Synthesis of Thermosensitive PNIPAM‐co‐MBAA Nanotubes by Atom Transfer Radical Polymerization within a Porous Membrane

Summary: Thermosensitive polymer nanotubes can be fabricated within an aminopropylsilane‐modified porous anodic aluminum oxide membrane by surface‐initiated atom transfer radical polymerization (ATRP) followed by template removal. DSC experiments prove that the synthesized PNIPAM‐co‐MBAA copolymer nanotubes have a reversible thermosensitive behavior. The temperature‐induced changes in dimension and shape of the nanotubes were studied by AFM in real time in an aqueous environment. It indicates that the nanotubes undergo a shape alteration from an “ellipse” to “circular” shape in water upon heating to LCST or above.

DSC curves of PNIPAM‐co‐MBAA nanotubes.     

RAFT Inverse Miniemulsion Polymerization of Acrylamide

RAFT inverse miniemulsion polymerization is demonstrated for the first time as an alternate way to synthesize hydrophilic polymer latexes. The kinetic behavior of inverse RAFT miniemulsion polymerization of acrylamide is similar to that observed in aqueous RAFT solution polymerization. A water‐soluble initiator provides better control than a lipophilic initiator in inverse RAFT miniemulsion polymerization under the conditions used here.

     

PEO‐Covered Nanoparticles by Emulsion Inversion Point (EIP) Method

This study reports the first PEO‐coated polymer nanoparticles synthesis by miniemulsion polymerization of nano‐emulsions prepared by the low‐energy emulsification method called EIP. The surfactant used was Brij 98, a PEO based non ionic commercial surfactant. The partial phase diagram of the system water/Brij 98/styrene was first determined. The Emulsion Inversion Point technique was then used on the water/Brij 98/styrene system to the formation of styrene‐in‐water nano‐emulsions. After miniemulsion polymerization, particle sizes as low as 36 nm were obtained. To the best of our knowledge, this method had not been used for polymerizable system up to now.

     

Effects of Fluctuation and Segregation in the Rate Acceleration of ATRP Miniemulsion Polymerization

In the ATRP and SFRP miniemulsion polymerization, a particle size range may exist in which the polymerization rate is larger than that of the corresponding bulk polymerization. Here, MC simulations are applied to clarify the reason for the acceleration. It is shown that the statistical variation of the trapping agent concentration (fluctuation effect) dominates the acceleration for good living conditions, while the segregation effect is important when the bimolecular termination is significant. Even for the segregation‐dominated conditions, the polymerization rate cannot be predicted accurately without accounting for the fluctuation effect.

     

Polymer Brushes by Nitroxide‐Mediated Polymerization

This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.

     

A General Strategy for Nano‐Encapsulation via Interfacially Confined Living/Controlled Radical Miniemulsion Polymerization

Summary: We propose and demonstrate the utility of an interfacial living/controlled (reversible addition fragmentation chain transfer, RAFT) radical miniemulsion polymerization in nano‐encapsulation. The principles and methodology behind this technique are readily scalable and highly efficient. The living/controlled nature of the system offers great opportunities to tune the properties of the polymer shell‐like thickness, surface functionality, molecular weight, and inner‐wall functionality by simply using a semi‐continuous polymerization technique.

Illustration of encapsulation principles by RAFT interfacial miniemulsion polymerization.     

Hybrid Nanocomposite Films from Mono‐ and Multi‐Functional POSS Copolyacrylates in Miniemulsion

Summary: The synthesis of aqueous dispersions of hybrid acrylic copolymer particles with either a monofunctional or a multifunctional polyhedral oligomeric silsesquioxane methacrylate comonomer has been performed by free radical heterophase polymerization. The miniemulsion process gives stable latexes, whereas the less controlled emulsion route results in colloidal instability of the products. The thermal and mechanical properties of the nanocomposite latex films have been preliminarily investigated.

The nanocomposite latex particles based on hybrid copolyacrylates with highly dispersed POSS cages.     

