Characterisation of the comonomer composition and distribution of copolymers using chemometric techniques

Chemometric techniques have been applied to FTIR and DSC data to correlate polymer composition. Since structural differences in the polymers with only hydrocarbon structure, often cause subtle changes in spectra, the ability of chemometric techniques is required to discern these differences. FTIR spectra and thermal fractionation using DSC were measured for 28 types of polyethylenes (PE) varying in chain branching type, content and distribution. Unsupervised clustering methods such as principal component analysis (PCA) and supervised discriminant analysis were used to classify the PEs according to their structural class. The DSC data was the more successful in both classifying PEs according to their class. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cationic copolymerization of 3-methyltetrahydrofuran and 3,3-dimethyloxetane: Structural study of the copolymers

The bulk cationic copolymerization of 3-methyltetrahydrofuran and 3,3-dimethyloxetane was studied at 0°C using acetylhexafluoroantimonate as initiator. Values of the composition of the copolymers and the dyad and triad probabilities were obtained by ¹H- and ¹³C-NMR spectroscopy. A kinetic scheme was proposed for this copolymerization and the values of the reactivity ratios were directly determined from the dyad probabilities. The experimental values of the triad probabilities were found to be in good agreement with those calculated from the reactivity ratios.     

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.     

Acrylonitrile–4-vinylpyridine copolymers effect of comonomer sequence distribution on properties

Acrylonitrile–,4-vinylpyridine copolymers were prepared in chloroform solution at 60°C with AIBN as initiator. Copolymer compositions were determined from their 15.01-MHz ¹³C-NMR spectra. Reactivity ratios of r_AN = 0.093 and r_4VP = 0.32 were calculated by the Kelen and Tudos method. The run number, number-average sequence lengths, and monomer sequence distributions were also calculated. The T_g values of the copolymers, their dye uptake, and degree of alkaline hydrolysis were influenced by the overall copolymer composition but particularly by the monomer sequence distribution in the copolymers.     

Triblock copolymers based on cyclic ethers: Preparation and properties of tetrahydrofuran and 3,3-bis(azidomethyl) oxetane triblock copolymers

Novel energetic thermoplastic elastomers (TPEs) based on tetrahydrofuran (THF) and 3,3-bis (azidomethyl) oxetane (BAMO) were prepared in this present study by cationic living polymerization. A bifunctional catalyst, triflic anhydride [(CF₃SO₂)₂)O] was selected to be an initiator for the polymerization THF and BAMO. The resulting polymers were characterized by IR, NMR, and DSC, which demonstrated that triblock copolymers with A-B-A type were formed. The polymers were indicated from thermogravimetric analysis (TGA) to have decomposed at approximately 243°C. The decomposition enthalpies were determined by DSC. These enthalpies were varied with the poly-BAMO contents of the copolymers. The synthesized polymers exhibited relatively good mechanical properties and thermoplastic characteristics at room temperature. © 1994 John Wiley & Sons, Inc.     

Model calculations of the distribution function of molecular weight and chemical composition of binary statistical copolymers

Model calculations based on the kinetics of free-radical copolymerization were carried out for the distribution functions of molecular weight and chemical composition, and for heterogeneity parameters of statistical copolymers. The calculations were conducted so as to depict the dependence of the heterogeneity parameters on the degree of conversion and to make possible an estimate of the maximal heterogeneity of statistical copolymers at given monomer reactivity ratios and rate constants. A comparison of the results obtained with a critical analysis of the feasibility of the determination of heterogeneity parameters by light scattering has revealed that, for statistical co polymers, this method can in principle be used with satisfactory accuracy only with samples of high degree of conversion and high molecular weight. The frequently used approximation P = 0 cannot be applied with out careful verification.     

Classification of homogeneous ethylene-octene copolymers based on comonomer content

Ethylene-octene copolymers prepared by Dow's INSITE™ constrained geometry catalyst technology present a broad range of solid-state structures from highly crystalline, lamellar morphologies to the granular morphology of low crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphological features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic superstructure. Type III polymers with densities between 0.93 and 0.91 g/cc have thinner lamellae and smaller spherulites. Type II materials with densities between 0.91 and 0.89 g/cc have a mixed morphology of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temperature, and the granular, nonlamellar morphology. © 1996 John Wiley & Sons, Inc.     

Electronic and vibronic dipole moments of CH2D

Isotopic substitution of a hydrogen atom by deuterium turns a non-polar ion such as CH₃⁻ into a non-centrosymmetric system, CH₂D⁻, suitable for rotational spectra detection in space. The vibrational contribution to the dipole moment of the ion is investigated in this paper. The electronic potential surface has been obtained in a first-order CI, starting from a full valence active space built by using projected localized orbitals, to which core valence correlation effects have been added to account for rehybridization. The vibrational functions are obtained in a basis of harmonic oscillators. Three levels of vibrational treatment are presented, i.e. harmonic, non-coupled and coupled modes. The final result for the transition moment in the lowest vibrational level, μ_v = 0.327 Debye, shows that CH₂D⁻ should be observed and may be a useful tracer of CH₃⁺ in interstellar chemistry.     

