1 research outputs found
UV-Triggered End Group Conversion of Photo-Initiated Poly(methyl methacrylate)
The analysis of photo-initiated polyÂ(methyl methacrylate)
via electrospray ionization-mass spectrometry (ESI–MS) (synthesized
by pulsed laser polymerization (PLP, at λ = 351 nm) of methyl
methacrylate (MMA) and benzoin as photoinitiator at 6 mJ/pulse laser
energy) evidences the presence of unidentified species. The determination
of the origin of these species requires a detailed investigation via
size exclusion chromatography-electrospray ionization-mass spectrometry
(SEC/ESI–MS) and chemically induced dynamic nuclear polarization-nuclear
magnetic resonance spectroscopy (CIDNP–NMR). It was found that
post-irradiation of benzoin-initiated polyÂ(methyl methacrylate) leads
to α-cleavage of the benzoyl fragment leading to a sequence
of cascade reactions, including the formation of an additional double
bond within the polymer chain as evidenced via ESI–MS. Furthermore,
the reaction products of the benzoyl radical post α-cleavage
(e.g., benzaldehyde, phenyl methyl ketone, methyl formate, or methane)
as well as the formed macroradical can be followed by CIDNP–NMR,
which allows establishing a reaction mechanism for the UV-induced
cleavage process. The study thus evidence thatî—¸if the integrity
of UV initiated polymers is to be kept intact during their synthesisî—¸very
low irradiation energies need to be employed