Synthesis, Characterization and Behavior in Aqueous Solution of Star‐Shaped Poly(acrylic acid)

Abstract

Summary: We report the synthesis of star‐shaped poly(acrylic acid) (PAA), with 5, 8, and 21 arms, by atom transfer radical polymerization of tert‐butyl acrylate. We employ the core‐first approach using glucose‐, saccharose‐ and cyclodextrin‐based initiators. Subsequent acidic treatment of poly(tert‐butyl acrylate) (PtBA) leads to star‐shaped poly(acrylic acid) (PAA). Alkaline cleavage of the arms enabled us to determine the initiation site efficiency. The PAA stars and arms were esterified to poly(methyl acrylate) (PMA). Molecular weight determination by means of GPC/viscosity, MALDI‐TOF MS and NMR end‐group determination showed that the initiation site efficiency is close to unity. Results from potentiometric titration of PAA arms and stars show that the apparent pKa values increase with increasing arm number, which is a direct result of increasing segment density. Osmometry measurements of aqueous solutions of the PAA stars result in osmotic coefficients between 0.05 and 0.38, indicating that most of the counterions are confined within the star. The confinement increases with arm number.

Cellulose-based graft copolymers prepared by simplified electrochemically mediated ATRP

“…DS is an important parameter that directly determines the grafting density of copolymers prepared in the subsequent step [3]. It should be noticed that, in previous studies using cellulose and its derivatives as the start- Chmielarz -eXPRESS Polymer Letters Vol.11, No.2 (2017) [42]; (f) apparent M n and M w /M n of the arms cleaved from the (co)polymers executed by THF GPC; (g) experimental DP of arm from dividing M n,app by the molar mass of the polymer's reiterating unit: DP n,app (per arm) = M n,app (arm)/M monomer [44]; (h) apparent efficiency of initiation calculated as: f i = (DP n,theo (per arm)/DP n,app (per arm)) · 100% [45]; (i) I app = - 1.32, -0.90, -0.54, -0.41, -0.28, -0.22, -0.16, -0.12, -0.08, -0.06, and -0.05 mA for each steps; (j) hydrolysis of PtBA blocks to PAA blocks [42]; (k) theoretical M n was determined (equation (d) ) and reduced by the value of PAA (from entry 3); (l) apparent M n was determined by THF GPC and reduced by the value of PBA (from entry 3); ing materials, the higher DS of BriB was very difficult to obtain and its values were often less than 1 [2,5,43], this is mainly due to the occupation on hydroxyl groups of cellulose by ester or ether groups.…”

“…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].…”

“…After filtered and washed, the white solid products were dried by air, dissolved in THF, passed through a neutral alumina column, and dried under vacuum for 14 days before NMR characterization. The PAA-b-POEGA blocks of cellulose-based graft copolymers were cleaved by alkaline hydrolysis Transformation to Cell-g-PAA graft polymers via hydrolysis according to procedure described in reference [42]. The polymer samples were purified [42] and then characterized by GPC to examine the growth of the copolymer arms with monomer conversion.…”

“…The PAA-b-POEGA blocks of cellulose-based graft copolymers were cleaved by alkaline hydrolysis Transformation to Cell-g-PAA graft polymers via hydrolysis according to procedure described in reference [42]. The polymer samples were purified [42] and then characterized by GPC to examine the growth of the copolymer arms with monomer conversion. Furthermore, the final polymer was characterized using 1 H NMR.…”