Organic solvent‐free catalytic hydrogenation of diene‐based polymer nanoparticles in latex form. Part II. Kinetic analysis and mechanistic study

Abstract

The central challenge that has limited the development of catalytic hydrogenation of diene-based polymer latex (i.e., latex hydrogenation) in large-scale production pertains to how to accomplish the optimal interplay of accelerating the hydrogenation rate, decreasing the required quantity of catalyst, and eliminating the need for an organic solvent. Here, we attempt to overcome this dilemma through decreasing the dimensions of the polymer substrate (such as below 20 nm) used in the hydrogenation process. Very small diene-based polymer nanoparticles were synthesized and then used as the substrates for the subsequent latex hydrogenation. The effects of particle size, temperature, and catalyst concentration on the hydrogenation rate were fully investigated. An apparent firstorder kinetic model was proposed to describe the rate of hydrogen uptake with respect to the concentration of the olefinic substrate (C¼ ¼C). Mass transfer of both the hydrogen and catalyst involved in this solid (polymer)-liquid (water)-gas (hydrogen) three-phase latex system is discussed. The competitive coordination of the catalyst between the C¼ ¼C and acrylonitrile units within the copolymer was elucidated. It was found that (1) using very small diene-based polymer nanoparticles as the substrate, the hydrogenation rate of polymer latex can be

Preparation of poly(styrene‐co‐butadiene) fine latex via a gemini surfactant‐induced low‐temperature initiation semibatch emulsion polymerization system

“…One example is that the catalytic hydrogenation of SBR will not be adversely affected by the “parent” polymerization. Catalytic hydrogenation of the carbon–carbon double bonds in the diene‐based polymers such as NBR and SBR, is an important process as the hydrogenated products HNBR and HSBR, become so‐called high‐performance elastomers, which are more resistant than their “parent” polymers towards oxidative and thermal degradation while maintaining their elastomeric properties in chemically aggressive environments . Crosslinking problems will greatly decrease the rate of catalytic hydrogenation.…”

New “Green” Route for Catalytic Latex Hydrogenation

“…This confirms that catalyst transport is the limiting step for the latex hydrogenation as mentioned in the introduction section. The predispersion process provided a higher concentration of RhCl(TPP) 3 inside the polymer particles before the hydrogenation was initiated and thus avoiding the mass transfer step of catalyst. In addition, RhCl(TPP) 3 has higher mobility in the polymer chains at elevated temperature, which is evidenced by the considerably shorter time required to reach a hydrogenation degree of 95 mol% at 160 °C than at 135 °C.…”

“…With increasing attention to sustainable development, it is very desirable to develop a "Green" technology, which would eliminate the need for a large amount of organic solvent and minimize the negative impact on the environment. Direct hydrogenation of NBR in latex/bulk form in the absence of any organic solvent is such an excellent success, which is of prime importance when HNBR in latex form is the desired end-use product or only surface/gradient hydrogenation of the product is required [3]. However, while considerable efforts have been made, the hydrogenation rate is still very slow even under a high catalyst loading and elevated reaction conditions [4].…”

Hydrogenation of Carboxyl Nitrile Butadiene Rubber Latex Using a Ruthenium-Based Catalyst

“…Catalytic latex hydrogenation is usually performed under high H 2 pressure. Transition metal complexes such as rhodium, ruthenium, palladium and rhodium ruthenium, are selected as catalysts [19][20][21]. Generally, rhodium and ruthenium catalysts are commonly employed.…”