A MECHANISTIC STUDY OF THE RADICAL COPOLYMERIZATION OF P-METHOXYSTYRENE WITH CITRACONIC ANHYDRIDE VIA C-13 NMR-SPECTROSCOPY

The composition and monomer unit sequence distribution of copolymers o f p-methoxystyrene (p-MST) with citraconic anhydride (CA) prepared in methyl ethyl ketone (MEK) at 50,0 +/- 0,1-degrees-C were determined ov er a range of comonomer feed mole fractions using C-13 NMR spectroscop y. The monomer units in these copolymers were found to display an incr easingly strong tendency to alternate as the mole fraction of CA in th e feed increases. The existence of a 1 : 1 charge-transfer complex for med between p-MST and CA in the feed was confirmed via UV spectroscopy and the equilibrium constant for complex formation was determined. Th e terminal, penultimate and complex-participation models were tested f or applicability to the mechanism of copolymerisation for this comonom er system. On the basis of copolymer composition data, the penultimate and complex-participation models were found to provide each an adequa te description of the mechanism of copolymerisation in the comonomer s ystem via non-linear least squares methods. The inadequacies of the te rminal and penultimate models in describing the copolymers were expose d more explicitly through an analysis of their comonomer unit sequence distributions using reactivity ratio related test functions.