Microcapsules with a cyclic polyphthalaldehyde (cPPA)
shell and
oil core were fabricated by an emulsification process. The low ceiling
temperature cPPA shell was made phototriggerable by incorporating
a photoacid generator (PAG). Photoactivation of the PAG created a
strong acid which catalyzed cPPA depolymerization, resulting in the
release of the core payload, as quantified by 1H NMR. The
high molecular weight cPPA (197 kDa) yielded uniform spherical microcapsules.
The core diameter was 24.8 times greater than the cPPA shell thickness
(2.4 to 21.6 μm). Nonionic bis(cyclohexylsulfonyl)diazomethane
(BCSD) and N-hydroxynaphthalimide triflate
(HNT) PAGs were used as the PAG in the microcapsule shells. BCSD required
dual stimuli of UV radiation and post-exposure baking at 60 °C
to activate cPPA depolymerization while room temperature irradiation
of HNT resulted in instantaneous core release. A 300 s UV exposure
(365 nm, 10.8 J/cm2) of the cPPA/HNT microcapsules resulted
in 66.5 ± 9.4% core release. Faster core release was achieved
by replacing cPPA with a phthalaldehyde/propanal copolymer. A 30 s
UV exposure (365 nm, 1.08 J/cm2) resulted in 82 ±
13% core release for the 75 mol % phthalaldehyde/25 mol % propanal
copolymer microcapsules. The photoresponsive shell provides a versatile
polymer microcapsule technology for on-demand, controlled release
of hydrophobic core payloads.