Synthesis and Characterization of Functional Polymeric Nanoparticles by Step-Growth Polymerization (Current PRF Type AC grant)
Our research in this area is intended to explore the designed manipulation of macromolecular architecture to synthesize unique polymeric materials with solubility, shape, dimensions, and functionality suitable for applications such as surfactants, paints and coatings, impact modifiers, rheology modifiers, and drug delivery agents. In my research group, we have recently developed a novel, general technique whereby nanometer-sized amphiphilic polymeric particles can be conveniently synthesized. This technique is based on self-assembly and polymerization reactions utilizing step-growth reactions to make star-shaped core–shell polymers. The technique allows any polymer functionalized on one chain end with a step-growth reactive functionality to combine with any crosslinkable monomers with which it can react. By taking advantage of self-assembly in selective solvents, micellization and continued crosslinking reactions result in polymer particles with controlled size and unique compositions and architectures. The synthetic method is compatible with a wide variety of monomers and functionalized polymers and has the potential to lead to a large number of new materials with useful properties. Scheme 4 depicts the general synthetic procedure and Figure 5 displays a TEM micrograph of the resulting nanoparticles.
Scheme 4. Synthetic procedure for the formation of nanoparticles from monofunctionalized polymers and step-growth crosslinkable monomers.
This depicts a very different technique for making stars and star-shaped nanoparticles. This is the first technique that involves step-growth type reactions as the core forming method. This is significant in that it leads to compositions never before achieved. Furthermore, the in-situ block forming and subsequent crosslinking reactions are unique.
The research will investigate the parameters that control the self-assembly and size of the particles produced. Parameters such as the composition and molecular weight of the mono-functionalized polymer chain, the composition of the core forming monomers, the reaction solvent, the reaction temperature, and reaction concentration will be investigated.
Figure 5. TEM micrograph of core – shell nanoparticles: PEO shell with 20 wt. % crosslinked polyurethane core.
Novel core–shell polymers of a number of different compositions will be synthesized and characterized as to their molecular weight, dimensions, and mechanical properties. Material compositions will be designed for specific applications and their potential for these applications will be investigated. Poly(ethylene glycol) shell polymers will be investigated for their solution properties, especially in terms of their performance as a surfactant. Polymer shells consisting of engineering polymers such as polylactide, polyamides, and poly(2,6-dimethylphenylene oxide) will be synthesized and their morphology and mechanical properties investigated to determine their potential for application as rheology and toughness modifiers.
Continued research is planned on the synthesis of inorganic-organic core-shell materials by this route. By performing the reaction with –Si(Cl) 3 funtionalized polymers and condensation with silicon tetrachloride, we have been able to produce polymer shell functionalized silica nanoparticles with controlled dimensions. The work is expected to continue the development of a novel polymerization method and will result in a wide variety of new architecturally modified materials from readily available precursors.