Showing papers on "Miscibility published in 1989"

The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)

Abstract: Shear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow-induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow-induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow-induced phase separation.

Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization, melting behavior, and miscibility

Abstract: Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.

Miscibility and immiscibility of polyamide blends

Abstract: Comportement en solution de melanges d'un polyamide aromatique amorphe, 3Me6T, dans une serie homologue de polyamides aliphatiques

Miscibility of poly(vinyl chloride) with styrene/acrylonitrile copolymers

Abstract: Poly(vinyl chloride) (PVC) is shown to be miscible with styrene/acrylonitrile copolymers (SAN) having AN compositions from 11.5 to 26%. Blend samples were prepared using several methods, including solution casting, melt mixing, and precipitation of solutions by a nonsolvent. It is shown that the blend phase behavior is affected by preparation method due to the solvent effect, or Δχ effect, and lower critical solution temperature (LCST) behavior. The intramolecular repulsion between styrene and acrylonitrile units in SAN is shown to be the cause of miscibility using heats of mixing obtained from low-molecular-weight analog compounds. An FTIR analysis supplements the above results.

Enthalpy relaxations in polymer blends and block copolymers: Influence of domain size

Abstract: It is now well known that enthalpy relaxation measurements can be used to establish polymer-polymer blend phase behavior when the glass transition temperatures of the two polymers are virtually coincident. In the most simple cases, the aging kinetics of an immiscible blend will be representative of the pure polymers superimposed upon each other. However, in many cases the situation is more complicated because of the presence of interface material. In this paper the relation between enthalpy recovery peak separation, domain size and interface thickness is considered. The discussion is based on relaxation experiments involving di-block copolymers of styrene and 2-vinyl pyridine, blends of polystyrene and poly(2-vinyl pyridine) and blends of poly(vinyl chloride) and poly(isopropyl methacrylate). If the amount of material in the interface is too large due to either a small average domain size or a thick interface no peak separation will occur. The first situation is found for the microphase separated block copolymer system whereas the second possibility occurs for blends of polymers which are on the verge of miscibility like poly(vinyl chloride) and poly(isopropyl methacrylate).

Interactions in SMA‐SAN blends

Abstract: Styrene/maleic anhydride (SMA) and styrene/acrylonitrile (SAN) copolymers have previously been shown to form miscible blends when the MA and AN contents do not differ too greatly. It is shown here that this is the result of a weak exothermic interaction between the MA and AN units by measuring the heats of mixing for appropriate liquid analogs of the various monomer units. The region of copolymer compositions for miscibility of SMA-SAN blends is predicted from the Sanchez-Lacombe mixture theory using net interaction parameters calculated from the analog calorimetry results via a simple binary interaction model for copolymers. Lower critical solution temperature behavior was observed for blends of copolymers having compositions near the edge of the miscibility region. Various glass transition, volumetric, and FTIR results are discussed in terms of the interactions observed.

FTIR investigation of interactions in blends of PMMA with a styrene/acrylic acid copolymer and their analogs

Abstract: Fourier-transform infrared (FTIR) spectroscopy was used to examine the interactions in miscible blends of a styrene (92%)/acrylic acid (8%) copolymer (SAA8) with poly(methyl methacrylate) (PMMA) From the residue or interaction spectra and shifts of carbonyl and carboxylic acid stretching bands, it is concluded that there is a significant specific interaction involving hydrogen bonding between the carbonyl groups of the PMMA and the carboxylic groups of the SAA8 Similar FTIR spectra of some low-molecular-weight liquid analogs for the various monomer units of these polymers do not indicate a comparable interaction This explains why direct calorimetry with these compounds fails to model correctly the expected exothermic mixing of the blends Furthermore, the role of the aromatic moiety in the SAA polymer appears to reduce the degree of self-association of the carboxylic acid groups based on results for the model compounds Coupled with molecular rigidity, the above mechanism makes the carboxylic acid units in SAA8 more available for interaction with the PMMA carbonyls

Controllable specific interaction and miscibility in polymer blends, 1. Hydrogen bonding and morphology

