclopropylcarboxylate, the conformer dominant in the liquid and vapour states has been demonstrated to exist in the crystal. Vibrational assignments are made for the ring modes and for those modes which are sensitive to conformational changes.     

Absorption and vibrational spectra of the surface properties of molecular monolayers with large light-induced dipole alterations

Absorption and surface-enhanced Raman spectra of monolayers of retinal and styryl pyridinium dyes were obtained. The results have yielded new information on the absorption properties of these highly polarizable molecules. Information on the structure of the monolayer films have been deduced from the vibrational spectra. Enhancement mechanisms have been characterized and vibrational assignments have been made for the surface-enhanced Raman spectra of these monolayers.     

Raman spectra and structure of biphenyl isoatomers (the S0, S1, T1 states and the cation and anion radicals)

The Raman and transient resonance Raman spectra of biphenyl (BP) and its perdeuterated analogue (BP-d₁₀) in three different electronic states (S₀, S₁ and T₁) and in two different ionized states (cation and anion) have been recorded in solution. The S₀ Raman spectra have also been measured for the crystalline state. The obtained set of spectra are analysed on the basis of the established vibrational assignments for the ground state of the planar (crystal) and the non-planar (solution) structures. The analysis suggests that BP in solution exists as a twisted structure in the S₁ state, but that it takes planar or nearly planar structures in the T₁, the cationic and the anionic states.     

不同结构形态的纳米氢氧化钕的Nd3+增强电子拉曼光谱的研究

利用X射线粉末衍射、透射电子显微术、电子衍射和场发射电子扫描显微术，对不同方法制备的形态、颗粒大小不同的纳米Nd（OH）3进行钕离子的增强电子拉曼光谱研究，发现晶体结构、形态不同的纳米Nd（OH）3由于配位环境变化，导致钕离子的电子拉曼光谱在2600-1600cm^-1附近拉曼谱带的峰形、峰位和峰的数目产生显著变化。     

Dynamics of structurally disordered poly(vinyl chloride)

Following our previous studies on poly(vinyl chloride) the influence of the existence of head-to-head defects on the vibrational properties and on the vibrational spectra of syndiotactic planar zig-zag poly(vinyl chloride) has been studied. The dynamical aspects and the spectroscopic consequences of the existence of such a kind of defects in an otherwise structurally regular polymer chain are discussed and some comments are made on the use of frequency correlations from model compounds for the interpretation of the infrared and Raman spectra of polymers. The dependency of a few characteristic frequencies on chain length is discussed.     

Fourier-transform infrared study of conformational changes in plasticized poly(vinyl chloride)

Fourier-transform infrared spectroscopy has been used for the detection of conformational changes induced by plasticization in atactic poly(vinyl chloride) (PVC). The amount of short trans syndiotactic sequences decrease upon plasticization. This change depends on the amount and kind of plasticizer. Difference spectra emphasize changes in the distribution of gauche defects in the chains as a function of temperature in plasticized PVC films.     

A Raman spectroscopic study of photochromic benzothiazolium dyes

Resonance Raman spectra using several excitation wavelengths have been obtained in the region 300–1750 cm⁻¹ for two photochromic benzothiazolium dyes containing a crown ether ring. Bands arising from both cis- and trans-isomers have been distinguished by comparing the spectra observed at different resonances and under different sample conditions. Preliminary assignments of the bands have been made, allowing insight into the changes in structure and bonding which occur on photoisomerization.