Heptane-soluble material from atactic polypropylene. II. Interaction with liquids

Reduced melting point and swelling measurements, involving heptane-soluble material from atactic polypropylene and over thirty liquids of differing chemical type, are reported. A value of 578 ± 40 cal. is obtained for the molar heat of fusion of a crystalline repeat unit which is much lower than values given for isotactic polypropylene. Some reasons for the low value are considered. Values of the polymer-solvent interaction parameter χ₁ for systems involving alkylbenzenes and n-alkanes suggest a solubility parameter of 7.9 ± 0.1 (cal./cc)^1/2 for the polymer. These values of χ₁ decrease with increasing molar volume of liquid. Polar liquids of comparable solubility parameter or molar volume are associated with higher values of χ₁. Intrinsic viscosities and values of the slope constant k′ are given for fractions in the molecular weight range 3,000–25,000 and six solvents at 25°C. The results suggest the following order of solvent power: cyclohexane ≈ cyclohexene > methylcyclohexane > trichloroethylene > decalin > carbon tetrachloride. Intrinsic viscosities are higher than those generally obtained for flexible polymers of comparable molecular weight, and the values of the Mark-Houwink exponent appear to be high. Some reasons for these high values are considered.     

Development of a correlation between the non-polar solubility parameter,refractive index and molecular structure. I. Aliphatic hydrocarbons

For non-polar liquids (e.g. the alkanes) the cohesion energy density (λ²) can be shown to be a function of the refractive index (nD ), molal volume (V) and molecular structure according to: where Δ is the non-polar solubility parameter and the increments g_ij are determined from molecular structure. The difference between values of Δ calculated by this formula and experimental data is <0.1% for the C₅–C₁₆ n-alkanes and <0.8% for the C₅–C₈ branched isomers. The main object of this correlation was to provide a method for estimating the London dispersion force contribution to the cohesive energy of branched polar liquids.     

High Regioselective Diels–‐Alder Reaction of Myrcene with Acrolein Catalyzed by Zinc‐Containing Ionic Liquids

The ambient zinc‐containing ionic liquids, MX‐ZnCl₂, functioning as both Lewis acid catalyst and green solvent, are employed for a high regioselective Diels–Alder reaction of myrcene with acrolein for the first time, where MX is either 1‐butyl‐3‐methylimidazolium chloride (BmimCl), 1‐ethyl‐3‐methylimidazolium bromide (EmimBr), N‐butylpyridinium bromide (BPyBr), or N‐ethylpyridinium bromide (EtPyBr). Compared with the analogous reaction performed over a ZnCl₂ catalyst in the conventional solvent dichloromethane, higher regioselectivity of the ‘para’ cycloadduct and excellent yield were achieved at shorter reaction time in these ionic liquids with optimized molar compositions of MX and ZnCl₂. These moisture‐insensitive ionic liquids can be easily separated from reaction products after simple washing with hexane, allowing their reuse with no obvious loss in activity.     

A method for estimating both the solubility parameters and molar volumes of liquids

The solubility parameters and molar volumes of substances can be used, in conjunction with suitable theory, to provide estimates of the thermodynamic properties of solutions; the solubility characteristics of polymer-solvent systems and the estimation of the equilibrium uptake of liquids by polymers are examples of the type of practical problems that are amenable to treatment. For low molecular weight liquids, the solubility parameter, δ, is conveniently calculated using the expression δ = (ΔE_v/V)½, where ΔE_v is the energy of vaporization at a given temperature and V is the corresponding molar volume which is calculated from the known values of molecular weight and density. For high molecular weight polymers, the volatility is much too low for ΔE_v to be obtained directly and hence recourse must be made to indirect methods for estimating δ for these materials. One such widely used method is based on Small's additive group “molar-attraction constants” which when summed allow the estimation of δ from a knowledge of the structural formula of the material; however, the density must still be determined experimentally. The proposed method of estimating δ, also based on group additive constants is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of the structural formula of the compound.     