Abstract: This paper concentrates on the effect of introducing hydrogen bonding into otherwise immiscible blends on their miscibility and morphology. 1,1,1,3,3,3-Hexafluoro-2-hydroxypropyl-containing units are incorporated in polystyrene which is then mixed with carbonyl-containing polymers such as poly(methyl methacrylate) and poly(butyl acrylate). The infrared study confirms the formation of hydrogen bonding and shows that the frequency shifts of hydroxyl stretching caused by the H-bonds are independent on whether the hydroxyl-containing units are in the monomer or connected to polystyrene or polyisoprene chains and whether they are randomly distributed along the chains or only located at the ends of the polymers. Hydrogen bonding in the blends dramatically enhances miscibility judged by differential scanning calorimetry and transmission electron miscroscopy (TEM). TEM observations reveal apparent and regular variations of the morphology in the blends with the content of the hydroxyl-containing groups, which implies that the morphological features of the blends, such as size of the dispersed phase, or extent of interpenetrating between the components are controllable simply by changing the structure and/or amount of the introduced groups forming the specific interaction in the blends.

Basic functionalization of polyethylene in the melt

Abstract: The production of a polymer containing basic functional groups via the reactive processing of polyethylene was investigated. Grafting of dimethylamino ethyl methacrylate, DMAEMA, to linear low-density polyethylene in the melt was carried out, and the effects of initiator type, feed composition, and reaction time and temperature were studied. The extent of grafting was determined by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy, and the degree of cross-linking was observed by measuring the products' melt indices. Thermal stability of the product was investigated using differential scanning calorimetry. Materials containing up to 3 wt% of grafted DMAEMA were prepared. The choice of appropriate feed compositions and reaction conditions allows the production of a material containing the maximum amount of grafted DMAEMA, while minimizing cross-linking. The grafted polyethylene produced under these conditions is more stable than the starting material, suggesting an antioxidant effect of the grafted moieties. The functional polymer produced should be of interest for the preparation of polymer blends with acidic polymers by virtue of the miscibility enhancement that could occur as compared with the hydrocarbon precursor.

Rigid rods with flexible side chains — A route to molecular reinforcement?

Abstract: Liquid-crystalline main-chain polyesters with polystyrene side chains of different length and number per main chain were synthesized using aromatic hydroxyfunctional polystyrene (PS) macromonomers, terephthalic acid derivatives and tert-butylhydroquinone as co-diol. The molecular weight of the polystyrene side chain was varied in the range from 1000 to 20000. The influence of this novel type of substituent on the solubility, thermal behaviour and miscibility with PS as a flexible matrix polymer is discussed. The properties of the new compounds are compared to those of the respective homopolyester. The graft copolyesters are, depending on the characteristics of the polymeric substituent, soluble in common organic solvents and their thermal transition points are lowered compared to the homopolyester. Compared to blends of the homopolyester, the improvement of miscibility of the polymer-substituted rigid rods with PS as an example for a flexible matrix polymer can be valued as a step to molecular reinforcement.

Partial miscibility behavior of the methane + ethane + n-docosane and the methane + ethane + n-tetradecylbenzene ternary mixtures

Abstract: Les compositions des phases, liquides et vapeur et les volumes molaires sont etudies a l'aide d'une relation fonction de la temperature et de la pression

Miscibility in poly-p-phenylene terephthalamide/nylon 6 and nylon 66 molecular composites

Abstract: Miscibility and crystallization of poly-p-phenylene terephthalamide (PPTA)/nylon 6 and nylon 66 composites prepared by coagulation of isotropic ternary sulfuric acid solutions were studied. The apparent crystallinity of nylon 6 and nylon 66 in molecular composites was investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. The solvation of nylon 6 crystals in PPTA matrix was observed when the PPTA content exceeds 70 wt%. Cross-hydrogen bonding seems to be responsible for the virtual disappearance of nylon 6 crystals. Specific interaction between PPTA and nylon 6 macromolecules and phase separation during thermal treatment has been discussed.

Characterization of Phase Behavior in Polymer Blends by Light Scattering

Abstract: It is well known that most pairs of high molecular weight polymers are immiscible. This is so because the combinatorial entropy of mixing of two polymers is dramatically less than that of two low molecular weight compounds [1–3]. The enthalpy of mixing, on the other hand, is often a positive quantity. Therefore, dissimilar polymers are only miscible if there are favorable specific interactions between them leading to a negative contribution to the Gibbs free energy of mixing. Miscible polymers tend to phase separate at elevated temperatures. This lower critical solution temperature (LCST) behavior is interpreted in terms of the equation of state or the freevolume contribution [1–3]. About 30 pairs of dissimilar polymers have been found to exhibit the LCST behavior.

