CHARACTERIZATION OF γ-IRRADIATED CRYSTALLINE POLYMERS Ⅰ. CHARACTERIZATION OF γ-RADIATION INDUCED CROSSLINKED POLYAMIDE 1010 BY CRYSTALLIZATION TEMPERATURE*

The effect of ~(50)Co γ-radiation on plain polyamide 1010 (PA1010 Ⅰ) and PA1010 containing dif-ferent amount of crosslinking agent (BMI) (PA1010 Ⅱ) both in vacuum and in air at room tempera-ture was investigated with DSC. It was found that the crystallization temperature T_c of crosslinkedsample determined with DSC at constant cooling rate decreased as the radiation dose increased. Thedifference between crystallization temperatures before and after crosslinking (T_(c_o)-T_(c_R) is linearlyrelated to the radiation dose for PA1010I. Based on the Charlesby-Pinner's equation an expressionwas derived S+S~(1/2)=A+B/(T_(c_o)-T_(c_R)) where S is the sol fraction, A and B are constants. Since thereis evidence that T_c is relative to S only and independent of the way of irradiation, the equation is alsoapplicable to the enhanced γ-irradiation crosslinked PA1010 Ⅱ. Therefore, determination of T_cof crosslinked polymer by DSC offers a convenient approach to study quantitatively the random andespecially non-random crosslinking reaction of crystalline polymer.     

Relation of the decay of free radicals in irradiated polyethylene to the molecular motion of the polymer and the configurations of the free radicals

Decay reactions of the free radicals produced in irradiated polyethylene (high-density and low-density materials) were examined in connection with the molecular motion of the matrix polymer. Three temperature regions, in which the free radicals decay very rapidly, at around 120, 200, and 250°K, were designated T_A, T_L, and T_B, respectively. The decay of the free radicals at these temperatures had activation energies in high-density polyethylene of 0.4 kcal/mole for T_A, 9.4 kcal/mole for T_L, and 18.4 kcal/mole for T_B. In low-density polyethylene these quantities were 0.7 kcal/mole for T_A, 23.1 kcal/mole for T_L, and 24.8 kcal/mole for T_B. Comparison of time constants for the decay reactions and for molecular motion of the matrix polymer indicate that the decay in T_A and T_B is closely related to molecular motion in the amorphous regions of the polymer. The decay of the free radicals at T_L in high-density polyethylene is due to molecular motion associated with local mode relaxation at lamellar surfaces, while that of low-density polyethylene is due to local mode relaxation in the completely amorphous region. Steric configurations of the free radicals which decay in the respective temperature regions were also investigated.     

Dissolution equation of polymer

The dissolution of the polar polymer, polyacrylamide (PAM), in water is studied kinetically. The rate of dissolution, ?, of PAM is determined by means of measuring the conductivity of water as dissolution of the polymer proceeds. The thickness of the swollen surface layer, δ, and the rate of swelling, ?, are determined with the aid of penetration and followed surface track by conductometric electrode. A kinetic equation reflecting PAM dissolution in water is obtained directly as 2? + ? = D?_s/δ, where D?_s is the average diffusion coefficient of solvent in polymer and is shown to be true in cases of nonpolar as well as polar polymers. © 1996 John Wiley & Sons, Inc.     

Determination of the ionic radii by means of the Kohn–Sham potential: Identification of the chemical potential

Under the Kohn–Sham theory, we examine solutions for the equations δT_S/δρ(r) = 0 and δT_S/δρ(r) = ν_KS(r) that link the chemical potential of the electronic system with the effective Kohn–Sham potential through μ = ν_KS(r) + δT_S/δρ. For single ions, we identify the chemical potential with the eigenvalue of the frontier orbital when the atom is in the limit of full ionization. For the case of cations, the chemical potential is found above ?(I + A)/2 and has the property of grouping ions with the same chemical characteristics. For the anion instead, the chemical potential is fixed at the ionization energy. By solving the above equations numerically, two radial points called r_? and r₊ are obtained and compared with the Shannon–Prewitt ionic radius. Moreover, we found for the halide series, that r_? is numerically equivalent to rm, the radii where the electrostatic potential has its minimum, but shows different behavior upon charge variation. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Pressure dependence of dielectric properties of chlorinated polyethylene vulcanizate. I. α relaxation and shift factors

