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UBC Theses and Dissertations

Synthesis and characterization of cationic latex bearing grafted chains Hritcu, Doina


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.

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