Patrice C. Hartmann

Aqueous behaviour of cationic surfactants containing a cleavable group.

The aggregation behaviour of two novel cationic RAFT agents (transfer surfactants); N,N-dimethyl-N-(4-(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium bromide (PCDBAB) and N-(4-((((dodecylthio)-carbonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium bromide (DCTBAB) in diluted solutions have been investigated by surface tension, conductimetry and microcalorimetry measurements. The thermodynamic parameters i.e. the critical micelle concentration (cmc), the degree of micelle ionization (alpha), the head group surface area (a 0), Delta H mic, Delta G mic and T Delta S mic are reported at 303 K. The thermodynamic parameters have been compared to those of the conventional surfactant cetyltrimethylammonium bromide (CTAB) in order to specify structural relationships. The obtained results have been discussed considering the hydrophobic behaviour of the S-C=S- linkage and the specific interactions that arise from the introduction of the benzene ring into the hydrophobic part.

Encapsulation of Clay by Ad-Miniemulsion Polymerization: The Influence of Clay Size and Modifier Reactivity on Latex Morphology and Physical Properties

The influence of clay platelet size and type of organic modifier (reactive or nonreactive) on highly filled hybrid latex morphology and physical properties of the resultant polymer/clay nanocomposites (PCNs) were investigated. The hybrid latexes, containing clay loadings between 30 and 50 wt % clay, were prepared using ad-miniemulsion polymerization. These materials have potential use in the packaging and coating industry since clay platelets are well-known for barrier property improvements. Comparative studies on the use of montmorillonite (MMT), a large clay platelet (average size: 50-500 nm), and Laponite (Lap), small-sized clay platelets (average size: 25-40 nm), were conducted. Two different clay modifiers were used to modify the clays, i.e., a conventional nonreactive modifier (cetyltrimethylammonium bromide (CTAB)) and a reactive modifier (vinylbenzyldodecyldimethylammonium chloride (VBDAC)). Transmission electron microscopy (TEM) imaging of the hybrid latexes clearly showed strong morphological dependency on both the type of modifier and the clay platelet size. Furthermore, TEM together with small-angle X-ray scattering (SAXS) showed that the extent of clay exfoliation was strongly dependent on the reactivity of the clay modifier, irrespective of the clay platelet size. Both the type of modifier and clay platelets size were found to have an influence on different physical properties of the resultant PCNs. The influence of clay size was clearly indicated by storage modulus and thermal stability behaviors, while that of the clay modifier was indicated by the T(g). Lap-based PCNs exhibited constant or increasing storage modulus and no change in thermal stability with increasing clay content, while MMT-based PCNs showed a decreasing trend in both storage modulus and thermal stability. PCNs based on clay modified with CTAB showed a decreasing T(g) with increasing clay content, while those based on clay modified with VBDAC showed an increasing trend. It was concluded that the clay platelet size and the type of modifier play a crucial part of both the latex morphology and the physical properties of the resultant PCNs.

Synthesis and Characterization of Novel Quaternary Ammonium RAFT Agents

Abstract Synthesis of three new cationic thio compounds suitable to control free‐radical polymerization according to the reversible addition fragmentation chain transfer (RAFT) process (reversible addition fragmentation transfer) is presented. Among them, two bear a quaternary ammonium group in the R group [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothionyl)thio)methyl)benzyl)ethanammonium bromide and N‐(4‐((((dodecylthio) carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammonium bromide, a dithioester and a trithiocarbonate, respectively]. The synthesis of a trithiocarbonate bearing an ammonium group in the Z group [i.e., 2‐((11‐((benzylthio)carbonothioyl)thio)undecanoyl)oxy)‐N,N,N‐trimethylammonium iodide] is also presented. Another three thio compounds, namely 1,4‐phenylenebis(methylene)dibenzenecarbodithioate, didodecyl‐1,4‐phenylenebis(methylene)bistrithiocarbonate, and 11‐(((benzylthio)carbonothioyl)thio)undecanoic acid, identified as other potentially interesting mono‐or difunctional RAFT agents, which were obtained as side products or intermediates, were isolated and fully characterized.

Chapter 12:Polymer–Clay Nanocomposites Prepared in Miniemulsion Using the RAFT Process

This chapter is a review on polymer-clay nanocomposites (PCNs) prepared in miniemulsion using the reversible addition-fragmentation chain transfer (RAFT) process.One of the most interesting research areas in nanotechnology is the inclusion of nanoparticles in polymers in order to enhance their physical properties e.g. thermal stability, barrier properties and mechanical properties. In the early 1990s the Toyota research group showed that the hydrated cations within the clay layers can be replaced by alkyl ammonium compounds. A reactive clay modifier leads to a strong interfacial adhesion between the clay and the polymer, and subsequently the exceptional mechanical properties during load bearing. The use of tailor-made transfer agents in free-radical polymerisation reactions allows one to achieve control of the polymerisation process. This results in polymers with low polydispersity indices and predictable molar masses. The discovery of the controlled polymerisation techniques, and in particular RAFT agents, was a milestone achievement. RAFT polymerisation now allows the preparation of polymer architectures that were never before envisaged to be possible. Thus, a combination of RAFT technology and clay nanotechnology for the synthesis of PCNs by RAFT-mediated polymerisation can allow the preparation of tailor-made materials with specific properties for niche applications.