Effect of Composition of PDMAEMA-b-PAA Block Copolymers on Their pH- and Temperature-Responsive Behaviors

Abstract

A series of poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) homopolymers and poly(2-(dimethylamino)ethyl methacrylate)-b-poly(acrylic acid) (PDMAEMA-b-PAA) diblock copolymers were synthesized by atomic transfer radical polymerization. Thanks to a fine-tuning of the hydrophobic-hydrophilic balance by varying the molecular weight of the polymers and the pH of the aqueous solutions, as well as the composition for the block copolymers, the lower critical solution temperature (LCST) and the aggregation-dissolution kinetics of PDMAEMA homopolymers and PDMAEMA-b-PAA block copolymers can be adjusted. For the block copolymers, the results show that larger relative size of the PDMAEMA blocks leads to an increasing tendency to form micellar aggregates and a decrease of the LCST of the aqueous solution, which is consistent with the increasing copolymer hydrophobicity. A significant difference of the stimuli-responsive behavior between PDMAEMA-rich and PAA-rich copolymers is observed, because the former exhibit thermo-responsive behavior in a broad temperature range of 40-60 °C in basic media, while the pH-responsive behavior is dominant, and only a weak thermo-responsive behavior is exhibited around the specific isoelectric point (IEP) in the latter case. The aggregation rate is strongly influenced by temperature, molecular weight, structure, and composition of the polymer. Specifically, temperature has a stronger effect than the molar ratio of the PDMAEMA segment in the copolymer (related to its hydrophobicity) and the chain molecular weight, although the PDMAEMA-b-PAA copolymers show faster aggregation rate than do the PDMAEMA homopolymers.

Micellization and gelatinization in aqueous media of pH- and thermo-responsive amphiphilic ABC (PMMA82-b-PDMAEMA150-b-PNIPAM65) triblock copolymer synthesized by consecutive RAFT polymerization

“…11,18,19 Thermo-responsive polymers can become hydrophobic from hydrophilic when the temperature is above a critical point, where a soluble-toinsoluble phase transition occurs, known as lower critical solution temperature (LCST).…”

“…8,9 During the past decade, hydrogels which can switch between free-owing liquid and free-standing gel states have attracted much interest. 10 In particular, great attention has been focused on the intelligent ones, which have broadly tunable characteristics, as they can exhibit a sol-gel transition in response to various external stimuli, such as pH, 11 temperature, 12 and ionic strength, 3 magnetic elds, etc.…”

Synthesis and Investigation of Double Stimuli-Responsive Behavior ofN-Isopropylacrylamide and Maleic Acid Copolymer in Solutions

“…ACCEPTED MANUSCRIPT 19 The maximum values of t eq obtained for poly(NIPAAm-co-MA) solutions were considerably larger than the duration of kinetic processes which have been observed for such stimuliresponsive polymers as poly(2-isopropyl-2-oxazoline), poly(alkyl-2-oxazoline) block copolymers, PDMAEMA block copolymers, some thermosensitive cationic diblock copolymers, polystyrene/poly(N-isopropylacrylamide) core-shell nanoparticles, and cylindrical brushes with 2-Isopropyloxazoline side chains [39][40][41][42][43][44]). In order to explain the high time durations for reaching plateau values of the solution characteristics after a temperature jump, we make the following assumptions.…”

“…In order to explain the high time durations for reaching plateau values of the solution characteristics after a temperature jump, we make the following assumptions. Firstly, in the overwhelming majority of works low-concentration solutions (c £ 0.001 g cm -3 ) were investigated using light scattering [28,[39][40][41][42][43][44][45][46], whereas the concentration of the investigated poly(NIPAAm-co-MA) solutions was 0.0150 g cm -3 . However, the time required for equilibrium achievement depends strongly on concentration, decreasing rapidly with decreasing c [31]; thus t eq might decrease for low-concentration poly(NIPAAm-co-MA) solutions.…”

Influence of the polymer structure over self‐assembly and thermo‐responsive properties: The case of PEG‐b‐PCL grafted copolymers via a combination of RAFT and ROP

“…16,17 Poly(ethylene glycol) (PEG) analogues represent a good alternative to the amide-based polymers. 18,19 They are alkenes that possess a hydrophobic portion represented by a methacrylate group and a hydrophilic moiety, consisting of a PEG chain.…”