Polymerization of organic compounds in an electrodeless glow discharge. X. Internal stress in plasma polymers

Owing to the unique mechanisms operative in plasma polymerization, a thin layer of plasma polymer deposited on the surface of a substrate shows a tendency to expand, indicating an internal stress in the layer. This stress, σ_s, has been estimated from the observed curling of composite membranes in which the thickness of the plasma coating, d, is much smaller than the thickness of a flexible substrate, D, according to the relation where R is the radius of the roll into which the composite films curl up and E is the modulus of the substrate polymer. The stress σ_s is found to depend on the kind of monomer used and to be of the order of magnitude 10⁸–10⁹ dynes/cm² with most of the monomers here employed.     

Isothermal and nonisothermal melt‐crystallization kinetics of syndiotactic polystyrene

Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter K_g for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm^?2, the fold‐surface free energy, σ_e = 52.3 ± 4.2 erg cm^?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002     

Copolymerization of styrene. IV. Copolymerization with esters of benzylidenecyanoacetic acid

Styrene was copolymerized in bulk with a number of esters of benzylidenecyanoacetic acid. The kinetic scheme of all pairs fitted the improved scheme of copolymerization, taking into account the effect of the penultimate unit. The Alfrey-Price Q and e values were calculated. Using the modified Taft equation, log (1/r₁) = ρ^*σ^* + δE_s, it was found that the relative reactivities of the ester monomers toward the polystyryl radical were correlated by the polar substituent constants σ^* of the ester alkyl groups (ρ^* = 0.14) and not by their steric substituent constants E_s (δ = 0.008).     

Effects of rigid segments on structure and properties of unoriented and oriented poly(p-phenylene terephthalamide-co-ethylene terephthalates)

In poly(p-phenylene terephthalamide-co-ethylene terephthalate) the rigid segments of p-phenylene terephthalamide are aggregated as crystalline domains above the weight fraction of the rigid segments, 6 wt%. The rigid segments disturb the crystallization of the flexible segments of poly(ethylene terephthalate) (PET) and are preferentially contained in the amorphous phase of the PET segments. The crystallinity of the PET segments decreased with increasing the content of the rigid segments in the copolymers and the glass transition temperature is decreased by the decrease of the crystallinity below the weight fraction of the rigid segments, 6 wt%, in spite of the depression of micro-Brownian motion of the PET segments due to the rigid segments. The values of Young's modulus E, yield stress σ_y and breaking stress σ_b for the zone-drawn copolymer were conspicuously increased by the rigid segments contained in it, in comparison with those of the zone-drawn PET homopolymer. Such higher values of E, σ_y, and σ_b of the copolymer are originated by greater increases in the orientation of amorphous chains in the copolymer. The rigid segments in the amorphous phase effectively depressed the thermal shrinkage of the zone-drawn and the zone-annealed copolymers.     

Influence of the presence of bubbles on the parameters of crystal nucleation in the 26Li<Subscript>2</Subscript>O · 74SiO<Subscript>2</Subscript> glass

The crystal nucleation in the glass of composition (mol %) 26Li₂O · 74SiO₂ has been investigated in the cases of homogeneous and heterogeneous nucleation. Parameters of homogeneous nucleation, such as the stationary nucleation rate I _st, the time of nonstationary nucleation τ, and the crystal growth rate U, have been determined. The temperature dependences of these parameters have been constructed. The surface energy σ at the nucleus-glass melt interface has been determined, and its temperature dependence has been obtained. The surface energy σ has been evaluated using the graphical method for solving the transcendental equation derived by transforming the relationships for the stationary crystal nucleation rate and the time of nonstationary crystal nucleation. The critical nucleus sizes r* and the free energy of formation of the critical nucleus Φ* have been determined. The heterogeneous nucleation on bubbles specially produced in the glass has been studied. It has been demonstrated that the presence of bubbles in the initial glass does not affect the crystal growth rate and substantially changes the nonstationary nucleation rate. The largest contribution to the change in the nucleation rate is made by “active” bubbles (filled by water vapor) formed in the glasses synthesized with the use of hydrated silicon dioxide.     

