Toward Understanding the Architecture (Branching and MWD) of Crosslinked Acrylic Latexes

Branching Analysis of Multivalent Conjugates Using Size Exclusion Chromatography-Multiangle Light Scattering

Multivalent conjugates (MVCs) (conjugation of multiple proteins to a linear polymer chain) are powerful for improving the bioactivity and pharmacokinetics of a bioactive molecule. Since this effect is highly dependent upon the valency of the conjugated proteins, it is imperative to have a technique for analysis of the conjugation ratio. Studies of MVCs have used size exclusion chromatography-multiangle light scattering (SEC-MALS), which allows for the separate and individual analysis of the protein and biopolymer components based on their specific refractive index increment and UV extinction coefficient constants to determine the number of proteins bound per biopolymer molecule. In this work, we have applied traditional branching analysis to the SEC-MALS data, with the primary assumption that the polymer backbone can be used as the linear counterpart. We demonstrated good agreement between the branching values and the valency determined by traditional analysis, demonstrating that branching analysis can be used as an alternative technique to approximate the valency of MVCs. The branching analysis method also provides a more complete picture of the distribution of the measured values, provides important branching information about the molecules, and lowers the cost and complexity of the characterization. However, since MVC molecules are both conjugate molecules and branched molecules, the most powerful approach to their characterization would be to use both traditional multivalent conjugate analysis and branching analysis in conjunction.

Effect of cross-linking on rheological properties and a model for flexibility-rigidity transition in SBS/PBMA LIPNs

A series of latex interpenetrating polymer networks (LIPNs) with various cross-linking levels were prepared with polystyrene-polybutadiene-polystyrene (SBS) and butyl methacrylate (BMA) by emulsion polymerization. The gel content of the resultant latex particles ranged from 13.2% to 90.8%, with the amount of cross-linking agent increased. The structural, thermal and rheological properties of the latex particles were investigated by laser particle analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry and torque rheometry. Furthermore, in order to study the effect of gel content on the flow properties, a model is shown to predict the existence of a flexibility-rigidity transition of SBS/PBMA LIPNs as the amount of cross-linking agent increased. Torque data were interpreted in terms of shear rate, shear stress and viscosity. The relationship between gel content of SBS/PBMA LIPNs and polyvinyl chloride compositions and their effect on plasticization performance were determined, and the predictions of the model have good agreement with their flexibility-rigidity transition.