Synthesis of poly(ethylene terephthalate) in benzyl imidazolium ionic liquids

In order to improve the method of synthesis of poly(ethylene terephthalate) (PET), a series of ionic liquids (ILs) based on benzyl imidazolium ([YBMIM][X], Y = NO₂, CH₃, F; B = benzyl; X = Tf₂N) were used to investigate the formation of PET at low temperature and pressure. High molecular weight PET (M_w up to 2.6 × 10⁴ g mol^?1) was obtained by two‐step polycondensation in these ILs at lower temperature (230–240 °C) than with traditional melt polycondensation (270–290 °C). Moreover, the molecular weight of the resulting PET was found to depend on the activities of the catalysts used in the ILs. The catalysts (Sb₂(OCH₂CH₂O)₃, Sb(OAc)₃, Sb₂O₃) used in the preparation of PET have little effect on the thermostability of the ILs. The ILs can decrease the viscosity of the reaction system, and thus small molecules can be easily removed. Copyright © 2012 Society of Chemical Industry     

Column fractionation of polymers. VII. Computer program for determination of molecular weight distributions from gel permeation chromatography

Gel permeation chromatography produces a type of differential molecular weight distribution directly and rapidly. Conversion of these data to conventional molecular weight distributions and plots of distributions is time-consuming. A computer program is described to perform these operations readily. Input data from the automated chromatograph, elution volume, and recorder deflection are converted to unit sensitivity and base line corrections applied. The curve is then numerically integrated and a calibration curve used to convert elution volumes into molecular weights. Various calibration curves can readily be introduced into the program. The output, in addition to tabulation of cumulative and differential molecular weight distributions, contains values of M?_n, M?_v, M?_w, M?_z, and M?_z+1. Importantly, a reduced absolute area, i. e., area computed for unit sensitivity on a unit concentration basis, is tabulated. An additional time-saving eature is the printing out of differential and cumulative molecular weight distribution curves and of a differential histogram.     

Dynamic light‐scattering characterization of the molecular weight distribution of unfractionated polyimide

Using a developed laser light‐scattering (LLS) procedure, we accomplished the characterization of an unfractionated polyimide (UPI) in CHCl₃ at 25°C. The Laplace inversion of precisely measured intensity–intensity time correlation function from dynamic LLS leads us first to an estimate of the characteristic line‐width distribution G(Γ), and then to the translational diffusion coefficient distribution G(D). By using a previously established calibration of D (cm²/s) = 3.53 × 10^?4 M^?0.579, we were able to convert G(D) into a molecular weight distribution. The weight‐average molecular weight M_w, calculated from the molecular weight distribution, agrees well with that directly measured in static LLS. Our results indicate that both the calibration and LLS procedure used in this study are ready to be applied as a routine method for the characterization of the molecular weight distribution of polyimide. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1670–1674, 2001     

Incipient stable bubble formation during bulk polymerization of methyl methacrylate under near‐isothermal conditions. II. Use of an anchor agitator

Methyl methacrylate is polymerized under near‐isothermal conditions in a 1‐l stainless steel batch reactor having a glass bottom and stirred with an anchor agitator. A camcorder is used to obtain images of the entrapped vapor bubbles at different times so as to identify the point, Bi, where stable clusters of vapor bubbles first (incipient) get formed. This is being referred to as the transition point. Data on the monomer conversion, x_m,Bi, the weight average molecular weight, M_w,Bi, and the viscosity, η_Bi, of the reaction mass at this point have been generated for a variety of experimental conditions. It is observed that the pressure above the liquid reaction mixture and the RPM of the stirrer have little effect on the results in the ranges studied. Correlations have been developed for x_m,Bi, M_w,Bi, and η_Bi, relating these to the initiator loading, I_o, and the constant set‐point temperature, T. Results are compared with those obtained earlier for reactors stirred with ribbon agitators. The transition point is useful for the design of the first stage of polymerization reactors. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Polymer degradation. V. Changes in molecular weight distributions during sonic irradiation of polyisobutene

Gel permeation chromatography was used to follow changes in the molecular weight distribution of a polyisobutene, initial M _v = 466,000, during degradation induced by sonic irradiation. Seven samples taken at times of 200–163,500 sec. were studied. In general, a steady decrease in molecular weight was observed, although a bimodal distribution was present after 20,000 sec. irradiation. Various measures of inhomogeneity, M _w/M _n, U, etc., were examined. The function, σ_n/M _w, where σ_n is the standard deviation of the number distribution, is considered as a measure of the relative distribution. It is shown to be almost constant throughout the degradation.     

Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights

Thermal properties of Fortron®

1 ®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, T_g, has been calculated to be 28.1 J°C^?1 mole^?1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The T_g of PPS increases with molecular weight. The T_g of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at ?92°C. Only the highest molecular weight could be quenched to a completely amorphous state.     

Low-rate dynamic contact angles on polystyrene and the determination of solid surface tensions

Low-rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis – profile (ADSA-P). It is found that 7 liquids yielded non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid-vapor surface tension times cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γ_lvcosθ depends only on γ_lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces (7–13, 24–26). The solid-vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions (33) is found to be 29.8 mJ/m², with a 95% confidence limit of ±0.5 mJ/m² from the experimental contact angles of 6 liquids.     

