Dielectric properties of aromatic polyesters: Relaxation behavior of poly(diethylene glycol terephthalate)

The dielectric behavior of a low molecular weight fraction of poly(diethylene glycol terephthalate) has been studied over the frequency range 10² to 10⁵ Hz for temperatures between ?67 and +51°C. Two relaxations, α and β, which exhibit pseudoactivation energies of 52 and 8 kcal/mole, respectively, have been found. The α relaxation, associated with the glass transition of the polymer, is amenable to a Williams–Landel–Ferry (WLF) analysis. The dipole moment ration 〈μ²〉/Nm² (where 〈μ²〉 is the mean square dipole moment of a chain consisting of N bonds and m² is the average of the squares of the bond moments) has also been calculated using the dielectric data obtained for the polymer in the undiluted state. The calculations yield 〈μ²〉/Nm² = 0.710, a value in very good agreement with that obtained from measurements in solution.     

Random-coil configurations of the polyformals. VI. Dipole moments of the stereochemically variable polymer prepared from 4-methyl-1,3-dioxolane

Mean-square dipole moments 〈μ²〉₀ for the (atactic) poly(4-methyl-1,3-dioxolane) chain [CH₂OCH(CH₃)CH₂O? ] were determined from dielectric-constant measurements carried out on two fractions dissolved in benzene. Simple examination of the chain structure leads to the predictions that this polymer should have a significantly larger value of 〈μ²〉₀ than poly(1,3-dioxolane) itself, but that 〈μ²〉₀ should be nearly independent of stereochemical structure. The first expectation is confirmed by the experimental results obtained, and the second by calculated results based on rotational isomeric state theory.     

Influence of the chemical composition and comonomer distribution on the dipole moments of 3,3-dimethyloxetane/tetrahydrofuran copolymers

Experimental values of the dipole moment ratio 〈μ₂〉/nm² and its temperature coefficient d ln 〈μ₂〉²/dT, where 〈μ₂〉 is the mean-square dipole moment of a chain with n skeletal bonds and m² is the mean square of the skeletal bond dipole moments, are reported for well-characterized random copolymers of 3,3-dimethyloxetane and tetrahydrofuran. The results are interpreted in terms of the rotational isomeric state theory in a manner consistent with that developed for the parent homopolymers. The theory gives a good account of the experimental results corresponding to copolymers in which the mole fraction of tetrahydrofuran lies in the range 0.11–0.89. It is found that whenever the copolymerization obeys Bernouillan statistics, the dipole moments are quite insensitive to the comonomer distribution. The theoretical analysis suggests, however, that the value of the dipole moment ratio of alternating copolymers of 3,3-dimethyloxetane and tetrehydrofuran should be near that of the parent homopolymer of lower polarity.     

Configurational properties of aromatic polyesters: Dipole moments of poly(diethylene terephthalate) chains

Dielectric constants have been determined for a fraction of poly(diethylene terephthalate) in benzene at several temperatures. The data indicate that the dipole moment ratio 〈μ²〉/Nm² is somewhat higher than that of poly(ethylene oxide), and its temperature coefficient is in the vicinity of zero. Both the dipole ratio and its temperature coefficient are in very good agreement with those predicted by the rotational isomeric state theory. Using this theory, the unperturbed dimensions of poly(diethylene terephthalate) were calculated and it was found that (〈r²〉/M)_∞ = 0.80 Ų (g mol wt)^?1, a value intermediate between those of poly(ethylene oxide) (0.57) and poly(ethylene terephthalate) (1.05).     

Random-coil dimensions and dipole moments of propylene–vinyl chloride copolymers

Mean-square unperturbed dimensions 〈r²〉₀ and dipole moments 〈μ²〉 have been calculated for propylene–vinyl chloride copolymers by means of rotational isomeric state theory. The calculations indicate that for these chain molecules 〈mu;²〉 is much more sensitive to chemical sequence distribution than is 〈r²〉₀, a conclusion in agreement with results of previous studies of ethylene–propylene copolymers and styrene-substituted styrene copolymers. In the case of propylene–vinyl chloride chains, both 〈r²〉₀ and 〈μ²〉 are most strongly dependent on chemical sequence distribution in the case of copolymers which are significantly syndiotactic in stereochemical structure. At equimolar chemical composition, increase in average chemical sequence length generally increases 〈r²〉₀ but decreases 〈μ²〉. Under some conditions, values of these statistical properties go through a minimum with increase in the reactivity ratio product r₁r₂, thus complicating the use of experimental values of these properties in the characterization of chemical sequence distributions in these copolymers.     