Isothermal crystallization of iPP in model glass-fiber composites

Isothermal crystallization of iPP in model glass-fiber composites is studied by DSC, and the basic energetic parameters of crystallization are determined. Unsized untreated and thermally treated glass fibers are used in model composites to determine the role of the surface on nucleation and crystallization processes. Thermally treated glass fibers are found to exhibit a predominant nucleating effect as compared to unsized untreated ones, and the crystallization proceeds faster, resulting in lower values for the half-time of crystallization (10–120 s). The energy of formation of a nuclei of critical dimensions at a given T_c is also lower, and it decreases as the content of the fibers in the composite increases. The surface free energy of folding, σ_e = 140 × 10⁻³ J/m², was determined for iPP in the composite containing 50% glass fibers, while for pure iPP, σ_e = 170 × 10⁻³J/m² was found. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 381–389, 1998     

Collisional Probing of the Transition-State Structure of a Bimolecular Reaction

The total cross section σ_B(E) for the Ca(¹D) + HBr → CaBr(B²Σ⁺) + H reaction as a function of collision energy has been measured using crossed atomic and molecular beams. The maxima exhibited by σ_B(E) with increasing energy are attributed to the opening of successive bending vibrational reaction channels that proceed via a [Ca(¹D) ⃛ Br ⃛ H]^‡ transition state. A dynamical model for the reaction may be constructed in terms of Landau-Zener probabilities for curve crossing at two locations on the reaction path, coupled with a preference for consumption of transition-state vibrational energy.     

Method for separating intramolecular and intermolecular interactions which influence polymer glass temperatures

It is shown that the glass temperature (T_g) for homopolymers of the type ? CH₂? CXY? can be expressed by a simple additive equation involving two terms: (1) a parameter E which is directly related to the molar cohesion energy and (2) a parameter E_s^* which is a measure of restricted rotation about valence bonds. E_s^*, at least for a large number of polymers, is related to the Mark-Houwink K_θ value (as measured in θ solvents at T_θ) via anti-log E_s^* ∝ 1/K_θ^2/3. It is also shown that for homologous series [e.g., poly(n-alkyl methacrylates)], there is a constant relationship between E and antilog E_s^*. The T_g values for copolymers may be estimated by a simple weighted (via mole fraction) summation of the E and E_s^* values of the components. When used in this form, a linear variation between T_g and composition is assumed, which may not be strictly correct but still yields useful approximations.     

Low energy ion‐solid interactions and chemistry effects in a series of pyrochlores

The effect of chemistry on low energy recoil events was investigated at 10 K for each type of atom in pyrochlores, using molecular dynamics simulation. Contour plots of the threshold displacement energy (E_d) in Gd₂Zr₂O₇ have been produced along more than 80 directions for each individual species. The E_d surface for each type of atom in Gd₂Zr₂O₇ is highly anisotropic; E_d of Zr exhibits the largest degree of anisotropy, while that of O_8b exhibits the smallest. The recommended values of E_d in Gd₂Zr₂O₇ based on the observed minima are 56, 94 and 25 eV, respectively, for Gd, Zr, and O. The influence of cation radius on E_d in pyrochlores A₂B₂O₇ (with A‐site ranging from Lu³⁺ to La³⁺ and B‐site ranging from Ti⁴⁺ to Ce⁴⁺) was also investigated along three directions [100], [110], and [111]. The E_d in pyrochlores strongly depended on the atom type, atom mass, knock‐on direction, and lattice position. The defects produced after low energy displacement events included cation antisite defects, cation Frenkel pairs, anion Frenkel pairs, various vacancies, and interstitials. Ce doping in pyrochlores may affect the radiation response, because it resulted in drastic changes in cation and anion displacement energies and formation of an unusual type of anti‐site defect. This work demonstrates links between E_d and amorphization resistance.     

