Bulk polymer/solvent interactions for polyethylene and EVA copolymers,below their melting temperatures

In this work, the Flory–Huggins parameters corresponding to the amorphous phase of a polyethylene (PE) and two ethylene–vinyl acetate (EVA) copolymers (with 18 and 33 % vinyl acetate content, respectively) samples, with different solvents have been determined below the melting temperature of the polymers, in order to quantify the bulk interactions of these polymer/solvent systems. The employed solvents were a dispersion solvent (cyclohexane), a polar solvent (vinyl acetate) and an association solvent (methanol). Initially, the inverse gas chromatography measurements allowed obtaining the retention volumes, activity coefficients and overall Flory–Huggins parameters of every polymer/solvent system. According to these parameters, in all cases, the more compatible solvent was cyclohexane, so it was selected as the probe to calculate the percentages of crystallinity at room temperature, whose results were in agreement the literature data (35 % for PE, 29 % for EVA18, and 12 % for EVA33). The percentage of crystallinity allowed determining the amorphous Flory–Huggins parameters which are the ones which take into account just the bulk interactions in a polymer/solvent mixture. The Flory–Huggins parameter results show that, to accurately study the vapor–liquid equilibrium between a polymer and a solvent (bulk interactions), when the range of studied temperatures is below the melting point of the polymer, it is crucial to calculate the amorphous contribution (χ _amorphous) on the overall Flory–Huggins parameter. In the case of this study, the lower the vinyl acetate content (higher crystallinity), the higher the difference between the overall and amorphous Flory–Huggins parameters is. Analyzing the interactions between the three polymeric materials and the solvents it can be noticed that, for the most compatible solvent (cyclohexane), χ _amorphous represents the less contribution, or the highest correction, to the overall Flory–Huggins parameter (around 50 % for PE and EVA18, and 79 % for EVA33, the less crystalline polymer).     

Inverse gas chromatography study of polyvinylacetate–solvent and polyethylene–solvent systems

In this article, the thermodynamic behavior of polyvinylacetate (PVAc)–solvent, and polyethylene (PE)–solvent mixtures have been studied by determining the thermodynamic sorption parameters (enthalpy, entropy, and free energy), the mass‐based solvent activity coefficients (Ω) and the Flory Huggins parameters (χ), by means of inverse gas chromatography (IGC) measurements. According to the Flory Huggins parameters of the PE–solvent mixtures, determined between 40 and 60°C the compatibility (the ability to interact with each other) of this polymer with the different types of solvents follows this order: dispersion solvents > polar solvents > association solvents. In the case of PVAc mixtures, the thermodynamic parameters were determined between 60 and 80°C, only for polar‐type and association‐type solvents due to, in the studied temperature range, the retention diagrams of dispersion solvents show that there are not bulk interactions. The Hildebrand solubility parameters of both polymers were also determined, according to Guillet procedure. The higher values of PVAc material (14.1 MPa^0.5 for PE and 19.8 MPa^0.5 for PVAc, at 60°C) are related to the strong interactions of vinyl acetate monomer. POLYM. ENG. SCI., 56:36–43, 2016. © 2015 Society of Plastics Engineers     

Effects of the pH,concentration, and solvents on the ultrasonic degradation of poly(vinyl alcohol)

The ultrasonic degradation of poly(vinyl alcohol) was investigated at different pHs of the solvent, in different water/solvent binary mixtures, and at different polymer concentrations. The samples were analyzed with gel permeation chromatography. The degradation rate coefficients were determined with a continuous distribution model. A higher degradation rate was obtained at pH extremes, in better solvents, and at lower polymer concentrations. The results are explained and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4888–4892, 2006     

Ultrasonic degradation of macromolecules in solution. Study of degradation kinetics by estimation of free-radical scavenger DPPH and solution viscosity measurements

The kinetics of degradation of butyl rubber in two solvents, cyclohexane and toluene, was studied by two independent techniques: viscosity measurements and free-radical estimation as a function of DPPH consumed. The general shape of the rate curves in the two cases is similar, but not identical. The rate given by estimation of DPPH is faster than that obtained from solution viscosity data. This has been attributed to the inherent limitations of the two methods for the quantitative determination of the number of breaks occurring in the polymer molecules. The rate is also reduced as the viscosity of the solution medium is increased, which may be correlated with the reduction of the cavitation effect responsible for degradation. The degradation rates in two solvent media initially having the same viscosity were unequal. This may be due to different solvent–solute characteristics, which means that the viscosity and cavitation change to different extents in the two cases throughout the course of degradation. The limiting degree of Polymerization (DP)_∞ obtained after prolonged irradiation has been found to be dependent on parameters such as intensity of irradiation, solution viscosity, and initial DP of the molecules.     

