Miscibility of a polyarylate with a liquid crystalline copolyester

The miscibility has been investigated for binary blends of a polyarylate (PAr) with a liquid crystalline copolyester of p-hydroxybenzoate and ethylene terephthalate units in a 6/4 molar ratio (PET/PHB). The binary blends were prepared by solution precipitation. The transitions of the PET/PHB have been measured with a rheometrics dynamic spectrometer. The phases in blends have been studied with a differential scanning calorimeter, by ther-mogravimetry and with a polarizing optical microscope. The blends exhibit two glass transitions (T_gs) over the composition range 10–90 wt %. The amorphous PET phase from the PET-PHB is found to be partially miscible with PAr, which leads to a decrease of the PAr T_g. The amount of this partially miscible portion of PET has been estimated by the Couch-man equation. On heat treatment of the blends at 250 to 300°C, transesterficiation takes place, as judged by the shift of the higher of the two T_gs. © 1993 John Wiley & Sons, Inc.     

Reinforcing thermosets with crystallizable solvents

This study demonstrates an approach to generate reinforcement in thermosetting polymers through crystal growth of crystallizable solvents. Emphasis is to identify the reaction conditions, which lead to suitable reinforcement in selected compounds. Crystallization behavior and miscibility of dimethylsulfone (DMS) in diglycidylether of bisphenol‐A epoxy monomer was investigated. Small angle laser scattering and optical microscopy were utilized to monitor phase separation and crystallization of DMS at different isothermal conditions during the cure process. It is shown that DMS crystals grow anisotropically to form faceted geometries and demonstrate possible structures to anchor into the epoxy matrix. The growth mechanism and the agility of crystals are shown to be affected by the cure reaction as well as depth of supercooling. A completely cured sample with 15 wt % DMS shows a broad map of rich morphologies from nanoscale particles to uniformly distributed macroscale, discontinuous fiber‐like crystals generated only by altering the curing conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 840–849, 2010     

Thermolysis of polyarylate model compounds

Thermal decompositions and pyrolyses of p-tert-butylphenol, 4,4'-isopropylidenediphenol (BPA), and their acetate and pivalate esters as model compounds for the polyarylate synthesis have been performed. Acetate esters decompose chiefly into phenols and ketene. Pivalate esters, unable to form ketene, are more stable. Acetates and pivalates undergo homolytic cleavage both at ester and alkyl groups. Styrene derivatives stabilize acetate esters, considerably reducing the amount of phenol formed during the decomposition. No intensely colored aromatic compounds were found, although this result is probably an artifact of the methods used. From this study we conclude that ketene is one source of colored materials during polyarylate synthesis. © 1992 John Wiley & Sons, Inc.     

Theory of crystallizable block copolymers

We present an equilibrium theory of diblock copolymers in which one of the blocks is crystallizable and the other is amorphous. The material is assumed to order in a lamellar structure of alternating semi-crystalline and amorphous layers with the chemical bonds which connect the copolymer blocks lying in the interfacial regions between the layers. The amorphous blocks are modelled as flexible chains, each with one end (the joint) anchored in an interface. Their contribution to the free energy is calculated via the self-consistent solution of the modified diffusion equations. The crystalline regions are modelled as folded chains, also with one end in an interfacial region (bonded to the corresponding end of an amorphous block). We find that the calculated amorphous block-free energies can be expressed as a single universal function depending on the total degree of polymerization of the amorphous block, its stretching, and a parameter proportional to the thickness of the interface. We have fitted an analytical form to this function, which can be used for any amorphous block, and we have combined it with our model of the crystallizable block to obtain scaling laws describing the equilibrium morphology.     

Solvent-induced shifts in electronic spectra of uracil

Highly accurate excitation spectra are predicted for the low-lying n-π* and π-π* states of uracil for both the gas phase and in water employing the complete active space self-consistent field (CASSCF) and multiconfigurational quasidegenerate perturbation theory (MCQDPT) methods. Implementation of the effective fragment potential (EFP) solvent method with CASSCF and MCQDPT enables the prediction of highly accurate solvated spectra, along with a direct interpretation of solvent shifts in terms of intermolecular interactions between solvent and solute. Solvent shifts of the n-π* and π-π* excited states arise mainly from a change in the electrostatic interaction between solvent and solute upon photoexcitation. Polarization (induction) interactions contribute about 0.1 eV to the solvent-shifted excitation. The blue shift of the n-π* state is found to be 0.43 eV and the red shift of the π-π* state is found to be -0.26 eV. Furthermore, the spectra show that in solution the π-π* state is 0.4 eV lower in energy than the n-π* state.     

