Dead-stop polymerization

Increasing the temperature of polymerization does not always lead to higher rates of polymerzation. Higher temperature leads to faster dissociation of the initiator and complete depletion of the initiator resulting in a "dead end" polymerization (Bohme and Tobol-sky (1966)). Dead-end polymerization refers to one in which initiator concentration decreases to such a low value that the polymerization stops short of completion and a limiting conversion of monomer to polymer is observed (Odian (1970)). 

The equilibrium is shifted completely to the right. Thanks to the presence of the phenolate group at the chain ends, the macromolecules could be counted by UV spectrophotometry (polytetramethylene oxide is transparent in the UV range). With the counter-ion B = BF termination was slow with B- = AlCl it was rapid. The active centres can be counted using the Saegusa and Matsumoto method and, together with a determination of the degree of polymerization and the concentration of macromolecules, the elementary constants can be determined (the dead-stop method). 

Intermittent initiation starts and stops polymerization by diffusion of many or no radicals into each droplet so that at any time 50% droplets grow and 50% are dead. 

The required MWD is then given by the distribution of dead (nongrowing) chains this is readily found as follows from GCf ). For those chain stopping reactions ih which the identity of the growing chain-stof ing remains intact (i.e., transfer to monomer or to chain-transfer agent and disproportionation), the distribution of dead polymers produced which have (previously) polymerized for t is simply proportional to C(r ). Denoting this distribution by 5,r, Af). we thus have... 

When some reagent that forces the polymerization to stop is added, the polymerization is really terminated to make dead polymer chains. 

When some reagent that forces the polymerization to stop is added, the polymerization is really terminated to make dead polymer chains. When a nucleophilic reagent such as allyltri-methylsilane was added, the polymerization terminated to give a stable dead polymer that could be well characterized by NMR spectroscopy. 

When a monomer, such as styrene, is transported or stored, an inhibitor is included in solntion to keep the styrene from polymerizing. An inhibitor, nsually an organic componnd, retards or stops an unwanted polymerization reaction. If an accident shonld occnr, this inhibitor can become separated from the monomer and a runaway polymerization may occur. Phenol — a deadly poison — is nsed as an inhibitor for vinyl chloride. Dibutylamine is used as an inhibitor for bntadiene. 

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