The influence of the solvent upon the low shear viscosity of styrene–acrylonitrile copolymer solutions

This paper describes the results of an experimental investigation concerning the effect of polymer–solvent thermodynamics on low-shear viscosity of copolymer soltions. Thermodynamic parameters and low-shear solution viscosities were measured for solutions of polystyrene homopolymer and styrene–acrylonitrile copolymers in four solvents: benzene, dioxane, methyl ethyl ketone, and dimethylformamide. The thermodynamic quality of a solvent for a polymer is characterized by free-energy-of-mixing parameters. These quantities are: the Flory-Huggins thermodynamic interaction parameter χ, the second virial coefficient (from light scattering), the intrinsic viscosity, and the polymer expansion factor. The thermodynamic interaction between a solvent and a polymer in solution influences the rheological behavior of the system. At low concentrations of polymer in solvent, the low-shear solution viscosity is larger in a good solvent than in a poor solvent. In solutions of higher concentration, the reverse may be true and the viscosity is often significantly larger in a poor solvent than in a good one. These results are not predicted quantitatively by existing theory. The parameters in existing viscosity correlation techniques are found to be solvent dependent. The so-called entanglement concentrations for polymer solutions are not unique for a particular polymer but are related to the free energy of mixing polymer with solvent.     

Influence of temperature on the ultrasonic degradation of poly(vinyl acetate) and poly(vinyl chloride)

This study investigates the effect of temperature on the ultrasonic degradation of polyvinyl acetate and polyvinyl chloride in chlorobenzene. The time evolution of molecular weight distribution was determined using gel permeation chromatography. Continuous distribution kinetics was used to obtain the degradation rate coefficients. The rate coefficients decrease with increasing temperature, and this is attributed to the increase of vapor pressure and the decrease of kinematic viscosity. The degradation rate coefficient also changes sharply near the glass transition temperature, indicating that this factor may play a role in the degradation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2818–2822, 2003     

Thermodynamic interactions of solvents with styrene–butadiene–styrene triblock copolymers

Fundamental thermodynamic interaction data for various solvents with two styrene–butadiene–styrene triblock copolymers (Kraton D-1101 and Kraton D-1300X) have been collected by the use of inverse gas chromatography at infinite dilution. Experimental results are presented for nine D-1101/solvent systems and nine D-1300X/solvent systems at 308, 328. and 348 K. Weight-fraction activity coefficients and Flory–Huggins χ interaction parameters have been calculated from the retention volumes. The χ parameter is used as a measure of the strength of interaction and therefore as a guide in the prediction of polymer–solvent compatibility. In addition, partial molar heats of mixing, ΔH_m^∞, and heats of solution, ΔH_s, were determined. The Hildebrand–Scatchard solubility theory was combined with the Flory theory in order to estimate the solubility parameter of the thermoplastic rubbers at the three different temperatures.     

Dynamics of lipase catalyzed enzymatic degradation of poly(bisphenol‐A carbonate)

Poly(bisphenol‐A carbonate) (PC) was degraded in solution at various temperatures (26–70°C) by different lipases, Candida Rugosa (CR), Hog Pancreas (HP), Lipolase (LL), and Novozyme (NV), in various solvents. The degradation of PC was monitored using gel permeation chromatography (GPC). The molecular weights of oligomers obtained were around ～1,400 irrespective of the lipases used. Continuous distribution kinetics was proposed to determine the rate coefficients of the polymers and deactivation of the enzyme. The FTIR analysis of the polymer before and after degradation showed that there is large reduction of carbonate linkages and generation of hydroxyl and acidic groups in the broken chains. The optimal temperatures for HP and other lipases were 50 and 60°C, respectively. HP showed higher degradation activity at lower temperatures and the overall degradability of the lipases was in the order of LL > CR > NV > HP. The effect of viscosity and polarity of the solvents on the degradation of the polycarbonate was also investigated. While the degradation rate decreased with viscosity, it increased with polarity for the solvents. © 2003 Wiley Periodicals, In6c. J Appl Polym Sci 91: 2391–2396, 2004     

