Acrylic polymers, commonly used in paints, can degrade
over time
by several different chemical and physical mechanisms, depending on
structure and exposure conditions. While exposure to UV light and
temperature results in irreversible chemical damage, acrylic paint
surfaces in museums can also accumulate pollutants, such as volatile
organic compounds (VOCs) and moisture, that affect their material
properties and stability. In this work, we studied the effects of
different degradation mechanisms and agents on properties of acrylic
polymers found in artists’ acrylic paints for the first time
using atomistic molecular dynamics simulations. Through the use of
enhanced sampling methods, we investigated how pollutants are absorbed
into thin acrylic polymer films from the environment around the glass
transition temperature. Our simulations suggest that the absorption
of VOCs is favorable (−4 to −7 kJ/mol depending on VOCs),
and the pollutants can easily diffuse and be emitted back into the
environment slightly above glass transition temperature when the polymer
is soft. However, typical environmental fluctuations in temperature
(<16 °C) can lead for these acrylic polymers to transition
to glassy state, in which case the trapped pollutants act as plasticizers
and cause a loss of mechanical stability in the material. This type
of degradation results in disruption of polymer morphology, which
we investigate through calculation of structural and mechanical properties.
In addition, we also investigate the effects of chemical damage, such
as backbone bond scission and side-chain cross-linking reactions on
polymer properties.