Modeling of Atom Transfer Radical Polymerization in Miniemulsion initiated by a Water-Soluble Radical Initiator

ZURMAN, AYELÉN; BRANDOLIN, ADRIANA; SARMORIA, CLAUDIA; ASTEASUAIN, MARIANO

San Francisco

Congreso; 2016 AIChE Annual Meeting; 2016

AIChE

Controlled Radical Polymerization (CRP) provides anefficient method for the synthesis of polymers with predetermined molecular weight,low polydispersity and controlled molecular architecture in mild reaction conditions.The latter feature has been one of the keys to its success with respect to theanionic polymerization, which requires stringent conditions.One of the most employed CRP techniques is atomtransfer radical polymerization (ATRP). It presents several advantages such asthe commercial availability of reactants, the simpleproduction of polymers with specific tailored functionalities and the widerange of monomers and temperatures used. Such advantages have motivated anintensive research in both academic and industrial worlds in the last few years,and have led to the development of several procedures for initiating an ATRP. Oneof those procedures is reverse ATRP. It employs more stable CuIIcomplexes in the initiation step and aconventional free radical initiator, making the system easier to handleand more compatible with industrial scaleprocesses than those using CuIcomplexes. Additionally,due to these features, reverse ATRP has been widely employed in dispersed systems.Aqueous dispersions are a good alternative forlarge-scale production, since they provide excellent heat transfer, processflexibility and ease of mixing and handling of the final product.The downside is the partitioning of species between aqueous andorganic phases, exit of radicals from particles and poor colloidal stability,among other complications. Miniemulsions are at present the most successful ofthe dispersed systems for CRP. They have demonstrated to be robust for thedifferent CRP techniques. In this work, a mathematical model was developed for areverse ATRP in miniemulsion using a water-soluble initiator. This model is ableto predict average molecular properties, such as number and weight molecularweights, as well as the full MWD. The model is derived from the deterministicbalance equations of the reacting species. Average properties are predictedusing the well-known method of moments and the MWD is modeled using theprobability generating function (pgf) technique. Thistechnique has proven to be capable of predicting the MWD for several systems accuratelyand efficiently in terms of computational time, without making anysimplifying assumptions or having any a priori information of the distributionshape. The model was formulated and solved in gPROMS (ProcessSystems Enterprise, Ltd.). It takes into account the chemical reactions in theaqueous and organic phases, the entry of oligoradicals into the polymerparticles as well as the partition of the catalyst and monomer in both phases.For the latter phenomenon, two different approaches have been used with similarresults, showing that both are valid for representing the mass transfer acrossthe interface in the system. The results were validated using experimental informationtaken from the literature. Most of the kinetic and diffusion parameters weretaken from the literature, with the exception of the ATRP activation anddeactivation kinetic constants which were estimated from experimental data. Ourresults show that the predicted average molecular properties as well as the MWDagree well with the experimental information.