Thermoresponsiveness of PDMAEMA. Electrostatic and Stereochemical Effects

Abstract

Isotactic triads are introduced into poly-(dimethylaminoethyl methacrylate) (PDMAEMA) when a Lewis acid yttrium(III)trifluoromethanesulfonate, Y(OTf) 3 , is present during the ATRP polymerization. The changes in the tacticities of the polymers are modest. However, the tacticity affects the phase separation process but in a different way in two studied cases, at pH 8 and 9. The pH, and thus the charge of the polymer, affects the balance between electrostatic and stereochemical effects. Upon the chain collapse, the zeta potential of the polymer decreases discontinuously at pH 9, whereas at pH 8 the potential keeps almost constant. However, even in the latter case the influence of the isotactic segments on the thermal transition may be observed. Increasing isotacticity is suggested to decrease the flexibility of the polymer chain. It also causes the polymers to adsorb in a more organized manner to the air/water interface than the atactic ones do. The change in the thermoresponsive behavior due to the changing tacticity of the polymer has been studied at the interface by observing the surface tension and by surface rheology and in the solution by conventional rheology. Differences in the elastic and viscous moduli owing to the different tacticities of the polymers are compared to those attributed to different molar masses and to varying pH.

Bioinspired thermo- and pH-responsive polymeric amines: Multimolecular aggregates in aqueous media and matrices for silica/polymer nanocomposites

“…Similar observation of a pre-transitional shoulder has been reported for neutral [30] and charged [31] thermally responsive polymers. The origin of this peak is not always clear and probably differs for different polymers.…”

“…Introducing neutral water-soluble blocks or grafts (e.g., poly(ethylene glycol)) into thermally responsive polymer backbones results in a faster demixing-remixing cycle due to the ability of water molecules to leave the polymer-rich phase and to return back [29]. Evidently, the presence of charged groups in PDEAPMA enhances penetration of the water molecules in the polymer-rich phase in a similar manner, and results in a smaller degree of thermal hysteresis (faster response) in comparison with other polymers such as poly(N-isopropylacrylamide) (PNIPAAM) [30,31]. Importantly, the value of DH derived from the heating and cooling scans was essentially the same, thus demonstrating the reversibility of the transition in the course of cooling.…”

Mechanistic Perspectives on Stereocontrol in Lewis Acid-Mediated Radical Polymerization

“…166 Tenhu and coworkers reported that the presence of Y(OTf) 3 could enhance isotactic content in the radical polymerization of dimethylaminoethyl methacrylate (DMAEMA). 167 The isotactic content of the resulting polymer increased from m ¼ 18 to 35% with the inclusion of 0.25 equivalents of Y(OTf) 3 . 167 Xu and coworkers recently reported that tacticity in the radical polymerization of a methacrylamide substituted with a chiral 2-hydroxy-1-phenylethyl auxiliary (HPEMAM) could be influenced by the inclusion of LA.…”

“…167 The isotactic content of the resulting polymer increased from m ¼ 18 to 35% with the inclusion of 0.25 equivalents of Y(OTf) 3 . 167 Xu and coworkers recently reported that tacticity in the radical polymerization of a methacrylamide substituted with a chiral 2-hydroxy-1-phenylethyl auxiliary (HPEMAM) could be influenced by the inclusion of LA. 132 The presence of Pr(OTf) 3 increased the isotactic content of the resulting polymer from m ¼ 14 to 62%.…”

Multi‐stimuli‐responsive self‐immolative polymer assemblies

“…Below the LCST, the polymer chains are soluble, but above the LCST an entropically driven phase separation occurs. Another well‐studied polymer that has an LCST is poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) . It differs from PNIPAAm in that it is responsive to both pH and temperature.…”