The effect of temperature on the behavior of poly(o-chloroaniline) salts: conductivity and spectral studies

Conducting poly(o-chloroaniline) salis have been prepared by chemical polymerization of o-chloroaniline with five different acids. Composition and the extent of dopant in poly(o-chloroaniline) salt systems have been determined. Poly(o-chloroaniline) samples have been heat treated at four different temperatures 150, 200, 275 and 375°C and characterized by electron paramagnetic, infrared and electronic absorption spectral measurements. Thermal stabilities of the chemically synthesized poly(o-chloroaniline) salts have been studied by spectral methods. It was found that the polymer is apparently stable up to 200°C, and at around 275°C crosslinking takes place. It is inferred that the electron paramagnetic resonance signal observed in the conducting material does not arise from the current-carrying species, but rather from neutral paramagnetic species. No definite correlation exists between conductivity and the extent of dopant or spin concentration.     

Degradation of polymer mixtures. VIII. Blends of poly(vinyl acetate) with poly(methyl methacrylate)

The degradation of blends of PVA and PMMA in the form of films cast from a common solution of the polymers has been studied by TVA, TG, and EGA (evolved gas analysis) for acetic acid. Volatile degradation products have been characterized by spectroscopic and GLC techniques. Molecular weight, spectral and thermal stability changes in PMMA extracted from partially degraded blends have been examined. These blends behave in a closely analogous manner to PVC-PMMA blends already investigated. The results suggest that the PMMA component of the heterogeneous blends is modified in two ways: (1) in a destabilization reaction series initiated by attack of acetate radicals generated in the PVA phase which migrate into the PMMA phase, and (2) in a stabilization reaction involving conversion of ester side groups to acid and subsequently to anhydride ring structures which act as blocking points for depolymerization. The rate of acetic acid production in the blend is less than in PVA degraded alone. The mechanism of degradation of PVA is reconsidered in the light of these results.     

One dimensional main-chain crystallization kinetics of poly(3-octylthiophenes) investigated by infrared spectroscopy

Time-resolved infrared spectroscopy has been used to study the melt crystallization behavior of poly(3-octylthiophenes) (P3OT), which is a typical conductive polymer among the family of poly(3-alkylthiophenes) (P3ATs). It is found that, during the isothermal crystallization process at high temperature, the alkyl side chains of P3OT always keep in disordered state, whereas the ordering packing of conjugated backbone takes place. In order to reveal the structural changes and the crystallization kinetics corresponding to the main-chain ordering process, two spectral regions that associated with π–π stacking and the effective conjugation length of P3OT have been analyzed in detail. The characteristic IR bands of crystalline and amorphous phase are identified in each spectral region. Moreover, a simple spectral method has been proposed to calculate the evolution of crystallinity during the isothermal crystallization process of P3OT. Of particular note, the distinct one-dimensional growth kinetic of P3OT crystal has been revealed by Avrami analysis.     

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3683–3688, 1997     

Infrared spectroscopic study of solid films of poly(ethylene glycol) doped with cations

The infrared spectra of solid films, prepared on a silicon plate of poly(ethylene glycol) doped with various cations (Li⁺, Na⁺, K⁺, Ca²⁺ and Ba²⁺), have been measured. The spectral analysis indicates that the films are non-crystalline and essentially amorphous. The polymer chain is significantly disordered by assuming diverse conformational states. The interaction between the ether oxygens of the polymer and the cation, as estimated from the C---O stretching wavenumber, is correlated to the size of the cation; the interaction is stronger for the cation with larger size.     

Role of triplet states of polymethine dyes in photogeneration of electron-hole pairs in poly(N-epoxypropylcarbazole) films

The external magnetic field effects on the spectral and luminescent properties of film composites based on photoconductive poly(N-epoxypropylcarbazole) doped with cationic polymethine and merocyanine dyes have been studied. The magnetic field effects on the intensity and kinetics of delayed fluorescence and recombination luminescence have been revealed. These effects are explained by participation in the photogeneration of charged pairs of singlet-triplet intersystem crossing in excited dye molecules.     

