Effects of the positive feedback loop in polymerization on the reaction-induced phase separation of polymer mixtures

Abstract

Phase separation of mixtures composed of a guest polymer dissolved in monomer of a host polymer was induced by photopolymerization. From the polymerization kinetics, it was found that for the host polymer with the glass transition temperature (Tg) higher than the experimental temperature, the Trommsdorff-Norrish effect emerges, providing a method to terminate the phase separation at various intermediate stages of the process and thereby a variety of morphologies can be constructed. For the host polymers with (Tg) lower than the experimental temperature, the freezing process of morphology is not complete, leading to the secondary phase separation inside the domains already generated by the primary process. The kinetics of this secondary phase separation indicates that the peculiar morphology like "sunny-side-up egg"-like structures was generated via spinodal decomposition. The experimental results obtained in this study show that the competition between photopolymerization and phase separation can provide a useful method of materials design in the micro- and sub-micrometer scales.

Control of Morphology in Polymer Blends through Light Self-Trapping: An in Situ Study of Structure Evolution, Reaction Kinetics, and Phase Separation

“…Overall, the data indicate that the final process by which binary phase morphology is achieved is phase separation along and coaxial to the filament axis. In terms of phase separation ceasing, the associated viscosity increase induced by the TN effect acts as a stopper to subsequent dynamics, as also observed in the studies of Miyata and co-workers. − This is indicated by the Si–CH 3 peak remaining constant over time soon after its sudden drop. Similar results are obtained for blends of 80/20 and 50/50 (see Supporting Information), which also correspond to their respective thermodynamic data.…”

“…This conversion at which a gel–sol medium is attained is different from the common gel point value (0.66 for trifunctional TMPTA and 0.5 for bifunctional PDMS) at which a solid infinite network is attained. Thereafter, sharp increases in p and N is characteristic of the Trommsdorff–Norrish (TN) autoacceleration effect, − induced by the increase in viscosity of the mixture and whose onset begins at the front end of the filament (i.e., where light enters the blend) and “propagates” along its length over time. This depth-dependent onset of the TN effect has not been previously observed and is most likely a result of the confinement and absorption of light along the filaments.…”

Patterning Perovskite Quantum Dots Using Photopolymerization

“…Generally, in the free-radical polymerization of vinyl monomers in the absence of solvents (bulk polymerization), the rate of polymerization (the rate of monomer consumption) sharply increases at some point as the conversion of monomer increases. This phenomenon is known as the Trommsdorff–Norrish effect (also called the gel effect or autoacceleration), due to which the percent conversion–time curve typically presents a sigmoidal feature. , In the case of photopolymerization, the characteristic time at which the polymerization rate reaches a maximum (the inflection point on the sigmoidal conversion–time curve) is shortened as the light intensity increases; however, the characteristic time gradually settles down to a certain value, and the polymerization kinetics (shape of the conversion–time curve) is not affected by the light intensity in the high-intensity range. , Thus, presumably, in a circumstance where I off is extremely high (blue curves, as shown in Figure a,b), no noticeable difference occurs in the kinetics of polymerization. Accordingly, the polymer concentration difference is not developed effectively; thus, the migration of CsPbBr 3 QDs does not occur.…”

“…46,47 In the case of photopolymerization, the characteristic time at which the polymerization rate reaches a maximum (the inflection point on the sigmoidal conversion−time curve) is shortened as the light intensity increases; however, the characteristic time gradually settles down to a certain value, and the polymerization kinetics (shape of the conversion−time curve) is not affected by the light intensity in the high-intensity range. 48,49 Thus, presumably, in a circumstance where I off is extremely high (blue curves, as shown in Figure 3a,b), no noticeable difference occurs in the kinetics of polymerization. Accordingly, the polymer concentration difference is not developed effectively; thus, the migration of CsPbBr 3 QDs does not occur.…”

Introduction to Focus Issue: Oscillations and Dynamic Instabilities in Chemical Systems: Dedicated to Irving R. Epstein on occasion of his 70th birthday

“…57,58 In this issue, the group of Tran-Cong-Miyata shows how competition between photopolymerization and phase separation can provide useful methods of material design in the micro-and sub-micrometer scales. 59 Combination of oscillating BZ reaction and specially designed polymer materials resulted in self-oscillating gels. 60 Structural modification of the polymers to tailor behavior is a challenging task.…”