N-Isopropylacrylamide/monoalkyl itaconate copolymers and N-isopropylacrylamide/itaconic acid/dimethyl itaconate terpolymers

Temperature- and pH-sensitive copolymers and terpolymers of N-isopropylacrylamide (NIPAAm) with itaconic acid (IA), monomethyl itaconate (MMeI), monobutyl itaconate (MBuI), monooctyl itaconate (MOcI), monocetyl itaconate (MCeI), and dimethyl itaconate (DMI) were prepared by free radical solution polymerization method. The dependence of coil-to-globule transition on pH and composition, molecular structures, and reactivities of monoalkyl itaconates, molecular weight distributions, and glass transition temperatures of copolymers and terpolymers were investigated using FT-IR and UV-visible spectroscopic techniques, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and acid-base titration methods. The temperature-/pH-dependent coil-to-globule transition measurements showed that, upon increasing the content and length of alkyl chains, the lower critical solution temperatures (LCSTs) were shifted to higher temperatures. This meant that with increase in the length of hydrophobic alkyl chain in the monoitaconates intramolecular intreactions between the carboxyl groups were suppressed and LCSTs increased. The aqueous solution behaviors of NIPAAm/IA/DMI terpolymers also revealed that, even if the terpolymer hydrophobicity is increased by adding DMI units, the presence of IA units overcame the decrease in hydrophilicity of the terpolymers. The presence of DMI units in the terpolymers balanced the hydrophilic character of IA. DSC results supported the ones obtained from the pH-dependent coil-to-globule transition measurements. An increase in both the chain length of alkyl groups attached to the monoitaconates and the contents of the mono- and dialkyl itaconates in the copolymers and terpolymers decreased the T_gs. In the case of NIPAAm/IA and NIPAAm/MMeI copolymers, the presence of the carboxyl groups forming hydrogen bonds increased the T_g, while the monoalkyl and dialkyl itaconates such as MBuI, MOcI, MCeI and DMI lead to a decrease in T_g of copolym_Sers and terpolymers because of the suppression of intramolecular interactions (resulting from the -COOH and -COO groups) through the longer alkyl spacers. The dependence of the thermosensitivity of these NIPAAm copolymers and terpolymers on different conditions of pH, and the nature and content of comonomers suggests that they can be useful in biotechnology and drug delivery applications which involve small changes in pH and temperature.