Surfmers using

Maleate Surfmers. Surfmers with allylic, acrylic and vinylic moieties tend to homopoly-merize and produce water-soluble polyelectrolytes if used above their CMC. This has shifted researchers attention to maleic derivatives that do not homopolymerize at normal temperatures because their ceiling temperature is too low. Tauer and co-workers have pioneered the synthetic work [4,15] which led originally to compounds like those given in Figure 6.49. An example of maleic-derived Surfmer used in emulsion polymerization lattices is reported in [16] and the advantages provided in commercial paint formulations are discussed later. 

The colloidal stable polymer dispersions, the monodisperse polymer particles, and high conversions (85-100%) can be obtained with most of the other macromonomers (MAL,VB, and MA) of PEO (MW>PEO=2000)) [76]. Also, when macromonomers are used (3.1 wt% based on styrene), there is practically no coagulum produced. This is not the case in the presence of polymerizable PEO surfactants (surfmer I R1=CH3(CH2)11-, R2=H, n=34 and surfmer II R =CH3 (CH2)n-, R2=H, n=42) despite the higher amounts of stabilizer used (up to 60 wt% of coagulum). Furthermore, the particles are more monodisperse with PEO macromonomer (Dw/Dn=1.025 for PEO-MA and 1.13 for PVPo) compared to those with surfmer. Comparatively poorer results were obtained with conventional surfactants such as ethoxylated nonylphenol, even when used in large amounts. 

Inisurfs, Transurfs and Surfmers may be used to reduce/avoid the use of conventional surfactants in emulsion polymerization. However, when Inisurfs and Transurfs are used, the stability of the system cannot be adjusted without affecting either the polymerization rate (Inisurfs) or the molecular weight distribution (Transurfs). Furthermore, the efficiency rate of Inisurfs is low due to the cage effect. It is therefore not obvious yet that these classes will become commercially significant. 

Most of the reactive surfactants used for emulsion polymerization have the reactive group at the end of the hydrophobic moiety of the molecule, on the assumption that the polymerization process takes place in the latex particle. Work of Ferguson et al. [14] shows indeed a lower stability of lattices produced with Surfmers with an acrylate group attached to the end of the hydrophilic chain than those produced with the equivalent terminated with an ethyl ester group. 

The work of Guyot [7] reviews the use and effects of ionic Surfmers in different polymerization processes. 

Maleic-derived Surfmers have been shown to be quantitatively bound to latex particles. For example the surface tension of the latex serum from the emulsion polymerization of styrene remains above 70mNm-1 after polymerization even if amounts in excess of 100 times the CMC are used (15). 

The simple maleate Surfmer (i.e. the neutralized hemi ester of a fatty alcohol) was used to prepare seeds of polystyrene latex which were grown with a shell of film-forming polymers. The reported incorporation yield was of the order of 75% [18]. The reported latex stability could be further improved by Surfmers in which the ester moiety was substituted for an amide moiety by reaction with a fatty amine. An overall improved stability and a reduced hydrolysis at high temperature were observed [19]. 

Performance enhancement ofmaleate Surfmers. Several options have been proposed to enhance the performance of maleate Surfmers. In particular the modulation of the reactivity has been considered, to achieve a controlled and moderate reactivity during most of the polymerization and a high conversion at the end of the process. These requirements limit the useful range of values of the reactivity ratios of the Surfmer/monomer systems [22]. 

However one constraint of alkoxylated Surfmers is their cloud point versus the polymerization temperature. If the former is lower than the latter, salting-out of the Surfmer occurs, with loss of surface activity and reactivity. The cloud point of nonionic alkoxylates can be adjusted to a certain extent by the choice of the alkoxylation initiator, the relative percentage of hydrophilic and hydrophobic alkoxylation moieties and their order of addition. Also, introducing some ionic character in the molecule (e.g. by weak polar groups that do not substantially affect the nonionic behavior of the molecule) may prove useful. Nevertheless there have been and there can be instances where nonionic Surfmers cannot be used. 

Reverse ethylene oxide/propylene oxide block copolymers (in which a hydrophilic core of PEO is terminated at both ends with hydrophobic PO moieties) are used in industrial applications. This is because of the different and unique performance properties compared to the conventional block copolymers, where a hydrophobic PO core is block copolymerized with EO. Dufour and Guyot [30] have built on this observation and synthesized Surfmers in which a PEG core (about 37 EO units) was tipped with about 10 PO units to further react with a chlorine-carrying polymerizable group or with maleic anhydride to produce reactive Surfmers. 

It was estimated that, if all the Surfmers contributed to stabilization, the surface coverage would be close to 20% at the end of the process. When Surfmer burial is considered, the minimum surface coverage is in the region of 14.7-15.0 % [35]. The authors have also studied the influence of the addition procedure on the evolution of the Surfmer conversion and concluded that, despite the low reactivity due to the presence of the alkenyl double bond, the incorporation could be increased to 72% from the original 58% obtained with a constant feeding rate. A mathematical model able to describe Surfmer polymerization was used in the optimization process [36]. 

