Polymerizations phase separation process

Although Eq. (13) has been reported to fit the data well for Cl = 3.5, and C2 = - 2.0, it provides no information on the phase separation process. In fact, there is little understanding about how the physical morphology and mechanical properties evolve with polymerization and time. The effect of various process parameters on the phase separation and morphology is obtained implicitly via final properties of the polymers. This is illustrated... 

Thermoset materials with a controlled morphology in the low pm-range are found in toughened thermosets where the second polymeric phase has been generated via a phase separation process. Indeed the methodology we sought to... 

The type of spinodal decomposition encountered in IPN formation differs from the classical temperature quench in the sense that a composition change constitutes the driving force, at a fixed temperature. In this case, the rate of composition change is deeply involved in the phase separation process [6 ], which severely limits the applicability of current spinodal theory. In fact. Binder and Frisch [ ] which assume the polymerization rate is rapid enough to limit the phase separation. On the contrary, in the experimental work by Lipatov et al. [ ], the rate of polymerization was kept to a minimum to make the conversion changes during the phase separation minimal. 

It is not easy to obtain a good dispersion of core-shell particles in an organic medium. The initial mixing operation is very important and can be made by extrusion. But to keep a good dispersion after cure it is necessary to control the miscibility of the shell, its reactivity with the thermoset precursors, and a possible phase-separation process of previously dissolved shell components, induced by the polymerization. An example of the quality of the resulting dispersions is illustrated in Fig. 8.11a and b. 

The synthesis of nanocapsules can best be obtained in miniemulsion using different approaches [107], One possibility is based on the phase separation process within a droplet during the polymerization [108], Here, vinyl monomers were polymerized in the presence of a hydrophobic oil. During the polymerization, the polymer becomes insoluble in the oil, leading to a phase separation. With properly chosen physicochemical properties of monomer and encapsulated material, a polymeric shell surrounding the liquid core can be formed. 

Figure 4. Schematic diagram of the polymerization induced phase separation process.

The phase separation in polymeric systems is determined by thermodynamic and kinetic parameters, such as the chemical potentials and diffusivities of the individual components and the Gibb s free energy of mixing of the entire system. Identification and description of the phase separation process is the key to understanding the membrane formation mechanism, a necessity for optimizing membrane properties and structures. 

The segregated core-shell microstmctures, consisting of a hydrophobic core surrounded by a hydrophilic shell, are of great praaical interest as their mechanical properties are mainly influenced by the core polymer and the chemical properties and solubility mainly by the shell monomer units. These materials have attracted increased attention because they not only maintain the funaions of both the core and shell components but also exhibit additional excellent optical, electrical, and magnetic properties. Polymeric core-shell microstmctures can be obtained through phase separation, which is realized by inductive polymerization," solvent extraction and evaporation,"" self-assembly of amphiphilic block copolymers,"" or sequential predpitation,"" which is intrinsically a self-assembly and phase-separation process. However, these methodologies are usually complicated and tedious. 

The environmental relative humidity is an additional factor to be considered during the phase separation process in polymer blends. Two different situations have been described depending on the condensation, or not, of water onto the polymeric films. 

Figure 15. Schematic representation of phase separation processes. From left-to-right Temperature induced phase separation solvent-induced phase separation reaction-induced phase separation (i.e., polymerization where two phase regions are entered with increasing degree of polymerization (DP)) and pressure-induced phase separation. < > = polymer concentration, S2 and SI solvent and nonsolvent PI and P2 = polymer 1 and polymer 2.

Until now, the formahon of capsules of size >1 im has predominantly been described, though for many applicahons - especially in medicine and high-resolution electronic inks - smaller capsules of 50 to 300 nm attract much more interest. The approach to synthesizing nanocapsules as described below is based on the principle of miniemulsion using the differences of interfacial tension and the phase separation process during polymerization to obtain a nanocapsule morphology. 

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