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Novel Synthesis of Gel Capsule by Esterification of Poly(acrylic acid) Gel

To synthesize a novel gel capsule containing a hydrophobic shell and hydrophilic core portions, we investigated the esterification of poly(acrylic acid) gel-1,8-diazabicyclo[5,4,0]undec-7-ene salt (DAA) with alkyl bromides. The esterification of DAA with benzyl bromide proceeded almost quantitatively in N-methyl-2-pyrrolidone (NMP) from the surface, although small amounts of carboxylic acids were produced as side products. The reaction gave a new gel capsule consisting of a hydrophilic unreacted core and hydrophobioc esterified shell, and finally afforded poly(benzyl acrylate) gel. Reactions of DAA with alkyl bromides were carried out under various conditions, and analyzed kinetically. The observed reaction rate markedly affected the molecular size of the alkyl halides and solvents rather than reactivity of their combinations. This suggests that the overall reaction depends markedly on diffusion rate of alkyl bromides and solvents through the reacted shell layer. The thickness of the shell layer was easily controlled by reaction conditions. The swelling of the gel capsule and release of Rose-Bengal from the gel capsule were studied. The results suggested that the structure of the shell layer controls properties such as the swelling rate, burst time, and releasing rate of chemicals.