ABSTRACTSYNTHESIS AND PROPERTIES OF SUBSTITUTED POLYLACTIDES AND SURFACE MODULATION OF SMALL SILICA NANOPARTICLESByQuanxuan ZhangPolylactides have been widely studied as a degradable material in environmental and biomedical fields due to their biodegradability and biocompatibility. However, the applications of polylactide has been limited by its high crystallinity, hydrophobicity and lack of functionalization; so strategies that provide routes to functionalized polyesters are necessary to produce materials with the desired physical and chemical properties. Development of those strategies has been one of the major efforts to expand the application of polylactides, especially as degradable delivery vehicles. A series of propargyloxy lactic acid derivatives using poly(ethylene glycol) with different lengths as spacers between propargyl group and lactic acid were prepared with high yield via hydrolysis of cyanohydrin from inexpensive starting materials without using column purification. The versatility of the developed method was also tested by the survival of alkene group in the synthesis of allyloxy lactic acid. An azido lactic acid was also prepared to act as an alternative approach to render click function to polylactides. This allows for easy access of building up a library of clickable α-hydroxy acids to prepare clickable substituted polylactides.Post-polymerization modification via click chemistry provides a convenient route to functionalized polylactides with a variety of new properties. We prepared clickable polylpropargyloxylactide that have pendant propargyl groups available for the attachment of chemical functionality using click chemistry without degradation of polymer backbones. The clicked degradable polylactides have thermo-responsive properties with lower critical solution temperatures (LCST) from room temperature to 68 oC. The prepared amphiphilic copolymers, mPEG-b-polypropargyloxylactide were self-assembled into micelles which were core cross-linked to improve the structural stability of the micelles with better controlled release of cargo molecules and response to the reducing reagent.The relationship between the glass transition temperature (Tg) of polylactide and its backbone structure was studied. The direct attachment of rigid and bulky substituents can be used to tune the Tg and thermal properties of polylactides and broaden the scope of their physical properties.Silica nanoparticles (SiNPs) have attracted much attention due to their chemical inertness, low or non toxicity, excellent thermal stability and especially, easy access of surface functionalization. A facile grafting route was developed to prepare stably mono-dispersed SiNPs in aqueous media via click chemistry. Different sized SiNPs were grafted with a broad range of surface chemistries (carboxylic acids, amines, alcohols and methoxy-terminated polyethylene glycol chains). The resulted SiNPs were purified by dialysis and stably dispersed in water and in vitro cell culture media with narrow size distributions and no aggregation.
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