The initiation of styrene polymerization with n‐butyllithium in toluene was investigated spectrophotometrically. The rate of the first step of initiation is first order in both monomer and catalyst, and the activation energy is 26.3 kJ · mol−1. The kinetic analysis revealed a number of kinetic transitions attributed to the formation of secondary aggregates from reacted and unreacted n‐C4H9Li. The molecular weight distribution narrows with increasing reaction temperature, indicating the activation energy of the last step of initiation to be higher than that of propagation.

A B S T R A C TThiol-containing antioxidants such a s 4-(mercaptoacetamido)-diphenylamine (MADA) undergo ready addition of -SH groups to the double bonds in diene rubbers in the presence of initiators. The reaction is a radical chain process leading to rubbers with improved thermooxidative resistance. The modification reaction has been carried out on high cis-polyisoprene and polybutadiene, and conditions under which the physicochemical properties (e.g., inherent viscosity, gel content, and microstructure) are less affected have been found. An oxygen absorption test and DSC were used as rapid methods for evaluation of thermooxidative stability of modified rubbers. The superiority of rubbers with MADA chemically attached (ranging from 1 to 4 phr) was shown by a circulating air oven test and by an extraction process which simulates the aggressive environments experienced by many rubbers under practical conditions. The results obtained show that a small degree of modification ( 1 phr MADA) is large enough to provide good thermooxidative stability without alteration of the molecular characteristics of the parent rubbers. At higher degrees, cistrans isomerization can occur. 52 5

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The effect of aromatic ethers (anisole and diphenyl ether) on the polymerization of styrene in toluene was investigated in the range of low ether concentrations. It was found that the process of initiation is not affected by the presence of ethers: the reaction order with respect to catalyst is unity and reaction rate is independent of ether concentration. Kinetic transitions, ascribed to the formation of secondary (mixed) aggregates were found to take place even in the presence of aromatic ethers. Propagation was also found to be insensitive to the presence of aromatic ethers in the investigated range. The reaction was of order 0.5 with respect to catalyst concentration and activation energy remained unchanged.

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