Formation of high-molecular-weight

Polyetherification is similar to a polycondensation process formation of high molecular weight polymer requires precise adjustment of composition to approximately 1 1 ratio of bisphenol to dihalosulfone. Trace amounts of water gready reduce the molecular weight attainable owing to side reactions that unbalance the stoichiometry (76). The reactivity of the halosulfone is in the order expected for two-step nucleophilic aromatic displacement reactions ... 

The addition polymerization of diisocyanates with macroglycols to produce urethane polymers was pioneered in 1937 (1). The rapid formation of high molecular weight urethane polymers from Hquid monomers, which occurs even at ambient temperature, is a unique feature of the polyaddition process, yielding products that range from cross-linked networks to linear fibers and elastomers. The enormous versatility of the polyaddition process allowed the manufacture of a myriad of products for a wide variety of appHcations. 

The effects of cosolvents on the reduced viscosity and yield are summarized in Table 9.5. DMAc and NMP lead to the formation of high-molecular-weight Bisphenol AF poly(formal) (7) in a high yield. The optimum reaction conditions are 48 mmol of DCM, 14 mmol of potassium hydroxide, and 5 ml of NMP for 5 mmol ofBisphenol AF, resulting in the formation ofBisphenol AF poly(formal) (7) with reduced viscosity of 4.62 dl/g in a 87% yield at 75°C.12... 

Johnston, J. A., et al.. Formation of high molecular weight complexes of mutant Cu, Zn-superoxide dismutase in a mouse model for familial amyotrophic lateral sclerosis. Proc Natl Acad Sci USA, 2000, 97(23), 12571-6. 

Redox polymerizations are usually carried out in aqueous solution, suspension, or emulsion rarely in organic solvents. Their special importance lies in the fact that they proceed at relatively low temperatures with high rates and with the formation of high molecular weight polymers. Furthermore, transfer and branching reactions are relatively unimportant. The first large-scale commercial application of redox polymerization was the production of synthetic rubber from butadiene and styrene (SBR1500) at temperatures below 5 °C (see Example 3-44). 

This experimental procedure must be followed carefully to avoid partial decomposition of ethyl a-(hydroxymethyl)acrylate. The reaction is stopped rapidly after the addition of the carbonate solution (5 min) to prevent formation of high molecular weight by-products which result from transesterification and Michael addition, both of which occur in the basic medium. However, about 25% of the product is lost. Addition of diethyl ether during cooling minimizes side reactions. 

Rubber is synthesized and sequestered on cytsolic vesicles known as rubber particles. Rubber transferase is localized to the surface of the rubber particles, and biosynthesis is initiated through the binding of an allylic pyrophosphate (APP, a pyrophosphate, produced by soluble trans- rtnyl transferases) primer. Progressive additions of IPP molecules ultimately result in the formation of high molecular weight cjT-l,4-polyisoprene. The rubber transferase also requires a divalent cation, such as Mg + or Mn +, as cofactor. 

Fuel performance problems initiated by light are not common. However, fuel quality can be affected. The primary concern of light exposure is fuel color darkening and the possible formation of high-molecular-weight deposits due to free-radical-initiated polymerization of fuel components. 

Distillate fuel can darken in color and can degrade to form sediment after exposure to air and/or heat for a period of time. Degradation is also accelerated by exposure to dissolved metal ions, especially copper. During this process, oxygen in the air reacts with fuel components to form compounds which are often dark in color and unstable. Also, condensation-type reactions can occur and result in the formation of high-molecular-weight, insoluble organic compounds. 

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