Nitroxide‐Mediated Radical Polymerization in Miniemulsion at Stationary State: Rationale for Independence of Polymerization Rate on Nitroxide Partitioning Using Oil‐Phase Initiation

Summary: Simulations based on the kinetics and mechanism of nitroxide‐mediated free radical polymerization (NMP) have been carried out in order to understand the hitherto largely unexplained effects (or lack thereof) of nitroxide partitioning in aqueous miniemulsion NMP. The focus has been on the miniemulsion NMP of styrene mediated by TEMPO and 4‐hydroxy‐TEMPO, two nitroxides with very similar activation‐deactivation equilibria, but very different organic phase‐aqueous phase partition coefficients. The general conclusion is that the organic phase propagating radical and nitroxide concentrations are unaffected by the partition coefficient in the stationary state, but the rate of polymerization and the extent of bimolecular termination increase with increasing nitroxide water solubility in the pre‐stationary state region. Specific NMP systems are, therefore, affected differently by nitroxide partitioning depending on whether polymerization predominantly occurs in the stationary state or not, which in turn is governed mainly by the activation‐deactivation equilibrium constant and the rate of thermal initiation.

Simulated organic‐phase propagating radical concentrations in the presence of thermal initiation for TEMPO‐mediated miniemulsion free radical polymerization of styrene for different nitroxide partitioning coefficients at 125 °C.     

Controlled Alternating Copolymerization of (Meth)acrylates and Vinyl Ethers by Using Organoheteroatom‐Mediated Living Radical Polymerization

Alternating copolymers comprised of (meth)acrylates and vinyl ethers with controlled molecular weights and polydispersities were synthesized for the first time by living radical polymerization using organotellurium, stibine, and bismuthine chain transfer agents. Combining living alternating copolymerization and living radical or living cationic polymerization afforded hitherto unavailable block copolymers with controlled macromolecular structures.

     

Microstructure,Kinetics, and Transport in Oil‐in‐Water Microemulsion Polymerizations

The kinetics of microemulsion polymerization depend on the structure of the initial microemulsion and the transport of species between the aqueous domain, the micelles, and the polymer particles. The water solubility of the monomer and the proximity of the initial microemulsion composition to a phase boundary are key considerations for studying microemulsion polymerization kinetics and producing the desired products. Complications frequently arise in the synthesis of copolymers or the incorporation of controlled polymerization mechanisms because of the compartmentalized nature of microemulsion polymerizations.

     

Xanthate‐Mediated Living Radical Polymerization of Vinyl Acetate in Miniemulsion

Summary: The MADIX/RAFT mechanism, employing a xanthate as the reversible chain‐transfer agent, has been shown to facilitate the living radical polymerization of vinyl acetate in miniemulsion. Methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) successfully mediated the polymerization which was initiated with either of the water‐soluble initiators 2,2′‐azobis{2‐[1‐(2‐hydroxyethyl)‐2‐imidazolin‐2‐yl]propane} dihydrochloride (VA‐060) or 2,2′‐azobis[2‐(2‐dimidazolin‐2‐yl)propane] dihydrochloride (VA‐044). The polymerizations exhibit living characteristics, demonstrated by the evolution of molecular weight distributions. The formulation of the miniemulsion produced stable latexes with no coagulum.

The number‐average molecular weight and PDI as a function of monomer conversion for the RAFT miniemulsion polymerization of vinyl acetate.     

Poly(4‐vinylbenzoyl azide): A New Isocyanato Group Generating Polymer

4‐Vinylbenzoyl azide was synthesized from p‐vinylbenzoic acid and polymerized by free radical polymerization. The obtained polymer contained acyl azide groups which were thermally transformed to the corresponding isocyanato groups. Reactions on these polymers with ethanol, hydroxyethyl methacrylate and 1‐pyrenebutanol proceeded quantitatively. Time‐resolved FT‐IR studies of the reactions with ethanol were carried out by varying the concentration and temperature. The effect of the solvent polarity on the Curtius rearrangement was investigated.

