Cationic poly(styrene) latices bearing grafted chains were synthesized by surface
initiated polymerization of N(2-methoxy-ethyl) acrylamide (MEA) on core latex. The 2-3
|j.m diameter core particles were produced by successive seeded growth polymerization
using a cationic azo-derivative as initiator. The area per charged group was found by
conductometric titration to be between 150 and 300 A².
The core latex was covered with a shell containing poly(styrene-co-acrolein) by a
seeded copolymerization procedure. The surface aldehyde concentration was determined
by reaction with hydroxylamine hydrochloride and titration. The surface aldehyde groups
were used as starting points for Ce(IV) redox initiated polymerization of MEA. The
amount of grafted MEA was estimated indirectly from unreacted monomer concentration.
The maximum tether coverage, 9.9 MEA groups/A², was obtained for an aldehyde surface
concentration of 2.8 groups/A². The probable chain conformation is a dense brush with an
equilibrium length from 20 to 133 A.
A model latex carrying cleavable chains was synthesized by using a shell containing
poly(styrene-co-hydroxy-ethyl acrylate). The procedure for producing the shell and for
grafting M E A was the same as for the aldehyde latex. The density of surface hydroxyl
groups was assessed by saponification of the ester bonds, followed by conductometric
titration of the carboxylic residues. In all experiments competing solution polymerization
of M E A occurred due to oligomer leakage from the bead. The grafted chains were
characterized by quantitative size exclusion chromatography (SEC) after saponification. The molecular weight showed an unusual trimodal distribution. The surface density of the
long chains was found to be between 4.4xl0⁻⁵ and 1.3xl0⁻⁴ chains/A². Short and
oligomeric chains had a density of about 6xl0⁻⁴ chains/A². The probable configuration of
each of these species is a mushroom, extending into solution to a maximum of 50 A.
The beads carrying grafted chains were used as stationary phases for SEC of proteins.
Experimental evidence for graft-mediated size exclusion, as predicted by two theoretical
models, was provided, demonstrating that SEC can be performed efficiently with nonporous
media.Science, Faculty ofChemistry, Department ofGraduat
