Block Copolymers of Poly(styrene) and Poly(acrylic acid) of Various Molar Masses, Topologies, and Compositions Prepared via Controlled/Living Radical Polymerization. Application as Stabilizers in Emulsion Polymerization

Abstract

A series of well-defined diblock, triblock, and star-block copolymers composed of polystyrene and poly(acrylic acid) were synthesized by controlled/living radical polymerization and used as stabilizers in emulsion polymerization under alkaline conditions. The structure of the copolymers, the size of the blocks, and the composition were varied and their efficiency as stabilizers was correlated with their structural characteristics. The block length was varied from 10 to 30 units for the polystyrene block and from 13 to 266 units for the poly(acrylic acid) block. The copolymers appeared to be efficient stabilizers down to a block copolymer-to-monomer ratio of less than 0.5 wt %. From the comparison of the effect of the different structures and compositions, it was shown that the diblock copolymers were particularly efficient and that the optimal composition was about 10 styrene units and a maximum of 50 acrylic acid units. The triblock and star-block copolymers with external hydrophilic blocks did not behave much differently than diblock copolymers. In contrast, for the triblock copolymers with an internal hydrophilic segment, the efficiency strongly depended on the respective length of both blocks. The evolution of the number of latex particles, N p, with the concentration of surfactant was also studied and N p was shown to be proportional to [surfactant]α over a wide range of surfactant concentrations. The value of α was a function of the block copolymer composition irrespective of the individual block lengths: it was 1 for block copolymers with a poly(acrylic acid) content lower than 75 mol % and decreased to 0.4 when the hydrophilic content was increased. This trend was correlated with the exchange dynamics of the stabilizer. The results obtained with various initiator concentrations, temperatures, and ionic strengths corroborated the previous observation that the important point to explain the evolution of α with the copolymer composition was the competition between nucleation of the micelles and exchange of the block copolymers between the micelles and the continuously created polymer /water interfaces in the system. The time scale of this exchange (which is very fast for small-molecule surfactants) was on the same order of magnitude as the nucleation step for emulsion polymerizations carried out in the presence of block copolymers.

Cellulose-based graft copolymers prepared by simplified electrochemically mediated ATRP

“…GPC traces of PAA arms cleaved from the cellulose-based graft polymers (Table 1, entries 3) shifts, 1.28-2.00 and 2.10-2.40 ppm, are attributed to the -CH 2 -(β), -CH 3 (b), and -CH-(α) of PtBA arms [46]. As shown in Figure 13, the disappearance of the characteristic strong peak at ~1.44 ppm corresponding to the methyl protons of the t-butyl group demonstrates the successful hydrolysis of PtBA block of the side chains [39][40][41][42]. In this spectrum the chemical shift, 11.33-12.87 ppm is attributed to the -OH (c′) group indicating the presence of PAA arms [47].…”

“…They were separated by filtration, washed with DCM. Finally, solvent and TFA were removed by rotating evaporation, vacuum drying at 50°C for 7 days and characterized using 1 H NMR [39][40][41][42]. The PAA arms of cellulose-based graft polymers were cleaved by alkaline hydrolysis according to procedure described in reference [42].…”

Triblock copolymers of styrene and sodium methacrylate as smart materials: synthesis and rheological characterization

“…Subsequently, they can be considered as the macromolecular counterparts of small-molecule surfactants and are therefore also called polymeric surfactants [2,17]. Amphiphilic block copolymers can be synthesized with a large variety of monomers [2] and architectures [18,19], which determine their aggregation behavior in water.…”

Recent Research Progress in the Synthesis and Properties of Amphiphilic Block Co-polymers and Their Applications in Emulsion Polymerization

“…In comparison to low-molecularweight surfactants, amphiphilic block co-polymers usually have a very low critical micelle concentration (CMC) and a low diffusion coefficient [9]. Moreover, their reduced mobility is an advantage in the coating industry, as mobile emulsifiers may weaken the polymer film properties, specifically with regard to adhesion [10]. In aqueous emulsion polymerization, the hydrophobic block can anchor on the particle surface while the hydrophilic blocks extend into the water phase and create a well-defined hydrophilic shell [10].…”