A semi-batch process for nitroxide mediated radical polymerization

A semi-batch process using nitroxide mediated polymerization, was explored for the design of low molecular weight solvent-borne coatings, typical of those used in the automotive industry. While living radical polymerization (LRP) offers many advantages in the control of polymer chain microstructure that may confer important physical and chemical property benefits to coatings, adapting LRP to a semibatch process poses significant challenges in the design and operation of the process. Using styrene monomer, various two-component initiating systems (free radical initiator, 4-hydroxy-TEMPO) were studied to understand the effects of different initiators on the course of polymerization. In addition, an alkoxyamine was synthesized and used as the initiating source. The initiators Luperox 7M75 and Luperox 231 give higher polymerization rates and reasonable control over polymerization, while benzoyl peroxide (BPO), Vazo 67, and the alkoxyamine are less effective. The number of polymer chains in the final product is always less than the theoretical value, reflecting poor initiation efficiency, probably resulting from undersirable termination reactions that become important due to the nature of the semi-batch process. Adding camphorsulfonic acid (CSA) or charging initiator concurrently with monomer during semi-batch feed, can increase the polymerization rate while maintaining the living character of the polymerization. The copolymerization of styrene and butyl acrylate is also shown to exhibit living character.