In situ monitoring of latex film formation by small-angle neutron scattering: Evolving distributions of hydrophilic stabilizers in drying colloidal films

The distribution of hydrophilic species, such as surfactants, in latex films is of critical importance for the performance of adhesives, coatings and inks, among others. However, the evolution of this distribution during the film formation process and in the resulting dried films remains insufficiently elucidated. Here, we present in situ (wet) and ex situ (dry) SANS experiments that follow the film formation of two types of latex particles, which differ in their stabilizer: either a covalently bonded poly(methacrylic acid) (PMAA) segment or a physically adsorbed surfactant (sodium dodecyl sulfate, SDS). By fitting the experimental SANS data and combining with gravimetry experiments, we have ascertained the hydrophilic species distribution within the drying film and followed its evolution by correlating the size and shape of stabilizer clusters with the drying time. The evolution of the SDS distribution over drying time is being driven by a reduction in the interfacial free energy. However, the PMAA-based stabilizer macromolecules are restricted by their covalent bonding to core polymer chains and hence form high surface-area disc-like phases at the common boundary between particles and PMAA micelles. Contrary to an idealized view of film formation, the PMAA does not remain in the walls of a continuous honeycomb structure. The results presented here shed new light on the nanoscale distribution of hydrophilic species in drying and ageing latex films. We provide valuable insights into the influence of the stabilizer mobility on the final structure of latex films

RAFT Polymerization of Methacrylic Acid in Water

Reversible addition–fragmentation chain transfer (RAFT) polymerization of methacrylic acid was successfully performed in water in the presence of a trithiocarbonate, the 4-cyano-4-thiothiopropylsulfanylpentanoic acid (CTPPA), as a RAFT agent. Several parameters such as the temperature, the concentration, the pH, the targeted polymerization degree, and the initiator concentration were studied. For pH value below the p<i>K</i>_a of MAA, well-defined PMAA chains with different molar mass up to 92 000 g mol^–1 exhibiting low dispersity (<i>Đ</i> < 1.19) were obtained under a broad range of synthetic conditions

Emulsion Polymerization of Vinyl Acetate in the Presence of Different Hydrophilic Polymers Obtained by RAFT/MADIX

The surfactant-free emulsion polymerization of vinyl acetate (VAc) was achieved using RAFT/MADIX-mediated polymerization-induced self-assembly (PISA) process in water. First, well-defined hydrophilic macromolecular RAFT agents (macroRAFT) bearing a xanthate chain end were synthesized by RAFT/MADIX polymerization of <i>N</i>-vinylpyrrolidone (NVP) and <i>N</i>-acryloylmorpholine (NAM) or by post-modification of commercial poly­(ethylene glycol). Chain extension of the macroRAFT with VAc in water led to the block copolymer nanoscale organization and the subsequent formation of stable and isodisperse PVAc latex nanoparticles with high solids content (35–37 wt %). The influence of various parameters, including the nature and functionality of the macroRAFT agent precursor, on the polymerization kinetics and particle morphology was also studied

Toward a Better Understanding of the Parameters that Lead to the Formation of Nonspherical Polystyrene Particles via RAFT-Mediated One-Pot Aqueous Emulsion Polymerization

The emulsion polymerization of styrene in the presence of hydrophilic poly­(methacrylic acid-<i>co</i>-poly­(ethylene oxide) methyl ether methacrylate), P­(MAA-<i>co</i>-PEOMA), macromolecular RAFT (reversible addition–fragmentation chain transfer) agents possessing a trithiocarbonate reactive group and 19 ethylene oxide subunits in the grafts was performed to create <i>in situ</i> P­(MAA-<i>co</i>-PEOMA)-<i>b</i>-polystyrene amphiphilic block copolymer self-assemblies. The system was studied using the following conditions: a pH of 5, two different compositions of the MAA/PEOMA units (50/50 and 67/33, mol/mol), different molar masses of the macroRAFT agents, and various concentrations of the latter targeting different molar masses for the polystyrene block. This work completes a previous one performed at pH 3.5, under otherwise similar experimental conditions, for which only spherical particles were obtained [Zhang et al. <i>Macromolecules</i> <b>2011</b>, <i>44</i>, 7584]. For both MAA/PEOMA compositions, the system led to different nano-object morphologies such as spherical micelles, nanofibers, and vesicles, depending directly on the molar masses of the hydrophilic and hydrophobic blocks. A pH of 5 was shown to be the best compromise to achieve nonspherical particles while keeping a good control over the chain growth

