Methyl mercaptan, reducing agent

Conversely it is possible to produce low-molar-mass oligomers or telomers by deliberately choosing an agent with a large value of Ca (e.g. methyl mercaptan, Ca 2x 10 in styrene), so that DP is reduced to 5 for a concentration of 0.001%. Further particular examples of chain transfer (e.g. to polymer to form branches) will be discussed later, together with the use of reversible-addition fragmentation transfer (RAFT) and other radical-mediated synthetic strategies. 

Precaution Highly flamm. very dangerous fire hazard exposed to heat, flame, oxidizers incompat. with oxidizing agents (can react violently), reducing materials (can produce methyl mercaptan), copper and alloys (can react corrosively)... 

The above explanation of autoacceleration phenomena is supported by the manifold increase in the initial polymerization rate for methyl methacrylate which may be brought about by the addition of poly-(methyl methacrylate) or other polymers to the monomer.It finds further support in the suppression, or virtual elimination, of autoacceleration which has been observed when the molecular weight of the polymer is reduced by incorporating a chain transfer agent (see Sec. 2f), such as butyl mercaptan, with the monomer.Not only are the much shorter radical chains intrinsically more mobile, but the lower molecular weight of the polymer formed results in a viscosity at a given conversion which is lower by as much as several orders of magnitude. Both factors facilitate diffusion of the active centers and, hence, tend to eliminate the autoacceleration. Final and conclusive proof of the correctness of this explanation comes from measurements of the absolute values of individual rate constants (see p. 160), which show that the termination constant does indeed decrease a hundredfold or more in the autoacceleration phase of the polymerization, whereas kp remains constant within experimental error. 

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