Abstract
A method is presented for synthesizing surfactant-free latexes comprising a starch-graft-vinyl polymer, (1) starting with a suspension of the highly branched starch amylopectin, either native or degraded, (2) then using ozonolysis to create free-radical initiation sites on this amylopectin scaffold, and (3) finally adding the monomer and inducing polymerization. The ozone simultaneously thins the starch and creates initiating/ grafting sites on the starch, from which starch-graft-copolymer latexes can be grown. The encapsulation of starch inside the hydrophobic polymer particles created by a heterogeneous free-radical polymerization process is demonstrated with energy-dispersive spectroscopy; this is the first time that the particle morphology of such a latex has been so characterized. The data unambiguously prove that low-molar-mass degraded starch can be encapsulated within a latex particle. The underlying mechanisms have been explored, and data quantifying the rates of production of hydroperoxides by ozone, the thermal decomposition of the starch hydroperoxides so formed, and the degradation of amylopectin by ozone are reported. The activation energy for the thermal decomposition of the starch macroinitiator, determined in this work to be 125 6 8 kJ mol!1, is consistent with the proposition that the initiating species are mainly hydroperoxides. Colloidally stable poly(styrene-co-n-butyl acrylate) latexes based on high-molar-mass amylopectin have been developed. These are stable against electrolytes (several months in 4 mol L!1 NaCl), with 20% of the starch effectively grafted to the particles. Films cast from such latexes are more pliable than starch films and are readily redispersed in water.