The complex dielectric constant was measured under elevated pressure for the α relaxation of vulcanized chlorinated polyethylene. Both temperature and pressure effects on the static dielectric constants, the activation enthalpy, and volume, and the pressure dependence of the glass-transition temperature were obtained. The dependence of shift factors on temperature was expressed by the Vogel–Fulcher–Tamman–Hesse (VFTH) equation: ?log a_T = A ? B/(T ? T₀). The parameters A, B, and T₀ for each pressure applied were calculated by minimizing the standard deviation between log a_T and experiments. The values of the parameters in the Williams–Landel–Ferry (WLF) equation: ?log a_T = C₁(T ? T_g)/[C₂ + (T ? T_g)], were also estimated from the resulting values of the VFTH parameters. All these parameters depended on pressure. The activation volume plotted against T ? T_g decreased with increasing pressure.     

Concentration Effects in Sec for Polymer/Polymer/Solvent Systems

Abstract

A model quantitatively describing the experimental shifts in elution volumes of polymeric solute A in the presence of another polymer B is developed. The concentration-dependent shrinkage of A coils has been evaluated from the intrinsic viscosity displayed by polymer A in the ternary solution formed by itself at c_A concentration + polymer B at c_B concentration + solvent. Resulting concentration effects depend on both polymer concentrations (c_A and c_B), on the intrinsic viscosities of both polymers in the solvent (|η|A and |η|B), on the Huggins' coefficients k_A and k_B, and on the quadratic concentration coefficients in the polynomial expansion of ηsp/c, namely k^′ _A and k^′ _B. Predicted elution volumes are compared with experimental ones for two different types of literature systems: those studying polymer A elution at diverse c_A concentrations in eluents consisting of mixtures of polymer B + solvent and those in which polymer A + polymer B mixtures are injected at once in the pure solvent used as eluent. In order to eliminate experimental uncertainties about k_i and k^′ _i (i=A, B) values, applied k^′ _i values were those obtained from the empirical correlation k^′ _i + 0.122 = k_i ² whereas k_i ones were obtained from Imai's equation.     

Second virial coefficients of homopolymers and copolymers of butadiene and styrene in tetrahydrofuran

Second virial coefficients have been measured in tetrahydrofuran for a series of anionically polymerized narrow distribution homopolymers and copolymers of butadiene and styrene. The results fit the general empirical equation A₂ = M^?1/4(0.0216w_B + 0.00995w_S + Cw_Bw_S), where M is the polymer molecular weight, w_B and w_s are the weight fractions of butadiene and styrene, and C is a constant which is zero for block polymers and equal to 7.9 × 10^—3 for random copolymers. The equation is independent of the degree of 1,2 addition of butadiene and fits data on both linear and tetrachain star-branched polymers within experimental error.     

Kinetic interpretation of the glass transition: Glass temperatures of n-alkane liquids and polyethylene

On the basis of an isoviscosity criterion for the glass transition (η_g ? 10¹³ poise) in liquids of low molecular weight, theoretical T_g values were calculated for the n-alkane series by the equation log η = log A + B/(T ? T₀), with the use of values reported by Lewis for the parameters. The T_g/T₀ ratio reaches a limiting value of 1.25 and ?_g = (T_g ? T₀)/2.3B = 0.027, a constant. Extrapolation to (CH₂)_∞ gives T_g = 200°K., T₀ = 160°K., and B = 640°K. This T_g is consistent with other estimates for poly-ethylene, and T₀ coincides with the temperature at which the “excess” liquid entropy for (CH₂)_∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E₀ = 2.3RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E₀ = 2.9 kcal./mole for polyethylene, 3.0 kcal./mole for polystyrene, 5.7 kcal./mole for polyisobutylene, and 1.9 kcal./mole for polydimethylsiloxane.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). III. Influence of temperature