Studies of poly(ortho-acylstyrenes). I. Syntheses and characterization

The syntheses of a number of o-acylstyrenes (o-acetyl through o-hexanoyl) have been described. Polymerizations were carried out radically at 80°C under high vacuum. While all polymerizations conform to the usual free radical kinetic scheme, rates are sensitive to the nature of the acyl substituent, and this has been ascribed to steric effects, the bulky substituents adjacent to the propagating radicals inhibiting the approach of monomer. Molecular weight and polydispersity data indicate that both combination and disproportionation occur during terminations. UV spectra consist of two absorptions associated with n → π^* and π → π^* transitions. ¹³C-NMR spectra have been analyzed and assignments made on the basis of spectral editing. The considerable variation of glass transition temperatures has been accounted for in terms of a combination of steric and dipolar interactions.     

New poly(phenylenevinylene)‐methyl methacrylate‐based photonic crystals

Monodisperse colloids have been prepared efficiently by copolymerization of methyl methacrylate and fluorescent first‐ and second‐generation poly(phenylenevinylene) dendrons under surfactant‐free emulsion polymerization conditions. The copolymers were characterized by UV–vis and fluorescence spectroscopy and size exclusion chromatography. Transmission electron microscopy revealed that the copolymers were microspheres with smooth surfaces and narrow dispersity. The bead diameter could be varied by changing the monomer/water ratio. The materials could be crystallized to give polymer opal photonic crystals. The emission was not affected by the periodic structure because of the large spectral distance between the emission and the pseudogap position. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2659–2665, 2010     

Influence of crystal polymorphism on crystallinity calculation of poly(l-lactic acid) by infrared spectroscopy

Vibrational spectroscopic methods have been used to determine the crystallinity of poly(l-lactic acid) (PLLA), which is the most popular bio-plastic today. However, it is found that influence of crystal polymorphism of PLLA on the quantitative method proposed for crystallinity calculation based on IR technique has seldom been considered. Herein, by preparing a set of PLLA specimens with different crystallinity and crystal forms, the absorption coefficient ratios between amorphous and crystal bands for evaluating the absolute crystallinity of PLLA α and α′ crystal form have been derived, respectively. In addition, a comparison of the proposed IR method with other techniques used to analyze crystallinity of PLLA such as X-ray diffraction (XRD) and differential scanning calorimetry (DSC) is presented. The origin of the disagreement on the results of quantitative measurements of crystallinity by different methods is also discussed. This study provides a simple spectral method to determine the crystallinity of PLLA with various crystal modifications.     

Vibrational analysis of poly(vinylidene fluoride)

A vibrational analysis has been carried out for the two crystalline forms of poly(vinylidene fluoride) (PVF₂). The Raman spectrum of the planar form of PVF₂ is also reported. The band assignments are made on the basis of the spectral properties including the infrared dichroism and Raman intensities. A force field is derived based on a force constant refinement procedure utilizing the frequency data for both crystal forms.     

Transition metal polymeric chelates: Spectral, magnetic, thermal behaviour of polymeric chelates of poly(resacetophenone diyl ethylene)s with Ni(II), Cu(II), Mn(II), Zn(II) and Co(II)

Polymeric chelates of the type [ML₂]_n where M = Ni(II), Cu(II), Zn(II) or Co(II), L = poly(resacetophenone diyl ethylene)s, andn= degree of polymerization, have been synthesized. Their structures have been elucidated on the basis of analytical, magnetic, electronic and IR spectral studies. Electronic spectra in conjunction with magnetic moments are in accord with an octahedral environment around the central metal ion in all polymeric chelates except Cu(II) and Zn(II) polymeric chelates which have been shown to possess square planar and tetrahedral geometries, respectively. IR spectral studies further suggest that the metal ions are coordinated through the oxygens of the carbonyl and the phenolic hydroxyl groups. All the chelates are paramagnetic except Zn(II), which is found to be diamagnetic.     

pH-induced structural changes of surface immobilized poly(L-lysine) by two-dimensional (2D) infrared correlation study

This paper reports the pH-induced structural changes in the surface immobilized poly(L-lysine)(PLL)film.Two-dimensional(2D) correlation analysis was applied to the Fourier transform infrared(FTIR)spectra of the surface-immobilized PLL film to examine the spectral changes induced by the alternations of the protonation state of the amino group in the side chain.Significant spectral changes in the FTIR spectra of the PLL film were observed between pH 7 and 8.The decrease in the protonation state of the amino group in the side chain induced spectral changes in the amino group as well as conformational changes in the alky]group in the side chain.From pH 1-8,the spectral changes in the amino and alkyl groups in the side chain occurred before those of the amide group in the main chain of the surface immobilized PLL film.     