Electrical conductivity of crystallizable polyphenylacetylene

The dc conductivity of crystallizable poly(phenylacetylene), made in the presence of ferric acetylacetonate and triethylaluminum, and its dependence on time, temperature, pressure, and crystallinity was determined. A decrease in conductivity upon annealing is probably attributable to an irreversible conformational transformation of the polymer. There is also a reversible decrease in conductivity upon compression which, under some conditions, corresponds to a volume of activation as high as 70 cm³/mole. Upon complexing with iodine the conductivity is increased by several orders of magnitude and activation energies and volumes are greatly reduced, even at iodine concentrations as low as 1.6 mole % iodine per monomer unit. Although an identification of unpaired spins with the charge carriers is probably not justified, defect states, whose presence is demonstrated by electron spin resonance, may play a major role in the charge transport process. The strong reversible decrease of the conductivity with an increase in pressure is plausible, if intermolecular charge transport is the rate-controlling step, an interpretation consistent with the large increase in conductivity upon complexing with small amounts of iodine.     

Solvent-induced crystallization of syndiotactic polystyrene in toluene

The diffusion of toluene in glassy syndiotactic polystyrene was analyzed for films with different thickness. It was found that the reduced sorption curves superimpose, denoting that the diffusion follows a Fickian behaviour. The intensity of transmitted light in a polarizing microscope was followed during swelling, and it was found that there is development of order and it is strongly diffusion-controlled. Films dried after immersion in toluene show a crystalline wide angle X-ray pattern, while in the swollen state the possibility of a liquid-crystalline-like state can be suggested.     

Solvent-induced crack growth in rubbery block polymers

The rapid cracking of lightly stressed rubbery block polymers of styrene and isoprene in certain liquids and vapors has been examined experimentally, by using model test pieces containing a single crack. Solvents which preferentially dissolve the rigid molecular end blocks rather than the rubbery center blocks are efficient cracking agents. The stress required for crack growth to occur is shown to be in accord with a simple energy criterion: the stored elastic energy must be sufficient to provide a characteristic energy for the newly formed surface. This characteristic energy ranges from values close to the surface energy of simple liquids up to about 100 times this value for thicker test pieces or slowly diffusing vapors, when some tearing of an incompletely swollen core is inferred. “Induction times,” before the initial crack starts to grow, are shown to be due to a progressive increase in stored energy under a constant stress as the material absorbs solvent and softens until the critical energy criterion is met. Thus, a timedependent fracture process is shown to be in accord with a constant energy criterion. Above the critical condition the rate of crack growth depends strongly upon stress, like tearing of amorphous elastomers, and the crack then accelerates rapidly.     

溶剂诱导聚合物结晶的研究进展

溶剂诱导结晶(SINC)又称为液体诱导结晶,它是结晶性高聚物在溶剂(或包括其蒸汽)作用下,在低于通常Tg下诱导结晶,而在高于通常Tg时能加速结晶的现象。本文主要对溶剂诱导结晶的机理、动力学和形态学进行了讨论。     

Solution properties of polyarylate in good and theta-solvents

Investigations have been carried out to determine the Mark-Houwink constants K and a in THF of a polyarylate based on an equimolar mixture of isophthalic and terephthalic acids and bisphenol A. An iterative method, involving intrinsic viscosities and GPC chromatograms, has been used. Molecular weight distributions and molecular weight averages are, in this way, accessible. Conformational characteristic magnitudes such as the characteristic ratio C_x and the steric factor σ have been calculated starting from data in good and θ-solvents.     

Ellipsoidal core-shell cylindrical microphases in PS-b-PB-b-PCL triblock copolymers with a crystallizable matrix

Polystyrene-block-polybutadiene-block-poly(ϵ-caprolactone) SBC triblock copolymers with a PCL matrix exhibit microphase separation into three different phases within the spherulitic superstructures. Mixing of the PS-block can occur upon melting of the PCL-block if the molecular weight is low enough. Even though the crystallization takes place well below the PS-glass transition, a deformation of the amorphous microphases into ellipsoidal core-shell cylindrical microdomains is observed by TEM. These copolymers have mechanical properties which are dominated by the PCL (poly(ϵ-caprolactone)) matrix with an influence of the amorphous blocks.     