Methyl methacrylate (MMA) was polymerized by radical initiation at 0, 25, 50, 75 and 100°C in DMF in the presence of preformed isotactic PMMA (iMA) or preformed syndiotactic PMMA (sMA) with different M?_v and also without preformed PMMA (“blank” polymerizations). From the tacticities of the formed polymers it is concluded that blank polymerization does not conform to simple Bernoulli statistics, but follows at least first-order Markov statistics. The formation of long syndiotactic sequences in the presence of iMA and long isotactic sequences in the presence of sMA denotes still higher-order Markov statistics. The stereoregulating action is improved by higher M?_v of the preformed polymer (matrix) and lower reaction temperature. These influences can be explained by assuming an equilibrium between polymer growth on the matrix and in the “free” solution. For polymerizations in the presence of iMA or sMA below 300°K, the differences in activation enthalpies (ΔH_s/i? – ΔH_i/s?) are practically equal to that for the blank polymerization, ca. 900 cal/mole, whereas the differences in activation entropies (ΔS_s/i? – ΔS_i/s?) differ considerably. (ΔS_s/i? – ΔS_i/s?) values are highly negative in the presence of iMA and highly positive in the presence of sMA. From these results it is concluded that the isotactic and syndiotactic polymer matrices exert a steric influence on the monomer addition process, thus promoting so-called stereospecific replica polymerization.     

Thermally induced incomplete high-spin (5T2) ⇌ low-spin (1A1) transition in solid bis[2-(2-pyridylamino)-4-(2-pyridyl) thiazolato]iron (II)

The ⁵⁷Fe Mössbauer effect in two samples (A and B) of [Fe(papt)₂] and in its solvates with CHCl₃ and C₆H₆ has been studied between 4.2 and 343 K and clearly indicates a temperature induced high-spin (⁵T₂) ? low-spin (¹A₁) transition in these compounds [paptH = 2-(2-pyridylamino)-4-(2-pyridyl) thiazole]. At 343 K, sample B shows a doublet with ΔE_Q = 2.03 mm s^?1 and δIS = +0.87 mm s^?1, characteristic of a ⁵T₂ ground state. At 257 K, a second doublet, typical for a ¹A₁ ground state, is observed and its intensity increases as the transition progresses but levels off below ～ 100 K. At 4.2 K, 83% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.56 mm s^?1 and δ^IS(¹A₁ = +0.32 mm s^?1. In an applied magnetic field, V_zz(¹A₁) < 0 and η ≈ 0.7 have been determined, whereas for the ^sT₂ ground state, V_zz(^sT₂) > 0, η ≈ 0.75, and an internal hyperfine field H_n ≈ ?13 kG have been observed. Similar results have been obtained with the other samples.Debye-Waller factors f5_T2 and f1_A1 were determined from the saturation corrected areas in the Mössbauer spectra, assuming Curie-Weiss dependence of the magnetic susceptibility for the ⁵T₂ and constant υ_cff for the ¹A₁ ground state. The temperature dependence of ?In f1_A1 closely follows the Debye model with Θ1_A1 = 165 K, whereas the same applies to ?ln f5_T2 only above ～ 210 K and Θ5_T2 = 134 K. The nature of the observed transition is discussed and the data presented are shown to be incompatible with a model based on a Boltzmann distribution between the two states.     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.     

Solubility and Enhanced Tension of Solute in Solution

Abstract

In solution, solute molecules B are coupled by attractive forces between them and all other molecules present; and these other molecules enhance the tension in the coupling force between solute molecules an amount π_B, the osmotic pressure of the solution solute. Two equilibria determine the n ^o _B moles of pure solute which dissolve in n ¹⁰ _A moles of pure liquid solvent. If at T the solute is solid and in excess, then 1) the n _B ^lsat moles of B in the n^l _A moles of A in a solution saturated with B are in thermodynamic equilibrium with the solid solute at the same T and p and 2) the n _B ^lsat moles of B and n^l _A moles of A may also be in chemical equilibrium with the moles of new molecular or ionic species formed in the solution. Solute molecules dissolve until the chemical potential of the solution solute, p^l _B(T p, x_B ^lsat), equals the chemical potential of pure solid solute at the same T and p, μ _B ^so(T, p). When the solution is saturated with B and the mole fraction of B is x_B ^lsat = n _B ^lsat/σj n ¹ _j, then the vapor pressures of the solid solute at T and p, the solution solute at T and p, and the pure undercooled liquid solute at T and p-π _B ^lsat are identical. If at T the n _B ^lo moles of pure solute and the n^l _A moles of pure solvent are liquids, then if molecules of B are allowed to dissolve in A while molecules of A are dissolved in B, the resulting solutions may 1) contain only molecules of A and B or 2) contain A and B which also react to form other ionic and molecular species. The two solutions may be identical or they may differ. In all cases, however, the mole ratio of n^l _Bn^l _A in both solutions must be identical.     

