Characterization of surface NH3+Cl- groups on poly(styrene-co-Boc-aminostyrene) microspheres obtained by controlled acidic treatment

Different samples of aminated latex of poly(styrene-co-Boc-aminostyrene) microspheres with mean diameters varying from 0.7 to 1.0 microm were prepared by dispersion copolymerization of styrene (ST) and Boc-aminostyrene (Boc-AMST). The copolymer compositions determined by nuclear magnetic resonance (1H NMR) were Boc-AMST/ST 6.9/93.1 mol/mol % (BOC7 sample) and Boc-AMST/ST 31.3/68.7 mol/mol % (BOC30 sample). The average molecular weights determined by gel permeation chromatography were 126 kDa (BOC7 sample) and 51 kDa (BOC30 sample). The latex containing NH-carbo-tert-butoxy groups (NH-Boc) were treated with 2 M HCl in isopropyl alcohol/water (1:1 vol/vol), at 50 degrees C for 3, 6, 9, 24, and 30 h, in order to control the extent of deprotection reaction of the NH-Boc. The deprotection reaction resulted in the formation of NH3+Cl- groups on the particle surfaces. The kinetic of the deprotection reaction was investigated by 1H NMR analyses and the yield varied from 20 to 40%. The resulting -NH3+Cl- groups on the microsphere surfaces were examined, in particular, by electron spectroscopy imaging (ESI) using an energy-filtered transmission electron microscope (EFTEM) that clearly demonstrated the presence of Cl on the particle surfaces. Scanning electron photomicrographs recorded for the above samples showed that the particle morphology was maintained after the acidic treatment.