pH-Dependent Switchable Permeability from Core-Shell Microcapsules.

We recently reported cationic cyclopolymerization of -vinylbenzaldehydes initiated by boron trifluoride to generate acid-sensitive poly(-(α-alkyl)vinylbenzaldehyde). Herein we report preparation of core-shell microcapsules (μCs) using flow-focusing microfluidic techniques with shells composed of poly(-(α-methyl)vinylbenzaldehyde) (PMVB) that release their payload in response to dilute aqueous acid solution. Release profiles of encapsulated fluorescein isothiocyanate-labeled dextran from μCs are controlled by varying the proton concentration and shell-wall thickness.

Triggered transience of metastable poly(phthalaldehyde) for transient electronics.

Triggerable transient electronics are demonstrated with the use of a metastable poly(phthalaldehyde) polymer substrate and encapsulant. The rate of degradation is controlled by the concentration of the photo-acid generator and UV irradiance. This work expands on the materials that can be used for transient electronics by demonstrating transience in response to a preselected trigger without the need for solution-based degradation.

α-Substituent Effect on -Vinylbenzaldehyde Cyclopolymerization.

The cationic cyclopolymerization of -vinylbenzaldehydes initiated by boron trifluoride is described. Unlike the incomplete conversion of -vinylbenzaldehyde () at 0 °C, α-methyl-substituted monomers () and () undergo cyclopolymerizations with complete conversions at -78 °C. On the other hand, α-phenyl-substituted monomer () generated indenyl alcohol () when subjected to cationic polymerization conditions.

Decreasing the alkyl branch frequency in precision polyethylene: pushing the limits toward longer run lengths.

A symmetrical α,ω-diene monomer with a 36 methylene run length was synthesized and polymerized, and the unsaturated polymer was hydrogenated to generate precision polyethylene possessing a butyl branch on every 75th carbon (74 methylenes between branch points). The precision polymer sharply melts at 104 °C and exhibits the typical orthorhombic unit cell structure with two characteristic wide-angle X-ray diffraction (WAXD) crystalline peaks observed at 21.5° and 24.

Precision polyethylene: changes in morphology as a function of alkyl branch size.

Metathesis polycondensation chemistry has been employed to control the crystalline morphology of a series of 11 precision-branched polyethylene structures, the branch being placed on each 21st carbon and ranging in size from a methyl group to an adamantyl group. The crystalline unit cell is shifted from orthorhombic to triclinic, depending upon the nature of the precision branch. Further, the branch can be positioned either in the crystalline phase or in the amorphous phase of polyethylene, a morphology change dictated by the size of the precision branch.