E.S.R. and D.S.C. investigations of phase transitions in polymorphic 4-n-alkoxybenzylidene-4′-n-alkylanilines

Abstract

It is shown that the McMillan parameter M = T _SAN/T _N1 (where T _SAN and T _NI are respectively the temperatures of the smectic A to nematic (SAN) and the nematic to isotropic (NI) phase transitions) is useful in analysing the crossover between second and first order behaviour of the S_NN transition in the nO.m homologous liquid crystal series (the 4-n-alkoxybenzylidene-4′-n-alkylanilines). Using a phase diagram of orientational ordering versus M for this series, as obtained in this work (from E.S.R. and D.S.C), a symmetric tricritical point with mean field exponent β₂ = 1 is demonstrated. In a preliminary study of E.S.R. linewidth parameters B and C of nitroxide spin probes dissolved in members of the nO.m series exhibiting a first order S_AN transition, critical-type divergences are observed near this transition. In the case where M is closer to 0.959 (the value at the tricritical point), these divergences appear similar to those previously observed in related nO.m members with a second order S_AN transition; however, they are considerably enhanced for an M value closer to unity (i.e. more removed from the tricritical point). This indicates the importance of coupling between orientational and positional order parameters in the observed critical-type divergences.     

Pulsed NMR of cis-polyisoprene solutions T1 and T2 relaxations,free volume,viscosity relationships

Previous pulsed NMR studies of polyisoprene have largely been concerned with entangled or crosslinked networks. This paper deals with (i) the relaxation of high molecular weight entangled; (ii) cross-linked; (iii) monodisperse low molecular weight; and (iv) high molecular weight polymer in the presence of tetrachloroethylene which, by increasing molecular mobility, can be expected to influence the NMR relaxation. For all four types of polyisoprene, the spin-lattice T₁, relaxation shows a minimum with position depending only on the free volume, as influenced by changes in temperature T and polymer concentration v₁,. For monodisperse polyisoprene of molecular weight 7200, insufficient to form an entangled network, the spin-spin relaxation decay constant T_2L is quantitatively related to the free volume ₁ by two parameters A′ and B″ when the free volume is altered by a change in temperature, or in polymer concentration (10–100/). This can also be expressed in the form where the parameter T_∞ at 100% concentration agrees with the value used to describe rheological properties. At other concentrations of polymer, T_∞ and B′ can be derived quantitatively from the coefficients of volume expansion of polymer and solvent. The variation of T_2L with molecular weight (T_2L ∝ M^?0.5) occurs via the A′ parameter. It is concluded that T_2L can be quantitatively related to the free volume available for molecular motion (as influenced by temperature and solvent concentration) as well as to molecular weight. Furthermore T_2L is simply related to viscosity n, over a wide range of temperatures and concentrations. T₂ can be used to analyse the molecular motions involved in theology.     

Salt rejection by polymer membranes in reverse osmosis. II. Ionic polymers

The water permeability K₁ [which is related to water flux J₁ per unit membrane area by J₁ = K₁(Δp ? ΔII)/ΔX, where Δp is the pressure difference, ΔII is the osmotic pressure of feed solution, and ΔX is the membrane thickness] of homogeneous ionic polymer membranes in reverse osmosis and their salt rejection R_s [which is given by R_s ≡ 1 ? (C_2″/C_2′), where C_2′ is the concentration of the salt in feed solution, and C_2″ is the concentration of salt in effluent] were examined with cationic and anionic membranes of block and graft copolymers. For ionic membranes, R_s and K₁ are related by K₁ = A exp { ? BR_s}, where A and B are constants. This equation was found to be independent of the ion charge, the chemical nature of the polymer, and film morphology. The principle of salt rejection by ionic membranes was explained by the difference in the transport volumes (volume elements available for transport) for mobile co-ions and water. The electric repulsive force between a fixed ion and a mobile co-ion decreases the transport volume of the latter, thus creating a transport depletion of salt flux relative to water transport. This transport depletion is governed by the amount of water sorbed by a fixed ionic site, which also determines the water flux. Consequently, R_s and K₁ for ionically charged membranes are related as described above. This relation significantly differs from that found between R_s and K₁ for nonionic polymer membranes, where the size and the solubility of ions in the membrane are mainly responsible for the transport depletion. The decline of R_s with increasing K₁ is much less in ionic membranes than in nonionic ones; however, in the high R_s region, K₁ for both ionic and nonionic membranes become similar as the dominant mode of water transport changes from flow to diffusion.     

