(244i) Modeling and Control of Reversible Addition-Fragmentation Chaintransfer (RAFT) Polymerization Reaction in a Batch Reactor

Modeling and Control of Reversible Addition-Fragmentation chain-Transfer (RAFT) Polymerization Reaction in a Batch Reactor
Ortiz-Arroyo Arturo*., Castro-Agüero Angela, Tututi-Avila, Salvadorb.
Universidad Autónoma de Tlaxcala, Av. Apizaquito S/N, Apizaco, Tlaxcala, Mexico.
*Corresponding author: arturo.ortiz@uatx.mx,a angel.castro@uatx.mx,bsalvador.tututi@uatx.mx

Abstract
Reversible addition-fragmentation chain-transfer (RAFT) is a versatile polymer synthesis technique with many potential applications because allows to obtain polymers with complex conformational structure. Additionally, this technique provides control of molecular weight and molecular weight distribution with narrow polydispersion index. An additional advantage is that RAFT process conditions are close to the usual free radical polymerization reactions. Then, RAFT polymerization can be carried out in bulk, aqueous solutions, organic solutions, suspensions, emulsions, etc., at low temperatures. Due to these characteristics and potential applications the subject has attracted attention from researchers as is reported by Moad et al, 2008 and 2009 were at the time of writing cited more than 500 related papers. The RAFT process uses free radical initiators and monomers but, additionally, includes a Chain Transfer Agent (CTA) also called RAFT agents being the Dithioesters the most commonly used agents.
Zhang & Ray, 2001 used the moment methodology to simulate the free radical polymerization of Methyl Methacrylate (MMA) using AIBN as initiator to show the effect of the reactor type. For that purpose, Batch, semi Batch, CSTR and CSTR in series reactors are simulated in isothermal steady and non-steady state. The resulting mathematical model consisted of 27 highly non-linear ordinary differential equations (ODE) which are not included for clarity.
In this work the simulation framework of Zhang & Ray, 2000 was used in a Batch reactor for which a simplified energy equation is added which includes heat effects to/from the reactor to complete the dynamic scheme. Batch reactors are devoted to the production of high quality but low volume products like polymers and are naturally time-varying, therefore their dynamics is of vital importance due to the fact that small variations in operation conditions may degrade the product quality if the problem is not detected and corrected fast enough.
A configuration of the reactor is proposed and identified and a PID controller is proposed for the reactor temperature considering that all the reactants are present in the initial time. To test the behavior of the controller the initiator and initial monomer concentrations are modified and the temperature is controlled with a split range setup in which cooling and heating media is admitted to the reactor jacket depending on the temperature level (fig 1). It is important to mention that the main problems with polymerization reactors are the heat release and the viscosity changes.
Due to the complexity of the reactor model a simple PI control strategy on open loop is implemented and tuned using several methodologies. As the Batch reactors are naturally variant it is desirable that all the information related to the reactive system would be incorporated to the control strategy.

Fig.1 Split Range control proposed for the reactor

Zhang, M., Ray, W.H. Modeling of “Living” Free-Radical Polymerization with RAFT Chemistry. Ind. Eng. Chem. Res., 2001, 40 (20), pp 4336–4352