New catalytic systems for the manufacture of poly(aspartic acid)

Aspartic acid (I), when heated to a temperature in excess of 180 °C, undergoes a solid-state condensation polymerization to afford the useful polymeric intermediate known as poly(succinimide) (II). Treatment of poly(succinimide) with aqueous base, such as sodium hydroxide, affords sodium poly(α,β-DL-aspartate) (III) also known as thermal poly(aspartate) (TPA). Acid catalysts, such as phosphoric acid have been added to the aspartic acid to afford higher-molecular-weight poly(succinimide) than is obtained in the non-catalyzed polymerization. Recently, new sulfur-based catalysts have been disclosed for the polymerization of aspartic acid. The sulfur-containing catalysts provide a route to highly biodegradable, low-color poly(aspartate)s in the molecular weight range of 2 000 to 20 000. A comparison of biodegradability, molecular weight, and spectral characteristics of the poly(succinimide)s and poly(aspartate)s derived from the catalyzed and non-catalyzed polymerizations is presented.     

Photoconductivity of poly(N-acryloylcarbazole)

The photoconductivity of poly(N-acryloylcarbazole) (PACz), with the pendant carbazolyl group only a short distance from the skeletal chain of the polymer but separated from it by a carbonyl group, is investigated and compared with that of poly(N-vinylcarbazole) (PVCz). There is no significant difference between PACz and PVCz in the temperature, light intensity, and spectral dependences of the photocurrent. The photoconductivity of PACz, however, is much inferior to that of PVCz and even to that of poly(N-carbazolylethylvinylether), a representative vinyl polymer with pendant carbazolyl groups far from the skeletal chain. The poor photoconductivity of PACz is discussed in relation to the intensity of the electronic interaction between neighboring carbazolyl groups in the polymer chain and to singlet exciton migration. It is attributed mainly to an extremely low efficiency of extrinsic carrier generation via a singlet exciton, which is due to the poor electron-donating character and the extremely short lifetime of a singlet exciton in the presence of the carbonyl group.     

Thermal degradation of poly(parabanic acid)

A variety of techniques were used to follow the thermal degradation of a poly(parabanic acid) (PPA-M). The kinetic data associated with the weight loss as a function of time at elevated temperatures indicates a random initiation process followed by depolymerization. Infrared and mass spectral techniques further confirmed the kinetic data by showing the presence of isocyanate and amide groups in addition to CO, CO₂, and nitric oxide gases being evolved. Incipient gelation occurs simultaneously with the formation of the amide. A reverse Hoffman rearrangement mechanism has been proposed which appears to be consistent with the available experimental data.     

Relaxations in poly(vinyl alcohol) and in poly(vinyl acetate) detected by fluorescence emission of 4-aminophthalimide and prodan

Steady-state and time-resolved emission spectroscopy (TRES) of the medium-sensitive probes 4-aminophthalimide (4-AP) and 6-propionyl-2-(dimethylamino)naphthalene (Prodan) were performed at 77 and 298 K in vacuum-sealed thin films of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). The two probes show similar red-edge effect in steady state emission and a red shift with time in TRES in PVA. In PVAc the red shifts are much smaller and the spectral shift for 4-AP is slower. 4-AP locates in highly polar environments in PVA, where H-bond interaction with the polymer is important. Prodan locates in less polar environments, as evidenced by the position of the emission maximum with respect to reference solvents. Consequently, the observed monoexponential spectral red shift with time of 4-AP in PVA and in PVAc is attributed to relaxation of the interaction of the probe with the hydroxy and acetate moieties, respectively. The more intense interaction of the lighter -OH moiety with the probes explains the greater and faster spectral shift observed in PVA compared to PVAc. The lifetime of this monoexponential spectral shift is independent of temperature in PVA and takes place with a highly negative activation entropy. This fact is attributed to a collective rearrangement of -OH groups to better interact with the excited state. This relaxation nevertheless does not account for the complete accommodation of the excited state. Prodan shows a linear variation of the spectral shift with time that can be explained by microheterogeneity. In PVA, the width at half-maximum of the emission spectra does not change with time for Prodan and it decays with a lifetime similar to the lifetime of the spectral shift in the case of 4-AP. The differences in the behavior of the probes are attributed to their different average location in the polymer matrix.     

