Photoinduced synthesis of polyester networks from methacrylate functionalized precursors: analysis of side reactions

Abstract

*Polyester networks can be prepared by ultraviolet (UV)-light-induced radical polymerization of methacrylate functionalized oligo(ε-caprolactone)s. The properties and functions of the obtained materials depend on defined network structures and may be altered, if crosslinking would occur by side reactions in other positions than the methacrylate endgroups. In order to explore whether and to which extent such side reactions occur, network synthesis as well as related model reactions were performed in the absence of photoinitiator. Hereby precursor structures (linear and four-arm star-shaped) and reaction conditions (in solution and in the melt) were varied. Unspecific side reactions were found only upon extensive UV irradiation for 60 min (26 mW cm -2 ) with minor but detectable alterations of physicochemical properties of the networks. The analysis of model reactions suggested minor photolytic cleavage of ester bonds during polymer network synthesis. However, the effect of these side reactions on network properties and functions appeared to be less relevant than an incomplete precursor integration because of a too short UV irradiation for crosslinking.

Microfluidic Templating and Initiator‐Free Photocrosslinking of Protein‐Loaded PCL Microcapsules

“…[ 21 ] However, capsule preparation by crosslinking in solution will be more challenging due to the need to preserve the double emulsion to be stable for extended periods under photocrosslinking conditions. For macroscopic samples, the methacrylate‐based photocrosslinking of PCL in the absence of a photoinitator was shown to proceed without major photodamage of the polyester, [ 25 ] which motivated the application of this methodology in the current study.…”

Size control of shape switchable micronetworks by fast two-step microfluidic templating

“…linear oligo(ε-caprolactone), oCL precursors bearing 2-isocyanatoethylmethacrylate (IEMA) end groups to create, after solvent extraction, defined MP of adjustable average diameter, and (ii) a melt-based crosslinking to convert MP to MN by network formation in the molten state, which is known to result in faster crosslinking and higher crosslinking densities compared to network formation in polymer solutions [27]. This second process should also prevent the aggregation of molten polymer droplets during crosslinking compared to bulk irradiation, as droplets will be continuously separated during transportation in a laminar flow in a microchannel.…”