Conformational analysis of serricornin: Application of molecular mechanics calculations to stereochemical assignment of serricornin,sex pheromone of cigarette beetle (Lasioderma serricorne F.)

Conformational analysis using molecular mechanics (MM) was performed for a determination of the stereochemistry of serricornin, the sex pheromone of the cigarette beetle (Lasioderma serricorne F.). An exhaustive conformational analysis using MM2 calculations with algorithms for covering torsional energy surfaces of flexible molecules furnishes coordinates and steric energies of all local energy minimum conformers of serricornin, both acyclic and the corresponding cyclic forms. These coordinates gave angles required for the calculation of vicinal H/H coupling constants (³ J _HHs) of each energy minima by Altona's modified Karplus equation. The Boltzmann distributions of all local energy minima were calculated from their steric energies to furnish populations of each energy minimum conformer. Populationweighted averaged³ J _HHs of four enantiomeric pairs, (S ^*,S ^*,S ^*)-, (S ^*,S ^*,R ^*)-, (S ^*,R ^*,S ^*)-, and (R ^*,S ^*,S ^*)-serricornins were calculated from the data above. The observed³ J _HHs of the naturally occurring serricornin, both acyclic and cyclic forms, are fitted best to calcd.³ J _HHs of (4S ^*, 6S ^*, 7S ^*)-acyclic and (3S ^*, 5S ^*, 6S ^*)-cyclic serricornin, respectively, among those of four enantiomeric pairs of serricornin.     

Accuracy of approximations for CIELAB chroma and hue difference computation

The transformation in CIELAB from differences in the L^*, a^*, b^* coordinates to those in lightness, chroma, and hue, ΔL^*, ΔC_ab^*, ΔH_ab^*, can be approximated by a rotation in 3-space. Expressions for the error in the approximation of chroma and hue differences are developed. Significant errors are introduced if either the hue angle or chroma difference between reference and sample colors are large. A computed example illustrates the use of the analysis. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 61–64, 1997.     

Structure development and isothermal crystallization behaviour of compatibilized PET/expandable fluorine mica hybrid nanocomposite

Summary The compatibilized PET/expandable fluorine mica (ME) hybrid nanocomposite (CN) prepared by in situ polymerization technique showed a partially exfoliated structure of ME in PET matrix by XRD analysis, owing to its broad crystalline peak accompanied by an increase of d-spacing as compared to PET/ME uncompatibilized composite (UC). The analysis by TEM revealed a better dispersion of ME in PET for CN as compared to aggregates of ME in case of UC. Further, the isothermal crystallization behaviour studied using DSC for the same at different crystallization temperature (T _c,) revealed a significant decrease of crystallization half time and remarkable increase of crystallization rates (almost 2 times than pure PET) for CN in contrast to UC. The Avrami exponent n lowered to 2.3 for CN as compared to 3.1-3.4 for pure PET at various T _c. The activation energy (E _a) determined from Arrhenius equation reduced dramatically for CN. These various observations could be explained based on the nucleation efficiency by ME accompanied by different crystallization/growth process occurring in case of hybrid nanocomposite.     

Photophysical processes and interactions between poly(ethylene terephthalate) and 1-amino-2-(2-methoxyethoxy)-4-hydroxy-9,10-anthraquinone

