  A mathematical model to describe the emulsion polymerization kinetics of co-
and ter-polymerizations is developed. The model is based on the classical
Smith-Ewart (SE) equations, within the pseudo-homopolymerization approach, with
state-of-the-art models for radical entry and desorption. For co- and
ter-polymerizations there are unknown parameters in the model which are related
to monomer-specific gel-effect coefficients, that are needed to compute the
bimolecular termination reaction rates. The unknown parameters are determined
through extensive calibration of the model on literature data for homo- and
co-polymerizations of \textit{n}-butyl acrylate (n-BA) and methyl methacrylate
(MMA). The so-obtained predictive model is then applied to the modelling of the
ter-polymerization of n-BA and MMA with 2-hydroxyethyl methacrylate (2-HEMA)
with sodium persulphate (SPR) as initiator: predictions for the time-evolution
of particle size and conversion are in excellent agreement with experimental
measurements using Dynamic Light Scattering (DLS) and Gas Chromatography (GC),
upon tuning the gel-effect coefficient related to 2-HEMA. The developed model
is used to quantify the surfactant surface coverage of the particles as well as
the total concentration of counterions in the system throughout the entire
polymerization process. This key information provides a way to rationalize and
control the coagulation behavior during the whole polymerization process.
