Photodimerization of Coumarin Functionalized Poly(alkyl Acrylate) and Poly(alkyl Methacrylate) Random Copolymers: Influence of Copolymer Composition on Photocrosslinking

Abstract

Coumarin‐containing poly(alkyl (meth)acrylates) were prepared via 70–80% esterification of hydroxy‐containing acrylic copolymers, then solution cast into thin films and photocrosslinked via the dimerization of coumarin derivatives with UVA light. The coumarin‐modified polymers crosslinked upon exposure and exhibited gel fractions between 74 and 99%. Coumarin dimerization efficiency increased with higher polymer mobility at the irradiation temperature. The effects of light intensity and irradiation time in photo‐dimerized systems followed the Bunsen‐Roscoe reciprocity law indicating that coumarin photodimerization depended only on dose. Thus, low intensities are overcome with longer times. This is an important advantage over photoinitiated free radical crosslinking which depends on irradiation intensity to the ½ power.

Keywords:

• photocrosslink
• coumarin
• UV‐Vis spectroscopy
• glass transition
• reciprocity

Acknowledgments

The authors thank the Macromolecules and Interfaces Institute at Virginia Tech and the National Science Foundation Summer Undergraduate Research Program at Virginia Tech for funding. This material is based upon work supported in part by the U.S. Army Research Laboratory and the U.S. Army Research Office under grant number DAAD19‐02‐1‐0275 Macromolecular Architecture for Performance (MAP) MURI. The authors also acknowledge the support of Avery Dennison and technical discussions with Dan Holguin and Yi Wei.