C.A. Barson

The reactivities of diarylbutadienes towards typical initiating radicals: the cases of the 1,4-and 2,3-isomers of diphenyl-1,3-butadiene

Abstract Studies have been made of the reactivities of 1,4-diphenyl-1,3-butadiene and 2,3-diphenyl-1,3-butadiene towards the benzoyloxy, p -fluorobenzoyloxy and 1-cyano-1-methylethyl radicals. The 1,4-isomer has very high reactivity towards the aroyloxy radicals but very low reactivity towards the substituted alkyl radical. The 2,3-isomer is moderately reactive towards all three initiating radicals. The results have been obtained by analyses for end-groups in samples of poly(methyl methacrylate) produced in the presence of one of the dienes with the appropriate source of initiating radicals.

A method for determining reactivity ratios when copolymerizations are influenced by the penultimate group effects of both monomers

Abstract A novel kinetic treatment is proposed for the copolymerization of two monomers M 1 and M 2 where the reactivities of all terminal groups are susceptible to penultimate group effects. By applying the conditions [M 1 ] ⪢ [M 2 ] and [M 1 ] ⪡ [M 2 ], as is possible using radiolabelled monomers, values of r 1 and r 2 respectively can be obtained which are independent of penultimate group effects. These values are then used to find values for the other reactivity ratios r 1 ′ and r 2 ′ . The method involves a solution for r 1 ′ and r 2 ′ by means of intersecting hyperbolas, each curve representing a given monomer feed ratio and copolymer composition ratio. Only one of the two points of intersection of any two hyperbolas is common to all pairs of such curves and provides values for r 1 ′ and r 2 ′ .

The temperature dependence of the monomer reactivity ratio in the copolymerization of styrene and cinnamic acid

Abstract Styrene (M1) has been copolymerized with cinnamic acid-carboxyl-C14 (M2) at temperatures between 40° and 90°, using azoiso-butyronitrile as initiator. The compositions of the copolymers have been obtained by radioactive assay; they have been used graphically to determine the reactivity ratio, r1, for the polystyryl radical at each temperature. Arrhenius parameters have been derived and, in conjunction with published data for the homopolymerization of styrene, have been used to determine the energy of activation and the frequency factor for cross-propagation. The frequency factors favour self-propagation whereas the energies of activation favour cross-propagation, with the former slightly predominating.

The temperature dependence of the monomer reactivity ratios in the copolymerization of styrene with methyl and ethyl cinnamates

Styrene (M1) has been copolymerized with the methyl and the ethyl esters (M2) of cinnamic acid (carboxyl 14C) at temperatures between 40 and 130°, using azoisobutyronitrile as initiator. The compositions of the copolymers have been determined by liquid scintillation counting; since [M1 ⪢ [M2], a simplified form of the copolymer composition equation could be used for determining the reactivity ratio r1 graphically. Arrhenius parameters have been derived; the energies of activation favour cross propagation whereas the frequency factors favour self propagation. Although the latter effect slightly predominates, there is no evidence of significant steric effects. These esters thus resemble cinnamic acid when copolymerized with styrene. Styrol (M1) wurde bei Temperaturen zwischen 40 und 130° und AiBN als Initiator mit dem Methyl- und Athylester (M2) der Zimtsaure (14C-COO) copolymerisiert. Die Copolymerenzusammensetzung wurde durch Flussigscintillation bestimmt. Fur [M1] ⪢ [M2] konnte eine vereinfachte Form der Copolymerisationsgleichung angewandt werden um r1 graphisch zu bestimmen. Die Arrhenius-Parameter wurden abgeleitet; die Aktivierungsenergien begunstigen das gekreuzte Wachstum wahrend die Hǎufigkeitsfaktoren das Eigenwachstum begunstigen. Obwohl der letztereEffekt leicht uberwiegt, wurde kein Hinweis auf sterische Hinderung gefunden. In der Copolymerisation mit Styrol verhalten sich diese Ester wie die freie Zimtsaure.