Viscosity–molecular weight relationships for poly(ethylene terephthalate) in hexafluoroisopropanol–pentafluorophenol using SEC–LALLS

Viscosity–molecular weight characterization of poly(ethylene terephthalate) (PET) in hexafluoroisopropanol (HFIP), pentafluorophenol (PFP), and HFIP/PFP is reported for the first time using size exclusion chromatography-low angle laser light scattering (SEC–LALLS) measurements. These strong solvents are capable of dissolving PET under very mild conditions and therefore minimize polymer degradation. In addition these solvents are capable of dissolving PET samples which have poor solubility in more traditional PET solvents such as orthochlorophenol (OCP) and phenol/tetrachloroethane (PTCE). By combining molecular weight information, obtained without the need of any SEC calibration curves, with intrinsic viscosity measurements, on several broad molecular weight PET samples, the Mark–Houwink coefficients for the five PET–solvent systems mentioned above have been determined. The coefficients correspond to those which would be obtained by using a large number of relatively monodisperse samples of PET covering a molecular weight range of about 2 × 10³ to 2 × 10⁵. Data is also provided which shows that intrinsic viscosities for PET in HFIP, PFP, HFIP/PFP, OCP, and PTCE can be determined from a single viscosity measurement at a finite concentration. Data for interconverting intrinsic viscosities determined in any of these five solvents is also given.     

Solution properties of hexamethylene diisocyanate based polyurethane cationomers

Summary Viscosity measurements of hexamethylene diisocyanate based cationomer in various polarity solvents and in water/solvent were performed. For the un-ionized sample in pure MEK and DMF, the reduced viscosities of both solutions follow the Huggins relation. For ionized samples in pure MEK and DMF, aggregation of the ionized hard segments still exist in the MEK and DMF solution in the high polymer concentration range, whereas chain expansion occurs in the DMF solution in the low polymer concentration range. For ionized samples in water/solvent mixtures, at a mixing ratio (by weight) of 0.12, the reduced viscosity indicates an aggregation behavior in MEK/water and a polyelectrolyte behavior in DMF/water. At a mixing ratio (by weight) between 0.24 and 4.44, the reduced viscosity indicates a polyelectrolyte behavior. The polymer particles change from a clear elastic gel to microspheres. For emulsions of the ionized samples, the reduced viscosity exhibits polyelectrolyte behavior.     

A novel method of selecting solvents for polymer electrospinning

The selection of a desirable solvent or solvent system as the carrier of a particular polymer is fundamental for the optimisation of electrospinning. Solvent selection is pivotal in determining the critical minimum solution concentration to allow the transition from electrospraying to electrospinning, thereby significantly affecting solution spinnability and the morphology of the electrospun fibres. 28 solvents diversely positioned on the Teas graph were studied for their solubility and electrospinnability for making polymethylsilsesquioxane (PMSQ) solutions. The results are combined and mapped on the Teas graph using different colour codes. Based on this new spinnability-solubility map, various solvent systems for PMSQ are methodically developed. Solvents are selected to produce binary solvent systems that have solvent parameters close to a good single solvent for electrospinning of the polymer solution. This work shows that solvents of high solubility do not necessarily produce solutions good for electrospinning. Polymethylsilsesquioxane solutions of the same concentration in solvents of partial solubility showed better spinnability than solutions in solvents of high solubility. A methanol-propanol binary solvent system produced electrospun fibres with high surface porosity, showing that high volatility and high vapour pressure difference among solvents mixed can induce phase separation in electrospinning. It is noteworthy that the binary solvent system mixing 2-nitropropane (high solubility) and dimethylsulphoxide (non-solvent), neither of which exhibited high volatility, also produced highly porous electrospun fibres. This demonstrates that phase separation can be induced by solubility difference in the electrospun polymer solution.     