Two-dimensional Raman and Raman optical activity correlation analysis of the alpha-helix-to-disordered transition in poly(L-glutamic acid)

Rich and complex Raman scattering and Raman optical activity (ROA) spectra have been measured monitoring the pH induced alpha-helix-to-disordered conformational transition in poly(L-glutamic acid). Two-dimensional (2D) correlation techniques have been applied to facilitate a comprehensive analysis of these two complementary spectral sets. Synchronous contour plots have identified band assignments of alpha-helical and disordered conformations, and have revealed bands characteristic of changes in the protonation state of the polypeptide. Asynchronous plots, on the other hand, have probed the relative sequential orders of intensity changes indicating a decrease in intensity of alpha-helical bands in the backbone skeletal stretch region, followed by a subsequent decrease in intensity in the extended amide III and amide I regions, underlying the appearance of disordered structure, including poly(L-proline) II (PPII) helix. The application of a 2D correlation 'moving' window has also disclosed two distinct phases during helix unfolding in the alpha-helix-to-disordered transition, occurring at approximately pH 4.9 and approximately pH 5.2, possibly a result of the difference in helical stability between the end and central regions of the alpha-helix. This paper demonstrates the potential value of combining 2D Raman, 2D ROA and moving window correlation techniques for the detailed investigation of complex and subtle changes of secondary structure during the unfolding mechanisms of polypeptides and proteins.     

The effect of temperature on the infrared spectra of poly(ethylene terephthalate)

Reversible and irreversible spectral changes are observed on heating of solvent-cast films of poly(ethylene terephthalate) (PET) between 30 and 230°C. The irreversible changes are due to the gauche-trans isomerization of the ethylene glycol segments and the corresponding changes in the symmetry and resonance characteristics of the aromatic rings. On the other hand, there are thermally reversible spectral changes. These reversible effects are primarily observed for the modes of the aromatic ring and the trans ethylene glycol segment. These reversible spectral changes include intensity variations and frequency shifts and are found to be linearly dependent on the measurement temperature. These reversible changes arise from changes in intermolecular and intramolecular forces as the temperature changes.     

Degradation of poly(terphenylenephthalide) at high temperatures

The thermal and thermooxidative degradation of poly(terphenylenephthalide) has been studied by thermal analysis, IR and UV spectroscopy, and mass spectrometry. On the basis of the spectral data and the chemical composition of degradation products, it has been shown that both the thermal and thermooxidative degradations of poly(terphenylenephthalide) are characterized by intramolecular cyclization reactions. Depending on the mode of closure of intermediates generated in the course of thermal decomposition of neighboring phthalide groups (head-to-head or head-to-tail), either phenyl-substituted anthraquinones, fluorenones, and fluorenes or symmetric and nonsymmetric dicyclic compounds containing end anthraquinone, fluorenone, and fluorene groups may be formed. The oxidation of poly(terphenylenephthalide) likewise gives rise to cyclic products—the compounds of xanthone and dibenzofuran series.     

Physico-chemical studies on the photostabilization of poly(1-butene) film

Thin films of poly(1-butene) with and withouto-phenanthroline bis(1,3-diphenyl triazine-1-oxide)-cobal(II) [I] in the temperature range of 233–333° K have been degraded in air from a UV light of 253.7 nm. The changes in weight average molecular weights, degree of degradation, quantum yields, enthalpy and free energy of activation, and carbonyl and hydroperoxide contents, were followed as a function of the time of irradiation. The inhibition effect ofI is discussed on the basis of the luminescence and UV spectral data. The chelateI behaves both as a thermal and UV stabilizer due to a combination of different kinds of activity in the same molecule.