Iodoform as a transfer agent in radical polymerizations

Abstract Iodoform has been examined as a reactive transfer agent in the radical polymerizations at 60°C of styrene and methyl methacrylate using azobisisobutyronitrile as initiator. The transfer constants have been determined by a procedure depending upon the determination of the initiator fragments incorporated as end-groups in the polymers. The polymerizations are retarded by iodoform; this effect is largely caused by an impurity, most probably elemental iodine, which is generated in the polymerizing systems by decomposition of the transfer agent. It is deduced that the transfer constants for iodoform with styrene and methyl methacrylate are ca. 10 and 3, respectively.

Application of a new approach to the determination of transfer constants for systems showing retardation

Degradative transfer reactions for diphenylpicrylhydrazine (DPPH-H), 1,3-diphenylpropene (DPP), and fluorene (FLU) have been examined using styrene and methyl methacrylate as monomers. A new procedure has been followed, depending upon analyses of polymers for end groups derived from azobisisobutyronitrile used as initiator for the polymerizations. The method requires information or assumptions about the efficiency of re-initiation during transfer particularly for a monomer, such as methyl methacrylate, for which disproportionation is prominent in the termination process. For DPPH-H, the efficiency of re-initiation is zero; for DPP and FLU with styrene, the efficiencies are close to unity but they are smaller when methyl methacrylate is used.

A method for determining reactivity ratios whenn copolymerizations are influenced by penultimate group effects

Abstract A novel kinetic treatment is proposed for the copolymerization of two monomers M 1 and M 2 when terminal −M 2 · groups are susceptible to penultimate group effects. If [ M 1 ] ⪢ [ M 2 ], as is possible experimentally when M 2 is radioactively labelled, a value of the reactivity ratio r 1 which is independent of penultimate group effects can be obtained. This value is then used to find values for the other reactivity ratios. The method involves a solution for reactivity ratios by means of intersecting curves, each curve representing a given monomer feed ratio and copolymer composition ratio.

Studies of end-groups in poly(methyl methacrylate) prepared using benzoyl peroxide in the presence of diphenylpropenes

Abstract Benzoyl peroxide, labelled with carbon-14 and tritium, has been used to initiate polymerization of methyl methacrylate; the numbers of benzoate and phenyl end-groups have been compared. The presence of 1,3-diphenylpropene or 1,2-diphenylpropene at low concentration in the polymerizing system increases the proportion of benzoate end-groups because the additive is effective in capturing benzoyloxy radicals. The relative reactivities at 60°C of methyl methacrylate, 1,3-diphenylpropene and 1,2-diphenylpropene towards the benzoyloxy radical are approximately 1,8 and 28. Very high reactivity of 9-(2-phenylethenyl)-anthracene towards this radical has been confirmed.

Copolymerizations involving methyl methacrylate, methyl acrylate, stilbene and p. fluorostilbene

Abstract Homopolymerizations and copolymerizations of methyl methacrylate (MMA) and methyl acrylate (MA) have been performed in the presence of either stilbene or p.fluorostilbene, labelled with carbon-14. It has been shown that at 60°C the polyMA radical is much more reactive than the polyMMA radical towards stilbene, the velocity constants for the reactions differing by a factor of about 300; similar results are found for p.fluorostilbene. The differences between the reactivities of the radicals are associated with steric effects arising from the presence of a methyl group at the alpha position in MMA.

The use of the radiotracer method to circumvent penultimate group and ceiling temperature effects in copolymerisation

Abstract The radiotracer method can be used to study copolymerisations of M 1 and M 2 under conditions where [M 1 ]⪢[M 2 ]. In these circumstances, the probability of two M 2 units becoming adjacent in the polymer chain during propagation is negligible. Experimentally derived reactivity ratios, obtained by a simple graphical solution of composition data, are realistic measures of relative reactivities even with systems where penultimate group effects or depropagation effects due to M 2 M 2 diads are normally significant.