     

New Star‐Shaped Metallo‐Polymeric Chromophores

The synthesis of new star‐shaped polymers, prepared by atom transfer radical polymerization of methyl methacrylate with tris(dialkylaminostyryl‐2,2′‐bipyridine) zinc(II) and iron(II) metalloinitiators, is reported. Their thermal and optical (absorption and emission) properties are discussed.

Structure of the star‐shaped polymers.     

On the Incorrectness of the Factor 2 in the Radical Termination Equation

The IUPAC recommended factor 2 preceding rate coefficients in the radical termination kinetic equations is claimed to be incorrect and confusing. This recommendation can lead to incorrect analysis of experimental data, especially while applying kinetic Monte Carlo simulations. The statement is based on the derivation of the corresponding relationships.

     

Polypeptoids by Living Ring‐Opening Polymerization of N‐Substituted N‐Carboxyanhydrides from Solid Supports

The nucleophilic living ring‐opening polymerization of N‐substituted glycine N‐carboxyanhydrides using solid‐phase synthesis resins is reported. By variation of experimental parameters, products with near Poisson distributions are obtained. As opposed to reversible deactivation radical polymerization, the living polymerization is demonstrated to be viable to high monomer conversion and through multiple monomer addition steps. Successful preparation of a multiblock copolypeptoid is proof for a highly living and robust character of the solid‐phase peptoid polymerization.

     

Interfacial Mass Transfer in Nitroxide‐Mediated Miniemulsion Polymerization

A mathematical model has been developed to describe the interfacial mass transfer of TEMPO in a nitroxide‐mediated miniemulsion polymerization (NMMP) system in the absence of chemical reactions. The model is used to examine how the diffusivity of TEMPO in the aqueous and organic droplet phases, the average droplet diameter and the nitroxide partition coefficient influences the time required for the nitroxide to reach phase equilibrium under non‐steady state conditions. Our model predicts that phase equilibrium is achieved quickly (< 1 × 10⁻⁴ s) in NMMP systems under typical polymerization conditions and even at high monomer conversions when there is significant resistance to molecular diffusion. The characteristic time for reversible radical deactivation by TEMPO was found to be more than ten times greater than the predicted equilibration times, indicating that phase equilibrium will be achieved before TEMPO has an opportunity to react with active polymer radicals. However, significantly longer equilibration times are predicted, when average droplet diameters are as large as those typically found in emulsion and suspension polymerization systems, indicating that the aqueous and organic phase concentrations of nitroxide may not always be at phase equilibrium during polymerization in these systems.

Influence of droplet phase TEMPO diffusivity, D_TEMPO,drop, on the predicted organic phase concentration of TEMPO.     

Polymeric Nanocapsules Containing Nematic LCs as Hydrophobes in Miniemulsion Polymerization

The distinct polymeric nanocapsule hybrid‐structures consisting of LCs in the core and PMMA or polystyrene in the corona domain were prepared by one‐step miniemulsion polymerization. Nematic LCs (4′‐pentyl‐4‐biphenylcarbonitrile and 4′‐heptyloxy‐4‐biphenylcarbonitrile) were especially adopted as hydrophobes that can suppress Ostwald ripening and had an important role to stabilize the miniemulsion droplets and control the size distributions of the latexes. The polymeric nanocapsule structures with narrow size distributions were confirmed by TEM and DLS measurements.

     

AGET ATRP in the Presence of Air in Miniemulsion and in Bulk

Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol⁻¹ and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol⁻¹ and a low polydispersity index ( = 1.14).

Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right).     

Synthesis of High Solid‐Content Latex using Alkali‐Soluble Resin as Sole Surfactant

Summary: A novel polymerization procedure to synthesize latex stabilized by alkali‐soluble resin (ASR) is detailed. According to this process, latexes with a high solid content and low viscosity are obtained using a substantially lower amount of ASR when compared with existing techniques. Similar rewet properties were found for the latexes obtained by a standard process and for the one obtained by the process described in this work.

Comparison of the particle size distributions obtained by conventional emulsion polymerization (○) and by miniemulsion polymerization (□).