Viscosities of moderately concentrated solutions of polyethylene in ethane,propane, and ethylene

The viscosities of moderately concentrated solutions of low-density polyethylenes in ethane, propane, and ethylene have been measured at low shear rate in the temperature range of 150–250°C and in the pressure range of about 15000–30000 psi. Within the precision of the measurements, the relative viscosity is independent of pressure over the range investigated but increases as the solvent is changed from propane through ethane to ethylene. The activation energy for the relative viscosity in ethane varies from about 0.5 to 2.5 kcal/mole as the concentration changes from 5 to 15 g/dl. Effects of polymer concentration and molecular weight on solution viscosity in ethane at 150°C have been determined, and all of the data can be represented by a single straight-line plot of the logarithm of relative viscosity versus the intrinsic viscosity (in p-xylene at 105°C) times concentration. This simple relation is valid over wide ranges of polymer concentration and molecular weight and over more than two orders of magnitude of relative viscosity. The solution viscosities of the polyethylenes in the three supercritical fluid solvents used appear surprisingly low at first sight. This behavior is partly a result of the low solvent viscosities but also might mean that the polymer has an abnormally low segmental friction factor compared to that in solutions under more familiar conditions.     

Miscibility studies on poly(ethylene glycol)/dextran blends in aqueous solutions by dilute solution viscometry

Miscibility of poly(ethylene glycol) (PEG) with dextran (Dx) was investigated by dilute solution viscometry. Dilute solution viscosity measurements were made on ternary systems, polymer (1)/polymer (2)/solvent (H₂O), for four different average molecular weights of PEG and Dx. The intrinsic viscosity and viscometric interaction parameters were experimentally measured for the binary (solvent/polymer) as well as for the ternary systems by classical Huggins equation. Degree of miscibility of these polymer systems was estimated on the basis of the four following criteria: (1) the sign of the Δk_AB, (2) the sign of α, (3) the sign of ΔB, and (4) the sign of the μ. Based on the sign convention involved in these criteria, immiscibility was observed in most systems. The miscibility of all these systems in accordance with the interactions between the unlike polymer chains rather the polymer–solvent interactions were investigated depending on molecular weight of polymer sample. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 453–460, 2004     

A study of some equation‐of‐state parameters of poly(methylhydrosiloxane‐co‐dimethylsiloxane) with some solvents by gas chromatography

Trace amount of methyl acetate, ethyl acetate, tert‐butyl acetate, pentane, hexane, and heptane were passed through the chromatographic column loaded with poly(methylhydrosiloxane‐co‐dimethylsiloxane) coated on Chromosorb W. The retention diagrams of the solvents on the copolymer were plotted by means of specific retention volumes at temperatures between 40 and 80°C by inverse gas chromatography technique. In this study, some thermodynamic interaction parameters such as Flory–Huggins polymer–solvent interaction parameter, equation‐of‐state polymer–solvent interaction parameter, effective exchange energy parameter, and weight fraction activity coefficients at infinite dilution of the solvent were determined. Then, the exchange enthalpy parameter and entropy parameter were determined by using a relation for the enthalpy interaction parameter of the equation‐of‐state theory, which is arranged for the inverse gas chromatography conditions. Later, the partial molar heat of sorption and the partial molar heat of mixing were obtained. The solubility parameter of this copolymer was determined as 6.64 (cal/cm³)^1/2 at room temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1627–1631, 2007     

Prediction of second virial coefficients from intrinsic viscosities

One of the most readily available characteristics of a polymer sample is its intrinsic viscosity in a particular solvent. This datum can often be estimated reasonably from a single relative viscosity measurement. A number of theories permit the calculation of the second virial coefficient of a polymer/solvent mixture given the intrinsic viscosity and polymer molecular weight. The intrinsic viscosity of the polymer under theta conditions is also needed, but this can be estimated, if necessary, from the molecular weight. This article compares the efficiencies of various alternative models for the prediction of second virial coefficients of a series of polymers and solvents. The most effective technique for this purpose first calculates the concentration-dependent equivalent hydrodynamic volume of a solvated polymer coil. This value is used with a primitive statistical mechanical theory for virial coefficients of hard-sphere suspensions to calculate the osmotic pressure or turbidity of the polymer solution. These simulated experimental values are fitted with a least-squares line as in the real experiment, and the second virial coefficient is derived from the slope. The computations are relatively simple; the average deviation between observed and predicted virial coefficient was less than 16% for a variety of polymer types, molecular weights, and solvents.     

