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The crystal structure of isotactic poly(2-vinylpyridine) (iP2VP) established in 1977 by Puterman et al. is shown to conform to a recently proposed frustrated packing scheme which involves three isochiral three-fold helices packed in a trigonal unit-cell, and observed in a number of polymers and biopolymers. Single crystals of iP2VP grown from thin films at high temperature (Tc = 200°C) display highly unusual morphologies with six (100) growth sectors but a three-fold overall symmetry apparent through different lame&r thicknesses in adjacent growth sectors, and oblique growth facets of three of the sectors. These features are morphological manifestations of the frustration of the helix packing, and support the P3 1or P32 space group of the unit-cell. The different lamellar thicknesses are mainly due to an isothermal thickening process, which has different impacts depending on the nature of the growth faces. Analysis of the growth features of frustrated structures can be of help when dealing with finer details of theories of polymer crystal growth

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Two analogous series of thermotropic main-chain polyesters, poly(alkyl-4,4’-diphenoxy terephtbalate)s and poly(alky1 terephthaloyl-bis4-oxybenzoate)s, have been analyzed by dielectric techniques. Analysis of the dielectric properties as a function of temperature and frequency show three main processes, termed (α, /3 and /3*. The cx transition has been associated with the glass transition of the amorphous phase. The low-temperature processes /3 and /3* have been related to the local motion of internal and external polar groups in the mesogenic unit. The activation energy and dielectric strength values associated with these relaxations have been determined, and a very important effect of the crystalline order on these parameters has been observed. The effect of the thermal history on the dielectric behaviour has also been studied

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This theoretical work evaluates the errors in average molecular weights due to instrumental broadening when a size exclusion chromatograph is fitted with ideal on-line Mn orMw, sensors, and a correction method is proposed to compensate for such errors. The basic assumptions are that linear homopolymers are analyzed, and that the instrumental broadening is uniform. It was verified that an ideal molar mass detector systematically underestimates the polydispersity and that such bias may be simply obtained from the spreading function polydispersity. The correction method uses an estimate of the instantaneous polydispersity. Such function can be directly obtained from the spreading function alone, since it is proven to be little dependent on the shape of the analyzed MWD

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A new 2,2’-bis(furyl)benzidine (FurylBZ) with a well-defined conjugation length was synthesized, and its polyimide was prepared through thermal imidization of the poly(amide acid) obtained from the polymerization with pyromellitic dianhydride. FurylBZ monomer and its polyimide film were characterized to exhibit intense blue light emission with a relatively narrow peak width in the photoluminescence. The relative fluorescence quantum yield was measured at room temperature to be 0.52 for FurylBZ in 1,Cdioxane and 0.074 for the polyimide in films. The polyimide was thermally stable up to 400°C. The polyimide is amorphous, due to the bulky fury1 side groups. However, the polyimide chains were favorably aligned in the film plane due to the rod-like chain characteristic

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A guest-host system of a nonlinear optical (NLO) arylphosphine oxide and polyhydroxystyrene (PSOH) has been investigated for secondorder nonlinear optics. The synthesized NLO-active arylphosphine oxides show spectroscopic properties in accordance with the proposed structures using n.m.r. spectrometry. These NO-active arylphosphine oxides and polymer matrix exhibit optical transparency down to 400 nm, and excellent thermal stability (Td > 345°C). An NLO-active chromophore with short absorption wavelength is desirable for application in frequency doubling. Moreover, the excellent thermal stability of the chromophore will prevent its decomposition during the poling process at elevated temperatures. The homogeneity of these guest-host NLO polymers are confirmed using scanning electron microscopy @EM). The second-order nonlinearity and temporal stability of these NLO polymers were also reported. The relationship between molecular motion and temporal stability are studied by dielectric analysis

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The formation of a polyethylene/polyurethane blend polymer via in situ polymerization of diols and diisocyanate monomers dispersed in a molten polyethylene matrix was investigated in an internal mixer. Two urethane systems were used in this study. The evolution of the blend morphology with increasing molecular weight of the polyurethane phase was discussed. The difference in viscosity between the minor and major phases has a controlling influence on the qualitative compounding behaviour exhibited. Furthermore, the viscosity ratio appears to be the physical parameter which governs the blend morphology development. The phase inversion was observed at ηd/ηm = 0.05. Beyond the phase inversion point, Wu’s model (Polym. Eng. Sci., 1987, 27, 335) quantitatively predicts the decrease of the size morphology with increasing molecular weight of the polyurethane phase. Nevertheless, high solubility of isocyanate monomers and low solubility of alcohols in molten polyethylene induce an imbalance stoichiometry which limits the degree of polymerization (molecular weight) during the blending process. A pre-polymerizing

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A water-insoluble dye was used to probe the particle nucleation loci in the semibatch emulsion polymerization of styrene (ST). Most of the dye molecules are present in the monomer droplets and some of them are solubilized in the monomer-swollen micelles. The extremely hydrophobic dye molecules cannot diffuse from the monomer droplets and micelles to the growing latex particles. Thus, determination of the amount of dye incorporated into the resultant latex particles provides valuable information on the particle nucleation mechanism. The mixed modes of particle nucleation (micellar and homogeneous nucleation) were proposed when the surfactant concentration ([S]) is above its critical micelle concentration (CMC). In the absence of micelles (i.e., [S] < CMC) most of the latex particles are produced via homogeneous nucleation. Monomer droplet nucleation cannot be ruled out because an appreciable amount of dye still can be detected in the resultant latex particles. The influence of the initiator concentration on the particle nucleation mechanisms was also investigated. The experimental data, again, support the proposed mixed modes of particle nucleation when [S] > CMC. Homogeneous nucleation plays an important role in the particle formation period when [S] < CMC

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The relationship between the charge-recombination luminescence (CRL), weak light emitted after u.v.-irradiation, and the development of properties during isothermal cure of epoxy/amine thermosetting resins was investigated. The changes in CRL were compared with the transitions and changes in properties during cure as measured through dynamical mechanical analysis on separate samples cured in a rheometer. It was shown that gelation did not lead to any detectable change in CRL, whereas vitrification caused a pronounced increase in CRL. Measurements on fully cured systems at different temperatures confirmed that CIU only was observed when the system was in the glassy state. It was also found that the decay kinetics of the CRL signal were essentially independent of the temperature and of the degree of cure of the sample

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The equation for polymer concentration fluctuation derived from Onuki’s equations of motion is coupled with Onuki’s postulate for the partial stresses generated by concentration fluctuation to formulate the dynamic structure factor S(q,t) [t is time and q the magnitude of the scattering vector]. The actual calculation is made for systems in which the elastic relaxation modulus L(t) is given by a linear combination of n exponential functions. It is shown that the corresponding S(q,t) consists of n + 1 exponential functions of time, and that the relative strengths and decay rates of these functions are related by a set of algebraic equations to the diffusion coefficient and cooperative diffusion coefficient, as well as the parameters characterizing L(t). These equations for n = 2 are used to analyze dynamic light scattering data on semidilute solutions of a polyisobutylene fraction in isoamyl isovalerate (0 solvent) and n-heptane (good solvent). The results give the instantaneous moduli of the solutions which are well compared with the rubbery plateau moduli from viscoelastic measurements, and the friction coefficients which are identical for both solvents when compared at comparable polymer concentrations

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The organic-inorganic hybrid interpenetrating network (IPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by 29Si n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100-300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50-100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size lo-20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network

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