Polymeric dispersants, high molecular weight

Yu, S.M. and Mecking, S. (2008) Extremely narrow-dispersed high molecular weight polyethylene from living polymerization at elevated temperatures with o-F substituted Ti enolatoimines. Journal of the American Chemical Society, 130,13204-13205. 

Dispersion aids for solvent-based paints function primarily as wetting agents, and are typically nonionic. They contain an anchor group, selected for its affinity to the particulates in the paint formulation, and a polymeric or high molecular weight group selected for compatability with the binder and solvent. 

Monomers may be polymerized using a water-soluble initiator while dispersed, by agitation, in a concentrated soap solution. In this emulsion system initiation occurs in the aqueous phase and propagation occurs in the soap micelles. Since the growing macroradicals are not terminated until a new free radical enters the micelle, high molecular weight products are rapidly obtained. The rate of polymerization and DP is proportional to the number of activated micelles. 

An intermediate polymerization technique between emulsion polymerization and suspension polymerization has been described. Here, the monomers are first dispersed in water containing a small amount of surfactant and a high molecular weight alcohol to form very small droplets of monomer. The polymerization is effected with a water-soluble free radical initiator, such as potassium per-oxydisulfate (4). 

The rate of formation of the low-molecular-weight polymer using 1,5-pentanediol as the initiator is shown in Figure 7. As in the preparation of the high-molecular-weight polymer, there was an initial slow reaction followed by a rapid one. Completion of the first part of the reaction was, in this case, characterized by disappearance of the initiator (21), as well as by dispersion of the catalyst. When this reaction was carried to complete consumption of monomer, addition of further monomer resulted in immediate resumption of the rapid rate. Once again, we see a similarity to a living polymerization. Both the rapid... 

Owing to the good solubility of many monomers and initiators in C02, dispersion polymerization is today the most investigated heterogeneous method used for the synthesis of high-molecular-weight C02-insoluble polymers. One central role for the performance of a successful dispersion polymerization is the surfactant. 

Rhenium complex (37) has been used in the ring-opening metathesis polymerization of strained alkenes such as norbornene.37 The alkenes of the polymer backbone are predominantly Z, the polymer exhibiting high molecular weight and poly-dispersity. 

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