Living free radical reactions originally were carried out in bulk or solution. Recently, this chemistry has been carried out in water-based systems (emulsion and miniemulsion living free radical polymerization). Significant colloidal instability early in the polymerization has been found in several of these systems. With the hypothesis that something unique to living free radical polymerization was causing colloidal instability beyond that found in conventional free radical emulsion polymerization, the swelling of polymer particles during the early stages of living free radical miniemulsion polymerization was investigated. A new superswelling state caused by the presence of a large number of oligomers was found. This superswelling could be used to explain the instability issues reported. The effect of various factors on the superswelling state was studied. It was found that superswelling state is rather sensitive to recipe variations. Simply increasing the costabilizer level and/or using a nonionic polymeric surfactant would probably eliminate superswelling and hence the instability.

In theory, a miniemulsion should be an ideal environment for “living” radical polymerization via the reversible addition−fragmentation chain transfer process (RAFT). Compartmentalization minimizes radical−radical termination events, and droplet nucleation eliminates the mass transfer limitation found in conventional “living” emulsion polymerizations. In practice, however, several phenomena were observed when using the RAFT technique, indicating a deviation from this idealized theory when the miniemulsion was stabilized by an ionic surfactant. Inefficient droplet nucleation, a steadily rising polydispersity over the reaction, and the appearance of a separate organic phase after initiation were all indications of particle instability. A distinct difference between standard polymerizations and those that involve highly active RAFT agents is the fact that in RAFT polymerization there is a time interval early in the reaction where oligomers dominate the molecular weight distribution. The presence of large quantities of oligomers is postulated to be the culprit behind the destabilization observed through a detrimental interaction with the ionic surfactant of the miniemulsion. Conductivity measurements verified the increase of free surfactant in the aqueous phase over the course of reaction. Despite this, results showed clear indication of “living” character with a linear evolution of molecular weight until roughly 40% monomer conversion, after which the molecular weight showed contributions from initiator-derived chains.

The plasticization of a polymer by solvent has a dramatic impact on both its thermal and mechanical behavior. With increasing demand for zero volatile organic compound materials and coatings, water is often the sole solvent used both in the polymer synthesis and in formulation and application; latex colloids derived from emulsion polymerization are a good example. The impact of water on the glass transition temperature of a polymer thus becomes a critical physical property to predict. It has been shown here that in order to do so, one simply needs the dry state glass transition temperature (T(g)) of the (co)polymer, the T(g) of water, and the saturated weight fraction of water for the sample in question. Facile calculation of the later can be achieved using water sorption data and the group additivity method. With these readily available data, we show that a form of the Flory-Fox equation can be used to predict the hydroplasticized state of copolymers in exceptional agreement with direct experimental measurement. Furthermore, extending the prediction to include the impact of the degree of ionization for pH responsive components, only with extra knowledge of the pK(a), was also validated by experiment.

ABSTRACT:The ultimate objective of hybrid miniemulsion polymerization is to produce a water-based crosslinkable coating through in situ grafting of a free radical growing acrylic polymer with an unsaturated resin. Certain authors have reported low grafting while others have reported higher. This article explores the factors that influence the grafting tendencies of these systems. Methacrylates such as methyl methacrylate (MMA) have a sterically hindered radical center that lowers its reactivity toward unsaturated resin. This steric hindrance from the methyl group forces grafting of this type of monomer to occur by abstraction of a hydrogen allylic to a resinous double bond. This chain transfer produces a relatively inactive radical on the resin that reduces the grafting efficiency. The transfer process also inherently produces some degree of terminated PMMA polymer within the particle. Grafting occurs in this type of system through termination of living PMMA chains with that radical produced on the resin. For relatively watersoluble monomers such as MMA, grafting efficiency is further lessened by homogeneous nucleation resulting from the monomer hydrophilicity. These newly created particles cannot contain alkyd due to its hydrophobicity and thus inability to transport across the aqueous phase, and hence cannot produce grafted polymer. Nonetheless, degree of grafting of nearly 50% was observed in these systems. For hybrid systems involving an acrylate monomer such as butyl acrylate (BA), virtually complete grafting with alkyd was observed. This is due to the uninhibited BA radical center allowing the molecule to add directly through a resin double bond. This process offers the possibility for complete grafting. Homogeneous nucleation is not involved in this system due to the insolubility of BA in the aqueous phase. Resin double bond content and degree of conjugation also play an integral role in the grafting process.

A computationally efficient Monte Carlo method was used to simulate the reaction kinetics and molecular structure development during free-radical copolymerizations with divinyl monomers. A single parameter was used to describe the reduced reactivity of the pendent vinyl groups incorporated within the polymer backbone. The simulation results were compared with published experimental data for the bulk copolymerization of methyl methacrylate with different levels of ethylene glycol dimethacrylate. The model was able to effectively predict the reaction kinetics, the gel point, and sol−gel fractions in both the pre-and postgel regimes, including the swelling index of the gel. In the postgel regime the cross-linked molecule becomes the primary locus of reactions, and all chains eventually become part of this massive cross-linked polymer network. The Monte Carlo method allows the determination of the complete molecular structure as it evolves with time, including properties like cross-linking density, number of free chain ends, primary cycles and loops, and the fraction of unreacted pendent vinyl groups.

In the present work, we describe the successful application of spiro[1H-isoindole-1,9'-[9H]xanthen]-3(2H)-one, 3',6'-bis(diethylamino)-2-[(1-methylethylidene)amino] ("FD1") as a smart indicator in epoxy-based coatings for the early detection of steel corrosion. The FD1 indicator was used for epoxy-based coatings on steel for its desirable property of "turn-on" fluorescence upon forming a complex with ferric ions produced at the anodic site during steel corrosion and because it does not prematurely fluoresce when mixed with the coating precursors (i.e., epoxy resin and amine). This indicator, after incorporation into a filled epoxy coating at a concentration as low as 0.5 wt %, was observed to become fluorescent in areas where corrosion started before any obvious sign of metal damage was observable. FD1 fluorescence was apparent both in areas around a scribed portion of the coating where the metal was exposed and in undercoating corrosion, where the coating surface was intact. This nondestructive method of early corrosion detection can help signal when maintenance is needed before the metal suffers serious damage.

Polymers produced as aqueous-based lattices are always saturated with water, and the "wet" T(g) of these polymers can be significantly lower than the equivalent "dry" T(g) of the same polymers. The differential scanning calorimeter is a simple and effective tool to determine the wet T(g), and raw latex can be used without any special sample preparation. It is necessary, as always, to include a preheat step in the DSC procedure in order that the thermal scan produces quality data. We show that this technique can be performed in many temperature ranges, including temperatures well below the freezing point of water. Extension to the measurement of both thermal transitions for composite latex particles shows that the wet latex data, and information contained in them, can be quite different from the dried polymer data obtained from the same instrument. Special considerations are necessary for polymers with wet T(g)'s near the freezing point of water.

Continuous and real-time detection of protein biomarker using a microfluidic graphene-based transistor functionalized with thrombin-binding aptamers.