Anisotropic polystyrene nanoparticles of diameters below 0.5 microm were prepared by coating the surface of cross-linked polystyrene latex particles with a thin hydrophilic polymer layer prior to swelling the particles with styrene and then initiating second-stage free-radical polymerization. Conditions were found so that all particles had uniform asymmetry. The effect of surface chemistry on the development of particle anisotropy during seeded emulsion polymerization of sub-0.5 microm diameter particles was studied. The extent and uniformity of the anisotropy of the final particles depended strongly on the presence of the hydrophilic surface coating. Systematic variation of the degree of hydrophilicity of the surface coating provided qualitative insight into the mechanism responsible for anisotropy. Conditions were chosen so that the surface free energy favored the extrusion of a hydrophobic bulge of monomer on the hydrophilic surface of the particle during the swelling phase: the presence of a hydrophilic layer on the particle surface causes this asymmetry to be favored above uniform wetting of the particle surface by the monomer. Kinetic effects, arising from the finite time required for the seed to swell with the monomer, also play a role.

Amphiphilic, RAFT-capped, (acrylic acid) x (styrene) y diblock copolymers (x = 10, y ) 10, 5, 0) were synthesized and used as stabilizers in emulsion polymerization. Above the critical micelle concentration (cmc) of the diblocks and under appropriate reaction conditions micelles of the more hydrophobic diblocks were sufficiently nonlabile to be nucleated and act as seed particles for latex particle formation. The key parameters which allow control over the system are diblock hydrophobicity and initiator concentration. A homogeneous nucleation mechanism is most likely to operate below the cmc of the diblocks.

Cooking and sensory properties of rice are largely determined by the amylose content and structure. For relationships between functional and structural properties, a more accurate method to determine the structure of amylose is required. Here we calibrate size exclusion chromatography (SEC) columns, using Mark-Houwink parameters for linear starch and pullulan standards, to obtain the true molecular weight distribution of linear starch. When the molecular weight distribution is reported relative to pullulan, rather than the actual molecular weight which is readily obtained from universal calibration, it is seen that the molecular weights of longer amylose chains are greatly underestimated. We validate the SEC method to enable the measurement of the hydrodynamic volume distribution of the starch by examining reproducibility and recovery. Analysis of the starch in the sample pre- and post-SEC shows that 20% of the carbohydrate is not recovered. Comparison of the weight-average degree of polymerization, X(w), of (undebranched) starch of pre- and post-SEC is made using iodine binding as well as Berry plots of data from multi-angle laser light scattering (MALLS). These both show that current SEC techniques for starch analysis lead to significant loss of high molecular weight material. Indeed, for the systems studied here, the values for X(w) after SEC are about three times lower than those before SEC. Iodine-starch complexes of pre- and post-SEC samples reveals that the SEC techniques give reliable data for the amylose fraction but not for amylopectin. We address reports in the literature suggesting that the conventional isoamylase method for debranching starch would lead to incomplete debranching and thus incorrect molecular weight distributions. However, it is shown using (1)H NMR that isoamylase can completely debranch the amylose (to within the detection limit of 0.5%), and by SEC that successive incubation with isoamylase, alpha-amylase, and beta-amylase can degrade the amylose-rich fraction completely to maltose. We develop a method to obtain a hot water soluble fraction (HWSF), rich in undamaged amylose molecules, directly from rice flour, avoiding the structural degradation of previous techniques. With appropriate sample handling, the formation of associations between starch chains is minimized. With the combination of calibrated and validated SEC methods, and an improved extraction of amylose from rice, the X(w) for both HWSF and debranched HWSF are found to be much larger than has previously been reported.