Terminated chains, controlled

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

Since the experiment is no longer reliant on the dithiocarbatnyl radical to both initiate and terminate chains (cf Section 9.3.2.1), lower reaction temperatures may be used (where the dithiocarbamyl radical is slower or unable to add monomer) and better control over the polymerization process can be obtained. The transfer constants for the benzyl dithioearbamates in polymerization of acrylic and styrcnic... 

Nylon 6,6 developed by W. H. Carothers of Du Pont in 1930s. Adipic acid, HMD A, 280-300 °C, 2-3 hr, vacuum. Trace of acetic acid terminates chains with acid groups and controls molecular weight. 

Of course the tertiary amine terminated polymer thus produced Is capable of being quaternlzed by alkyl halides and this has been confirmed experimentally. Moreover, It can be reacted with further living polyTHF to yield a polymer possessing a quaternary ammonium salt moiety at a point along the chain controlled by the relative molecular weights of the two living THF polymers reacted In the system, and again experiments have shown this to occur. 

Diffusion of the macroradicals controls can be assumed to be the termination reaction. However, that is not the case the termination rate constant is absolutely independent of the degree of polymerization, as shown in Table I. Therefore, the assumption must be that the diffusion of the segment at the end of the radical chain controls the termination process (as long as the Trommsdorff effect is not rate-determining). 

Chain propagation occurs by the growing chain free radical attacking either the butadiene or styrene monomer. The active radical chain can react with mercaptan to form a new mercaptyl radical and a terminated chain. The mercaptyl radical then can initiate an additional chain. The molecular weight of the chain P can be controlled by the concentration of mercaptan via this chain transfer mechanism. 

Termination is controlled by the chain carrier produced by the more highly exothermic step, or by the exothermic step if the other step is endothermic. 

For example, for the biforked compound in Fig, 7, the values of Ub obtained are close to 4.5 and are weakly temperature dependent. This number (=4,5 molecules in each elementary cluster of the column) would correspond to an average paraffinic crown formed by 18 alkyl chains. Now, considering a disc of diameter of 30 A equal to the length of the rigid core, its circumference corresponds precisely to 18 times the average distance between molten aliphatic chains (about 5 A). Thus, the circumference of the columnar rigid core seems to be an essential parameter to control with respect with the number of terminal chains in each molecule in order to fully embed the core in... 

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