Mapping Photolysis Product Radical Reactivities via Soft Ionization Mass Spectrometry in Acrylate, Methacrylate, and Itaconate Systems

Abstract

Electrospray ionization-quadrupole ion trap mass spectrometry (ESI-MS) was utilized to access the polymeric product spectrum generated by the pulsed laser polymerization (PLP) of methyl acrylate (MA) at -35 °C in the presence of the photoinitiators 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzoin, benzoin ethyl ether (BEE), and bis(2,4,6-trimethylbenzoyl)phenylphosphinoxide (Irgacure 819) to study the reactivity of primary and potential secondary derived radical fragments from photolytically induced fragmentation. Similarly, the polymeric products generated from the PLP of dimethyl itaconate (DMI) at 0 °C using the aforementioned photoinitiators as well as benzil and 2,2′-azobis(isobutyronitrile) (AIBN) were studied using ESI-MS. The PLP products of methyl methacrylate (MMA) initiated with Irgacure 819 at -25 °C were also examined. Polymerization systems utilizing Irgacure 819 give complex product spectra due to the formation of second generation radical species resulting in several initiator fragments incorporated into a single polymer chain. Termination products, both combination and disproportionation, were identified with high accuracy. The reactivity of the various derived radical fragments toward the monomers employed is summarized for the current and a previous study in tabular form. Energy deposition into the MA/photoinitiator systems is found to have no influence on the product distributions of the MA polymers produced via photoinitiation under the conditions examined. For various photoinitiators employed, products congruent to that of chain transfer to monomer species in the DMI photopolymerizations are observed, conclusively illustrating that chain transfer to monomer is a significant reaction pathway in itaconate free radical polymerizations.

A Perfect Couple: PLP/SEC/ESI‐MS for the Accurate Determination of Propagation Rate Coefficients in Free Radical Polymerization

“…Some evidence suggests that upon photo-dissociation of benzoin, two types of radicals are created with differing ability to initiate and terminate the polymerization reaction. [66,67] Figure 1 shows a typical spectrum of poly(methyl methacrylate) (pMMA) obtained from PLP. One can see that except for two closely spaced clusters of peaks per repeat unit, the spectrum is remarkably free from side products.…”

Limitations of radical thiol‐ene reactions for polymer–polymer conjugation

“…For the photo-initiator DMPA it is known that its benzoyl fragment is a fast initiator whereas the second fragment might only be available for termination or proton abstraction, potentially aiding the overall process. 64 However, as only very limited data on initiation efficiencies are available to date, such a hypothesis remains speculative and an extensive experimental series would be required to confirm it. Regardless, as the initiation rate depends on the type of initiator and the ene (and of course the thiol with respect to the rate of proton abstraction), this implies that one needs to evaluate suitable initiators for each particular system, an approach that is not very promising if thiol-ene is proposed as a universal conjugation tool.…”

Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching

“…Benzoin was chosen as initiator since it decomposes into two equally well-initiating fragments and hence does not create radicals that may persist for extended lifetimes in the polymerization mixture. [ 28 ] Specifi c termination of initiator-derived radicals with MCRs can thus be assumed to be not operational. Other initiators, [ 21 ] such as 2,2-dimethoxy-2-phenylacetophenone (DMPA), may exhibit such behavior.…”