The Influence of External Electric Field on Local Orientations and Phase Transitions in Polymer Liquid Crystals (PLCs)

The starting point is our previous study of influence of the internal molecular mean field of dipole‐dipole interactions on local orientation and phase transitions in polymer liquid crystal (PLC) systems of longitudinal chains.^{[1, 2]} Electric dipoles are created by LC mesogen moieties. The longitudinal PLC is a macromolecule of consecutively copolymerized LC and flexible polymer sequences. We now amplify the model by inclusion of dipole‐external electric field interactions. We find that the external fields can seriously modify the local orientational order of the system and affect phase transition parameters dependent on that order. In particular, the external fields induce the formation of disoriented nematic phases with negative values of the second order orientation parameter 〈P₂〉 for LC sequences in the longitudinal PLCs while the first order parameter 〈P₁〉 is positive. However, some rapid decreases in 〈P₁〉 are observed at points of positive‐to‐negative transitions of 〈P₂〉; thus the LC disorientation manifests itself. The limiting case of the monomer liquid crystal (MLC) systems is included also.     

Dipole moment characterization of phenol–, o-cresol–, and p-cresol–formaldehyde resins

Dipole moments and their temperature dependence have been measured in p-dioxane for fractionated novolac phenol–, o-cresol–, and p-cresol–formaldehyde polymers. The phenol–formaldehyde fractions covered a molecular weight range of 200 to 6100, and the limiting dipole moment ratio 〈μ²〉/xm² is 1.48. The p-cresol–formaldehyde dipole-moment ratio at a DP of 4 is 2.47, whereas the phenol–formaldehyde dipole-moment ratio is 1.40. That for o-cresol–formaldehyde is intermediate in value. The dipole-moment temperature coefficients are positive for p-cresol chains and negative for the phenol–formaldehyde chains. These results indicate that the hydroxyl groups along the p-cresol–formaldehyde polymer are highly ordered, with the aromatic rings closer to the sterically hindered planar position than in the phenol–formaldehyde polymers.     

Steady-state and pulsed studies of the radiation-induced polymerization of methyl methacrylate

In order to quantify our fluorogenic molecular probe studies on the radiation-induced polymerization of methyl methacrylate (MMA), measurements have been made of the monomer conversion, C _M, and polymer molecular weight distribution as a function of dose for bulk MMA polymerized by steady-state (⁶⁰Co γ-rays) and nanosecond-pulsed (3 MeV electrons) radiation. In all cases, C _M was found to increase close to linearly with dose up to ca. 30%. Above this conversion, autoacceleration of polymerization (the gel or Trommsdorff effect) occurs in the γ-irradiated samples. From the low-conversion steady-state data, using dose-rates of 0.21 and 2.7 Gy/s, the parameter 〈k _p〉 ² G(R^.)/2〈k _t〉 = 0.011 and 0.015 lmol^-1 s^-1 (100 eV)^-1 respectively have been determined (with 〈k _p〉 and 〈k _t〉 the average rate coefficients for bimolecular propagation and termination respectively, and G(R^.) the yield of the chain-initiating free radicals per 100 eV (G = 1 (100 eV)^-1 0.1036 μ mol J^-1)). From the 5 Hz repetitive pulse data the value of 〈k _p〉 G(R^.) = 1700 lmol^-1 s^-1 (100 eV)^-1 has been determined. Taking 〈k _p〉 = 342 lmol^-1 s^-1 from the literature results in G(R^.) = 5.0 (100 eV)^-1 and 〈k _t〉 = 2.7 × 10⁷ lmol^-1 s^-1.     

Excluded-volume effect for various chain models. I. Application to optical anisotropy and end-to-end distance of linear polymers

A study of the effect of excluded volume on the mean-square optical anisotropy 〈γ²〉 and the mean-square end-to-end distance 〈R²〉 has been carried out for polymer chains of up to 2000 bonds. The calculations have been made for models assuming (a) equiprobability of internal rotations and (b) interdependence of short-range intramolecular interactions. All the results indicate that 〈γ²〉 is practically insensitive to the excluded-volume effect. Concomitantly the behavior of 〈R²〉 has been analyzed.     

