Efficiency of low-molecular-weight and high-molecular-weight alkoxyamines in the synthesis of polystyrene

Resumo

The influence of the structure of high-molecular-weight alkoxyamines (obtained in situ from C-phenyl-N-tert-butylnitrone and 2-(benzylideneamino)-2-methyl-1-phenylpropanol-1-N-oxide) and their low-molecular-weight analogs on styrene polymerization in the temperature range 70—110 ° was analyzed. The controlled synthesis of polystyrene in the presence of low-molecular-weight alkoxyamines was revealed to occur most efficiently at 110 °. The use of high-molecular-weight alkoxyamines makes it possible to perform the controlled process under lower-temperature conditions (70—90 °), when the constant polymerization rate and linear increase in the molecular weight with conversion are observed, and the synthesis of polymers with fairly low polydispersity (M_w/M_n ~ 1.26) is also possible. The quantum chemical calculations showed that the energy of the C-ON bond in alkoxyamines is determined by the length of the chains at the nitroxide fragment rather than the structure of the substituents. It is found that the equilibrium dissociation constants of high-molecular-weight alkoxyamines are caused by both the structure of the nitroxide fragment and molecular weights.