Monodisperse, Thermoresponsive Microgels Based on Poly(ethylene Glycol) Derivative Polymers

University Of North Texas, Denton TX

Investigators

Abstract

TECHNICAL SUMMARY: Synthesizing monodisperse polymer colloids is usually the first step toward the study of self-assembling processes and especially important for the fabrication of nanostructured materials. The current available polymer colloids include polystyrene, polymethyl methacrylate (PMMA) and poly-N-isopropylacrylamide (PNIPAM) spheres and their derivatives. The objective of this proposed project is to create new monodisperse, thermo-responsive polymer colloids based on poly(ethylene glycol) derivative polymers, joining in these well-known colloids of polystyrene, PMMA, and PNIPAM. The central idea is to synthesize these colloids with copolymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGETH2MA), poly(ethylene glycol) methyl ether methacrylate (PEGMEA), poly(ethylene glycol) acrylate (PEGA) and their derivatives using precipitation polymerization method. The first two components give the low critical solution temperature (LCST) near the physiological temperature while the third component (PEGA) provides a functional group. Under proper chemical compositions and reaction conditions, PEG derivative microgels with a very narrow size distribution may be obtained. As a result, these PEG derivative microgels can be used as building blocks to fabricate hydrogels with colloidal crystal structures. This proposed project consists of five specific aims. The first is to synthesize and characterize PEG derivative microgels that should be monodisperse, thermoresponsive, and with functional groups. The second aim is to synthesize biodegradable PEG derivative microgels by first synthesizing biodegradable PEG-polylactic acid macromer and then using them as crosslinkers for microgels. Self-assembling processes of the PEG derivative microgels will be explored by establishing the relationship between crystallization kinetics with the softness (low mechanical modulus) of the microgels. (Aim 3) Hydrogels with colloidal crystalline structures will be synthesized using PEG derivative microgels as both crosslinkers and as a light diffraction lattice (Aim 4). Aim five will focus on preparation of PEG-microgels-based colloidosomes and build a theoretical model that will describe swelling kinetics of a gel shell such as colloidosomes. NON-TECHNICAL SUMMARY: This proposed project is innovative because if successful, it will lead to a new class of polymer colloids that have thermal responsive properties and monodisperse size distribution. In contrast to polystyrene spheres and PMMA spheres that are hydrophobic, the proposed PEG derivative particles are hydrophilic and have a thermally responsive volume phase transition near the physiological temperature. Different from PNIPAM microgels that are extremely soft in terms of elastic modulus, the PEG derivative microgels will be denser, harder and easier to form a crystalline structure as revealed by the feasibility study. Furthermore, in the past two decades the most research on thermally responsive polymer microgels has focused on PNIPAM and its derivatives. However, the extraordinary thermo-sensitive properties of PNIPAM have not been transferred into a biomedical breakthrough. One of the major hurdles is that PNIPAM monomer is carcinogenic or teratogenic. Thus, finding a biocompatible polymer microgel replacement of PNIPAM will be one of the major advancements in this field. The proposed project will provide direct support for two graduate students and broaden the participation of underrepresented groups. This program will integrate its undergraduate educational efforts with three existing programs that promote research experiences: the Texas Academy of Mathematics and Science, the Ronald F. McNair Post-baccalaureate Achievement Program at UNT, and NSF-UNT REU summer program. From this proposed inter-disciplinary project, both graduate and undergraduate students will gain valuable experimental and analytical skills in the rapidly growing fields of polymers, colloids and nanostructured materials. The basic sciences established in this research will have impacts not only in polymer sciences but also in biomedical technology.