Synthesis of amphiphilic block copolymers.
Subramanian Alamelu Suriya.
Date of Issue2008
School of Materials Science and Engineering
The importance of amphiphillic block copolymers is emphasized by the ability of such materials to demonstrate molecular self assembly by phase segregation due to the incompatibility between the chemically different segments. Segregation here is limited to microphase as the opposing entities are covalently bonded and thus giving rise to well defined structural morphologies of nano order. Such self assembled constructions have potential applications as templates for synthesis of other nanomaterials, over which there is poor control in size and form. The project includes the synthesis and characterization of new block copolymers with biodegradable and hydrophobic segments and biocompatible hydrophillic segments through sequential controlled polymerization routes, study of solution properties of such copolymers and the evaluation of their assembly behavior. Copolymer synthesis comprises the polymerization of e-caprolactone monomers by ROP and subsequent copolymerization of DMAEMA onto PCL by ATRP. The copolymer chemical structures were evaluated by NMR, GPC and FTIR analysis. The temperature transitions of the polymers were evaluated by DSC. Solution behaviour of copolymer micelles was studied using DLS and the assembled structures were observed by TEM and AFM. Copolymers of targeted molecular weights in the range 6000-16000 g/mol were obtained through the optimization of ATRP synthesis conditions. The weight fraction of hydrophillic segments was varied between 20 and 80 percent. More than one type of aggregates was consistently observed in aqueous copolymer solutions whose diameters were in the ranges 20-50nm and 90-200nm. Micelles sizes show concentration and pH dependence while the morphology of the self assembled structures is controlled by pH and PDMAEMA content. Well defined biocompatible and partially biodegradable copolymers with narrow molecular weight distributions have been synthesized and shown to have stable self assembly behavior.