Emulsion Polymerization Of N-butyl Methacrylate Research Articles

On Particle Size Distributions in Catalytic Chain Transfer Emulsion Polymerization: Chain-Extension and the Use of Derived Macromonomers as Reactive Surfactants in Emulsion Polymerization.

Catalytic chain transfer emulsion polymerization (CCTP) and subsequent chain extension via reversible addition-fragmentation chain transfer (RAFT) were used to synthesize amphiphilic macromonomers (MM), in the form of polymer latexes. The macromonomers consisted of two blocks whose first was a random copolymer of methacrylic acid and methyl methacrylate, at 35:65 mol:mol, while the second block was n-butyl methacrylate P[(MAA-co-MMA)-block-PBMA]. The block copolymer colloids were disintegrated and micellized upon addition of ammonia. The resulting nanosized polymer dispersions were used as reactive surfactants in the emulsion polymerization of n-butyl methacrylate. For this, a dual stage slow-fast monomer feed profile was used. The final polymer latexes were in the sub-100 nm range for the particle diameter at 30% w/w total polymer content. The emphasis of the work is to discuss and find an explanation for the observed particle size distributions in the three consecutive emulsion polymerization steps. The particle size distribution of the ω-unsaturated macromonomer latex synthesized by CCTP emulsion polymerization was found to be much broader than expected. This discrepancy is attributed to an extended particle nucleation period. The chain extension step in the macromonomer latex preparation showed considerable secondary nucleation. The presence of water-soluble macromonomer species from the CCTP emulsion polymerization step assured that control of chain growth persisted. The use of the amphiphilic macromonomers as reactive surfactants in the form of a nanosized aggregate seed dispersion showed that the average particle diameter could be tuned and that the molecular weight distributions could be regulated, when monomer starved conditions were used in the emulsion polymerizations.

Nitroxide-Mediated Polymerization-Induced Self-Assembly of Block Copolymers at the Surface of Silica Particles: Toward New Hybrid Morphologies

Silica/polymer latexes with concentric core–shell–corona, half-capped, snowman-like vesicular, tadpole- and centipede-like morphologies have been produced by nitroxide-mediated polymerization-induced self-assembly (PISA) performed in the presence of aqueous suspensions of colloidal silica. A hydrosoluble brush-like PEO-based macroalkoxyamine (P[(poly(ethylene oxide) methyl ether methacrylate)12-co-styrene]-SG1, Mn = 11 700 g mol–1 and Mw/Mn = 1.11) was first adsorbed onto the surface of submicronic silica particles. The obtained suspension was then used in the emulsion polymerization of n-butyl methacrylate with 8 mol % of styrene. This led to the formation of amphiphilic block copolymers (BCPs) that self-assembled in situ at the silica surface into well-defined hybrid nano-objects of various morphologies, in agreement with the principles of polymerization-induced micellization. The influence of the pH was more specifically investigated, using silica particles of different size ranging from 30 to 230 nm. ...

Synthesis of Multipod-like Silica/Polymer Latex Particles via Nitroxide-Mediated Polymerization-Induced Self-Assembly of Amphiphilic Block Copolymers

We report the first nitroxide-mediated synthesis of multipod-like silica/polymer latexes by polymerization-induced self-assembly (PISA) of amphiphilic block copolymers in aqueous emulsion. A water-soluble brush-type PEO-based macroalkoxyamine initiator composed of poly(ethylene oxide) methacrylate and a small amount of styrene (P[(PEOMA950)12-co-S1]-SG1, Mn = 11 700 g mol–1 and Mw/Mn = 1.11) was synthesized and physically adsorbed on the surface of silica particles through hydrogen-bonding interactions. The adsorbed macroalkoxyamine initiator was subsequently employed to initiate the emulsion polymerization of n-butyl methacrylate with a small amount of styrene under mild conditions (85 °C). Kinetic analysis indicates that the polymerizations exhibit the same behavior (i.e., the same reaction rates and the same level of control) as those reported in our previous work in the absence of silica under otherwise similar experimental conditions [Qiao Macromolecules 2013, 46, 4285−4295]. This observation is fully consistent with a PISA process taking place at the silica surface. The resulting self-assembled block copolymers formed polymer nodules randomly distributed around the central silica spheres. Varying the macroinitiator concentration or the silica particle size enabled the successful formation of hybrid particles with dumbbell-, daisy-, or raspberry-like morphologies using this new surface-PISA process.

