Polymer Mixtures 1 Compatibility

Nishi, T., Wang, T.T., and Kwei, T.K (1975) Thermally induced phase separation behavior of compatible polymer mixtures. Macromolecules, 8 (2), 227-234. 

PED Pedemonte, E. and Lanzavecchia, L., Compatible polymer mixtures. Evaluation of the interaction parameter from heat of solution measrrrements, J. Color. Anal. Therm. Thermodyn. Chim., 17, 519, 1987. 

Dynamics of compatible polymer mixtures (with F. Brochard) Phvsica. 118A. 289 (1983). 

Kwei TK, Nishi T, Roberts RE. A study of compatible polymer mixtures. Macromolecules 1974 7 667-74. Yu AJ. Concept of compatibility in polyblends. Adv Chem 1971 99 2-14. 

The above examples of e-beam sensitive polymer blends were concerned with compatible polymer mixtures. Intuitively, compatibility would seem to be necessary for lithographic performance. However, a recent paper describes e-beam resists based on apparently incompatible PMMA and poly(a-methylstyrene) blends. Although considerable information concerning contrast, sensitivity and plasma etch resistance are given, imaging and resolution results are not presented. 

Koleske J V, Lundberg R D (1969), Lactone polymers. I. Glass transition temperature of poly-e-caprolactone by means on compatible polymer mixtures , J Polym Sci, Part A-2, 7, 795-807. 

The term compatibility is used extensively in the blend literature and is used synonymously with the term miscibility in a thermodynamic sense. Compatible polymers are polymer mixtures that do not exhibit gross symptoms of phase separation when blended or polymer mixtures that have desirable chemical properties when blended. However, in a technological sense, the former is used to characterize the ease of fabrication or the properties of the two polymers in the blend [3-5]. 

Compatible Polymer Blends A term indicating commercially useful materials, mixture of polymers with strong repulsive forces that is homogeneous to the eye. 

There are many definitions of polymer compatibility. On one hand, compatible polymers are the polymer mixtures that have desirable physical properties when... 

The heat distortion temperature of impact-resistant polystyrene may also be improved by polymer blends. Those of impact-resistant polystyrene with poly-2,5-dimethylphenylene-1,4-oxide (PPO) are particularly interesting (90). Polystyrene and PPO are molecularly compatible and mixtures of them have glass transition temperatures which vary virtually linearly with composition. A further advantage of these compositions which should not be under-estimated is their better flame resistance. 

Finally, we should mention the phenomenon of incompatibility of mixtures of polymer solutions. It applies to nearly all combinations of polymer solutions when the homogeneous solutions of two different polymers in the same solvent are mixed, phase separation occurs. For example, 10% solutions of polystyrene and poly(vinyl acetate), each in benzene, form two separated phases upon mixing. One phase contains mainly the first polymer, the other phase mainly the second polymer, but in both phases there is a certain amount of the other polymer present. This limited compatibility of polymer mixtures can be explained thermodynamically and depends on various factors, such as the structure of the macromolecule, the molecular weight, the mixing ratio, the overall polymer concentration, and the temperature. 

Thus most of the time one obtains phase-separated systems in which the macromolecules of component A are not at all or only to a limited extent miscible with the macromolecules of component B, i.e., polymer A is incompatible or only partially compatible with polymer B. The synonymical terms polymer blend , polymer alloy , or polymer mixture denote miscible (homogeneous) as well as immiscible (heterogeneous) systems consisting of two or more different polymers. 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Where the two phases are completely compatible, a homogeneous polyblend results which behaves like a plasticized resin (one phase). If two polymers are compatible, the mixture is transparent rather than opaque. If the two phases are incompatible, the product is usually opaque and rather friable. When the two phases are partially compatibilized at their interfaces, the polyblend system may then assume a hard, impact-resistant character. However, incompatible or partially compatible mixtures may be transparent if the individual components are transparent and if both components have nearly the same refractive indices. Furthermore, if the particle size of the dispersed phase is much less than the wavelength of visible light (requiring a particle size of 0.1/a or less), the blends may be transparent. 

In order to further improve the mechanical properties of these organic plastic crystals, especially at higher temperamres, mixtures with compatible polymers... 

