The
strength of combining experimental design and advanced kinetic
Monte Carlo (kMC) modeling to understand step-growth network synthesis,
commencing with a linear/star polymeric precursor, is illustrated
considering three chemistries: (i) para-fluoro-thiol
reaction (PFTR); (ii) nitrile imine-mediated tetrazole-ene cycloaddition
(NITEC); and (iii) star poly(ethylene oxide-stat-propylene
oxide) (sPEG)-amine-epoxy click reaction. Chemical parameters are
determined based on small-molecule systems (monofunctional analogues)
and diffusion parameters based on literature data and higher-network-yield
data. Overall model validation is performed considering molar mass
and spectroscopic experimental data. As basic support, kMC modeling
provides the evolution of the complete size exclusion chromatography
trace for both the soluble and the insoluble fraction at any time.
In more detail, kMC modeling allows one to construct, whenever desired,
two-dimensional traces such as the distribution of species with a
given molar mass and number of cross-linking points (CPs) of a given
type (e.g., with at least three cross-links), still
differentiating between the soluble and insoluble fractions. Ultimately,
postprocessing of kMC modeling results allows one to calculate distributions
regarding distances between specific functional groups and the molecular
pore size distribution upon considering a three-dimensional representation
of the molecular buildup of individual network molecules. Also, the
(relative) importance of reaction pathways can be assessed. It is,
for instance, shown that diffusional limitations on intermolecular
reactions determine how far a polymer network yield can be pushed,
with a strong effect due to an intrinsically fast maleimide incorporation
step, specifically for NITEC. Too long linear precursor building blocks
should be avoided as they induce too prominent diffusional limitations.
Too short linear precursor building blocks promote intramolecular
reactions. With the sPEG building blocks, a well-defined structure
is obtained, as confirmed by the narrow distribution regarding the
distances between dye molecules added in the polymerization recipe.