Binary Polymer Systems Research Articles

Miscibility of Poly(methyl methacrylate)-/Poly(vinyl acetate) Blend in 2-Dimensional State at the Air/Water Interface

The miscibility in binary polymer systems in 2-dimensional state at the air/water interface was investigated by the relationship between the mean molecular area at a constant surface pressure and the mole fraction of one component in the binary mixtures of poly(methyl methacrylate)(PMMA) and poly(vinyl acetate)(PVAc). Compatibilization of the immiscible PMMA/PVAc blend at the air/water interface was achieved by introducing carboxyl acid to either of the two component polymers.

Development and evaluation of verapamil resinates-loaded controlled release microcapsules using a binary polymer system in drug release rate modulation

The application of polystyrene-​divinylbenzene sulfonic acid-​based ion exchange resins as a carrier system for the sustained delivery of verapamil hydrochloride was primarily evaluated. A large degree of variation in the loading efficiencies (drug loaded: 19.17-​48.86​%)​, was obsd. between the different drug-​resin complexes depending on resin type and drug​/resin ratio. Upon comparing different carrier resins at drug​/resin ratio of 1:1, verapamil release in either 0.1 N HCl or phosphate buffer (pH 7.4) was in the order of Amberlite MB-​1 > Amberlite IRP-​69 (Na+) ≥ Amberlite IR-​120 (Na+) > Dowex-​50 W (Na+)​. For further retardation of the drug release rate, microencapsulation of the strongly acidic cation exchange resin (Amberlite IR-​120 (Na+)​) loaded with verapamil hydrochloride (drug​/resin ratio of 1:1, resinate drug content: 48.86​%, core​/coat ratio of 1:2) was carried out by means of a modified emulsion-​solvent evapn. / extn. technique (ESE​/E) using different coating polymers, namely Et cellulose (EC)​, cellulose acetate phthalate (CAP)​, cellulose acetate butyrate (CAB) as well as CAB​/polystyrene (PS) binary polymer systems. The effect of polymer type, polystyrene concn. and core​/coat ratio on the yield, size distribution as well as release characteristics and surface topog. of the microcapsules were investigated. The results obtained revealed that polystyrene utilization as a complementary wall material at a particular compn. of 70:30 (​%) of CAB to PS was found to improve greatly the microcapsule yield, reduce the av. microcapsule size and modulate the in-​vitro release of the entrapped drug. On the other hand, the entrapment efficiencies increased and the release rate decreased with increasing microcapsule size and​/or theor. drug loading of CAB​/PS (30​%) - microcapsules. Kinetic assessment of the release data using different math. models showed that the drug release from CAB or CAB​/PS (7.5​%)​-​microcapsules (core​/coat ratio of 1:2) was found to be best explained by a Fickian-​diffusion kinetics (a diffusion-​controlled model for a planar matrix)​, whereas the calcd. exponential release exponents (n values) of the empirical equation (Mr/M∞ = Ktn) indicated that the release behavior of CAB​/PS (30​%) - microcapsules was a non-​Fickian-​diffusion kinetics, confirming that a diffusion / chain relaxation-​controlled release mechanism was operative. Overall, this study demonstrated that the prepd. CAB​/PS microcapsules were capable of releasing their drug content gradually for an extended period of time, irresp. of variations in the pH of the gastrointestinal tract and exhibited slower release rates as compared with the com. sustained-​release product (Isoptin(SR) tablets)​.

Comparative study of kinetics of structure formation in binary polymer systems and inorganic glasses

Early and late stages of phase separation in polybutadiene — diethylphthalate and sodium-silicate glasses were studied within the framework of Cahn-Hilliard and Lifshitz-Slezov theories, mean sizes of phase particles, correlation length and diffusion coefficients were estimated. It has been shown that the main features of kinetics and morphology of the phase decomposition process are similar for both inorganic glasses and polymer solutions, absolute values of diffusion coefficients at different stages of the process are almost equal to the self-diffusion coefficient of the slowest component.

