Synthesis and solution properties of a new class of pH -responsive associating ionic polymers

Abstract

A new class of pH-responsive hydrophobically associating ionic polymers (cationic polyelectrolytes, anionic polyelectrolytes, and polyzwiterions) has been synthesized using Butler's cyclopolymerization technique involving hydrophilic and hydrophobic diallylammonium salts and sulfur dioxide. These polymers have been characterized by NMR for hydrophobe level and static light scattering for molecular weight. The hydrophobic monomers: N,N-diallyl- N-octdecylammonium chloride, N,N-diallyl- N-dodecylammonium chloride, N,N-diallyl- N-(mono-, di-, tri-octyloxybenzyl) ammonium chloride, N,N -Diallyl-N-(3,5-bis(3,5-di(octyloxy)benzyloxy)) benzylammonium chloride and hydrophilic monomers: N,N-diallyl- N-carboethoxymethylammonium chloride, diallyldimethylammonium chloride, 3-(N,N-diallylammonio)propanesulfonate were synthesized and used for the polymerization. The polymers showed that concentration (C*HA) of less than 1 wt% was required for the manifestation of hydrophobic association in salt (NaCl)-free and salt-added solution. This is indeed a notable improvement over the previously reported C*HA (ca. 15-17 g/dL) for the associating cyclopolymers having ∼C10-C14 pendents. In some polymer solutions, the presence of sodium chloride is shown to enhance the hydrophobic association tremendously. A series of terpolymers of N,N-diallyl-N-carboethoxymethylammonium chloride, and sulfur dioxide containing single-tailed (N,N-diallyl-(4-octyloxy)benzylammoniun chloride, twin-tailed (N,N-diallyl-(3,5-dioctyloxy)benzylammoniun chloride, and tripled tailed (N,N-diallyl-(3,4,5-trioctyloxy)benzylammoniun chloride, was synthesized in the presence of constant level of octyloxy tail. The terpolymers with the triple-tailed hydrophobe exhibited the most pronounced viscosity increase. To study the effect of charge density on the association behavior of the terpolymers, the pH-responsive cationic acid salt (CAS) polymers derived from hydrolysis of polymers having carboethoxy pendents, were treated with different equivalent of NaOH to afford polybetaines (PB), anionic polyelectrolytes (APE) as well as polymers PB/APE containing various proportions of zwitterionic (PB) and anionic fractions (APE) in the polymer chain. It was found that PB/APE polymer with a ratio of 33:67 for the zwitterionic and anionic fractions in the polymer chain, respectively, gave the highest viscosity value.