Poly polymeric dispersion agent

Currently, there is concern about the use of ammonium perfluorooctanoate (APFO), also known as C8 , which is necessary for the manufacture of fluorinated plastics and elastomers in water. C8 is a perfluorinated anionic surfactant used as a dispersing agent in the polymerization and copolymerization of many fluoropolymers, including poly(tetrafluoroethylene) (PTFE), poly(vinylidene... 

Typical suspending agents for the vinyl acetate polymerization are poly(vinyl alcohol) [particularly a grade represented as approximately 88% hydrolyzed poly(vinyl acetate)], gum arabic, hydroxyethyl cellulose, methyl cellulose, starches, sodium polyacrylate or sodium polymethacrylate, gelatin, and an equimolar copolymer of styrene and maleic anhydride neutralized with either sodium hydroxide or aqueous ammonia. Water-insoluble dispersing agents or... 

An unusual synthetic application of a soluble macromolecular reducing reagent described by Smith is the use of aqueous solutions of hydrazonium polyacrylate or hydrazonium poly[2-(acryl-amido)-2-methylpropanesulfonate] to prepare stable colloidal dispersions of red, amorphous selenium. (34). In these reactions, the solutions were prepared sufficiently dilute so that each macromolecular hydrazonium polyacrylate could react individually. When a solution of H2Se02 was added to this polymeric reducing agent, the selenious acid molecules in the... 

Surfactants are also used as dispersing agents for dyestuffs in the plastics industry. Furthermore, they are used to a large extent as emulsifiers for emulsion polymerization e.g. poly(vinyl chloride) (PVC). 

On the other hand, by free radical suspension polymerization of MMA in n-heptane solution in the presence of poly(styrene)-Wocfc-poly(ethene-aZt-propene) (SEP) as a dispersing agent, PMMA samples were prepared with similar molecular weights and polydispersity under both conventional and microwave conditions [37]. The reactions were run for 1 h at 70 °C with different monomer (9.0-28.3vol.%), SEP (21.7-5.4 wt%), and AIBN (1.0-0.27 wt%) concentrations (Table 1). In a typical experiment, 30 ml of the reaction mixture was fed into a 50-... 

Dispersion of the powder in the vehicle. This requires adequate wetting of the powder (external and internal surfaces) by the liquid vehicle, necessitating the use of a wetting/dispersing agent, mostly a nonionic surfactant (such as poly-sorbates) or polymeric surfactant (such as Poloxamer). This process is described in detail in Chapter 7. 

Aqueous miniemulsion polymerization of styrene was performed in the presence of CeFis-I as CTA, yielding particles with a good control of the molecular weights, in contrast to emulsion polymerization where the transfer agent efficiency was low due to a slow diffusion of the hydrophobic perfluor-ohexyl iodide from the monomer droplets to the active particles during polymerization.The chains were capped with iodine as evidenced by the successful chain extension upon addition of butyl acrylate. The miniemulsion process was also successfully applied to the preparation of triblock copolymers PS-b-PDMS-b-PS starting from a telechelic diiodo-poly(dimethylsiloxane) macrotransfer agent. A somewhat similar procedure was used to prepare PVAc-b-PDMS- -PVAc triblock copolymers, but the polymerization was performed under UV irradiation (instead of thermal initiation) and in the absence of radical initiator. In this case, the aqueous dispersion medium was a key parameter to achieve a controlled polymerization (Scheme 19). ... 

In the suspension polymerization of vinyl chloride using LPO and a water-soluble reducing agent [16,17], Fe(OH)2 (produced by in situ reaction of a ferrous salt and an alkali metal hydroxide), the conversion was 80% and 65% by using a Na maleate-styrene copolymer and poly(vinyl alcohol) as the dispersing agent, respectively. The reaction was carried out according to the recipe presented in Table 1. 

In the case of diisopropyl peroxydicarbonate [159], an 80-20 20-80 mixture of partidly saponified poly(vinyl acetate) and a cellulose ether was used as the dispersing agent. The suspension polymerization or copolymerization of vinyl chloride was carried out in the presence of a compound having a -SH, -OH, or -CO2H groups in order to reduce the amount of chain transfer agent required. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Moad et al. [291] showed that the type of RAFT agent is important. Using a very reactive RAFT agent (with a transfer constant of about 6000), similar to that used in the work of De Brouwer and Monteiro, resulted in a broad poly-dispersity in ab initio styrene polymerizations with ionic surfactant, which was ascribed to the fact that the RAFT agent was not uniformly dispersed in the polymerization medium. The use of less reactive RAFT agents (with transfer constants of 10-30) did not result in destabilization and the final polymer had a polydispersity close to 1.4. 

---