Solvent-induced porosity in ultrathin amine plasma polymer coatings

Plasma polymers deposited from n-heptylamine onto silicon wafers have been found to form a porous microstructure when immersed in water and other solvents, with pores of dimensions and densities that vary considerably between coatings deposited under different plasma conditions. This solvent-induced pore formation was found to correlate with the observed percentage of extractable material. With low radio frequency (rf) power inputs, the resultant softer coatings possess considerably more extractable material than coatings deposited at higher applied power levels. The porosity is thus proposed to result from the formation of voids created by the extraction of soluble low-molecular-weight polymeric material, which produces shrinkage stress that the coating, firmly attached to the substrate, cannot relieve by macroscopic contraction. The microscopic contraction of plasma polymer volume creates voids that appear to span the entire film thickness. The effect of aging plasma polymers in air was also investigated. For films deposited at low power it led to reduced extraction of soluble material and different pore morphology, whereas for films deposited at higher rf power levels, the extracted amounts and pore formation were the same for aged coatings. It was also found that the density of surface amine groups was lower for films deposited under the two lowest power settings, in contrast to the commonly held belief that the use of minimal applied rf power aids retention of functional groups. These porous plasma polymer coatings with surface groups suitable for further interfacial chemical immobilization reactions may be useful for various membrane and biotechnology applications.     

Solvent-induced crystallization. II. Morphology

The Morphology of quenched poly(ethylene terephthalate) (PET) films crystallized by low-molecular-weight organic penetrants is studied by scanning electron microscopy. Films with thicknesses from ca. 1 mil (0.0025 cm) to ca. 35 mil (0.1 cm) were exposed to methylene chloride (MeCl₂) and N,N-dimethylformamide (DMF) in the temperature ranges 0–38°C and 22–70°C, respectively. The effects on the surface and internal structures of contact with liquids and saturated vapors were examined. Severe porosity at the surface results from contact with the liquids, but only minor surface roughness appears following contact with vapors. Internal porosity developed in the thinnest films (ca. 1 mil) during crystallization in liquid environments. Here, the internal void fraction is greatest along the film centerline and decreases with increasing crystallization temperature. A mathematical model discussed previously accounts for the observed behavior.     

Solvent-induced crystallization of nylon-6I

The ability of various hydrogen bond-forming solvents to induce crystallinity in nylon-6I was studied using DSC, FTIR spectroscopy, and x-ray diffraction. Comparison was made with predictions using the solubility parameter, which is related to possibilities of interaction formation. General predicted tendencies agreed with experimental results, in agreement with proposed influence of solvent-polymer interactions in the solvent-induced crystallization process. FTIR investigation of polymers treated with methanol and methanol-d shows that polymer segments forming hydrogen bonds with solvent molecules crystallize preferentially. It is therefore concluded that hydrogen bond exchanges with the solvent favor chain rearrangements leading to crystallization. © 1995 John Wiley & Sons, Inc.     

Nuclei stability in dilute solutions of crystallizable polyethyleneoxide

Dilute solutions of crystallizable polyethyleneoxide in dimethylformamide have been studied in the temperature range above the apparent clearing points of crystalline suspensions. The presence of a high temperature association mechanism, on which crystalline nucleation superimposes at lower temperature, has been demonstrated by light scattering and viscosity measurements.     

Microphase separation in solutions of crystallizable segmented polyurethane

At present time the level of microphase separation together with polymer nture is considered to be a main factor in determining the physico‐mechanical properties of polyurethane materials. The researches show that realization of a certain polymer structure and properties of polymer are defined by microstructure of polyurethane chain. The purpose of this work was to study physico‐chemical regularities between nucleation and growth of microphase aggregations in crystallizable segmented polyurethane compstions as a function of the phase state of the system during transferring from comon solvent to a selective solvent. Besides we investigated the architecture of macromolecules, associates and phase particles of segmented polyurethane (SPU) formed in different regions of the phase diagram.