Rheology of PVAc–MMT–STAB

Polyvinyl acetate (PVAc) is considered to be an acceptable environmental friendly adhesive, and montmorillonite (MMT) is a cheap and accessible natural nano-mineral. In this work, MMT was first organically activated by octadecyl trimethyl ammonium bromide (STAB). The intercalated nano-composite, MMT–STAB, was then polymerized with VAc. The influence of various additions of MMT–STAB on the rheology of PVAc–MMT–STAB was analysed using the power-law function equation and the Cross–Williamson model viscous equation. The results showed that MMT–STAB was able to improve the rheology of PVAc. The PVAc and PVAc–MMT–STAB all were pseudo-plastic non-Newtonian fluids, with a flow index (i) of 0.93. The apparent viscosity (η), fluid consistency (Ï), characteristic time of materials (ζ), zero shear viscosity (η ₀), weight average molecular weight (M _w), number average molecular weight ( M _n) and the solid content (O), all increased with increasing additions of MMT–STAB as a result of the polymerization process. All properties, apart from ζ, showed a maximum with the addition of 2.0 wt%. The limiting viscosity (η _∞) was 0 mPa s for all samples of PVAc or PVAc–MMT–STAB. Their storage stability was found to be excellent. The reasonable addition of MMT–STAB in polymerization was found to be no more than 2.0 wt% of VAc. In addition, both PVAc and PVAc–MMT–STAB exhibited the normal stress effect (or Weissenberg effect), also known as the 'pole-climbing phenomenon'.     

Viscometric determination of the molecular weight of polymers in the low molecular weight region

In order to overcome the difficulty of the determination of the molecular weight of a polymer in the low molecular weight region by viscometry using the Mark–Houwink–Sakurada (MHS) equation, we have proposed the Dondos–Benoit relationship [η]^?1 = A₂ + AM^?1/2, for a number of polymer–solvent systems, for which we give the numerical values of the parameters A₁ and A₂. Furthermore, we suggest a method for the determination of the above parameters using the MHS constants a and k.     

Rheology of a cellulose graft copolymer. Comparison with other closely packed gel thickeners

Hydrolyzed cellulose–polyacrylonitrile graft copolymer is a polyelectrolyte gel suspension with a high viscosity in water. It is a closely packed swollen gel particle suspension in the appropriate concentration range and has similar rheological properties to other thickeners of this type. Viscosities η in either water or salt solution are reduced to a single master curve by use of the reduced viscosity function η/cQ, where c is weight fraction of polymer and Q is swelling volume in excess solvent of the same ionic strength. The effective molecular weight between crosslinks, M_c, determined from shear modulus, corresponds to M_c values for other closely packed gel thickners of similar η/cQ. Among all examples of this class of thickener, the plateau values of η/cQ, which occur at cQ > 2, are approximately inversely proportional to M_c.     

A VSE equation of state for liquids. VI. Polymethylene 450–650 K

This is the sixth and final paper in the series under the above title. In prior papers, a VSE equation of state was proposed and applied to a variety of liquids at ambient pressure, but over broad ranges of temperature. Comparisons of thermodynamic quantities calculated from the equation were made with published measured values. In the present paper v, α, s, γ, c_v, and c_p are calculated for polymethylene from our equations between 450 and 650 K, but extensive corresponding values have not been measured on polymethylene at these temperatures. One approximate value of c_p and one value of γ, measured on high-density polyethylene, show that our predicted values for polymethylene must be of the correct order of magnitude. Several characteristics of the liquid state, observed during the progress of this study (1954–1979), are listed and discussed.     

Molecular Orbital Based Design Guideline for Hypergolic Ionic Liquids

Currently, monomethyl hydrazine is the most widely used hypergolic rocket fuel. Due to its high toxic vapor, there is a thrust towards developing low‐toxic hypergolic fuels. Ultra‐low vapor pressure ionic liquids are one such potential category of fuels. However, designing ionic liquid with ignition delay comparable to monomethyl hydrazine is a challenge, because fundamental understanding of the hypergolic nature of ionic liquids is far from clear. This work used the computed energy gap values between the highest occupied molecular orbitals (HOMO) of the anions for a series of ionic liquids and the lowest occupied molecular orbital (LUMO) of HNO₃, and variation in the computed relative heats of formation, ΔH_f, of these anions to develop correlations to predict hypergol activity between an ionic liquid fuel and nitric acid as the oxidizer. The observed trends in HOMO LUMO energy gap and ΔH_f values can be used successfully to verify not only hypergolicity of known systems but also the lack of this phenomenon in OH⁻ and BF₄⁻ based ionic liquids. It was shown that through suitable substitution of electron withdrawing or electron donating groups in the anion, the energy gap and the ΔH_f values could be tailored into an optimal range that would have a high probability for the new system to exhibit hypergolic reactivity. To validate our method, we suggest herein new ionic liquid structures for synthesis and experimental screening.     

