Nanosized polyurethane/poly(n-butyl methacrylate) (PU/PBMA) hybrid latex particles (∼50 nm) with various compositions were successfully prepared using a redox-initiated miniemulsion polymerization process. Studies were carried out on the miscibility of PU prepolymer and BMA monomer, PU/BMA droplet formation, and polymerization kinetics. This process provides a new method to synthesize nanosize hybrid latex particles using a relatively small amount of surfactant. A suitable chain extension process was developed, where a hydrophobic chain extender was used to introduce intraparticle crosslinking while maintaining the original small particle size of the nanosize PU/PBMA hybrid latexes. The ratio of PU to BMA, the amount of grafting agent (hydroxyethyl methacrylate; HEMA), and the presence of the hydrophobic chain extender have little influence on the particle size of the final latexes compared to the seeded emulsion polymerization processes. This illustrates the advantage of this process, whereby the final particle size is less sensitive to the composition and amount of cross-linking agent or chain extender.

The increase in industrial interest in the incorporation of alkoxysilanes in organic polymer coatings arises from their ability to form self-cross-linkable films at room temperature. In the past few years, many patents were published, offering solutions for avoiding premature cross-linking of alkoxysilane-containing latexes and for obtaining good film-forming properties without using organic solvents. The present paper proposes a miniemulsion approach for the incorporation of alkoxysilanes into acrylate latex systems in order to protect the silane moieties from hydrolysis and premature cross-linking by reducing their contact with water. Vinyltriethoxysilane (VTES)/n-butyl acrylate (BA) copolymer latexes were synthesized by both conventional emulsion and miniemulsion procedures. The amount of coagulum and conversion were determined by gravimetry. Differences in coagulum levels were observed with respect to the copolymerization procedure (1.1−32.7 wt % based on monomers in conventional systems vs 1.2−5.5 wt % on monomers in miniemulsion systems for a VTES feed of 1−50 mol %) and acrylate/alkoxysilane molar ratio. Gas chromatography was used to determine the reactivity ratios of VTES/BA pairs by analyzing the evolution of unreacted comonomers during copolymerization. The reactivity ratios between the alkoxysilane and acrylate differed by 2 orders of magnitude for VTES (monomer 1) and BA (monomer 2), where r 1 = 0.044 and r 2 = 8.56. These results were confirmed by FT-IR analysis of the copolymer composition (r 1 = 0.086, r 2 = 8.51).

Since the first conceptual and mathematical descriptions of emulsion polymerization were advanced over forty years ago, new processes have necessitated new and modified theories for the nucleation and growth of polymer particles in the presence and absence of micelles and submicron monomer droplets. The advances in our understanding have been con siderable and yet numerous uncertainties remain; prediction continues to be the ultimate goal.The use of multiple monomers, introduced through a number of often complex process variations, greatly complicates the development of these predictive models. An understanding of the development and control of particle microstructure and morphology during emulsion polymerization is an intense area of investigation, driven by the com mercial need and application of polymer particles possessing narrowly defined properties. Advances in our abilities to prepare and characterize these particles continue to evolve.

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Hexagonal noncontiguously packed (HNCP) arrays of submicrometer-sized particles trapped at an air-water interface are successfully transferred to solid substrates. The long-range order of the hexagonal arrays at the interface can be improved by compression-relaxation cycles. The interparticle distance (i.e., the periodicity of the hexagonal array) can be controlled by varying the degree of compression of the particle film. The critical characteristics of the substrate surface are hydrophobicity (advancing water contact angle of >70 degrees) and a charge complementary to the surface of the particles. Suitable silicon and glass substrates are easily prepared by treatment with commercially available organosilicon compounds. Two transfer processes have been developed. When the parallel transfer process is used, the HNCP arrays are deposited on the solid substrates with minimal pattern distortion. The vertical dipping transfer distorts the pattern and renders a sense of directionality perpendicular to the dipping direction. This surface patterning technique is applied to fabrication of subwavelength grating for antireflection in the visible region. Antireflective HNCP arrays comprising varied particle diameters and pattern periodicities are fabricated on glass substrates to demonstrate the effects of these parameters on the antireflection performance.