Properties of liquid-crystalline copper(II) complexes and their binary mixtures

Abstract: Eight new copper compounds with mesogenic properties from the series of the bis{1-[4-trans-(4-alkylcyclohexy1)phenyl]-alkylpropane-1,3-dionato} copper(II) complexes have been prepared The thermal behaviour of these compounds was investigated by means of polarizing microscopy and differential scanning calorimetry (DSC) measurements The mesophase, which could be found in most of them, is of the monotropic nematic type This has been confirmed by miscibility experiments The physical data of a binary mixture with an enantiotropic mesophase are also presented In addition the crystal structures of two of the compounds are reported

Formation of polymer‐polymer complexes and blends in the system poly(acrylic acid)‐poly(vinyl methyl ether)

Abstract: The formation of a 1:1 polymer-polymer complex from poly(acrylic acid) and poly(vinyl methyl ether) has been detected by viscosity measurements in aqueous solution, and the glass transition temperature of the isolated complex has been determined. Infrared spectroscopy indicates that specific hydrogen bonding occurs between the components of the complex. Miscible blends of the two polymers can also be formed (at all compositions) and, although hydrogen bonding occurs, the structures of the blends are likely to be dissimilar to that of the complex.

Phase behavior of blends of poly(vinyl chloride) with an α‐methyl styrene/acrylonitrile copolymer

Abstract: Poly(vinyl chloride), PVC, is shown to be miscible with an α-methyl styrene/acrylonitrile copolymer, αMSAN, containing 30 percent AN by weight using differential scanning calorimetry for blends prepared by several methods. Melt blending gave single Tg mixtures; whereas, solution techniques gave results that depended on the solvent choice and the manner in which it was removed. These blends do not phase separate on heating prior to significant PVC decomposition (∼250°C) in contrast to PVC/SAN blends which have much lower cloud points. Repulsion between α-methyl styrene and acrylonitrile units in the copolymer is the principal cause for miscibility of this system as shown by an analysis based on a binary interaction model using calorimetry data for low molecular weight liquid analog compounds.

Polycaprolactone-based block copolymers. II. Morphology and crystallization of copolymers of styrene or butadiene and ε-caprolactone

Abstract: Three series of amorphous semicrystalline poly(styrene-b-e-caprolactone)s have been synthesized with polystyrene blocks of 6000 (series A), 40000 (series B), and 70000 (series C) molecular weight, respectively. In these materials, the polymer miscibility evolves from a situation where a diffuse interphase involves the major part of the volume of the copolymer (series A) to a sharp phase separation as observed for copolymers with the longest PS block (series C). The crystallization of PCL blocks is mainly governed by the phase morphology. In copolymers of series A, the crystallization rate of PCL blocks is slowed down the more as the miscibility with PS increases, and ultimately the degree of crystallinity Xc decreases significantly. When phase separation is sharp, Xc changes dramatically at the phase inversion and decreases when PS forms the continuous phase. At the inversion Xc depends on the mean size of the PCL microdomains as compared with the thickness of the crystalline lamellae. The periodicity of the phase morphology as observed by TEM is influenced by the solvent used in casting films, whereas monolamellar monocrystals can be obtained by a self-seeding technique.

Miscibility of poly(ethylene oxide) with poly(N-vinyl pyrrolidone): DMTA and DTA studies

Abstract: Dynamic mechanical thermal analysis and calorimetric studies are reported on blends of poly(ethylene oxide) (PEO) with poly(N-vinyl pyrrolidone) (PVP) between 80% and 40% PEO. DMTA curves show a peak corresponding to a phase of pure PEO and another peak which can be attributed to blended material. The calorimetric analysis shows an appreciable melting point depression and a marked decrease in the crystallization rate as the PVP content increases. The melting point depression follows the Nishi-Wang equation, giving an interaction parameter of −0.50. These studies suggest the existence of microphases in the blend.

Diffusion and segregation phenomena in miscible binary polymer blends during crystallization

Abstract: Etude de melanges binaires de polyethylene chlore contenant 56,3% en poids de chlore avec une polycaprolactone; comparaison avec le PVC