Analysis of the melt viscosity and glass transition of polystyrene

The melt viscosity, the glass transition, and the effect of pressure on these are analyzed for polystyrene on the basis of the Tammann-Hesse viscosity equation: log η = log A + B/(T ? T₀). Evidence that the glass transition is an isoviscosity state (log η_g ? 13) for lower molecular weight fractions (M < M_c) is reviewed. For a polystyrene fraction of intermediate molecular weight (M ? 19,000; t_g = 89°C.), it is shown that B is independent of the p–v–T state of the polymer liquid and that dT₀/dP = dT_g/dP. This is consistent with the postulate that B is determined by the internal barriers to rotation in the isolated polymer chain. Relationships are derived for flow “activation energies” at constant pressure and at constant volume, and for the “activation volume.” Values for polystyrene along the zero-pressure isobar and along the constant viscosity, glasstransition line are reported. For the latter, ΔV_g* is constant and corresponds to about 10 styrene units. The “free volume” viscosity equation: log η = log A + b/2.3?, is reexamined. For polystyrene and polyisobutylene, ?_g/b = 0.03, but ?_g and b themselves differ appreciably in these polymers. The parameter b is the product of an equilibrium term Δα and the kinetic term B, and none of these is a “universal” constant for different polymers. The physical significance of the free volume parameter ?, particularly with regard to the “excess” liquid volume, remains undefined. Two new relationships for dT_g/dP, one an exact derivation and the other an empirical correlation, are presented.     

Star-shaped block copolymers. III. Surface and interfacial properties

Surface and interfacial activities of A(B)₂ star-shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture [A-B or A(B)₂] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock [A-B] or star-shaped block [A(B)₂] copolymer. The limiting value is, however, attained at significantly lower concentration with the star-shaped copolymers. Their ability to fill the interface is accordingly higher.     

STUDY ON LIGHTLY SULFONATED SYNDIOTACTIC POLYSTYRENE IONOMERS

Sulfonated syndiotactic polystyrene ionomers (SsPS) with 1.8 mol% degree of sulfonation have been studied.WAXD shows that the crystallinity of SsPS ionomers was decreased with increasing diameter size of the counter ions andsPS>SsPS-H>SsPS-K>SsPS-Zn. Moreover, SsPS ionomers only have a α cystal form, while original sPS has two crystalforms: α and β crystal form. TGA shows that the thermal stability of SsPS ionomers is higher than that of the original sPSand SsPS-Zn>SsPS-K>SsPS-H. DSC shows that all the glass transition temperatures (T_g) of SsPS ionomers are higherthan that of the neat sPS and SsPS-Zn>SsPS-Na>SsPS-K>SsPS-H. However, the melting temperature (T_m) andcrystallization peak temperature (T_p) of SsPS ionomers are lower and SsPS-H>SsPS-Zn>SsPS-K>SsPS-Na, while thecrystallinity (X_c) of SsPS-Zn is the lowest. Nonisothermal crystallization kinetics shows that the Avrami index of sPS andSsPS-H are both about 4, suggesting the nucleation growth of SsPS-H with lower degree of sulfonation still keeps its three-dimension form. FTIR spectra of SsPS ionomers show a splitting absorption band for asymmetric stretching vibration ofsulfonation group. The CH in-plane bending vibration of benzene ring shifted to higher wavenumber and the symmetricstretching vibration of sulfonation group changed slightly with different counter ion neutralized SsPS ionomers.