Thermodynamic study of polymer–solvent systems by reversed-flow gas chromatography

Reversed-flow gas chromatography, a new method for studying heterogeneous catalysis, diffusion, adsorption, evaporation, and other related phenomena, is now applied to the determination of activity of the solvent in a polymer–solvent system in the whole range of polymer concentration, as well as for the calculation of excess partial molar thermodynamic functions of mixing. The systems used were polystyrene in cyclohexane, polyvinylacetate in cyclohexanone and polyvinylpyrrolidone in methanol. In the first system, which was studied in detail, weight fraction activity coefficients (a₁/w₁) at several temperatures (333.8–348.1 K) and various polymer concentrations (0.020–0.131 g/g) were determined. From the latter parameters weight fraction activity coefficients at infinite dilution (a₁/w₁)^∞ were computed. Flory–Huggins interaction parameters x and solubility parameters δ₂ were also determined. Finally, the thermodynamic parameters found by the present method are compared with those determined by other techniques or calculated theoretically.     

Ultrasonic degradation of solutions of poly(vinyl acetate) in tetrahydrofuran

The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in tetrahydrofuran (THF) at 20, 25, 30, and 35°C to investigate the effects of the temperature and solution concentration on the rate of degradation. The degradation kinetics were studied with viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of THF, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of THF and the viscosity and concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in the collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2373–2376, 2005     

Solubilities,viscosities and unperturbed dimensions of poly (2,6-diisopropylphenyl methacrylate)

The dilute solution properties of poly(2,6-diisopropylphenyl methacrylate) (PDPP) in various solvents were studied by viscosity, exclusion chromatography and osmotic pressure measurements. The Mark-Houwink-Kuhn-Sakurada relationships were established. The unperturbed dimensions, the rigidity factor σ, the characteristic ratio C∞ and the thermodynamic parameters were determined using the Stockmayer-Fixman equation and from data in theta solvent (binary mixture). The rigidity factor of PDPP is abnormally high. The conformational behaviour of this polymer is analysed in terms of the effect of the side chain structure. The results are compared with other polymers of the same series.     

Comparative studies on the effects of casting solvent on physico‐chemical and gas transport properties of dense polysulfone membrane used for CO2/CH4 separation

The effects of casting solvents on the physico–chemical and transport properties of polysulfone membranes were investigated. Comparative analysis of the properties of membranes prepared from a new solvent (diethylene glycol dimethyether, DEG) and other commonly used solvents (1‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, dimethyl sulfoxide and N,N‐dimethylformamide) were performed using gas permeation, X‐ray diffraction, scanning electron microscopy, thermogravimetric, and Fourier transform infrared spectroscopy analyses. The degree of polymer–solvent interaction was evaluated using the solvent molar volume, and Hansen and Flory–Huggins parameters. Membrane prepared from DEG displayed a relatively higher permeability of 29.08 barrer and CO₂/CH₄ selectivity of 23.12 compared to membranes prepared from other solvents. This improved performance was attributed to the better interaction between the DEG solvent and polysulfone than other solvents that were considered. DEG has the highest molar volume of 142.280 cm³/mol and the lowest Flory–Huggins parameter of 0.129. Thus a thorough evaluation of polymer–solvent interaction is very crucial in preparing membranes with optimum performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42205.     

Vapor–liquid equilibria for benzene/polybutadiene and cyclohexane/polybutadiene systems at 333, 355, and 373 K using gas chromatography

A perturbation chromatography apparatus has been designed and constructed for determining the vapor–liquid equilibrium between a two-component (solvent/helium) vapor phase and a two-component (polymer/solvent) liquid phase. The apparatus performed very well, giving reproducible and reliable results that agree with independent, previously reported studies. All tests of the equipment indicated that it was successful in meeting the conditions of low column pressure drop, small perturbations, and slow flow rate that are required for perturbation chromatography. Binary polymer/solvent data were obtained for polybutadiene (PBD)/benzene or polybutadiene/cyclohexane systems at solvent partial pressures to 40 kPa and for n-hexane at infinite dilution, all at the three temperatures of 333.15, 355.00, and 373.15 K. The experimental data for each system can be represented within experimental error by the Flory–Huggins polymer solution theory using a single binary interaction parameter that is independent of temperature and concentration.