Functional poly(methylstyrene) latex particles : synthesis, characterization and applications

Abstract

Preparation of functional polymer latex particles with monodisperse size and well-defined surface functionalization is of scientific and technical interest because of their extremely large inner surface and a wide range of applications in the fields of biomedical and biochemical. In this study, the functional poly(methylstyrene) (PMS) latex particles bearing aldehyde and carboxylic acid groups with various particle size are prepared and characterized and some applications in binding specific DNA sequences are also studied. The major contents of this study are summarized as follows: 1. Preparation and characterization of ultrafine functional PMS latex particles A convenient method to prepare ultrafine PMS latex particles with aldehyde groups on the surface was developed. PMS latexes with well-defined sizes ranging from 26-81 nm in diameter were first prepared via microemulsion polymerizations, using cetyltrimethylammonium bromide (CTAB) as surfactant. The surface oxidation of PMS microlatexes were then carried out in the presence t-butyl hydroperoxide catalyzed by copper (ll) chloride. Kinetics of the oxidation of PMS particles was studied, and aldehyde group was found to be the major functional group on the particle surface. Furthermore, the effect of particle size on the oxidation of PMS microlatexes as well as the relationship between stability of the functionalized PMS microlatexes and their degree of oxidation were examined. 2. Preparation of functional Poly(methylstyrene) latex particles in an emulsifier - free emulsion system Highly monodisperse emulsifier-free PMS latex particles were prepared via an emulsifier-free emulsion polymerization, using 2,2'-azobis-(2-amidineopropane) dihydrochloride (V-50) as an initiator. The kinetics of the polymerization was studied and effects of initiator concentration, ionic strength in the aqueous phase, and polymerization temperature on the polymerization reaction are examined. A combination of kinetic studies and molar mass distribution of the polymer chains revealed that the polymerization followed the micellization nucleation mechanism. Results showed that the appropriate initiator concentration was necessary in order to obtain monodisperse and stable latex particles. The size of PMS particles decreased with the increase of initiator concentration and reaction temperature at a constant ionic strength, and the conversion of latexes increased significantly with increasing initiator concentration. On the other hand, the size increased as the ionic strength of aqueous phase increased, but the change of ionic strength had little effect on the particle size distribution. The SEM micrograph showed that an agitation rate of 350 rpm or higher was a necessity for the preparation of highly monodisperse poly(methylstyrene) latex particles. Purification of the latexes by dialysis was followed in order to remove residual monomer, initiator and electrolytes. The kinetics of oxidation of PMS latexes at different oxidant concentration was studied, and the effects of catalyst concentration, pH value and reaction temperature on oxidation were also investigated. The degree of oxidation increased with reaction time, but the emulsions of highly oxidized PMS latexes were found to be unstable. An increase of oxidant concentration enhanced the rate of oxidation, while the catalyst concentration had little influence on it. The addition of base and acid to latexes inhibited the oxidation reaction and the oxidation degree increased with increasing reaction temperature. 3. Surface characterization of functional poly(methylstyrene) latex particles in an emulsifier-free system. The amount of aldehyde groups on the particle surface was determined using the 2.5 pH method, and the amount of carboxylic acid groups on the particle surface were measured by conductometric and potentiometric titration methods. Surface morphology of latex particles was observed by the SEM. The control of the aldehyde content on the particle surface could be easily achieved by manipulating the reaction conditions such as the oxidant concentration. 4. Application of the functional PMS latex particles in biology Binding of DNAs to the functional PMS latex particles was carried out in order to examine the efficiency of binding DNA. The Binding was also carried out in different salt concentration. The results showed that the functional PMS latex particles had a good binding efficiency at normal condition. The addition of salt inhibited the binding reaction.