Monomer Equilibrium and Transport in Emulsion and Miniemulsion Polymerization.

The dual concepts of monomer equilibrium and monomer transport in emulsion and miniemulsion polymerization are discussed in depth. The concepts must be considered together since, first, dispersed-phase polymerizations (in this case emulsion and miniemulsion polymerizations) are by their nature multiphase systems that function only due to interphase mass transfer; and second, because phase equilibrium determines the driving force for monomer transport in these (and all heterophase reaction) systems. Concepts of polymer particle swelling are reviewed, and the question first addressed by Paul Flory in the 1950s: Are emulsion polymerizations transport or reaction limited? is revisited in detail.

Kinetic Phenomena in Mechanochemical Depolymerization of Poly(styrene).

Synthetic polyolefinic plastics comprise one of the largest shares of global plastic waste, which is being targeted for chemical recycling by depolymerization to monomers and small molecules. One promising method of chemical recycling is solid-state depolymerization under ambient conditions in a ball-mill reactor. In this paper, we elucidate kinetic phenomena in the mechanochemical depolymerization of poly(styrene). Styrene is produced in this process at a constant rate and selectivity alongside minor products, including oxygenates like benzaldehyde, via mechanisms analogous to those involved in thermal and oxidative pyrolysis. Continuous monomer removal during reactor operation is critical for avoiding repolymerization, and promoting effects are exhibited by iron surfaces and molecular oxygen. Kinetic independence between depolymerization and molecular weight reduction was observed, despite both processes originating from the same driving force of mechanochemical collisions. Phenomena across multiple length scales are shown to be responsible for differences in reactivity due to differences in grinding parameters and reactant composition.

Fundamentals of Emulsion Polymerization.

A comprehensive overview of the fundamentals of emulsion polymerization and related processes is presented with the object of providing theoretical and practical understanding to researchers considering use of these methods for synthesis of polymer colloids across a wide range of applications. Hence, the overview has been written for a general scientific audience with no prior knowledge assumed. Succinct introductions are given to key topics of background science to assist the reader. Importance is placed on ensuring mechanistic understanding of these complex polymerizations and how the processes can be used to create polymer colloids that have particles with well-defined properties and morphology. Mathematical equations and associated theory are given where they enhance understanding and learning and where they are particularly useful for practical application. Practical guidance also is given for new researchers so that they can begin using the various processes effectively and in ways that avoid common mistakes.

Kinetics of prebiotic depsipeptide formation from the ester-amide exchange reaction.

In this work, we introduce a kinetic model to study the effectiveness of ester-mediated amide bond formation under prebiotic conditions. In our previous work, we found that a simple system composed of α-hydroxy acids and α-amino acids is capable of forming peptide bonds via esterification followed by the ester-amide exchange reaction. To further understand the kinetic behavior of this copolymerization, we first tracked the growth of initial species from a valine/lactic acid mixture in a closed system reactor. A mathematical model was developed to simulate the reactions and evaluate the rate constants at different temperatures. We found these reactions can be described by the empirical Arrhenius equation even when reaction occurred in the solid (dry) state. Further calculations for activation parameters showed that the ester-mediated pathway facilitates amide bond formation by lowering activation entropies. These results provide a theoretical framework that illustrates why the ester-mediated pathway for peptide bond formation is efficient and why it would have been more favorable on the early Earth, compared to peptide bond formation without the aid of hydroxy acids.

Enzyme-initiated miniemulsion polymerization.

Enzyme-catalyzed polymerization in vitro has gained considerable attention in the last two decades as an efficient tool in the polymerization of various monomers, such as saccharides, esters, phenols, and aromatic anilines; however, the polymerization of vinyl monomers using enzymes has been more limited, perhaps due to the hydrophobicity of most common vinyl monomers. Enzyme-initiated miniemulsion polymerization is demonstrated herein as a way to polymerize hydrophobic vinyl monomers such as styrene. By application of enzyme-initiated radical polymerization in miniemulsion, stable poly(styrene) latexes are prepared with a particle size near 50 nm. A very small amount of enzyme and surfactant is required to facilitate the miniemulsion polymerization, whereas a relatively high polymerization rate and conversion are achieved.

On the stability of miniemulsions in the presence of RAFT agents.

The colloidal stability of miniemulsions in the presence of RAFT or other control agents for controlled free radical polymerization is examined. A derivation, based on Lifshitz-Slyozov-Wagner (LSW) theory, is proposed here to evaluate the effect of a RAFT agent on the diffusional stability of the miniemulsions before the onset of polymerization. Results indicate that, depending on the hydrophobicity of the control agent, its presence may augment or detract from the effectiveness of the costabilizer in preventing diffusional instability due to Ostwald ripening.