Pulsed laser studies of cationic reactive surfactant radical propagation kinetics

Abstract

Pulsed laser polymerization coupled with size exclusion chromatography (PLP-SEC) was implemented to study the micellar radical homopropagation kinetics of cationic surfmer, polycaprolactone choline iodide ester methacrylate (PCLnChMA with n=2 average polyester units), at concentrations of 5, 10, and 20 wt% in aqueous solutions at 25, 50, 70, and 85 °C. PCL2ChMA can propagate in both aqueous and compartmentalized phases, with the relative importance of the two reaction loci changing with temperature. As the corresponding saturated macromonomer concentration, [M], inside the growing polymeric micelles cannot be easily determined, only the product of propagation rate coefficient (kp) and [M] are measured by PLP-SEC; at 25 °C, a minimum kp of 863 ± 95 Lꞏmol-1 ꞏs-1 is estimated assuming bulk [M]. (Macro)monomer composition drifts for batch acrylamide (AM)/PCLnChMA micellar copolymerizations in D2O at 50 °C are well represented by the apparent reactivity ratios rAM = 0.31 ± 0.03 and rPCL3ChMA = 8.79 ± 0.38.

PLP-SEC Investigation of the Influence of Electrostatic Interactions on the Radical Propagation Rate Coefficients of Cationic Monomers TMAEMC and MAPTAC

“…This provides a radical flux range suitable for obtaining PLP-structured MMDs and represents an immense advantage compared to use of sparingly water-soluble photoinitiators (e.g., 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone) that allow only a limited variation in the radical flux due to their low solubility in aqueous solutions of ionized monomers. 12,17 The PLP-structured MMDs and reliable k p values were also obtained at a high c LiTPO of 50 mmol•L −1 , i.e., at the concentration for which one can expect an inhomogeneity in spatial distribution of radical concentration as a result of a significant decrease in laser intensity in the direction of the laser beam due to the photoinitiator absorbance. 35 Second, the SEC operating conditions are chosen to ensure both adequate calibration and to suppress non-size-exclusion phenomena during elution caused by enthalpic interactions, a nontrivial task for SEC analysis of ionized polymers.…”

“…The relatively high dn/dc values of the polymers provided a MALS signal of sufficient quality for an accurate estimation of k p values. It can be noted that SEC conditions identified in this work for pTMAEMC, pMAPTAC, and pDMAEMA can be recommended for characterization of various cationically ionized polymers as they have been successfully used for characterization of a methacrylate-type cationic surfmer 17 as well as copolymers of TMAEMC with acrylic acid. 32 As TMAEMC and MAPTAC are permanently ionized monomers, it is expected that the solution pH should not affect k p values.…”

“…e . , [ 2 -(methacryloyloxyl)ethyl]trimethylammonium chloride (TMAEMC), 15 [2-(acryloyloxyl)ethyl] trimethylammonium chloride (TMAEAC), 16 surfmer polycaprolactone choline iodide ester methacrylate, 17 and zwitterionic monomers. 18 The mechanistic picture of chain growth, already challenging for nonionized monomers due to the presence of hydrogenbonding interactions, 19−21 is further complicated by the presence of electrostatic interactions influenced by: (i) the number and type of ions entering the polymerization system as ionized monomer or added salts; (ii) the ions that associate with the polymer chains formed during reaction, affecting the chain conformation and the degree of counterion condensation; and (iii) the continuously changing ratio of small ions to polyions during polymerization due to monomer consumption.…”

“…Pulsed-laser polymerization combined with size-exclusion chromatography (PLP-SEC) provided the means to access accurate propagation rate coefficients, k p , that opened the possibility to obtain accurate termination and transfer rate coefficients . In the last two decades, PLP techniques were also applied to determine rate coefficients for the aqueous solution polymerization of fully ionized anionic monomers, i.e., sodium acrylate (AANa) , and sodium methacrylate (MAANa), − cationic monomers, i.e., [2-(methacryloyloxyl)­ethyl]­trimethylammonium chloride (TMAEMC), [2-(acryloyloxyl)­ethyl] trimethylammonium chloride (TMAEAC), surfmer polycaprolactone choline iodide ester methacrylate, and zwitterionic monomers . The mechanistic picture of chain growth, already challenging for nonionized monomers due to the presence of hydrogen-bonding interactions, − is further complicated by the presence of electrostatic interactions influenced by: (i) the number and type of ions entering the polymerization system as ionized monomer or added salts; (ii) the ions that associate with the polymer chains formed during reaction, affecting the chain conformation and the degree of counterion condensation; and (iii) the continuously changing ratio of small ions to polyions during polymerization due to monomer consumption .…”

Active Ester Containing Surfmer for One-Stage Polymer Nanoparticle Surface Functionalization in Mini-Emulsion Polymerization

“…As aforementioned, a wide range of surfmer molecules has been developed so far and polymeric particles have been developed using surfmers bearing cationic [ 29 , 30 , 31 ] or anionic head groups [ 32 , 33 , 34 ], as well as non-ionic [ 35 , 36 , 37 ]. The positive charge on cationic surfmers is commonly derived from quaternary ammonium groups [ 31 , 38 , 39 , 40 ] and may include functional moieties, for instance in fluorinated surfmers [ 29 , 41 ]. A prominent cationic surfmer example is the p -(11-acrylamido)undecanoyloxyphenyl dimethylsulfonium methyl sulfate (AUPDS), a water soluble surfmer that presents an active ester functionality that acts as an anchor group.…”