Development of surface-initiated atom transfer radical polymerization for the synthesis of functional biomaterials
Laibinis, Paul E.
Doctor of Philosophy
The research presented in this thesis is focused towards applying Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) for the synthesis of functional biomaterials. ATRP is a method of living radical polymerization which gives control over the polymer chain length and the end group. SI-ATRP is carried out after immobilization of the molecules that initiate ATRP on surfaces (Gold, Glass, and Silicon). When a surface modified with the initiator molecules is exposed to polymerization solution, the resulting polymer chains are covalently bound; yielding a densely grafted polymer brush. I have developed the SI-ATRP of commercially available oligo(ethylene glycol) methacrylate (OEGMA) monomers to prepare nanoscale poly(OEGMA) coatings that expose PEG chains in high surface density. Protein adsorption for plasma proteins (lysozyme, fibrinogen, and albumin) as measured by XPS shows that, these coatings exhibit remarkable resistance against protein adsorption that depends on the attributes of the monomer. Polymer films thicker than 3 nm are effective in retarding protein adsorption with the level of proteins adsorbed on these films being 99.4% less than that on a bare Silicon surface. I have also evaluated the effects of chain length and end group of the monomers on the kinetics of their polymerization and the wettabilities of the resulting films. Poly(NiPAAm) gels that exhibit a thermal phase transition at 32°C have been widely studied for possible applications in drug delivery systems. I have applied SI-ATRP to synthesize diblock, random, and gradient copolymer brushes of NiPAAm and OEGMA with a goal to obtain polymeric films with an outer biocompatible surface and an inner bulk capable of swelling-deswelling transition. XPS and wetting studies are employed to characterize these coatings. Reactivity ratios in the copolymerization of NiPAArn and OEGMA through SI-ATRP are determined by application of the Mayo-Lewis terminal model of copolymerization. Observed monomer reactivity ratios---r1 (for NiPAAm) and r 2 (for PEGMA, MW 300)---are 0.07 and 3.85, respectively. Finally, the techniques developed above are applied to create a nanoscale device capable of photothermally triggered drug release. Nanoshell-PNiPAAm hybrids are synthesized by SI-ATRP of NiPAAm on gold nanoshells and characterized by XPS and TEM.
Physical chemistry; Polymer chemistry