The viscoelastic properties of rubber–resin blends. II. The effect of resin molecular weight

In blends of rubber and low molecular weight resins, the compatibility of the system controls the viscoelastic properties and ultimately the performance of the composition as a pressure sensitive adhesive. The effect of the resin molecular weight on compatibility was examined by studying rubber–resin blends prepared from resins which represent a range of molecular weights. Viscoelastic properties were measured using a mechanical spectrometer on 1:1 blends of rubber and a series of polystyrene resins and poly(vinylcyclohexane) resins. Based on plots of G′ and tan δ vs. temperature, blends of natural rubber and polystyrene resin show incompatibility at resin M_w of about 600 and above. Blends of natural rubber and poly(vinyl cyclohexane) are incompatible at resin M_w of about 1800, but are compatible at M_w of about 650. Blends of styrene–butadiene rubber and polystyrene resins are compatible at resin M_w of about 650 but appear to contain a low volume incompatible phase at M_w of about 900. Therefore, the compatibility of a rubber–resin blend depends upon the molecular weight of the resin. Even systems expected to be compatible will show evidence of incompatibility as the molecular weight of the resin is raised above some limiting value.     

Capture of H2S from binary gas mixture by imidazolium‐based ionic liquids with nonfluorous anions: A theoretical study

Selective capture of H₂S from gas mixture is essential to reduce its undesirable high corrosiveness and toxicity. Ionic liquids have been proposed as a promising material, and there is a need to clarify the capture mechanisms and search for optimal combination of cation and anion for application. This work aims to elucidate the interactions between H₂S and nonfluorous imidazolium ionic liquids (NIILs) at a molecular level. The effects of hydroxyl group on the tail of alkyl chain, and combinations of imidazolium cations and nonfluorous anions on H₂S capture are explored using quantum chemistry calculations. Furthermore, molecular dynamics simulations are used to explore the microstructural features of NIIL–H₂S–CH₄ mixture systems. It is found that the hydroxyl groups in the cations is essential in governing the absorption properties of NIILs, including the interaction sites for hydrogen bonding, interaction geometries and energies, diffusion coefficients, and organization of H₂S and CH₄ around cations and anions. A molecular viewpoint to design appropriate ionic liquids for promoting their applications for H₂S capture is provided. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3824–3833, 2013     

Molecular weight distribution of a segmented copolymer of PET–PCL

A recently developed method of combining both the results of static and dynamic laser light scattering (LLS) was applied to characterize the segmented copolymer of poly(ethylene terephthalate-co-caprolactone) (PET–PCL) with 48% PET content. Unlike the traditional three-solvent method proposed by Bushuk and Benoit for copolymers, this method requires only two solvents. For each solvent, the apparent weight average molecular weight (M_w,app) was measured by static LLS. Then M_w,app was used as a constraint to convert the line-width distribution from dynamic LLS into the apparent molecular weight distribution. Finally, the two apparent molecular weight distributions were combined to give both the true molecular weight distribution and the estimated chain composition distribution of the copolymer. We found that the PET–PCL sample with 48% PET is nearly uniform in the chain composition. © 1995 John Wiley & Sons, Inc.     

Influence of molecular structure on the rheological and processing behavior of polyethylene resins

The rheological and processing behavior (melt fracture performance) of linear lowdensity polyethylenes (LLDPEs) is studied as a function of both the weight average molecular weight (M_w) and its distribution (MWD). A number of LLDPE resins having different molecular characteristics were tested, with essentially one characteristic (M_w or MWD) changing at a time. The first series of resins consisted of nine samples having a wide range of polydispersities (3.3–12.7) and nearly constant M_w and short chain branching. The second series had six resins with varying M_w (51,000–110,000) but fixed MWD (about 4). The influence of M_w and MWD on the viscosity profiles, linear viscoelastic moduli as expressed by means of a discrete spectrum of relaxation times, extrudate swell, and melt fracture behavior for these resins is reported. Correlations between the molecular characteristics of the resins and their rheological and processing behavior are also reported. It is found that for a given molecular weight, the optimum melt fracture performance is obtained at a specific polydispersity value, and it is characterized by a minimum relaxation time for the resin defined in terms of recoverable shear.