Phosphines: Chain transfer studies with styrene and methyl methacrylate

Abstract

AbstractThe nature of the trivalent phosphorus radical (R2P) was explored through chain transfer studies. The chain transfer constants with styrene and methyl methacrylate were determined at 60°C. for a series of phosphines; namely, the phenyl‐, 2‐cyanoethyl‐, bis(2‐cyanoethyl)‐, and octyl‐compounds. The transfer constants were all greater than one and comparable to those for thiols. The Qtr–etr constants (Alfrey‐Price scheme extended to chain transfer) were calculated and used to discuss structural effects on reactivity. The Qtr–etr parameters for several thiols were also calculated here for the first time and provide additional information concerning their utility. The Qtr–etr values allow the thiols to be compared directly with the phosphines. Comparison indicates that in radical displacements, while both classes are electron acceptors, the phosphines are generally less “electrophilic” than the thiols. The Qtr–etr values for these two important classes of transfer agents permit the transfer constants for these compounds to be calculated with any monomer for which Q–e values are available.