Preparation of high molecular weight

The preparation of high molecular weight PPT in HMPA/NMP shows a strong dependence of inherent viscosity on reactant concentrations. In 2 1 (by volume) HMPA/NMP, the highest inherent viscosity polymer is obtained when each reactant is present in concentrations of ca 0.25 M higher and lower concentrations result in the formation of polymer of lower inherent viscosities. A typical procedure is as foUows 1,4-phenylenediamine, HMPA, and NMP are added to an oven-dried resin ketde equipped with a stirrer and stirred for ca 15 min with cooling to — 15°C, foUowed by the addition of powdered terephthaloyl chloride to the rapidly stirred solution. The reaction mixture changes to a thick, opalescent, paste-like gel in ca 5 min. 

Oxidative coupling polymerizations represent a general reaction for the preparation of high molecular weight linear polymers from many 2,6-di- and... 

Since the late 1940s, NCA polymerizations have been the most common technique used for large scale preparation of high molecular weight polypeptides [13]. However, these materials have primarily been homopolymers, random copolymers, or graft copolymers that lack the sequence specificity and monodispersity of natural... 

The ring-opening polymerization of dilactide (dimeric cyclic ester of lactic acid) allows the preparation of high molecular weight, optically active polyesters of lactic acid. The configuration of the asymmetric carbon atoms of the monomer is retained when the polymerization is initiated with SnCl4 or Et2Zn, for example ... 

Domb, A., and Langer, R. Polyanhydrides I. Preparation of high molecular weight polyanhydrides. J. Polym. Sci. Polym. Chem. 25 3373-3386, 1987. 

C.E. Lowe, Preparation of high molecular weight polyhydroxyacetic ester, US Patent 2668162, assigned to DuPont, February 2,1954. 

The minimization of the formation of a bulk phase during polymerization constitutes an important factor in the success of this method, since the rate of the process as well as the molecular weight is much lower in bulk polymerization. A relatively low temperature, a small amount of electrolyte, a suitable amount of water, and an optimum amount of surfactant minimize the occurrence of a bulk phase. The preparation of high molecular weight polystyrene latexes with low size dispersity by concentrated emulsion polymerization was examined in some detail in [19]. 

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