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

Abstract

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 Tgs. In the case of NIPAAm/IA and NIPAAm/MMeI copolymers, the presence of the carboxyl groups forming hydrogen bonds increased the Tg, while the monoalkyl and dialkyl itaconates such as MBuI, MOcI, MCeI and DMI lead to a decrease in Tg of copolymers 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. Copyright © 2009 John Wiley & Sons, Ltd.

Network structure and temperature dependence swelling behavior of PEG-b-Poly (NIPAM-co-AMPSA) hydrogels in water

“…According to the reported results [16], the shape of the Q v /T curve is changed in accordance with the ionic comonomer content in the copolymers; the equilibrium degree of swelling (Q v ) is higher and the LCST value is shifted to higher temperatures, from 35 to 40°C. Hence, the copolymer hydrogels of NIPAM and ionic comonomer have been studied extensively [17][18][19].…”

Impact of Polymer Network Inhomogeneities on the Volume Phase Transition of Thermoresponsive Microgels

“…Such spatial inhomogeneities are particularly common in pNIPAAm‐based hydrogels. Their extent is markedly influenced by the experimental conditions during the gelation process: typically, gels made by fast polymerization initiated by large amounts of initiator and/or polymerized at high temperatures are strongly inhomogeneous, whereas those formed by gentle reactions at lower polymerization temperature are more homogeneous 30, 32–34. Despite this knowledge, however, it is unclear to what extent spatial inhomogeneites affect the nature of the volume phase transition of pNIPAAm‐based hydrogels.…”

Effect and Evolution of Nanostructural Complexity in Sensitive Polymer Gels

“…In addition to this macroscopic assessment, several studies have focused on nanometer‐scale concentration fluctuations that occur during gel volume phase transitions, primarily using light and neutron scattering . Again, a particular challenge in this effort is to decouple scattering from the static heterogeneous distribution of the polymer network mesh sizes on length scales of ξ = 1–10 nm, as sketched in Figure C, additional static polymer‐network heterogeneity on length scales of ξ stat = 10–100 nm, as sketched in Figure D, and co‐existing dynamic density fluctuations spanning a scale ξ dyn that covers both the above domains . Several experimentalists have focused on critical concentration fluctuations that arise and diverge at the volume phase transition point of sensitive gels to classify their universality .…”

“…An additional level of irregularity can be encountered on larger length scales: many polymer networks and gels, both supramolecular and covalent, display spatial inhomogeneities of their crosslinking density on a length scale of several tens of nanometers, as illustrated in Figure D. In covalent polymer networks, such structural complexity is usually a consequence of uncontrolled inhomogeneous chain crosslinking, depending on the experimental conditions during the gel formation, as modeled by replica‐field approaches . In supramolecular polymer networks, similar heterogeneity can arise due to clustering and stacking of the transient crosslinking junctions …”

“…The challenge in the attempt to study the effects of nanostructural complexity on the properties of polymer gels is to prepare them such as to exhibit defined degrees of spatial polymer‐network inhomogeneity. This is difficult to achieve, because it must rely on a sound understanding of the impact of the experimental parameters at the moment of the gel formation on the nano‐ and micro­meter‐scale structures of the resulting gels . To circumvent this challenge, a simple way to form polymer gels with controlled inhomogeneity is to assemble them from micrometer‐sized particulate gel building blocks, referred to as microgels .…”