Influence of length and structure of aryl boronic acid crosslinkers on organogels with partially hydrolyzed poly(vinyl acetate)

Organogels composed of 40% hydrolyzed poly(vinyl acetate) (40PVAc) and three arylboronic acids have been formed and characterized in several liquids to gain insights into the role of crosslinker length and structure on the properties of the gels. Data from ¹H NMR, steady-state and time-resolved fluorescence, and rheology have been employed to correlate the degrees of crosslinking and the bulk physical properties of the gels. Benzene-1,4-diboronic acid (1,4-BDBA) and 4,4′-biphenyldiboronic acid (bPDBA) formed gels with 40PVAc that were stable for longer periods than those with benzene-1,3-diboronic acid. Surprisingly, the steady-state and time-resolved fluorescence properties of 1,4-BDBA or bPDBA were affected very little in solution upon addition of two model diols (1,3-propanediol and 1,2-ethanediol) or even 40PVAc. Furthermore, 40PVAc appeared to form crosslinks more efficiently, resulting in stiffer gels, with bPDBA than with 1,4-BDBA. We attribute these trends to the greater length, flexibility, and linearity of bPBPA. Overall, the results reported here demonstrate that minor structural changes in the crosslinker can alter significantly many of the bulk properties of two-component organogel networks. They also provide a clear ‘blueprint’ for making gels with specific desired properties for a range of applications that require virtually water-free systems.