Molecular structure,vibrational spectra,first order hyper polarizability,NBO and HOMO–LUMO analysis of 4-amino-3(4-chlorophenyl) butanoic acid

The Fourier transform infrared (FT-IR) and Fourier transform Raman (FTR) spectra of 4-amino-3(4-chlorophenyl) butanoic acid were recorded in the regions 4000–400 cm⁻¹ and 4000–100 cm⁻¹, respectively, in the solid phase. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and Raman scattering activities, highest occupied molecular orbital, lowest unoccupied molecular orbital energy, energy gaps and thermodynamical properties such as zero-point vibrational energies, rotational constants, entropies and dipole moment were computed at the Hartree–Fock/6-31G(d,p) and three parameter hybrid functional Lee–Yang–Parr/6-31G(d,p) levels of theory. The vibrational studies were interpreted in terms of potential energy distribution (PED). The results were compared with experimental values with the help of scaling procedures. Most of the modes have wave numbers in the expected range and are in good agreement with computed values. The first order hyperpolarizability (β_total) of this molecular system and related properties (β, μ, 〈α〉 and Δα) are calculated using HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond-like weak interaction has been analyzed using natural bond orbital (NBO) analysis by using B3LYP/6-31G(d,p) method. The results show that electron density (ED) in the σ1 and π1 antibonding orbitals and second-order delocalization energies E⁽²⁾ confirm the occurrence of intramolecular charge transfer (ICT) within the molecule.     

Conformations et stereoregularite de poly 2 vinyl pyridines—I Etude experimentale

Study of the average molecular optical anisotropy 〈γ²〉 of atactic and isotactic poly 2 vinyl pyridines of low polydispersity has been carried out in various solvents by means of depolarized Rayleigh scattering (D.R.S.) Experimental evidence (D.R.S. and viscosity) for free charges both on atactic and isotactic chains has been found in methanol and dimethyl formamide; their effect on 〈γ²〉 has been analyzed. The influence on molecular optical anisotropy of thermodynamic quality of the solvent has also been studied. Finally, comparison of the experimental optical anisotropies of atactic and isotactic structures reveals the strong effect of stereoregularity on the physical property under study.     

Composition and Homogeneity of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈В〉 Solid Precursors and LiNbO<Subscript>3</Subscript>〈В〉 Batches

Nb₂O₅〈В〉 solid precursors and LiNbO₃〈В〉 batches prepared on their basis, which can be used for preparing optical-quality lithium niobate single crystals and pore-free piezoelectric ceramics, have been studied by laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The compositions of powdery samples pelletized without binder have been determined. The calculated mean-square deviations Sr of laser ablation ICP-MS have been used to show a homogeneous distribution of the boron dopant over Nb₂O₅〈В〉 precursors and LiNbO₃〈В〉 batches.     

Factors determining the reactivity of the bromine atom toward haloalkanes

Experimental data concerning reactions of the bromine atoms with haloalkanes and carbonyl compounds (25 reactions) have been analyzed within the intersecting parabolas model. The following factors have an effect on the activation energy of these reactions: enthalpy of reaction, triplet repulsion, electronegativity of reaction center atoms, dipole–dipole and multidipole interactions of the reaction center with polar groups, and the interaction of π electrons with electrons of the reaction center. The increments characterizing the contribution from each factor to the activation energy of the reaction have been calculated. The increment ΔEμ, which characterizes the dipole–dipole interaction in the transition state, and the dipole moment of the polar group (μ) are correlated by the following empirical equation: ln(ΔE _μ/Σμ) = ?0.14 + 0.47(ΔE _μ/Σμ) ? 0.024(ΔE _μ/Σμ)².     

Solution properties of poly(N-vinyl carbazole)—II. Thermodynamic properties in various solvents

Thermodynamic properties of dilute solutions of Poly-N-vinyl carbazole obtained by cationic polimerization have been studied by viscometry in various solvents. The validities of some excluded volume theories have been tested and the unperturbed dimensions have been calculated. The dependence of molecular dimensions, 〈s²〉, on molecular weight and viscometric equations have also been determined.     