Kinetics of Droplet Growth in Gelatin/Maltodextrin Mixtures Following Thermal Quenching

Rates of droplet growth, following the thermal quenching of gelatin/maltodextrin mixtures into the incompatible region of the phase diagram, have been obtained from turbidity measurements. The results from experiments carried out at temperatures that prohibit the involvement of biopolymer conformational ordering and gelation are in good agreement with those obtained by similar studies of binary synthetic polymer systems and with theoretical predictions. For mixtures that would phase separate at temperatures above the gelatin ordering temperature (T0) but which are quenched directly to temperatures below this, droplet growth shows modified kinetics owing primarily to restrictions imposed by the viscosifying continuous phase. However, for a mixture that was initially observed to be miscible following quenches to temperatures below T0, it is proposed that biopolymer ordering induces phase separation, which was found to occur after significant delay periods.

Disorder in Binary Polymer Systems near Their Critical Region Studied by Low-Frequency Raman Spectroscopy

Low-frequency Raman spectra of a diblock copolymer of polystyrene and polyisoprene (PS−PI) and a polystyrene−polybutadiene blend (PS−PB) have been studied. Low-frequency features, viz., the quasi-elastic lines, Boson peaks, and vibrational lines, if present, have been fitted to known theoretical expressions. It has been found for the first time that, in the diblock, the Boson peaks manifest themselves at frequencies characteristic for homopolymers; that is, big enough regions formed by pure components exist in the diblock. The temperature dependence of the overall integrated intensity in the low-frequency region undergoes a break at the order−disorder transition temperature of the PS−PI diblock and manifests a marked nonlinearity near the temperature of macrophase separation of the PS−PB blend.

Modelling of high-pressure phase equilibria using the Sako–Wu–Prausnitz equation of state: I. Pure-components and heavy n-alkane solutions

A cubic equation of state (EOS) proposed by Sako, Wu and Prausnitz (SWP) [T. Sako, A.H. Wu, J.M. Prausnitz, J. Appl. Polym. Sci. 38 (1989) 1839–1858.] is used to correlate phase equilibria in systems containing small and large molecules. Two pure-component parameters are fitted to vapour pressures (volatile molecules) and to liquid density data (non-volatile molecules and polymers), respectively. New pure-component parameters for nitrogen and a series of 1-alkenes are reported. The parameter estimation procedure for polymers and polymer-like substances such as heavy n-alkanes is refined. For this purpose, the repulsion parameter b is refitted to describe the correct slope of the PV-isotherms. This was found to be necessary to improve the phase-equilibrium calculations of binary polymer systems. Binary systems of ethylene with heavy alkanes or alkenes and one ternary system (ethylene/eicosane/tetracontane) are investigated. It is shown that one temperature-independent binary interaction parameter is sufficient to describe the phase equilibrium in these binary systems. The accuracy of the correlation in systems containing a heavy alkane is comparable or better than the results obtained from the Peng–Robinson (PR) EOS.

Charge- and energy-transfer processes at polymer/polymer interfaces: A joint experimental and theoretical study

When an exciton approaches the interface between two conjugated polymers, either energy or charge transfer can take place. We present a detailed experimental investigation of these processes in various binary polymer systems. The results are interpreted in the context of quantum-chemical calculations that provide estimates of the relative energies of intrachain versus interchain excited states in pairs of various PPV-related chains. In particular, we show that charge-transfer occurs at the interface between MEH-PPV and a cyanosubstituted PPV derivative, whereas energy transfer takes place at the interface of PPV with the same cyanosubstituted polymer. @S0163-1829~99!08031-5#

Excited-state energy- and charge-transfer at polymer/polymer interfaces

Abstract When an exciton diffuses to the interface between two conjugated polymers, either energy- or charge-transfermay take place. We present an experimental investigation of these processes in various binary polymer systems. These results are consistent with calculations of the relative energies of the intrachain and interchain excited states on pairs of different PPV-related chains. In particular, we show experimentally and theoretically that charge transfer occurs at the interface between MEH-PPV and a cyano-substituted PPV derivative, whereas energy transfer occurs at the interface of PPV with the same cyano-substituted polymer.

