Zwitterionic polymers have been intensively studied for numerous applications, including antifouling, drug delivery, lubrication, anti-icing, oil-water separation, etc. However, their structure-solution-behavior relationship has not been well understood. To study the effects of N-substituents on the behavior of zwitterionic poly(sulfobetaine methacrylate)s (PSBMAs) in water, we synthesized a series of PSBMAs with various N-substituents. With the simultaneous increase of the lengths of two symmetric N-n-alkyl substituents, we found that the solution behavior of PSBMAs in water changed from upper critical solution temperature (UCST) thermoresponsive to water-soluble, lower critical solution temperature (LCST) thermosensitive, and water-insoluble. Similar solubility changes were observed when the length of one N-n-alkyl substituent of PSBMAs was gradually increased while the other N-methyl substituent was kept. The observed diverse solution behavior was believed to result from the competition between the steric reduction of electrostatic zwitterionic interactions and the increase of hydrophobic effect with increasing n-alkyl lengths. When an N-n-hexyl was replaced with cyclohexyl while keeping the other N-methyl substituent, the PSBMA was converted from an LCST thermosensitive to a totally water-soluble polymer due to the decreased hydrophobic effect. The understanding obtained from this study will facilitate the design and synthesis of thermosensitive water-soluble PSBMAs and further expand the applications of zwitterionic materials in various areas.

Thermosensitive water-soluble zwitterionic poly(sulfobetaine methacrylate)s

ACS Spring Meeting 2021

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