Polymer blends solubility parameters

An excimer is an electronically excited molecular complex formed between two suitably oriented aromatic rings when one of them has been promoted to an excited state by absorption of energy. The normal characterization parameter is the ratio of the excimer fluorescence intensity to the monomer fluorescence intensity, R, where the monomer refers to the uncomplexed aromatic ring. Of importance for our work is that it is a common feature of the photophysical behavior of the aryl vinyl polymers, as described in a recent review [48]. The objective of this section is to demonstrate the sensitivity of excimer fluorescence to those variables expected to influence the free energy of mixing in polymer blends solubility parameters of the two components, concentration, temperature and molecular weight. 

With careful experimented design, inverse gas chromatography can be a viable method for the determination of the polymer-polymer interaction coefficient B23. The variation of apparent B23 values with the probe is shown to be related to the chemical nature of the probe and not due solely to experimented error. A method is presented to allow the estimation of the true B23 value. Experiments were performed on a 50/50 blend of poly(epichloro-hydrin)/poly( -caprolactone) at several teqperatures. Polymer and blend solubility parameters were determined. 

Notwithstanding the general incompatibility of polymers and copolymers, polymers with solubility parameters that differ by 0.5 unit are compatible although their structures may differ. Thus, poly (methyl methacrylate) (PMMA), poly (ethyl acrylate) (PEA), poly (vinyl chloride) (PVC), and poly (butadiene-co-acrylonitrile) (90/10-60/40) form useful compatible blends because their solubility parameters are in the range 9.2-9.4. The difference in solubility parameters resulting in compatibility may be as much as one unit when the polymers are of relatively low molecular weight. 

The main aim for FCC gasoline desulfurization is to remove thiophenic sulfur compounds. Membranes made from polar polymers with solubility parameter close to thiophenic sulfur are used for desulfurization of gasolines by PV It is evident that solubility parameter of primary sulfur components of gasolines, that is, thiophenic sulfur components, is 19-21 (J/cm )", while for other hydrocarbons, these values are 14-15 (J/cm )". This difference can be exploited for separation by PV. Solubility parameter values of most of the polymers used as membrane material lie in the range of 21-26 (J/cm )". Thus, membranes made from these polymers afford good selectivity for thiophenic sulfur. Apart from various homopolymers, chemically and physically modified polymers have also been used for per-vaporative desulfurization. Some of these modifications include using different types and amounts of cross-linkers, blending two polymers, and copolymerization. Composite and treated ionic membranes have also been tried for this separation. Polymer membranes tried for this separation include PDMS/PAN, PDMS/PEI, PDMS/PES, PDMS/ ceramic, polyetherimine (PI)/polyester, PEG/PES, and PU/PTEE. ... 

Calculation of the radius of interaction for solvents and resins can be made easy through the use of the computer spreadsheets SPWORKS.WKl and EVAPSP.WKl (Figures 19.3 and 19.4). These spreadsheets contain the partial solubility parameters for 289 solvents and some 166 resins and polymers. The solubility parameters of any solvent blend derived from TERTBLEN.WKl or 7BLEND.WK1 can be added to the solvent-resin spreadsheets. Similarly, one... 

Of particular interest is the fact that two plasticisers of similar molecular weight and solubility parameter can, when blended with polymers, lead to compounds of greatly differing properties. Many explanations have been offered of which the most widely quoted are the polar theory and the hydrogen bonding theory. 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

Lohse et al. have summarized the results of recent work in this area [21]. The focus of the work is obtaining the interaction parameter x of the Hory-Huggins-Stavermann equation for the free energy of mixing per unit volume for a polymer blend. For two polymers to be miscible, the interaction parameter has to be very small, of the order of 0.01. The interaction density coefficient X = ( y/y)R7 , a more relevant term, is directly measured by SANS using random phase approximation study. It may be related to the square of the Hildebrand solubility parameter (d) difference which is an established criterion for polymer-polymer miscibility ... 

For making compatible blends, the polymers should have comparable polarities and viscosities. The oil needs to be selected properly so that its solubility parameter is close to those for blend components. The cure system should be efficient for all constituent rubbers and the filler system needs to be appropriate. Finally, cost consideration should be taken into account to provide a commercially viable product. 

Most blends of polymers are immiscible. Solubility parameter considerations predict that miscibility may be possible when small differences (e.g. <0.5) in... 

Flory-Huggins Approach. One explanation of blend behavior lies in the thermodynamics of the preceding section, where instead of a polymer-solvent mixture, we now have a polymer-polymer mixture. In these instances, the heat of mixing for polymer pairs (labeled 1 and 2) tends to be endothermic and can be approximated using the solubility parameter. The interaction parameter for a polymer-polymer mixture, Xi2, can be approximated by... 

The first question to be discussed is the polymer miscibility which governs the blend morphology. The solubility parameters of BMIs is 12-135 (cal cm 3)0,5 vs. 11-12 (cal cm"3)0,5 for the high-performance thermoplastics [112]. We can expect an important non-miscibility however, the morphology will also depend on some other factors (conversion at the gel point, viscosity...) and as a result different types of morphologies were identified. 

In these expressions, SA and 8B are the solubility parameters of polymers A and B, defined for simple liquids as the square root of the energy of vaporization per unit volume (17,18), and XA and XB are the degrees of polymerization of the blend components. When XAb < (XAB)cr compatibility is predicted in all proportions. 

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