The review provides recommendations to prevent early Surfmer polymerization and the consequent burying, so as to achieve a high degree of Surfmer incorporation at the end of the polymerization process. There are also hints on the possible use of Surfmers in dispersion and micro emulsion polymerization. 

Copolymers 59 [181] and terpolymers 60 [182] were synthesized by micellar copolymerization and characterized with respect to their molecular and solution properties. The subject of further investigations was the interaction with low molecular weight surfactants [181,183]. Another interesting use was made of hydrophobized sulfopropylammonio monomers as surface-active monomers (or surfmers ) [184]. Their use in emulsifler-free emulsion polymerizations [185] reduced the water uptake and improved the mechanical stability of the resulting filmed latexes. 

A carboxylato surfmer III has been studied by Guillaume, Guillot and Pichot [22], for the purpose of preparing latexes carrying only carboxylic surface groups. Sodium acrylamido undecanoate (SAU) has been used, with a cmc at 25 °C of 5 x 10" mol/1. It has been utilized in copolymerization with styrene (S) and butylacrylate (B), initiated at 70 °C by an azocarboxy compound. The reactivity ratios with S and B were measured (S) or estimated (B) from the Q, e scheme the partition coefficient of SAU and of the comonomer between water and organic phases were also measured, so that a simulation of the copolymerization process was obtained which shows an S shape for the conversion of SAU, indicating that most of that surfmer is polymerized only at... 

A recent paper by a Rusian team [18] describe tte use of a few new surfiners, one being cationic, namely JV-decylaceto-2-methyl-5 vinylpyridinium bromide (V), and the others being anioic, namely decyl (or dodecyl), sodium ethyl sulfonate, methacrylamides (VI), decyl (or dodecyl)-phenyl (Na or K sulfonate) acrylate (VII), and decyl ester of sodium (or K or NH4) sulphocin-namic acid (VIII). These surfmers were used for emulsion polymerization of styrene, butylacrylate or chloroprene, in the presence of KPS or AIBN without any other surfactants. It should be noted that the consumption of these surfactants take place early in the polymerization process which is faster than in... 

Diblock polyoxyethylene-polyoxypropylene styrenic macromonomers, with the polymerizable group at the end of the hydrophobic part have been prepared and used in styrene emulsion polymerization [34]. Latexes of high stability towards added electrolyte have been obtained. However the HLB was not well-optimized so that a high amount of coagulum was formed (Surfmer XI). 

A lot of mechanistic problems remain to be solved. It is not so clear, at the moment, why most of the inisurfs studied up to now have such a low efficiency, whatever their structure. On the other hand it is quite remarkable that, even with that low efficiency, they are able to allow the preparation of stable latexes under acceptable experimental conditions. Another problem is the control of the nucleation both with inisurfs and transurfs, there are indications that the particle number and size may not very sensitive to the amount of reactive surfactants, and more dependent on the amount of monomer used. Such behavior, up to now, has not been explainal Very few studies have been devoted to the reactivity of these surfactants, i.e., reactivity ratios for the surfmers, transfer constants for the transurfs and initiator efficiency for the inisurfs. Both the reactivities and the partition coefficient between the water and the organic phase have to be determined. In addition the reactivities may dependent on the other components of the recipe, for instance due to the effect of the ionic strength on the cmc. 

In the domain of polymer stabilization (polymerization in dispersed media as well as using physico chemical procedures), it becomes of first importance to anchor the surfactant onto the surface of the particles not only to avoid flocculation, but also to limit water pollution. In the case of emulsion polymerization, a good way to overcome these drawbacks is to use polymerizable surfactants (also called "surfmers") [4-6]. 

The hydrophobic monomers styrene and MMA were copolymerized with the sodium salt of vinylbenzylsulfosuccinic acid as a polymerizable surfactant grafting of the surfactant onto the particles was estimated to be about 50-75% [51]. A polymerizable surfactant was formed by the esterification of hydroxypropylmethacrylate or hydroxyethyhnethacrylate with succinic anhydride [53]. However, in addition to the surfmer, sodium dodecyl sulfate (SDS) was employed to provide a sufficient stability to the latexes. A mono-fluorooctyl maleate surfactant was used to stabilize the polymerization of styrene in miniemulsion [55]. Although the polymerizable moiety was not fixed at the end of the fluorinated chain (the hydrophobe part), the surfactant could be copolymerized with the styrene monomer. Subsequently, on comparison of the infrared (IR) spectra (vibration of -CF2 and -CFj) before and after dialysis, it was estimated that 92% of the surfactant had remained grafted post-dialysis. 

Surfmers , i.e. surfactants which also acted as copolymerisable monomers, were synthesised from the hemi-ester of a fatty alcohol and maleic anhydride and were then used in the preparation of self-crosslinking dispersions by seeded semi-continuous emulsion polymerisation of acrylate monomers. Water-borne exterior wood stains were prepared from the dispersions and their properties were studied. The use of surfmers as sole emulsifiers in emulsion polymerisation was considered and data were obtained on the effects of surfmers on film formation, water barrier properties, gloss retention and mechanical properties. Environmental aspects of the use of products involving surfmers were examined. 6 refs. 

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