On the calculation of molecular dipole moments

The approximation made in the calculation of molecular dipole moments by including only the point charges and the atomic dipoles is evaluated in different all-valence (or all)-electrons MO procedures. In the CNDO method, the use of the exact formula after retransformation of the atomic basis into Slater orbitals gives poorer values than the Pople-Segal's procedure.     

Geometrical derivatives of dipole moments and polarizabilities

Molecular dipole moments and polarizabilities, as well as their geometrical derivatives, are given analytical expressions for multiconfiguration self-consistent-field and configuration interaction wavefunctions. By considering the response of the electronic wavefunction induced by electric field and geometrical displacement terms in the Hamiltonian, the response of the total electronic energy to these terms is analyzed. The dipole moment and polarizability are then identified through the factors in the energy which are linear and quadratic in the electric field, respectively. Derivatives with respect to molecular deformation are obtained by identifying factors in these moments which are linear, quadratic, etc., in the distortion parameter. The analytical derivative expressions obtained here are compared to those which arise through finite-difference calculations, and it is shown how previous configuration-interaction-based finite difference dipole moment and polarizability derivatives are wrong. The proper means of treating such derivatives are detailed.     

Amine-hydrogen halide complexes: experimental electric dipole moments and a theoretical decomposition of dipole moments and binding energies

The Stark effect has been observed in the rotational spectra of several gas-phase amine-hydrogen halide complexes and the following electric dipole moments have been determined: H(3)(15)N-H(35)Cl (4.05865 +/- 0.00095 D), (CH(3))(3)(15)N-H(35)Cl (7.128 +/- 0.012 D), H(3)(15)N-H(79)Br (4.2577 +/- 0.0022 D), and (CH(3))(3)(15)N-H(79)Br (8.397 +/- 0.014 D). Calculations of the binding energies and electric dipole moments for the full set of complexes R(n)()(CH(3))(3)(-)(n)()N-HX (n = 0-3; X = F, Cl, Br) at the MP2/aug-cc-pVDZ level are also reported. The block localized wave function (BLW) energy decomposition method has been used to partition the binding energies into contributions from electrostatic, exchange, distortion, polarization, and charge-transfer terms. Similarly, the calculated dipole moments have been decomposed into distortion, polarization, and charge-transfer components. The complexes studied range from hydrogen-bonded systems to proton-transferred ion pairs, and the total interaction energies vary from 7 to 17 kcal/mol across the series. The individual energy components show a much wider variation than this, but cancellation of terms accounts for the relatively narrow range of net binding energies. For both the hydrogen-bonded complexes and the proton-transferred ion pairs, the electrostatic and exchange terms have magnitudes that increase with the degree of proton transfer but are of opposite sign, leaving most of the net stabilization to arise from polarization and charge transfer. In all of the systems studied, the polarization terms contribute the most to the induced dipole moment, followed by smaller but still significant contributions from charge transfer. A significant contribution to the induced moment of the ion pairs also arises from distortion of the HX monomer.     

Electro-optical investigations of the dipole moments of nanoparticles

In this paper, the electric properties of polar nanoparticles are examined. Special attention is paid to the terminology, classification and the physical bases of the different electric moments. A short history of the electro-optic studies of dipole moments of nanoparticles and the electro-optic Conferences is presented. The connection of the polar properties with the particle electric charge is considered. The potential of the colloid electro-optics for studying the properties of anisometric, anisotropic polar nanoparticles is discussed in details. Examples of such studies are presented. A comparative analysis is made of the potential of dielectric, electro-optic and dielectrophoretic measurements for studying the electric properties, size, shape and structure of polar nanoparticles.     

Crystallization behaviour of polyoxetanes: poly(oxetane), poly (3,3-dimethyloxetane) and poly(3,3-diethyloxetane)

The influence of the crystallization temperature on the melting behaviour and crystalline structure of polyoxetane (PTO), poly(3,3-dimethyloxetane) (PDMO) and poly(3,3-diethyloxetane) (PDEO) has been studied using differential scanning calorimetry (DSC) and X-ray techniques. When PTO is crystallized by cooling from the relaxed melt state, only the orthorhombic modification is obtained. However, PDMO and PDEO can be crystallized in two different modifications depending on crystallization temperature. The effect of the substituents in the stability of main chain conformations in crystalline state is discussed.