The effect of 1-amino-2-(2-methoxyethoxy)-4-hydroxy-9,10-anthraquinone (C. I. Disperse Red 59) on the phototendering of poly(ethylene terephthalate) (PET) was assessed. The photophysical processes occurring in the polymer, the dye, and the dyed polymer were determined. The energy and nature of the dye and polymer electronic excited states were assigned on the basis of absorption and luminescence properties. Irradiation failed to produce dye-sensitized phototendering of PET; however, the titanium dioxide delusterant in commercial PET did function as a sensitizer in the presence of moist air. The phototendering of blank-dyed PET yarn was found to obey (pseudo-) zero-order kinetics k = 1.69 × 10^?19 per cent breaking strength loss/quantum absorbed/cm². The dye exhibited fluorescence from a lowest, ～51.5 kcal/mole, singlet charge-transfer (C-T) excited state but did not phosphoresce. The PET possessed a complex fluorescence spectrum attributed to similar ¹(n,π^*)₁ excited states, ～78.1 kcal/mole, while its phosphorescence derives from a proposed ³(π,π^*) state, ～69.8 kcal/mole, populated by intersystem crossing from a ¹(π,π^*) state, ～92.3 kcal/mole. The dyed polymer exhibited a PET-sensitized delayed fluorescence from the dyestuff involving triplet–singlet transfer by a dipole–dipole (Coulumbic) long-range resonance excitation mechanism. The transfer process was characterized by an experimentally determined critical transfer distance, R₀, of approximately 40 Å.     

Mechanical properties and superstructure of poly(ethylene terephthalate) fibers zone-drawn and zone-annealed by CO2 laser heating

A laser-heating zone-drawing and zone-annealing method using a continuous-wave carbon dioxide laser was applied to poly(ethylene terephthalate) (PET) fiber to improve its mechanical properties. The as-spun fiber was zone-drawn under a applied tension (σ_a) of 4.44 MPa at a laser power density (PD) of 6.08 W cm⁻², and then the laser-heated zone-drawn fiber was zone-annealed. The laser-heating zone-annealing was carried out in three steps: the first annealing was carried out under σ_a = 139 MPa at 4.83 W cm⁻²; the second annealing was carried out under σ_a = 283 MPa at 4.83 W cm⁻², and the third annealing was carried out under σ_a = 432 MPa at 3.45 W cm⁻². The surface temperature distribution of the fiber irradiated with the CO₂ laser was measured by using an infrared thermographic camera equipped with a magnifying lens. The relation between the laser power and the surface temperature of the fiber became clear in the laser-heating zone-drawing and the laser-heating zone-annealing. The fiber obtained finally had a birefringence of 0.239, a degree of crystallinity of 55%, a tensile modulus of 19.8 GPa, and a storage modulus of 25.7 GPa at 25°C. In FTIR measurements, a trans conformation increased with the processing, but a gauche one decreased. The laser-heating zone-drawing and zone-annealing method was found to be effective in producing the PET fiber with high modulus and high strength. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2775–2783, 2001     

Relationship between the chain fold period in poly(ethylene terephthalate) and the crystallization temperature

The dependence of the fold period in poly(ethylene terephthalate) (PET) crystals on overcooling was investigated by the small-angle x-ray diffraction method, for samples crystallized at 150°C to 260°C. The equilibrium melting point T_m, determined simultaneously, was 278°C ± 2°C. Using these results, the surface free energy σ_e was calculated.     

Reverse osmosis separations for some alcohols and phenols in aqueous solutions using aromatic polyamide membranes

The performance of aromatic polyamide membranes for reverse osmosis separations of eight alcohol and four phenol solutes in dilute aqueous solutions has been studied. The Taft polar parameter σ^* for the solutes studied were in the range of ?0.3 to 1.388. Positive solute separations were obtained for each one of the solutes. In the σ^* value range of ?0.3 to 0, data on PR/PWP ratio scattered close to 1, and solute separation decreased with increase in σ^*. For the phenol solutes, PR/PWP ratio decreased and solute separation increased with increase in σ^*. The results are interpreted on the following basis. The aromatic polyamides are more nonpolar than cellulose acetates. In the σ^* range of ?0.115 to ?0.3, solute separation is governed primarily by polar interactions; in this range, solute transport parameter D_AM/Kδ is well correlated by the expression D_AM/Kδ = C^* exp (ρ^*σ^*). The solute separation for ethyl and methyl alcohol solutes (σ^* = ?0.1 and 0, respectively) is reduced by the nonpolar character of the membrane material. Positive solute separation for each of the phenolic solutes is due to preferential sorption of solute at the membrane-solution interface caused by both the nonpolar character of the membrane material and acidity of the solutes.     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

