Styrene and methyl methacrylate have been polymerized at 25° using α,α′‐azo‐bis‐isobutyronitrile labeled with C14 as initiator. The numbers of initiator fragments per polymer molecule have been determined by measurements of the average molecular weights of the polymers by osmometry and the specific activities of the polymers and the initiator by gas counting. It is found that polystyrene radicals combine at 25° and that for polymethyl methacrylate radicals at this temperature disproportionation occurs about twice as frequently as combination.
Styrene has been polymerized at 60° and methyl methacrylate at 0 and 60° using 2,2′‐azo‐bis‐isobutyronitrile labeled with C14 as initiator. The average number of labeled end groups per molecule has been determined for the various polymers and so the relative importances of combination and disproportionation have been assessed. It has been found that polystyrene radicals undergo combination at 60°. In the case of methyl methacrylate, disproportionation occurs about 6 times as frequently as combination at 60° and about 1.5 times as frequently at 0° the activation energy for disproportionation is about 4 kcal. per mole greater than that for combination. The copolymerization of styrene and methyl methacrylate at 60° has been studied by this technique. It is found that when polystyrene radicals interact with polymethyl methacrylate radicals at this temperature combination occurs. The rates of initiation in the copolymerizations have been determined by a new method; the rate of this step is found to be virtually independent of the composition of the monomer mixture.
The effect of increasing viscosity on the course of polymerization reactions has been studied for some time. The cause of the acceleration of the polymerization rate often observed has been shown to be due to the decrease in the rate at which polymeric radicals react with each Subsequently, polymerization rates decrease to a much greater extent than can be attributed to the decrease in monomer concentration. The develop ment of the thermal nonstationary state method of measuring apparent velocity coefficients for the growth and termination reactions has made it possible to analyze these effects quantitatively and to study the influence of environment upon them. This has been done for vinyl acetates and for the first 35% polymerization of methyl methacrylate.' The present paper deals with the whole range of the polymerization of methyl methacrylate. In addition, some observations have been made when a crosslinking agent (ethylene glycol dimethacrylate) is added and also when precipitation of the polymer occurs in the presence of a solvent for the monomer, but not for the polymer.
EXPERIMENTAL
MaterialsCommercially supplied methyl methacrylate was purified by several washings with 10% aqueous sodium hydroxide, followed by many washings with distilled water. Subsequent to drying with anhydrous sodium sulfate, the material was fractionally distilled under 81 mm. of nitrogen; the fraction distilling between 39.8 and 40°C. was collected, re-distilled, transferred to a high-vacuum line, and immediately outgassed. After prepolymerization by irradiation with U.V. light, the monomer was distilled under high-vacuum conditions into a graduated receiver and finally into a second graduated receiver joined to the reaction vessel.
of the theory of thermal chain reactions was laid. Subseqhent reaction between the per-acid and further aldehyde by a non-chain mechanism gave rise to'the final product of autoxidation, the carboxylic acid, and this secondary process was found to be almost insensitive to the action of ultra-violet light, i.e. :(a) Aldehyde + Oxygen + Per-acid (b) Aldehyde +-Per-acid + Carboxylic acid Backstrom concluded that the chain carriers involved in stage (u) were of a free-radical nature and suggested that the propagation steps were of the form :
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.