The free‐radical copolymerization of α‐methylstyrene and styrene has been studied in toluene and dimethyl phthalate solutions at 60°C. Gas chromatography was used to monitor the rate of consumption of monomers. For styrene alone, the measured rate of polymerization Rp and M̄n of the polymer coincided with values expected from previous studies by other workers. Solution viscosity η affected Rp and M̄n of styrene homopolymers and copolymers as expected on the basis of an inverse proportionality between η1/2 and termination rate. The rate of initiation by azobisisobutyronitrile appears to be independent of monomer feed composition in this system. Molecular weights of copolymers can be accounted for by considering combinative termination only. The effects of radical chain transfer are not significant. A theory is proposed in which the rate of termination of copolymer radicals is derived statistically from an ideal free‐radical polymerization model. This simple theory accounts quantitatively for Rp and M̄n data reported here and for the results of other workers who have favored more complicated reaction models because of the apparent failure of simple copolymer reactivity ratios to predict polymer composition. This deficiency results from systematic losses of low molecular weight copolymer species in some analyses. Copolymer reactivity ratios derived with the assumption of a simple copolymer model and based on rates of monomer loss can be used to predict Rp values measured in other laboratories without necessity for consideration of depropagation or penultimate unit effects. The 60°C rate constants for propagation and termination in styrene homopolymerization were taken to be 176 and 2.7 × 107 mole/l.‐sec, respectively. The corresponding figures for α‐methylstyrene are 26 and 8.1 × 108 mole/l.‐sec. These constants account for the sluggish copolymerization behavior of the latter monomer and the low molecular weights of its copolymers. The simple reaction scheme proposed here suggests that high molecular weight styrene–α‐methylstyrene copolymers can be produced at reasonable rates at 60°C by emulsion polymerization. This is shown to be the case.

The free radical copolymerization of methacrylonitrile, styrene, and a-methylstyrene was studied at 60 OC in toluene solution. Copolymer composition was calculated from the composition of the unreacted monomers, as measured by g.1.c. Reactivity ratios measured previously for the three monomer pairs involved were used with the simple terpolymerization equation to predict polymer composition. Agreement between predicted and experimental polymer compositions was satisfactory. The behavior of a-methylstyrene can be described by a simple model without reference to ceiling temperature or penultimate effects because sequence lengths of this monomer in the terpolymers are short.A true azeotropic feed composition was not investigated, but several monomer mixtures produced copolymers with compositions which varied so little from that of the feed that the systems could be considered to be azeotropic for practical synthetic purposes. This behavior is in accord with expectations.Analytical accuracy of the gas chromatographic techniques was examined and means are suggested to make the best use of this method in copolymerization studies.La copolymCrisation par radicaux libres de methacrylonitrile, styrene, et a-methylstyrene a ete etudiee a 60 "C en solution dans le toluene. La composition du copolymere a ett calculee a partir de celle des monomeres restants par c.g.1. Les rapports de reactivite precedemment mesurts pour les trois monomeres impliques pris deux a deux, ont CtC utilises dans la simple equation de terpolymtrisation pour prtvoir la composition du polymtre. Un accord satisfaisant entre les compositions calculee et trouvte a etC obtenu. Le comportement de I'a-mCthylstyrene peut itre decrit par un modele simple sans faire reference a la temperature "de plafond" ou a des effets prtterminaux car !es longueurs des sequences de ce monomtre dans les terpolymeres sont courtes. La composition d'une alimentation azeotropique vraie n'a pas Ctt recherchee car de nombreux melanges de monomeres ont donne des copolymtres dont la composition differe tellement peu de celle de I'alimentation, qu'il est possible de considtrer ces systtmes comme Ctant azeotropiques, a des fins de synthese pratique. Cette attitude est conforme aux previsions.La precision analytique des techniques de chromatographie en phase gazeuse a ete examinee et des moyens ont ett proposes afin de faire le meilleur usage de cette methode a des etudes de copolymtrisation.

No abstract

No abstract

No abstract