Development of biphenyl monomers and associated crosslinked polymers with intramolecular pi-pi interactions

Monomers containing biphenyl moieties were employed to create two sets of covalently crosslinked polymers that displayed noncovalent interactions in their 3-dimensional network. The biphenyls (precursors) used were 2-phenylphenol, 4-phenylphenol and 4,4′-dihydroxybiphenyl, and their acrylated forms were synthesized and named as 2-phenylphenolmonoacrylate, 4-phenylphenolmonoacrylate, and 4,4′-dihydroxybiphenyldiacrylate, respectively. These were characterized by differential scanning calorimetry, nuclear magnetic resonance, and Fourier transform infrared spectroscopy to confirm the successful acrylation reaction. Polymers were synthesized via free radical polymerization reactions with varying crosslinker contents, and their network properties were characterized using swelling studies and compressive modulus tests. Interestingly, swelling studies did not show the expected decreasing swelling ratio with increasing crosslinker content, while compression testing indicated the expected trend of increasing modulus with increasing crosslinking density. The unexpected swelling results are hypothesized to result from the intramolecular interactions between the biphenyl side groups that result in noncovalent crosslinks.