Temperature-, pH- and CO2-Sensitive Poly(N-isopropylacryl amide-co-acrylic acid) Copolymers with High Glass Transition Temperatures

Abstract

A series of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAm-co-PAA) random copolymers were synthesized through free radical copolymerization in MeOH. The incorporation of the acrylic acid units into PNIPAAm tended to enhance the glass transition temperature (T g ), due to strong intermolecular hydrogen bonding between the amide groups of PNIPAAm and the carboxyl groups of PAA, as observed using 1 H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopic analyses. The lower critical solution temperature (LCST) increased upon increasing the pH of the aqueous solution containing PNIPAAm-co-PAA because the COOH groups of the PAA segment dissociated into COO − groups, enhancing the solubility of the copolymer. In addition, high-pressure differential scanning calorimetry revealed that the LCSTs of all the aqueous solutions of the copolymers decreased upon increasing the pressure of CO 2 , suggesting that CO 2 molecules had displaced H 2 O molecules around the polar CONH and COOH groups in PNIPAAm-co-PAA, thereby promoting the hydrophobicity of the copolymers in the aqueous solution. In addition, the values of T g of a film sample increased upon treatment with supercritical CO 2 , implying that intermolecular interactions in the copolymer had been enhanced after such treatment.

Synthesis and Self-Assembly of Multistimulus-Responsive Azobenzene-Containing Diblock Copolymer through RAFT Polymerization

“…In aqueous solution, poly(NIPAM) generally collapsed, with dense globule chains forming at approximately 32 °C. The LCST of the NIPAM macro-CTA was 32.6 °C, consistent with the findings reported in the literature for the LCST of poly(NIPAM) [30][31][32][33]. The transparent aqueous solution containing the NIPAM macro-CTA became opaque at temperatures higher than the LCST, as illustrated in Figure 3 displaying the results obtained from UV spectroscopic analyses.…”

Minimizing the Strong Screening Effect of Polyhedral Oligomeric Silsesquioxane Nanoparticles in Hydrogen-Bonded Random Copolymers

“…We determined the molecular weights through GPC analyses. In addition, we calculated the reactivity ratios ( r PAS and r PMAPOSS ) using the Kelen and Tudos method [14,31,32]; Figure 3 displays the results graphically. We obtained values of r PAS and r PMAPOSS of 0.93 and 0.51, respectively, indicating a tendency for random copolymerization of these two monomers.…”

“…Random copolymers usually feature a higher fraction of hydrogen bonding interactions and higher glass transition temperatures when compared with their corresponding polymer blend systems, due to compositional heterogeneities [14,18,29,30,31]. Thus, in this study, we attempted to induce hydrogen bonding between the C=O units of PMA-POSS and the OH units of PVPh through the free radical copolymerizations giving a series of PVPh- co -PMAPOSS random copolymers (Scheme 1D).…”

Polyethersulfone microfiltration membrane modified by an amphiphilic dithiolane‐containing copolymer for improving anti‐protein‐fouling performance and rejection of nanoparticles

“…Finally, a stoichiometric of MAPEG, MALA, MAHA, CDB and AIBN were added into the Schlenk tube dissolved in 3.0 mL THF. The solution was deoxygenated via enough freeze‐pump‐thaw cycles and then was stirred at 65°C for 48 hours 26‐28 . To stop the RAFT polymerization, the Schlenk tube was quenched into liquid nitrogen.…”