Microphase Separation and Crystallization in H‑Bonding End-Functionalized Polyethylenes

Well-defined, crystalline, low molar mass polyethylene PE_<i>x</i> (where <i>x</i> is the molar mass 1300 and 2200 g mol^–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE₁₃₀₀-NH₂, PE₁₃₀₀-DAT, and the equimolar blend PE₁₃₀₀-Thy/DAT-PE₁₃₀₀ all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH₂ or PE-DAT. For PE₁₃₀₀-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small proportion of nonfunctionalized PE chains to segregate and crystallize separately to the PE-Thy chains. The confinement of PE chains between Thy domains lead to a conventional monolayer form in which extended PE chains were interdigitated. The volume fraction of Thy or DAT end-groups was a key parameter in the organization in all these systems: the PE crystallinity was higher with longer PE chains (i.e., a low volume fraction of Thy or DAT units), but the mesoscopic organization of the supramolecular PE was less regular

Effect of the pH on the RAFT Polymerization of Acrylic Acid in Water. Application to the Synthesis of Poly(acrylic acid)-Stabilized Polystyrene Particles by RAFT Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid (AA) in water was studied in detail at different pHs using 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA) as a control agent and 4,4′-azobis­(4-cyanopentanoic acid) (ACPA) as an initiator. Well-defined hydrophilic macromolecular RAFT agents (PAA-CTPPA) were obtained and further used directly in water for the polymerization of styrene. The corresponding polymerization-induced self-assembly (PISA) process was evaluated at different pHs and it was shown that working in acidic conditions (pH = 2.5) led to well-defined amphiphilic block copolymer particles (<i>Đ</i> < 1.4) of small size (below 50 nm). When the pH increased, the control over the growth of the polystyrene (PS) block was gradually lost. Chain extension experiments of PAA-CTPPA with <i>N</i>-acryloylmorpholine (NAM), a hydrosoluble and non-pH sensitive monomer, performed at different pHs showed that the very first addition–fragmentation steps that occurred in water were impeded when PAA was ionized leading to partial consumption of PAA-CTPPA and thus to PS molar masses higher than expected. Varying the PAA-CTPPA concentration at pH = 2.5 led in all cases to stable particles composed of well-defined block copolymers with PS segments of different molar masses

Batch Emulsion Polymerization Mediated by Poly(methacrylic acid) MacroRAFT Agents: One-Pot Synthesis of Self-Stabilized Particles

The present paper describes the successful one-pot synthesis of self-stabilized particles composed of amphiphilic block copolymers based on poly­(methacrylic acid) (PMAA) obtained by polymerization-induced self-assembly. First, controlled radical polymerization of MAA is performed in water using the RAFT process by taking advantage of our recent results showing the successful RAFT polymerization of MAA in water [Chaduc Macromolecules 2012, 45, 1241−1247]. The so-formed hydrophilic macroRAFT agents are then chain-extended <i>in situ</i> with a hydrophobic monomer to form amphiphilic block copolymer chains of controlled molar mass that self-assemble into stable nanoparticles. Various parameters such as the pH, the molar mass and the concentration of the PMAA segments or the nature of the hydrophobic block have been investigated

Xyloglucan-Functional Latex Particles via RAFT-Mediated Emulsion Polymerization for the Biomimetic Modification of Cellulose

