Investigation of Growth and Degradation Behaviors of Biodegradable Polyester Brushes and Their Applications

Polymer brushes fabricated from degradable polyesters including poly(lactic acid) (PLA), poly(glycolic acid) (PGA) and poly(epsilon-caprolactone) (PCL) were prepared via ring opening polymerization (ROP) on silicon substrates. These are proposed as a possible, dynamic layer that might gradually expose and activate an array of biosensors. The growth conditions for PGA and PCL brushes were investigated by varying the temperature and solvent. Different optimal conditions were established for growth of PGA and PCL brushes. These differences were explained by (1) the different activation barriers for the ring opening step (2) and the position of the polymerization/depolymerization equilibrium. Similar degradation behaviors of both PGA and PCL brushes to the previously studied PLA brushes were demonstrated. Only neutral or basic conditions were applicable for brush degradation which was consistent with a backbiting mechanism. CV experiments provided comparable results to ellipsometry measurements: PGA brushes degraded faster than PCL brushes under similar conditions. The antifouling property of these brushes were tested using a single protein buffer solution containing bovine serum albumin (BSA) under physiological conditions. The degradation and protein adsorption behaviors of PLA, PGA, PCL brushes and their co-polymer brushes with oligo(ethylene glycol) (OEG) and poly(ethylene glycol) (PEG) were studied. Fabrication of degradable polyester brushes with moderate protein resistance was demonstrated. Furthermore, characterization methods including ellipsometry, ATR-FTIR spectroscopy and a protein assay were applied to monitor the adsorbed protein on flat substrates.;A strategy for improving the properties of polymer (i.e. molecular weight distribution: PDI) synthesized via free radical polymerization (FRP) was proposed and investigated. The local heating effect of microwave absorbers under microwave irradiation was tested in order to achieve an accelerated initiation rate close to the surface compared to the propagation rate presumably farther from the surface, which might lead to a lower PDI of the resulting polymer. Surface initiated free radical polymerization (SI-FRP) of styrene was performed on azo initiator (ATCS) modified Fe2O3 nanoparticles by microwave irradiation under different working modes and conditions. Under the SPS working mode, both low monomer conversion (<20%) and small PDI (<1.5) were obtained. These results were explained by (1) a reduced propagation rate due to the fast formation and decomposition of radical initiators (2) and the reduced chain transfer effect under low monomer conversion. Neither results obtained from experiment nor from a model calculation supported the local heating effect of Fe2O3 nanoparticles. Furthermore, the reproducibility of SI-FRP on another microwave absorber, silicon, was found to be poor. The variation of temperature across a silicon sample under same conditions was monitored by an external IR camera and underestimation of the surface temperature is likely to be the cause of the problem. The local heating effect of Si sample was probed by coating the substrate with an insulator layer (SiOx) and by placing the sample in different positions. The results indicate the surface temperature of the substrate was higher than the bulk solution due to a saturation of heat transfer in the open-vessel system. However, this might deviate from results obtained under the actual experimental conditions where the system was sealed. Furthermore, the surface temperature of silicon was shown to be poorly controlled under practical conditions. A thick insulator layer attached to the silicon surface might alleviate these problems.