Experiments on the Internal Structure of Latexes Using SmallAngle Neutron Scattering

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The purpose of this research is to obtain basic information about the kinetics of formation and how these kinetics affect the final structure of latex particles. These materials are used as coatings and paints, also as impact modifiers. The value of this work to modern industry is that with an improved understanding of the structure and behavior of latex particles, better materials can be produced. Questions relating to film formation kinetics, strength of materials, and special purpose applications including medicine and biotechnology depend on a detailed knowledge of the structure and behavior of the latexes. Structured latexes are submicron sized particles, with some unique internal morphology, suspended in a fluid medium, most often water. When the dimensions of the chains are about half those of the latex diameter, some type of segregation is present, with the first polymerized material appearing near the center of the particle. Technologically, the most significant structured latex is the core-shell type with a rubbery core and a glassy shell. This type generically represents high-impact polymers, and more specifically ABS (acrylonitrile-butadiene-styrene) plastics and acrylic impact modifiers. The PIs plan to look at both homopolymer and copolymer latexes using small-angle neutron scattering (SAS) to follow the course of the polymerization. To elucidate homopolymer structure, polystyrene will be used. They plan to test the hypothesis that polystyrene of molecular dimension about half of the latex particle size segregates into what appears to be a core and a shell, with the first polymerized chains tending to be near the center of the particle. The question of how much segregation exists before the second portion of the monomer is polymerized, and how the extent of segregation changes during polymerization, will be the subject of planned experiments. The model assumes that the internal viscosity of the system is high, and/or vitrification is occurring, the final system being below its glass transition temperature, and the polymer soluble in the monomer. To look at copolymer systems, small-angle neutron scattering measurements will be made before polymerization of the second component is initiated, and several times during the polymerization. The results should elucidate if segregation occurs or, if not the rate of desegregation decrease as the internal viscosity of the system increases and/or if the glass transition of monomer-plasticized particles is approached.