Thiol‐ene emulsion step polymerization in a photochemical stirred tank reactor: Molecular weight, cyclization, and fragmentation

Abstract

Unlike many step polymerizations, the polymerization of bifunctional thiol and alkene monomers can be carried in emulsion to prepare a range of sulfur‐containing polymer particles differing markedly from conventional emulsion chain polymers. This study examines how the change of polymerization mechanism affects polymer molecular weight, structure and composition. A 2,2′‐dimercaptodiethyl sulfide/diallyl phthalate emulsion is photopolymerized in a photochemical stirred‐tank reactor equipped with Light‐emitting diodes (LEDs) to yield a 30% solids content latex with a high weight‐average molecular weight (100 kDa) and a broad molecular weight distribution (Đ = 8.5). Intramolecular cyclization occurs during polymerization by the addition of a thiyl radical to the unsaturated end group of the same molecule. Irreversible ring‐closure takes place to produce “dead” cyclic oligomers in the early stage of the reaction, whereas chain‐growth continues at high conversion. Consequently, the particles are composed of high molecular weight linear chains and a fraction of stable oligomer cycles, showing a broad and bimodal molecular weight distribution. The linear poly(thioether) chains include occasionally disulfide units due to thiyl radical recombination. The reversibility of disulfide bonds causes a decrease of molecular weight during storage. The addition of radical inhibitor to the latex stops fragmentation of SS bonds.

Continuous Polymer Synthesis and Manufacturing of Polyurethane Elastomers Enabled by Automation

“…To integrate polymer synthesis and manufacturing, a semicontinuous batch PU polymerization process was developed that enabled the delivery of freshly synthesized PU resins directly into the bed of the 3D printer. SCBS was chosen for this application due to the long reaction time and large viscosity increase of the resins during polymerization. ,,, For the SCBS setup, fluid handling enabled by peristaltic pumps transferred reagents to a stirred reactor; − after polymerization, the PU oligomer dissolved in acrylates are pumped directly into the resin bed of the 3D printer and processed (a more detailed description of the experimental setup can be found in SI) (Figure ). The entire sequence was automated; therefore, starting the pumps resulted in the synthesis and processing of PU oligomers without any additional user intervention.…”