Theoretical determination of the theta temperature for solvent–polymer systems

The miscibility behavior of five binary polymer–solvent systems was studied by means of the Flory–Huggins theory. The theta temperature and the entropic and energetic Flory–Huggins parameters were calculated for these systems. The coordination number in the Flory–Huggins model and the interaction energy parameters were determined using a molecular simulation technique based on a Monte Carlo approach, which takes into account the constraints associated with excluded volume. In all cases, the critical temperature (Tc) values were calculated and compared with the experimental data. Thermodynamic parameters were obtained by plotting 1/Tc versus 1/x212+1/2x2 curve, where x2 is the degree of polymerization. This study shows a further application of the Flory–Huggins theory combined with molecular simulation techniques, for the model parameter determination, which was previously proposed by C.F. Fan, B.D. Olafson, M. Blanco, Macromolecules 25 (1992) 3667 [1]. In addition, the limitations of the methodology proposed by C.F. Fan, B.D. Olafson, M. Blanco, Macromolecules 25 (1992) 3667 [1], for miscibility calculations of binary polymer systems, are further discussed with special attention given for the model parameter determination.

Compatibility studies of polymer–polymer systems by viscometric techniques: nitrile-rubber-based polymer blends

Interactions in binary polymer systems have been analysed from the viscosity behaviour. Dilute solution viscosity measurements were made on three different ternary polymer (1)/polymer (2)–solvent (3) systems, i.e. acrylonitrile–butadiene rubber (NBR)/polystyrene, NBR/poly(styrene– co–acrylonitrile), NBR/poly(acrylonitrile– co–butadiene–styrene) in chloroform, as a function of blend composition. The polymer–polymer interaction parameter χ i(p–p) and the corresponding polymer–solvent interaction parameter χ i(p–s) were determined for all the blend systems. In order to predict compatibility, the interaction parameter term Δ b, obtained from modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight-average intrinsic viscosities of the two polymer solutions taken separately are used. These results were correlated with the experimentally determined densities and were found to be in agreement. Finally, the results are correlated with spectroscopic evidence.

Quantitative uses of the x-ray photoelectron spectroscopy valence band region in the analysis of polymer blends

Valence band spectra from similar polymers frequently show significant differences in appearance. Recent improvements in x-ray photoelectron spectroscopy instrumentation allow for valence band (VB) spectra with good signal to noise to be rapidly acquired. This study utilizes the VB region for the quantitative determination of the surface composition of several binary polymer systems using multiple linear regression. The systems evaluated include: poly(vinyl chloride)/poly(methylmethacrylate) blends which phase separate, chemically derivatized poly(vinyl methyl ketone), miscible polybutylmethacrylate isomers used in a study of liquid crystal alignment, and acrylate copolymers whose surface composition has been quantified using time-of-flight secondary ion mass spectrometry. For systems in which comparisons to core level spectra are possible, good agreement is found between quantification of core level and valence band spectra.

Chain correlations in linear and ring polymer blends

Our recent studies on linear–polymer blends are extended to include the linear/ring and ring/ring polymer systems. By means of the free energies of mixing, ring–polymer blends are found to be the most deviating from the Flory–Huggins theory presenting χ-parameters (interaction parameters) that depend more strongly on concentrations and molecular weights. The free energies are found to be smaller in the case of the ring–polymer blends, i.e., these blends are predicted to be the most stable, in accord with cloud-point experiments. The related neutron scattering χeff parameters are found to present higher concentration dependence than the χ-parameters of these systems. By means of their mean-square radii of gyration, both ring and linear chains are found to contract when a binary polymer system approaches the phase separation limit. Close to the spinodal, the contraction is relatively stronger for the chains of the smaller concentrations and lengths, while the three systems obtain an ideal behavior at the large molecular weight, N→∞, limit.

