Molecular weight polymerization

Acyclic C5. The C5 petroleum feed stream consists mainly of isoprene which is used to produce rubber. In a separate stream the linear C5 diolefin, piperylene (trans and cis), is isolated. Piperylene is the primary monomer in what are commonly termed simply C5 resins. Small amounts of other monomers such as isoprene and methyl-2-butene are also present. The latter serves as a chain terminator added to control molecular weight. Polymerization is cationic using Friedel-Crafts chemistry. Because most of the monomers are diolefins, residual backbone unsaturation is present, which can lead to some crosslinking and cyclization. Primarily, however, these are linear acyclic materials. Acyclic C5 resins are sometimes referred to as synthetic polyterpenes , because of their similar polarity. However, the cyclic structures within polyterpenes provide them with better solvency power and thus a broader range of compatibility than acyclic C5s. 

Synthesis of oligomeric or low-molecular weight polymeric metallocenes (M = Fe or Ru) in which the separate metallocene units are held... 

High molecular weight polylactides, 20 298 High molecular weight polymeric... 

Figure 1. Schematic drawing of two planarization processes using (A) a low molecular weight polymeric resin and (B) a low viscosity, liquid monomer.

The performance of high molecular weight polymeric flocculants is heavily dependent on the physical conditions of their application. Recommended treatment conditions are ... 

Even though the solubility product of Pu(OH)4 is 1 X 10 56, some Pu4+ must remain in solution as the equilibrium is established. The monomeric Pu(OH)4 and the very low molecular weight polymeric species are able to pass through an ultrafilter, and Lindenbaum and West-fall (22) found that as much as 5% of the hydrolysis species remained ultrafilterable after 72 hours at pH 11. These unfilterable species may be either true radiocolloids or pseudocolloids. The latter likely occur as a result of minute impurities in the solutions which act as nuclei on which the polymeric or ionic species adsorb (14). However, this point has been the subject of extensive debate (36, 37, 39), and opinions vary as to whether pseudocolloids form in this manner, or in fact whether there are such species at all. In general the term colloidal plutonium will be used throughout this paper to indicate all of the insoluble plutonium hydrolysis products and polymeric species of colloidal size. 

Fig. 8. Effect of photoirradiation on the polymerization of VCZ initiated by NaAuClj 2H20 at 30° C,in the presence of air. Solvent nitrobenzene. [VCZ] = 0.25 M, [AunlJ = 1.0 x 10- M. (1) (- -) time-conversion, polymerization in the dark (2) (-o-) time-conversion, a hard glass, cylindrical polymerization vessel was irradiated by a 300 W mercury lamp from a distance of 28 cm (3) (-O-) polymerization time-molecular weight, polymerization in dark...

The molecular weights and molecular weight distributions of lower molecular weight polymeric flocculants are determined by viscosity measurements. High molecular weight acrylamide-based polymers are characterized by light scattering techniques. 

If the conformational switching is that between high-molecular weight polymeric species, then the structural transition between them can be highly co-operative but the assembly remains by and large isodesmic. So, co-operativity is a required but not a sufficient condition for creating nucleated supramolecular polymerizations. 

Propagation of the polymerization occurs nearly exclusively by head-to-tail reactions, with only a small fraction of head-to-head reactions. The relative ratio of these two reactions is only a function of temperature and has been found to be independent of molecular weight, polymerization solvent, and method of polymerization. The head-to-head addition yields a 1,2-glycol structure in the resulting poly(vinyl alcohol), which in turn influences the degree of crystallinity, strength, solubility, and thermal stability. 

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