Theoretical analysis of conformational energies,unperturbed dimensions,and dipole moments of poly(dichlorophosphazene)

A theoretical analysis of the conformational energies of poly(dichlorophosphazene) (PDCP) is presented. The results indicate that the bond pair P? N? P possesses a considerable conformational freedom, whereas the bond pair N? P? N is relatively rigid. This difference explains the low glass transition temperatures T_g and large end-to-end distances measured for polyphosphazenes. A statistical model containing four rotational isomers (ie., trans, gauche, cis, and negative gauche) is developed and used to calculate unperturbed dimensions and dipole moments of PDCP. The results, obtained at 25°C with n = 400 skeletal bonds (200 repeating units), were C_n = 〈r²〉₀/nl² = 13.5; C_T = 10³d(ln〈r²〉₀)/dT = ?3.0 K^?1; D_n = 〈μ²〉/nμ = 0.35; D_T = 10³d(ln〈μ²〉)/dT = ?3.4 K^?1. All the calculated magnitudes are extremely sensitive to the energy E_σ that controls the statistical weights of the conformations tg, tc, tg^?, gt, ct, and g^?t relative to tt for the bond pair P? N? P. A qualitative explanation for this sensitivity is discussed.     

Unperturbed dimensions of polystyrene derivatives. II. Poly-3,4-dichlorostyrene and poly-p-cyclohexylstyrene

The relationship of intrinsic viscosity to the number-average molecular weight has been obtained for poly-3,4-dichlorostyrene and poly-p-cyclohexylstyrene in a few solvents. Values of (〈L²〉₀/M)^1/2 have been estimated for poly-3,4-dichlorostyrene and poly-p-cyclohexylstyrene through the use of the treatment of Stockmayer and Fixman. The values of (〈L〉₀/M)^1/2 have been obtained as 2.18 ± 0.08 and 2.52 ± 0.07 for poly-3,4-dichlorostyrene and poly-p-cyclohexylstyrene, respectively. The σ value of a series of polystyrene derivatives has been found to increase with the bulk of side groups. This seems to indicate that the σ value is mainly determined by the steric repulsion between side groups.     

Second and third-order nonlinear optical properties and molecular parameters of azo chromophores: semiempirical analysis

The static and frequency dependent average polarizability (〈α〉), first- and second-hyperpolarizabilities (〈β〉 and 〈γ〉) and highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energies of nonlinear optical chromophores with nitro acceptors 1–5 have been investigated by using the Austin Model 1 (AM1), Modified Neglect of Diatomic Overlap (MNDO), MNDO with d orbitals (MNDO-d), Parameterization Method 3 (PM3), Recife Model 1 (RM1) and Parameterization Method 6 (PM6) methods within a time-dependent Hartree–Fock (TDHF) approaches. The electronic properties of chromophores 1–5 have been reported by employing two-state model calculated at Zerner's spectroscopic version of the Intermediate Neglect of Differential Overlap singly excited configuration interaction (ZINDO/S-SCI) method. Also, the molecular hardness (η) and electronegativity (χ) parameters have been obtained by using molecular frontier orbital energies. The 〈α〉, 〈β〉, 〈γ〉 HOMO, LUMO energies, η and χ parameters have been investigated with respect to the choice of different semiempirical methods.     

Polarized Raman studies of crystalline and amorphous orientation in polyethylene

Polarized Raman intensities have been obtained from thin films of oriented low-density polyethylene (PE) immersed in silicone oil to minimize surface scattering. Studies were made using the 1170 cm^?1 crystalline band and the 1081 cm^?1 amorphous band, and from these the orientation averages 〈cos² θ〉 and 〈cos⁴ θ〉 were calculated. These were found to compare favorably with the values of 〈cos² θ〉 for the polymer chain in the crystalline and amorphous phases obtained from measurements of infrared dichroism. Both orientation averages could be theoretically fitted by using reasonable parameters.     

Influence of excluded volume on the conformational property of tail-like chain on the simple cubic lattice

The influence of excluded volume on the conformational property of linear tail-like chain with one end attached to a flat surface is investigated by means of dynamic Monte Carlo method. Conformational properties such as mean-square end-to-end distance 〈R²〉, mean-square radius of gyration 〈S²〉 and mean asphericity parameter 〈A〉 are calculated for random walking (RW) and self-avoiding walking (SAW) tail-like chains on the simple cubic lattice. We find that the EV has nearly the same effect on 〈R²〉 as on 〈S²〉: (1) 〈R²〉_SAW/〈R²〉_RW≈〈S²〉_SAW/〈S²〉_RW∝n^0.204±0.05, where n is the chain length, and (2) the limiting value of 〈R²〉/〈S²〉≈7.7 for both chains. The distribution P(R) of the SAW tail-like chain can be expressed as a R⁴ correction of that of the RW one. We find that the value 〈A〉 of the SAW tail-like chain is bigger than that of the RW tail-like chain for all chain lengths, and the limiting values are 0.446±0.006 and 0.403±0.005 respectively.