Synthesis and Properties of Ionically Modified Polymers with LCST Behavior

Abstract

Ionically modified LCST polymers were synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM) with various cationic, anionic, and amphoteric comonomers, resulting in products with comparable molecular masses and charge concentrations. The temperature-dependent phase transition behavior of the copolymers was investigated in water, aqueous sodium chloride solutions, and mixtures of water with dimethylformamide (DMF) using light transmission measurements, static light scattering, viscometry, and sedimentation experiments in an analytical ultracentrifuge. The LCST of the cationic modified copolymers remains unchanged compared with the homopolymer, but it is increased as a result of an amphoteric or anionic modification. Phase transitions are accompanied by conformational changes followed by aggregation processes. These changes are enhanced in the presence of salt. The phase transition of poly-NIPAM-co-MADAMBQ ((methacryloyloxy)ethyl)dimethylbenzylammonium chloride) in 0.5 M NaCl was studied in detail investigating the temperature dependence of molecular parameters as intrinsic viscosity, particle mass, radius of gyration, second virial coefficient, and sedimentation coefficient.

Facile synthesis of triple‐stimuli (photo/pH/thermo) responsive copolymers of 2‐diazo‐1,2‐naphthoquinone‐mediated poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)

“…However, in the architectures bearing segmented monomer sequences, such as block and graft copolymers that are often found synthetically challenging, the LCST tends to be remained unchanged as that of PNIPAM 22–27. Meanwhile, the LCST behavior can also be affected by other factors, such as pH,28–31 solvent,32–35 ionic strength,36–40 and so forth, and these characters can be utilized to make “smart” materials 41–43…”

Preparation of nano‐ and microparticles through self‐assembly of azobenzene‐pendent ionomers

“…On the other hand, thermosensitive ionomers reversibly formed particles in responding to the temperature stimuli. [12][13][14] Azobenzene derivatives have two important properties, i.e., a nonlinear optical property and photoresponsive isomerization. [15][16][17] Many research groups have studied the thin film preparation from azobenzene-containing polymers and their application to the optical devices.…”

Electrostatic self-assembly of thermally responsive zwitterionic poly(N-isopropylacrylamide) and poly(ethylene oxide) modified with ionic groups

“…The introduction of charged groups into the PNIPAM chain affects its LCST and prevents the coagulation of the colloidal particles formed above the LCST [12][13][14]. At 6-7 mol% incorporation, a cationic monomer does not affect the LCST of PNIPAM, a carboxybetaine monomer raises it to 43 8C, while the negatively charged copolymer does not exhibit phase transition up to 90 8C [15]. The structure of the aggregated species depends on the degree of ionization of the comonomer [16].…”