Anionic chain polymerization isocyanate

Many authors divide polymerizations into chain reactions and stepwise reactions. Of course, all reactions proceed in steps, that is, one reaction step follows another. Termolecular reactions are rare but in the organic chemistry sense, the term stepwise reaction signifies that intermediate products can be isolated and subsequently again made to react. This means that, in the absence of impurities, certain reactions can be frozen. In actual fact, anionic addition polymerizations can be frozen at low temperatures and made to run again at higher temperatures. That this procedure is not possible in the presence of water or carbon dioxide is an experimental consideration and not a conceptual difficulty. If we lived in an isocyanate atmosphere, no steps could be isolated in the polyamide synthesis. Thus, such classifications are based on experimental expertise, which can never be the basis of a physical definition. 

Phosphoramidate anion also reacts with isocyanates to give carbodiimides [40, 41]. However, the procedure is limited by the tendency of many isocyanates, especially the striaght-chained aliphatic ones, to polymerize in the basic medium [42]. 

The polymerization of butyl isocyanate and other achiral monomers (74) using optically active anionic initiators 75—81 affords optically active polymers.152 156 The poly-74a (Mn = 9000) obtained using 75 exhibits [a]435 +4 1 6°. The optical activity of the polymers arises from the helical part extending from the chain terminal bearing the chiral group originat-... 

Anionic polymerizations can be terminated by addition of another molecule, which will introduce an co-functional group in the chain. Excess carbon dioxide or cyclic anhydrides lead to terminal carboxylic groups, whereas addition of excess phosgene produces an acid chloride function. Similarly, isocyanates generate coamide functions, and lactones yield co-hydroxyl groups. 

The number of monomers that undergo chain-growth polymerizations is large and includes such compounds as alkenes, alkynes, allenes, isocyanates, and cyclic compounds such as lactones, lactams, ethers, and epoxides. We concentrate on the chain-growth polymerizations of ethylene and substituted ethylenes and show how these compounds can be polymerized by radical, cation, anion, and organometallic-mediated mechanisms. 

Small angle neutron scattering (SANS) measurements were performed on poly(isoprene) networks at different uniaxial strains, i.e., 1,0 < X (extension ratio) <2.1. The networks were prepared from anionically polymerized, a, oo-dihydroxy-poly(isoprene) precursors (H-chains) and the corresponding poly(isoprene-dg) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrofuran solutions by trifunctional crosslinkers, tri-isocyanates. The two components of the radius of gyration of elastic strands, parallel and perpendicular to the strain axis, were determined from the vSANS data of the networks with 8% and 15% D-chains. Two molecular weights of D-chains, 26,000 and 64,000, crosslinked with approximately the same molecular weight H-chains (29,000 and 68,000 respectively) were examined for the deformation behaviors. 

More specifically, the hydroxyl terminated polymer is polystyrene (PS-OH). This latter can be prepared relatively easily following classical anionic polymerization procedures. The isocyanate moiety involved in the polymer chains is 3-isopropenyl-a, a -dimethylbenzyl isocyanate (TMI), which is randomly distributed along the chain. If the polymer backbone bearing TMI is identical or miscible with PS-OH, the reactive system is homogeneous. 

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