The Use of Sulfur Monochloride as an Alternative Sulfur Feedstock for the Synthesis of High-Performance Commodity and Specialty Optical Polymers

Abstract

This dissertation reports on a new class of polymers termed sulfenyl chloride inverse vulcanization polymers detailed in four chapters. Sulfur monochloride is a highly reactive and inexpensive sulfur feedstock obtained from the reaction of elemental sulfur with chlorine. The use of sulfur monochloride as a suitable feedstock for the synthesis of high refractive index sulfur containing polymers will be discussed herein. The development of these polymers from the reaction of sulfur monochloride and olefins was detailed, and their properties were also discussed. The first chapter is a review summarizing the early and recent works done on the synthesis of sulfenyl chloride-based polymers, the mechanism leading to the formation of products and the analysis of the products formed were discussed. Three main types of sulfur monochloride mediated polymers were discussed. Polymers from amines poly(phenyldiamino)disulfides, thiols (tetrasulfides), and olefins (polyhalodisulfides) with a major focus on the formation of polymers from olefins (polyhalodisulfides). The formation of regioisomers viz the Markovnikov and the anti-Markovnikov routes were detailed. The properties of polymers synthesized from S2Cl2 and olefins were listed and the criteria required to improve the molecular weights were also given. Diolefins of intermediate reactivity separated by a rigid core were given as the criteria for obtaining polymers with tunable high molecular weights. The glass transition temperatures of polymers made with S2Cl2 were also given except in the formation of poly(phenyldiamino)disulfides due to their weak -NSSN- bonds. The potential applications of polyhalodisulfides in the fabrication of optical components, high RI polymers and optical components such as lenses including the use of poly(phenyldiamino)disulfides as electrode materials and chemical sensors for thiols were also highlighted. The second chapter gives a detailed description of the synthesis and characterization of linear and networked polyhalodisulfides made from allylic comonomers and S2Cl2. The thermal and mechanical properties of these polyhalodisulfides were modulated by varying the rigid core of the comonomer and the chain length of the olefin. The polymers also exhibited fairly high refractive indices and Abbe number and thus their suitability for optical components was established. The versatility of this polymerization was further demonstrated by their formation of bulk high refractive index thermosets when trifunctional olefins were employed and segmented block copolymers by selective choice and design of comonomers. These polyhalodisulfides also showed robust mechanical properties reaching up to 28 MPa for the highly crosslinked polyhalodisulfide. The structure of the polyhalodisulfide was also elucidated to contain either the Markovnikov or the anti-Markovnikov structure and the dihydrodioxolium microstructure when the comonomer is an allylic ester. In summary, this chapter shows the highly facile synthesis of polyhalodisulfides and the robustness of the thermal, mechanical, and optical properties of these polymers. The third chapter details an in-depth study into the synthesis of a high refractive index low-cost photopolymer resin from sulfur monochloride and allyl methacrylate called disulfide methacrylate resin (DSMR) and the potential application of the resin in the fabrication of optical components such as lenses. The high processability of DSMR was evidenced in the ability to be both photo and thermally polymerized into thick bulk windows devoid of defects possessing high refractive index (~1.57), high Abbe number (35) and high optical transparency (~80% at 30 mm thickness). The versatility of DSMR shown in the fabrication of high aspect ration microstructures and in 3D printing of solid shapes using the HARP technology will be discussed. The polymer obtained from DSMR showed robust thermal and mechanical properties which allows for fabricated polymer preforms to be machined into desired shapes similar to glass cutting was demonstrated by diamond turning- a tool for precise machining- a piece of 30 mm thick window into a plano-convex lens. The fourth chapter discusses a detailed characterization of polyhalodisulfides using a combination of one-dimensional and two-dimensional NMR spectroscopic methods. The structure of polyhalodisulfides formed from diallyl isophthalate and S2Cl2 was studied by comparing the NMR spectra of similar model compounds. This study showed the mechanism of the formation of all regioisomers formed from allylic esters (Markovnikov, anti-Markovnikov and dihydrodioxolium regioisomers) and their composition in the polymer matrix with the anti-Markovnikov regioisomer being the favored microstructure and an equal composition of the Markovnikov and the dihydrodioxolium regioisomeric microstructure. The modulation of the regioisomeric composition with temperature was also discussed.