Nitroxide-Mediated Polymerization-Induced Self-Assembly of Poly(poly(ethylene oxide) methyl ether methacrylate-co-styrene)-b-poly(n-butyl methacrylate-co-styrene) Amphiphilic Block Copolymers

Well-defined water-soluble brush-type homopolymers and copolymers entirely composed of poly(ethylene)oxide methacrylate (PEOMA) units with PEO side groups of various chain lengths (Mn = 300 and 950 g mol–1) were synthesized by nitroxide-mediated polymerization (NMP) using a low molar mass unimolecular alkoxyamine initiator (so-called BlocBuilder) and N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethyl propyl) nitroxide (SG1) in the presence of a small amount of styrene. The resulting SG1-capped macroalkoxyamines possessed the predicted molar masses based on the monomer/initiator molar ratio and narrow molar mass distributions. They were then employed to initiate the emulsion polymerization of n-butyl methacrylate with a low amount of styrene under mild conditions (85 °C) leading to amphiphilic block copolymers that in situ self-assembled into sterically stabilized particles. Kinetics study confirmed the living character of the polymerization, while SEC analysis indicated the presence of a small fraction of dead chains formed by irreversible homotermination reactions. Spherical latex particles with diameters comprised between 60 and 300 nm were obtained at pH 4.2 when decreasing the macroinitiator concentration from 7.2 to 1.2 mM in agreement with the in situ formation of block copolymers. As expected, only the macroinitiators with long PEO side groups, and whose cloud points were above the reaction temperature, led to stable latex suspensions. A drastic change in particle morphology with the formation of vesicles and anisotropic objects was observed when increasing the suspension pH from 4.2 to 6.7. As the macroalkoxyamine initiator contained only one terminal methacrylic acid unit, such a strong effect of pH on particles morphology was not expected. The observed results were interpreted in terms of a salting out effect induced by the concomitant increase of ionic strength upon neutralization of the alkoxyamine initiator. Hence, particle morphologies could be tuned from spherical to elongated micelles and vesicles by the addition of increasing amounts of sodium chloride at a fixed pH of 4.2, which confirmed the above hypothesis.

Nitroxide-Mediated Surfactant-Free Emulsion Polymerization of n-Butyl Methacrylate with a Small Amount of Styrene

Nitroxide-mediated emulsion polymerization of n-butyl methacrylate (BMA) can produce highly living and well-controlled polymer chains when polymerized in the presence of 10 mol % styrene (St) using a one-pot, differential monomer addition technique. When n-BMA-co-St is polymerized in the presence of a surfactant above the critical micelle concentration, bimodal particle size distributions are obtained, likely as a result of combined micellar and aggregative nucleation mechanisms. This phenomenon is not observed for the more hydrophilic monomer system of methyl methacrylate and styrene. In the absence of surfactant, however, it is possible to prepare stable, monomodal latexes. Using N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1), we report the first nitroxide-mediated polymerization of n-butyl methacrylate with a small amount of styrene in a facile surfactant-free emulsion polymerization system. The surfactant-free system requires no separate macroinitiator synthesis step and produces highly living polymers with monomodal particle size distributions. The initiator efficiency can be increased by the addition of methyl acrylate or by the addition of surfactant at concentrations below the critical micelle concentration in the absence of methyl acrylate.

Studies on atom transfer radical emulsion polymerization of n-butyl methacrylate

Atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) in water-borne media, catalyzed and initiated by CuCl/4,4-di (5-nonyl)-2,2-bipyridine (dNbpy) and Ethyl 2-bromopropinate (BrCH3CHCOOC2H5) was conducted. The influence of several factors, such as the amount of surfactant, catalyst, initiator and the reaction time, temperature on the stability of the latexes and the control of the polymerization was investigated. The nucleation mechanism of the latexes, thermodynamic data and activation parameters for the ATRP emulsion polymerization of BMA were also reported.

Effects of Agitation on Oxygen Inhibition, Particle Nucleation, Reaction Rates, and Molecular Weights in Emulsion Polymerization of n-Butyl Methacrylate

Oxygen-free conditions are required during emulsion polymerization reactions to eliminate the inhibition effect of oxygen on the free-radical mechanism of polymerization. Results of a kinetic study of the emulsion polymerization of n-butyl methacrylate using a 1-dm3 reaction calorimeter indicate that oxygen, even in concentrations as low as 1 ppm, not only prolongs the induction period that precedes the chain propagation but also influences the particle nucleation and molecular weights. Agitation promotes the transfer of residual oxygen from the reactor headspace into the emulsion and, therefore, has an effect on the particle nucleation step and other reaction events that follow.

Effect of Surfactant Concentration on Particle Nucleation in Emulsion Polymerization ofn-Butyl Methacrylate

The effect of surfactant concentration on particle nucleation in emulsion polymerization of n-butyl methacrylate has been studied using sodium dodecyl sulfate as the surfactant and potassium persulfate as the initiator. The rates of reaction as a function of time were determined for surfactant concentrations above and below critical micelle concentration of the surfactant. The order of dependence of the particle number on the surfactant concentration was found to be different in different ranges of surfactant concentration. This has been explained on the basis of the predominant phenomenon that affects particle nucleation in each range of surfactant concentration. In the range where the end of particle nucleation is determined by a critical surfactant coverage necessary for colloidal stability, the particle number is expected to increase in proportion to the third power of the surfactant concentration. It has been shown how a size-dependent volumetric growth-rate of particles can result in different exponents in the Smith−Ewart equation relating the particle number to surfactant concentration. A constant volumetric growth rate of particles is assumed in the Smith−Ewart theory of particle nucleation.