Equilibrium is relatively easily achieved in dilute solutions and studies of such systems form the foundation of modern theories of compatibility. Application of such theories to practical problems involves the assumption that useful polymer mixtures require the selection of miscible ingredients and that compatibility can therefore ultimately be explained in terms of thermodynamic stability of the mixture. 

The procedures outlined have a practical use. but it should be realized that the subparameter models have some empirical elements. Assumptions such as the geometric mean rule (Eq. 12-6) for estimating interaction energies between unlike molecules may have some validity for dispersion forces but are almost certainly incorrect for dipolar interactions and hydrogen bonds. Experimental uncertainties are also involved since solubility loops only indicate the limits of compatibility and always include doubtful observations. Some of the successes and limitations of various versions of the solubility parameter model are mentioned in passing in the following sections which deal brielly with several important polymer mixtures. 

Kramer, E. J. Mechanisms of Toughening in Polymer Mixtures, in Polymer Compatibility and Incompatibility — Principles and Practices (ed. K. Sole), MMI Press, Midland, MI, 1982, p. 251... 

D. Schwahn, G. Meier, K. Mortensen, and S. Janssen (1994) On the N-scaling of the ginzburg number and the critical amplitudes in various compatible polymer blends. J. Phys. II (France) 4, pp. 837-848 H. Frielinghaus, D. Schwahn, L. Willner, and T. Springer (1997) Thermal composition fluctuations in binary homopolymer mixtures as a function of pressure and temperature. Physica B 241, pp. 1022-1024... 

Morphology. Phase inversion in polymer mixtures occurs when the volume fraction of the dispersed phase becomes equal to or exceeds 0.5 (14). The driving force is to minimize the interfacial energy of the system. This is not the case here because the volume fraction of the rubber-rich phase at phase inversion is about 0.85. After inversion, the fraction of the continuous rubber-rich phase is only 0.28, and it increases to 0.63 at 12.5% rubber content. Initially, the components are fully soluble and compatible, but as the reactions proceed, the molecular weight of the products increases and phase separation results. The ability to separate and invert is dependent on the viscosity of the medium. The unsaturated polyester forms a gel at conversions as low as 2 to 5%, and both the ability to separate and to invert is impeded. Thus the morphology depends on the two competing effects of phase inversion and... 

Mixtures of polymer chain belonging to the same chemical species but with different isotopic compositions (deuterated and non-deuterated) have been widely used for experimental studies of polymer structures, since good neutron beams became available. This technique, combining the preparation of adequate samples and neutron scattering experiments, enabled the experimentalists to determine the size of polymer chains (polystyrene or polydimethylsiloxane), in all kinds of polymer mixtures or concentrated polymer solutions. However, the technique relies on the fact that the deuterated and non-deuterated isotopic varieties of a same polymer are compatible with one another. It is admitted that under the experimental conditions described above, the mixture constitutes a unique phase. In fact, the mixing energy of deuterated and non-deuterated chains is probably very small. However, it is non-zero, in particular, because of differences in atomic volumes and polarizabilities. Thus, there is no doubt that demixtion may occur in mixtures of deuterated and undeuterated chains of very high molecular masses. 

Here we rather focus on effects of external surfaces (e.g. hard walls) on polymer blends. In general, one expects that the forces between the wall and monomers of type A will differ from those between the wall and monomers of type B, as it generally occurs at the surfaces of small-molecule mixtures as well [365]. For polymer mixtures that are partially compatible, the interactions in the bulk (as described by the Flory-Huggins x-parameter) must be relatively small, however, since the entropy of mixing is down by a factor of N (for simplicity, the following discussion is restricted to a symmetric mixture, Na = Nb = N). However, there is no reason that the difference of wall-A and wall-B forces is similarly small [125]. Thus one may expect rather pronounced surface enrichment effects in polymer mixtures [125], Indeed some experimental evidence for this prediction has been found [37, 38, 126, 127]. 

Nesterov and Lipatov studied the compatibility of mixtures of crystallizable polymers (77) and the effects of quartz fillers on polymer-solute interactions (78). Information on the compatibility of these systems was obtained via the determination of melting points and crystallinities of the mixed stationary phases. Depending on the polymers considered a single melting transition at an intermediate temperature or distinct melting transitions for each polymer could be detected. 

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