Synthesis of well-defined complex polymer architectures by iterative growth

Abstract

The 'pursuit of precision', inspired from nature's relationship between molecular structure and physiological function, has led to the conception of complex architectures. 'Living' radical polymerization (LRP) produces polymer building block precursors with a chemical functionality on either end of a linear polymer chain, and in combination with near-quantitative 'click' reactions, provides a facile method to construct structurally diverse architectures such as cyclics, dendrimers, stars and bio/inorganic-hybrids. Building complex polymer architectures has been driven by the quest to obtain new and predictable solution and bulk properties. Incorporating sequence control into these architectures through the judicious choice of monomer or macromers will have the potential to create advanced polymer materials with unique properties and functions that are commonly found in biological systems. This will lead to material design with potential applications as adaptive materials, catalysts, and use in vaccine and drug delivery.First, a series of symmetric and asymmetric complex polymer architectures were synthesized from polystyrene PSTY building blocks. Two PSTY building blocks of similar molecular weight were synthesized using ATRP. The telechelic building block consisted of a halide group on one end and both a hydroxyl and alkyne group on the other end. These telechilic polymer chains were coupled togather by sequential growth to produce three, four or seven HO-functionalities equally spaced along the polymer backbones. The key was to maintain the halide end-group on the telechelic polymer chain during the CuAAC coupling reaction after each sequential growth. This was accomplished by using the combination of the PMDETA ligand and toluene as a solvent to produce significantly faster rates of CuAAC coupling reaction over halide abstraction. The HO-functionalities were then converted to azide groups allowing further CuAAC reactions with either alkyne polymeric dendrons or cyclics to produce equally spaced grafts along the backbone. The relative hydrodynamic volume ratios of these grafted structures to their corresponding linear analogues were lower but similar to that found from the graft (i.e. dendron or cyclic) itself. Moreover, the same relative change in the hydrodynamic volume was independent of the number of grafts, suggesting that by combining many dendrons or cyclics on a polymer backbone, the effect on the coil conformation was minimal. This methodology was further extended to produce an asymmetric block copolymer consisting of one block with two dendron grafts and the other block with two cyclic grafts.Then, a new iterative sequential growth (ISG) strategy was developed which allows the synthesis of sequence defined polymers by direct azidation of alcohols. Four low molecular weight macromers of PSTY, poly(t-butyl acrylate) P t BA, and poly(methyl acrylate) PMA were prepared by either ATRP or SET-LRP with low dispersity values and poly(ethylene glycol) PEG was obtained from a commercial source. The mac...