Herein, we report a novel class of latex particles composed of a hemicellulose, xyloglucan (XG), and poly­(methyl methacrylate) (PMMA), specially designed to enable a biomimetic modification of cellulose. The formation of the latex particles was achieved utilizing reversible addition–fragmentation chain transfer (RAFT) mediated surfactant-free emulsion polymerization employing XG as a hydrophilic macromolecular RAFT agent (macroRAFT). In an initial step, XG was functionalized at the reducing chain end to bear a dithioester. This XG macroRAFT was subsequently utilized in water and chain extended with methyl methacrylate (MMA) as hydrophobic monomer, inspired by a polymerization-induced self-assembly (PISA) process. This yielded latex nanoparticles with a hydrophobic PMMA core stabilized by the hydrophilic XG chains at the corona. The molar mass of PMMA targeted was varied, resulting in a series of stable latex particles with hydrophobic PMMA content between 22 and 68 wt % of the total solids content (5–10%). The XG-PMMA nanoparticles were subsequently adsorbed to a neutral cellulose substrate (filter paper), and the modified surfaces were analyzed by FT-IR and SEM analyses. The adsorption of the latex particles was also investigated by quartz crystal microbalance with dissipation monitoring (QCM-D), where the nanoparticles were adsorbed to negatively charged model cellulose surfaces. The surfaces were analyzed by atomic force microscopy (AFM) and contact angle (CA) measurements. QCM-D experiments showed that more mass was adsorbed to the surfaces with increasing molar mass of the PMMA present. AFM of the surfaces after adsorption showed discrete particles, which were no longer present after annealing (160 °C, 1 h) and the roughness (<i>R</i>_q) of the surfaces had also decreased by at least half. Interestingly, after annealing, the surfaces did not all become more hydrophobic, as monitored by CA measurements, indicating that the surface roughness was an important factor to consider when evaluating the surface properties following particle adsorption. This novel class of latex nanoparticles provides an excellent platform for cellulose modification via physical adsorption. The utilization of XG as the anchoring molecule to cellulose provides a versatile methodology, as it does not rely on electrostatic interactions for the physical adsorption, enabling a wide range of cellulose substrates to be modified, including neutral sources such as cotton and bacterial nanocellulose, leading to new and advanced materials

Deciphering the Mechanism of Coordinative Chain Transfer Polymerization of Ethylene Using Neodymocene Catalysts and Dialkylmagnesium

Ethylene polymerizations were performed in toluene using the neodymocene complex (C₅Me₅)₂NdCl₂Li­(OEt₂)₂ or {(Me₂Si­(C₁₃H₈)₂)­Nd­(μ-BH₄)­[(μ-BH₄)­Li­(THF)]}₂ in combination with <i>n</i>-butyl-<i>n</i>-octylmagnesium used as both alkylating and chain transfer agent. The kinetics were followed for various [Mg]/[Nd] ratios, at different polymerization temperatures, with or without ether as a cosolvent. These systems allowed us to (i) efficiently obtain narrowly distributed and targeted molar masses, (ii) characterize three phases during the course of polymerization, (iii) estimate the propagation activation energy (17 kcal mol^–1), (iv) identify the parameters that control chain transfer, and (v) demonstrate enhanced polymerization rates and molar mass distribution control in the presence of ether as cosolvent. This experimental set of data is supported by a computational investigation at the DFT level that rationalizes the chain transfer mechanism and the specific microsolvation effects in the presence of cosolvents at the molecular scale. This joint experimental/computational investigation offers the basis for further catalyst developments in the field of coordinative chain transfer polymerization (CCTP)

Well-Defined Amphiphilic Block Copolymer Nanoobjects via Nitroxide-Mediated Emulsion Polymerization

Water-soluble macroalkoxyamines are shown to be particularly well-suited initiators for nitroxide-mediated emulsion polymerization. They lead to the synthesis of amphiphilic block copolymers that self-assemble in situ into well-defined nanoobject morphologies, in agreement with the principles of polymerization-induced micellization. Depending on the molar mass of the hydrophobic block, the formed nanoparticles are hairy spherical micelles, nanofibers, or vesicles. The nanofibers are the most intriguing and spectacular structure and strongly affect the physicochemical properties of the aqueous dispersions