Self-Assembly of Precision Polyolefin Block Copolymers and Sugar-Polyolefin Conjugates
Nowak, Samantha Raina
Sita, Lawrence R
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Self-assembling materials have become ubiquitous in modern society. Thus, a great challenge exists in developing nonpolar building blocks for self-assembling materials in a simple, efficient, and scalable manner. It is also important to find new ways in which to utilize such building blocks in a versatile manner. In this work, precision polyolefins and end-group functionalized poly(-olefinates) (x-PAOs) were successfully used as simple, easily accessible nonpolar building blocks for the development of new nanostructured materials. Specifically, living coordination polymerization (LCP) was employed to generate well-defined crystalline-amorphous BCPs. Although the low degree of incompatibility between the two hydrophobic blocks would typically prevent microphase separation, the high degree of conformational asymmetry between the blocks was sufficient to induce the formation of nanostructures. Additionally, x-PAOs were used as macroinitiators for ring-opening polymerization to produce self-assembling amphiphilic polyolefin-b-polyester diblock copolymers. The development of nanostructured ‘smart’ materials that can respond to external stimuli on practical time scales and moderate conditions also remains a challenge and is a topic of great academic and industrial interest. For thermoresponsive systems in the solid-state, the goal of establishing extremely low kinetic barriers for order-to-order nanostructural transitions has not yet been reached. Notably, the synthesis and characterization of a new class of low molecular weight atactic sugar-polyolefin hybrid conjugates was carried out, and the study demonstrated that these new materials can meet this challenge. These amphiphilic hybrid conjugates consist of hydrophobic x-PAO “tails” chemically tethered to hydrophilic saccharide “head” groups and display organized nanostructures in the bulk and within ultra-thin films with sub-10 nm features. The conjugates studied displayed a rich and dynamic self-assembly behavior in the form of multiple ‘order-to-order’ phase transitions within the bulk and ultrathin-films (< 100 nm), which were investigated by SAXS/GISAXS with a synchrotron x-ray source as a function of temperature. These results demonstrate the utility of sugar-polyolefin conjugates as nanostructured smart materials for nanotechnological applications and show that precision polyolefins and x-PAOs are excellent nonpolar building blocks for self-assembling materials.