Zwitterionic poly(sulfobetaine methacrylate)s in water: from upper critical solution temperature (UCST) to lower critical solution temperature (LCST) with increasing length of one alkyl substituent on the nitrogen atom

Abstract

Increasing the alkyl length on nitrogen of the polymer changes behaviour from UCST, to soluble, LCST, and insoluble.

Thermoresponsive behavior of poly[trialkyl-(4-vinylbenzyl)ammonium] based polyelectrolytes in aqueous salt solutions

“…Similar effects have been used to explain the LCST behavior of PNIPAm [87][88][89][90] and polysulfobetaines with long alkyl chains. 91 The negative enthalpy of dissolution keeps the polymers in solution at low temperatures and this is modulated by anion-polycation interactions, which may also make the overall entropy of dissolution less negative. The effect of salt concentration on the cloud point can be explained by ion pairing with the cationic ammonium group present in the repeating units.…”

“…This is in a stark contrast with the other polycations of the series as PC2N has only T cU whereas PC4N and PC5N both have only T cL . A similar change in behavior has been observed for a series poly(sulfobetaine methacrylate)s. 91 The polymers were shown to have either an LCST or a UCST, depending on the length of the alkyl substituent in the quaternary ammonium.…”

Constrained thermoresponsive polymers – new insights into fundamentals and applications

“…In addition to poly(phosphobetaines) high attention is especially focused on poly(sulfobetaines) [280][281][282]. Extensive studies in aqueous solution have shown that the thermoresponsive behavior depends on a variety of parameters, such as concentration, ionic strength, as well as the molecular weight and the spacer length between the charges of the monomers [50,51,283,284]. In particular, the influence of salt ions, which trigger a so-called antipolyelectrolyte effect by screening of the zwitterionic charges, was intensively investigated [285].…”

Effect of end-groups on sulfobetaine homopolymers with the tunable upper critical solution temperature (UCST)

“…[24][25][26] Therefore, developing more effective methods to increase the UCST of polyzwitterions has always been key to broadening the applications of this "smart" materials. A number of ways exist to change the UCST of PDMAPS, which include: gradually increasing the length of one linear alkyl substituent on the nitrogen atom to transfer the UCST to the lower critical solution temperature (LCST); [27] using a hydrophilic spacer group to increase the cloud point (CP) and thereby separate the cationic and anionic moieties; [28] hydrophobically modifying sulfobetaine to make the UCST more accessible; [29] and co-polymerizing the 2-(diisopropylamino)ethyl methacrylate (DPA) with PDMAPS to give the polymer dual thermoresponsiveness. [30] However, the chemistry required to synthesize such responsive monomers or copolymers is complicated and costly; the hydrophobically modified monomer affects the biocompatibility of materials in the biomedical field; the monomer feed ratio and the conversion need to be strictly controlled to achieve multiple responsiveness; increasing UCST compromises response time due to the large proportion of the other component; lacks reproducibility of UCST and adjustable temperature range because of the complicated steps in copolymerization.…”