No abstract

We report a microencapsulation procedure based on rapid solvent evaporation to prepare microcapsules with hydrophobic core materials and low-ceiling-temperature polymer shell wall of cyclic poly(phthalaldehyde) (cPPA). We use and compare microfluidic and bulk emulsions. In both methods, rapid solvent evaporation following emulsification resulted in kinetically trapped core-shell microcapsules, whereas slow evaporation resulted in acorn morphology. Through the systematic variation of encapsulation parameters, we found that polymer-to-core weight ratios higher than 1 and polymer concentrations higher than 4.5 wt % in the oil phase were required to obtain a core-shell structure. This microencapsulation procedure enabled the fabrication of microcapsules with high core loading, controlled size, morphology, and stability. This procedure is versatile, allowing for the encapsulation of other hydrophobic core materials, i.e., mineral oil and organotin catalyst, or using an alternative low-ceiling-temperature polymer shell wall, poly(vinyl tert-butyl carbonate sulfone).

A series of poly(vinyl ester sulfone)s are synthesized and are found to rapidly degrade in the presence of base. Solution phase NMR indicates that the sensitivity of these polymers to base depends on the identity of the ester functional group of the polymers. From most to least sensitive these are poly(vinyl chloroacetate sulfone) > poly(vinyl acetate sulfone) > poly(vinyl benzoate sulfone) > poly(vinyl pivalate sulfone). Significantly, these polymers were more reactive to base than the aliphatic poly(1-hexene sulfone). Additionally, degradation of these polymers in bulk occurs rapidly with exposure to aqueous solutions of base. The polymers are stable in water and possess good barrier properties; films of 30 μm thickness allow on average <1% crossover of dye over 7 days. Based on the data collected, poly(vinyl ester sulfone) polymers are promising for use in microcapsules, in particular, for applications where sustained or staged release would benefit from a series of different microcapsule compositions.

Thermally triggerable polymer films that degrade at modest temperatures (≈85 °C) are created from a blend of cyclic polyphthalaldehyde (cPPA) and a polymeric thermoacid generator, poly(vinyl tert-butyl carbonate sulfone) (PVtBCS). PVtBCS depolymerizes when heated, generating acid which initiates the depolymerization of cPPA into volatile byproducts. The mass loss onset for 2 wt% PVtBCS/cPPA is 22 °C lower than the onset for neat cPPA alone in dynamic thermogravimetric analysis experiments. Increased concentrations of PVtBCS increase the rate of depolymerization of cPPA. Raman spectroscopy reveals that the monomer, o-phthalaldehyde, is the main depolymerization product of the acid-catalyzed depolymerization of cPPA. The PVtBCS/cPPA blend is a promising material for the design and manufacture of transient electronic packaging and polymers.