A mathematical model for computer simulation of the direct continuous esterification process between terephthalic acid and ethylene glycol. Part II: Reaction rate constants

It has been confirmed that the reaction model proposed previously, which can express simultaneously the oligomer properties and the distillate properties under low esterification pressure, is applicable to a continuous direct esterification process in a practical plant. The experimental data of the first esterification reactor (RA-1) was obtained under low reaction pressures (atomospheric or 1 kg/cm²G) with the pilot plant throughput based on poly(ethylene terephthalate) (PET) polymer production of about 50 kg/h. The Arrhenius' parameters, frequency factor, and apparent activation energy, were determined fitting the experimental data of the pilot plant by using the Simplex method as an optimization technique. The activation energy of diethylene glycol (DEG) formation, E₇, is about twice as much as those of the esterifications, E₁, E₂, E₃, and E₄. The activation energies are E₁, = 19640 cal/mol, E₂ = 18140, E₃ = 22310, E₄ = 18380, E₅ = 2810, E₆ = 14960, and E₇ = 42520 cal/mol. Good agreement was obtained between experimental data and calculated predictions for several oligomer and distillate properties. The vapor-liquid equilibrium can be expressed by Raoult's law with little problem of practical use.     

Anomalous behavior of electrical conductivity of solubilized collagen solutions with thermal denaturation

The temperature dependence of the electrical conductivity, σ, for a collagen solution was measured in the temperature region including the thermal denaturation temperature, t_d. The σ increased with temperature, t, but decreased at ca. 40°C, and then again increased. In this temperature region, a change of optical rotation, α_D, was observed. The change is due to the thermal denaturation. The differential curve of σ vs. t gave clear deflection points and a large peak at ca. 40°C. The t_d could be estimated from the peak temperature. The t_d decreased with the increase in the concentration of collagen and with the decrease in the heating rate. These measurements were carried out for the collagen prepared by various methods. Some of them showed one peak; others had two peaks. The t_d obtained by the measurement of σ correlated with that obtained by the measurement of α_D. The activation energy of σ, ΔE_a, obtained from the linear relationship between log σ and 1/T, increased with the concentration of collagen, but was unchanged for the heating rate. The ΔE_a obtained for various types of collagen showed a constant value. © 1993 John Wiley & Sons, Inc.     

Craze fibril formation and breakdown

As crazes grow in areal extent they also increase in width. The areal growth involves craze tip advance which has been shown to occur by the Taylor meniscus instability. Craze widening, at least for air crazes, occurs by drawing more fibrillar material from the craze-bulk polymer interfaces at essentially constant extension ratio. Simple arguments will be given to predict the scale of the fibrillation in terms of the stress S at the craze tip and interfaces and an effective polymer surface energy (Γ) where: which assumes that all entangled chain crossing the surface are broken [γ represents the van-der-Waals (intermolecular) surface energy, d is the entanglement mesh size, v_E is the entanglement density, and U_b is the energy required to break a single backbone bond]. These arguments also give the rate of fibrillation as a function of S, a nominal plastic resistance σ_y and Γ and can explain the fact that the stress for crazing increases relative to that for shear deformation as the entanglement density of the polymer is increased. The geometrically necessary entanglement loss (either by scission as assumed above or by disentanglement- at temperatures just below T_g) that accompanies fibril formation has important consequences for fibril stability. The probability p that a given entangled chain is lost can be computed from simple geometrical considerations knowing the fibril diameter D, its extension ratio λ and the mesh size d; p increases rapidly as Dλ^½ becomes comparable to or less than d. These concepts can be tested in blends of high molecular weight polymer with chains of the same polymer that are too short to entangle.