Compatibility of polymer blends

One practical example of demixing that might be attributed to a difference in crystallizability is the incompatibility in blends of polymers with different stereochemical compositions. The stereochemical isomers contain both chemical and geometrical similarities, but differ in the tendency of close packing. In this case, both the mixing energy B and the additional mixing entropy due to structural asymmetry between two kinds of monomers are small. However, the stereochemical differences between two polymers will result in a difference in the value of Ep. Under this consideration, most experimental observations on the compatibility of polymer blends with different stereochemical compositions [89-99] are tractable. For more details, we refer the reader to Ref. [86]. 

Glass transition temperature is one of the most important parameters used to determine the application scope of a polymeric material. Properties of PVDF such as modulus, thermal expansion coefficient, dielectric constant and loss, heat capacity, refractive index, and hardness change drastically helow and above the glass transition temperature. A compatible polymer blend has properties intermediate between those of its constituents. The change of glass transition temperature has been a widely used method to study the compatibility of polymer blends. Normally, the glass transition temperatme of a compatible polymer blend can be predicted by the Gordon-Taylor relation ... 

No attempt is made to review solution theory. For a thorough treatment on this subject, numerous authoritative monographs (3, 4, 5, 6, 7) are available. We discuss only those thermodynamic considerations which have some bearing on the discussion of compatibility of polymer blends. 

The compatibility of polymer blends has been a snbject of mnch interest. Polymer blends are systems with two (or more) polymers, most of which are incompatible (immiscible). Finding compatible polymer pairs is an important task in the design of snch advanced materials. Moreover, several new polymeric materials with interesting properties involve novel structures, which go beyond the well-known ones (linear, branched, cross-linked, and network). Such novel strnctnres, e.g., starlike polymer and dendrimers may require new concepts for selecting proper solvents and generally for nnderstanding their solnbility behavior. "... 

Such cubic equations of state as van der Waals correlate very satisfactorily the UCST-type behavior for polymers solutions, as shown by Harismiadis et al. ° A generalized correlation of the interaction parameter of the van der Waals equation of state for polymer blends based exclnsively on polystyrene blends has been presented. By nsing this equation, the van der Waals eqnation of state can be used as a predictive tool for investigating the compatibility of polymer blends. Predictive GC thermodynamic methods such as Entropic-FV, GC-Flory, UNIFAC, and UNIFAC-FV perform rather poorly, at least from a quantitative point of view. Entropic-FV performs best among these models, on a qualitative basis. For semiquantitative predictions in polymer blends, the approach proposed by Coleman et al. is recommended. 

Wei et al. [98-101] investigated the transesterification mechanism and reaction rate in blends of PC and an LCP (PHB/PET60/40). More recently, Guo [109-111] suggested experimentally that transesterification was a result of the compatibility, instead of a prerequisite of compatibility, e.g., transesterification was determined by the initial compatibility of polymer blends. This is an academic argument, but the presence of transesterification at least favors the compatibilization in in situ composites. Further investigation of the transester-iflcation in LCP blends is needed in the coming years. 

These interaction parameters were determined in order to establish the compatibility of polymer blends and of chains of block copolymers. There are also determinations for blends poly(vinylchloride)-poly-e-caprolactone [27], polystyrene-poly (vinyl methyl ether) [28], polystyrene--polydimethylsiloxane above (120—180°0) and below (50—80°0) the glass... 

A number of polymer surface parameters, e.g. surface free energy and surface charge, are responsible for blood interaction phenomena. Regarding the correlation of hydrophilidty and thrombocyte adhesion, Ikada et al. determined a maximum of thrombocyte adhesion for a contact angle region between 60 and 80° [95]. Van Wachem et al. showed that the best blood compatibility of polymer blends is achieved for moderate wettability [96]. The influence of polar and dispersive components of the surface tension on blood compatibility was described by Kaelble and Coleman [97,98]. They found that polymers with high dispersive (y ) and low polar components (yP) of surface tension show better blood compatibility than polymers with low dispersive interactions. Furthermore, a nega-... 

Sabzi, F. and Boushehri, A. (2006) Compatibility of polymer blends. 1. Copolymers with organic solvents. J. Appl. Polym. Sci., 101, 492-498. 

Compatibility of polymer blends is often achieved through favorable specific interaction such as hydrogen bonding. Although a fundamental understanding of the pertinent thermodynamics plays a crucial role in the preparation of blends, there are few useful molecular thermodynamic models for polymer blends with specific interactions, a major exception is the classical incompressible model developed by Flory and Huggins [7-8]. The objective of this work is to develop an approximate but theoretically based molecular model for predicting compatibility of polymer blends within the framework of a lattice model. 

Fifty-six isothermal data sets for vapor-liquid equilibria (VLB) have been used for 15 polymer-HSolvent binaries, 11 copolymer-nsolvent binaries and for 30 polymer-polymer-solvent ternaries to study compatibility of polymer blends. The equilibrium solubility of a penetrant in a polymer depends on their mutual compatibility. Equations based on theories of polymer solution tend to be more successful when there is some kind of similarity between the penetrant and the monomer repeat unit in the polymer, e.g., for nonpolar penetrants in polymers which do not contain appreciable polar groups. Expected nonideal behavior has been observed for systems containing hydrocarbons and poly(acrylonitrile-co-butadiene). The role of intramolecular interaction in vapor-liquid equilibria of copolymer-nsolvent systems is well documented for poly(aciylonitrile-co-butadiene) that have higher affinity for acetonitrile than do polyaciylonitrile or polybutadiene. 

Although, 23 data reported in this work yield useful information concerning compatibility of polymer blends, but the value of 33 should be taken with caution. Extrapolation of the X 23 values for the limiting case of zero solvent concentration is probably the main cause of uncertainty. In addition, as discussed in the text, the solvent used for the study may also affect the value of 33. 

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