| Nanosized polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) hybrid latex particles (∼50 nm) with various compositions were successfully prepared using a redox-initiated miniemulsion polymerization process. This process provides a new method to synthesize nanosize hybrid latex particles using a relatively small amount of surfactant.; Studies were performed ranging from fundamental research on the redox-initiated miniemulsion polymerization of n-butyl methacrylate (BMA) using a Mettler RC1 reaction calorimeter, the preparation of isocyanate-terminated urethane prepolymers using methylene-di-p-phenyldiisocyanate (MDI) or isophorone diisocyanate (IPDI) reacting with polypropylene glycol diol (PPG-diol; molecular weight = 2,000 g/mol) and a small amount of hydroxyethyl methacrylate (HEMA), miniemulsification and miniemulsion polymerization of PU/BMA droplets, chain extension of urethane in the obtained nanoparticles, film formation of the resulting hybrid latexes, and evaluation of the mechanical and surface properties of the resulting films. A suitable chain extension process was developed to introduce interparticle crosslinking while maintaining the original small-size of the obtained hybrid nanoparticles. DMA and stress-strain tests show that intimate mixing of the PU and PBMA chains was achieved at the molecular level in the PU/PBMA hybrid system, while typical two-phase composite behavior was observed in a PU-PBMA latex blend system. The presence of the non-crosslinked PU phase significantly increased the maximum strain of the PU/PBMA hybrid films with some sacrifice of the tensile strength and Young's modulus. However, in the PU-PBMA latex blend system, the presence of the PU decreased not only the maximum strain, but also the tensile strength and Young's modulus.; Fundamental research on the miniemulsion polymerization of BMA initiated by the hydrogen peroxide/ascorbic acid redox initiation system was carried out in terms of the order of addition, feed strategy, initiation mechanism, reaction temperature, surfactant concentration, and initiator concentration. The influence of the presence of ferrous ion (Fe2+) on the redox initiation system was also studied. It was found that a low polymerization temperature and a fast initiation and polymerization rate are the key parameters needed to obtain small-sized particles via the miniemulsion process. The use of a redox initiator in the miniemulsion polymerization of BMA can result in the formation of nanoparticles as well as nearly 100% droplet nucleation. |