Application of Binary Polymer System in Drug Release Rate Modulation. 2. Influence of Formulation Variables and Hydrodynamic Conditions on Release Kinetics

The significance of factors such as drug solubility, polymer molecular weight, drug loading dose, compression force, and hydrodynamic conditions on drug release from a swellable hydrophilic delivery system was investigated. Hydroxypropyl methylcellulose (HPMC) and pectin were major polymeric constituents of the delivery system. Nifedipine, prednisolone, theophylline anhydrous, and diltiazem hydrochloride with solubilities of<0.001%, <0.1%, <1%, and >50%, respectively, were used as drug models. Results show that changes in pectin:HPMC ratios, HPMC molecular weight, and hydrodynamic conditions exert notable influences on release rate and release duration from the designed system. In the case of prednisolone, drug loading up to 30% (w/w) of the matrix composition (pectin:HPMC K4M; 3:6) had no effect on zero-order release kinetics, and the delivery system was insensitive to changes in compression force (2000 to 5000 lb). For nifedipine, theophylline, and diltiazem, determination of mean dissolution time (MDT) for 50 and 80% drug release provided accurate information on release behavior. The dominating effect of matrix composition over variations in drug solubilities in controlling drug release from the delivery system was evident from similarities in dissolution profiles. It is further shown that hydrodynamic stress and intensity of fluid flow causes greater attrition at the swollen periphery and is responsible for dramatic increases in release rates. This latter observation confirms that the mechanism of drug release from this swellable system is erosion dependent. Influence of polymer molecular weight and drug solubility on release kinetics and the potential of the delivery system is discussed.

Application of a Binary Polymer System in Drug Release Rate Modulation. 1. Characterization of Release Mechanism

A new binary polymer matrix tablet for oral administration was developed. The system will deliver drug at variable rates according to zero-order kinetics for total drug content and is manufactured by direct compression technology. Highly methoxylated pectin and hydroxypropyl methylcellulose (HPMC) at different ratios were used as major formulation components, and prednisolone was used as the drug model. The results indicate that by increasing pectin:HPMC ratios, release rates are increased, but zero-order kinetics prevail throughout the dissolution period (e.g., 3–22 h). Different pectin:HPMC ratios provide a range of viscosities that modulates drug release and results in rapid hydration/gelation in both axial and radial directions, as evidenced by photomicrographic pictures. This hydration-gelation contributes to the development of swelling/erosion boundaries and consequently to constant drug release. Combination of these particular polymers facilitates rapid formation of necessary boundaries (i.e., gel layer and solid core boundaries) to control overall mass transfer processes. The drug fraction released (Mt/M∞), release kinetics, and mechanism of release were analyzed by applying the simple power law expression Mt/M∞=ktn, where k is a kinetic constant and the exponent n is indicative of the release mechanism. The calculated n values for pectin:HPMC ratios of 4:5, 3:6, and 2:7 were >0.95, which is indicative of a Case II transport mechanism (polymer relaxation/ dissolution). The achievement of total zero-order kinetics is due to the predictable swelling/erosion and final polymer chain deaggregation and dissolution that is regulated by the gelling characteristics of polymers in the formulation.

Interfacial behavior of phase separated asymmetric compressible binary polymer blends

Our theory for the interfacial properties of compressible binary polymer systems [J. Chem. Phys. 98, 8994 (1993)] is generalized to treat phase separated asymmetric binary blends. The theory is illustrated by using a Sanchez–Lacombe approximation for the homogeneous system free energy and a Cahn–Hilliard–de Gennes expression for the square gradient contribution. These two ingredients enable the same theory to describe both the compositions of the coexisting phases and the interfacial properties. The coupled equations for the two concentration profiles are numerically unstable, and our perturbation–variational method for symmetric blends is extended to treat blends with asymmetry due to differing polymerization indices and/or interaction parameters. The zeroth order approximation, which uses a hyperbolic tangent interpolation between the generally different densities in the coexisting phases, is found to be extremely accurate in predicting the interfacial tensions and widths. Illustrations of the theory are provided for systems with upper and with lower critical solution temperatures, as well as with hour-glass miscibility gap type phase diagrams. The higher order perturbation–variation contributions mainly affect the total density variation through the interface, exhibiting several different patterns of density redistributions to lower the interfacial free energy. Computations are also provided for the pressure dependence of the interfacial properties.

