(164f) Microflow System for Controlled Synthesis of Ethylene-Vinyl Acetate Copolymers: Continuous Copolymerization and Kinetic Study

Ethylene-vinyl acetate copolymers (EVA) are important materials with a brand spectrum of application, such as encapsulation material for photovoltaic modules, diesel fuel additives, adhesive and painting materials. In particular, EVA with very high VA content (≥ 80 wt%) is one of the most valuable products among all of the EVA related materials. As it can be used to synthesize ethylene-vinyl alcohol (EVOH), which is one of the most popular gas barrier materials. The Ethylene content in EVA is a key factor that determines its further usage. However, most of the industrial process producing EVA is conducted in batch reactor, which faces the problem of heterogeneous reaction environment and temperature control. As a result, it is difficult to synthesis EVA with well-defined ethylene content in commercial scale.

To solve the problem, a microflow system was proposed to facilitate the synthesis of EVA with controlled ethylene content. The microreactor is reported to excel in mixing, heat removal and residence time control and has been elegantly used to perform reactions under complicated and extreme conditions like multiphase process with improved result. In our current work, we have utilized the ability of micromixer to produce gas bubble to accelerate the dissolution of ethylene in solvent. By doing so, the continuous flow synthesis of EVA by solution free radical copolymerization was realized homogeneously.

The microflow copolymerization process is proved to be better at controlling ethylene content in EVA copolymer by ¹³C NMR spectra, which indicate that EVA obtained in microflow system has less ethylene concentrated sequence than EVA obtained in batch reactor. Ethylene content can be conveniently altered by adjusting the ethylene flow rate or solvent flow rate while not restricted by ethylene pressure. The platform can also be used to investigate reaction mechanism and kinetics efficiently and accurately by operating the microflow system in a stop-flow method. For example, we have developed a simple kinetic of copolymerization and measured the reactivity ratios of ethylene and vinyl acetate copolymerization in tert-butyl alcohol and dimethyl carbonate. The microflow system is demonstrated to be a powerful tool in kinetic and mechanism study and even engineering application of copolymerization processes involving monomers that are gas phase under conventional condition.