  Sequential infiltration synthesis (SIS) consists in a controlled sequence of
metal organic precursors and co-reactant vapor exposure cycles of polymer
films. Two aspects characterize a SIS process: precursor molecule diffusion
within the polymer matrix and precursor molecule entrapment into polymer films
via chemical reaction. In this paper, we investigated SIS process for the
alumina synthesis using trimethylaluminum (TMA) and H2O in thin films of
poly(styrene-random-methyl methacrylate) (P(S-r-MMA)) with variable MMA
content. The amount of alumina grown in the P(S-r-MMA) films linearly depends
on MMA content. A relatively low concentration of MMA in the copolymer matrix
is enough to guarantee the volumetric growth of alumina in the polymer film. In
pure polystyrene, metal oxide seeds grow in the sub-surface region of the film.
In-situ dynamic spectroscopic ellipsometry (SE) analyses provide quantitative
information about TMA diffusivity in pristine P(S-r-MMA) matrices as a function
of MMA fraction, allowing further insight into the process kinetics as a
function of the density of reactive sites in the polymer film. This work
improves the understanding of infiltration synthesis mechanism and provides a
practical approach to potentially expand the library of polymers that can be
effectively infiltrated by introducing reactive sites in the polymer chain.