Interpolymer association between poly(vinylpyridines) and poly(mono‐n‐alkyl itaconates). Effect of the n‐alkyl substituent

AbstractThe binary polymeric systems formed by some poly(mono‐n‐alkyl itaconates) and poly(2‐vinylpyridine) or poly(4‐vinylpyridine) are studied. Depending on the solvent, two different types of material have been synthesized. On the one hand, using methanol as common solvent, we have obtained solid polymer‐polymer complexes the composition of which is determined by the initial mixing conditions. On the other hand, pyridine avoids the complexation process, allowing to obtain a true solution of both polymers and, therefore, a solid polymer blend of known composition by solvent casting. Yields of the complexation and stoichiometries of the polymer‐polymer complexes have been analysed. In this way, a favoured composition in the range from 3:2 to 1:1 for the mole ratio (referring to repeating units) ratio poly(mono‐n‐alkyl itaconate):poly(vinylpyridine) was observed depending on the poly‐(mono‐n‐alkyl itaconate used). Differential Scanning Calorimetry and thermogravimetry have been employed to study the thermal behaviour of complexes and blends. Viscometry measurements have been performed to analyse the interactions in solution. One of the aims of this work has been to analyse the effect of the side group of the poly‐(mono‐n‐alkyl itaconate) in the mixing process as well as in the characteristics of the final products. In this way, higher complexation yields have been obtained using poly‐(mono‐n‐alkyl itoconates) with longer n‐alkyl side groups due to the additional stabilisation by solvophobic interactions. On the other hand, the poly(mono‐n‐alkyl itaconates) with longer n‐alkyl groups form polymer‐polymer complexes with a higher proportion of poly(4‐vinylpyridine), presumably due to their slower kinetics of complexation.

Specific heat peculiarities at the glass transition of binary polymeric systems

Specific heat peculiarities at the glass transition of binary polymeric systems

Binary polymer systems—interactions in solutions and their relationship to solid state compatibility

The interactions in binary polymer systems were analysed from the viscosity behaviour. For this purpose, the equations developed by both Krigbaum and Wall, and their modified forms by Williamson and Wright, and Catsiff and Hewett were used. The interaction between polymers in various systems has been qualitatively interpreted on this basis and correlated with results of spectroscopic studies. For the three binary systems examined, polyvinyl chloride (PVC)/polyethylene-co-vinyl acetate (EVA), polyvinyl chloride (PVC)/polystyrene-co-acryonitrile (SAN) and EVA/SAN, calculation of the interaction coefficient between unlike polymer molecules by the Krigbaum and Wall model modified by Williamson and Wright was found to be more applicable than the Catsiff and Hewett model and the original model proposed by Krigbaum and Wall.

Study of the miscibility and the phase behaviour of amorphous binary blends of poly(hydroxy ether of bisphenol A) and poly(styrene- co-acrylonitrile)

The phase behaviour of the binary polymer system consisting of poly(hydroxy ether of bisphenol A) (Phenoxy) and poly(styrene- co-acrylonitrile) (SAN) has been investigated by means of visual observations, light transmission measurements, differential scanning calorimetry and dynamic mechanical thermal analysis. The influence of both the blend composition and the copolymer composition of SAN on the miscibility of these binary blends was examined. All of the Phenoxy SANx ( x=5, 10.4, 15, 16.9, 29, and 34 wt% AN) blends studied were partially miscible. The composition of the two phases and the interaction parameters were calculated from measurements based on the glass transition temperatures.

Thin films of a binary polymer system: poly(vinyl acetate)/poly(dimethylsiloxane) layers at the air/water interface

Thin films of a binary polymer system: poly(vinyl acetate)/poly(dimethylsiloxane) layers at the air/water interface