Synthesis, characterization and application of polymers with diverse architectures and properties
Description
Functional polymers and soft materials are of interest due to the ability to easily tune their physical and biological properties to address needs in a range of fields. Recent development of 'click' reaction, especially the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, enables the synthesis of complex architectures of polymers easier than traditional methods In order to characterize the polymers accurately, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was utilized with a rigorous calibration to insure the precision of mass measurements. Mathematical models were investigated to optimize the accuracy of characterization for both the repeating units and end groups of polystyrene. Further studies on polymers containing azide end group revealed the evidence for formation of the metastable ion during the MALDI-TOF MS, using azido-polystyrenes (PS) and azido-poly(ethylene glycol) (PEG) as examples 3, 6 and 12-arm star polymers were prepared by coupling well-characterized azido- PS and azido-PEG to a series of alkynylated dendritic cores. Various methods of purification were explored to remove trace amount linear polymers. MALDI-TOF MS was employed to verify that the structures of star polymers exhibited narrow distributions, as well as average molecular weights, and expected residual masses that agreed with theoretical calculations. 3-arm star block copolymers were synthesized and characterized as well Using the similar CuAAC condition, the surface of deep-cavity cavitands were modified with a variety of azido-functionalized polymer side chains. The modification with monodiperse azido-PEG and azido-G-3-dendron generated truly monodisperse products, as confirmed by MALDI-TOF MS. Water-solubility was imparted on the cavitand by grafting 2k PEG side chains, while maintaining the properties of encapsulation of small guest molecular such as dodecane The combination of CuAAC and MALDI-TOF MS enabled the identification of trace amount of dimeric products formed during the synthesis of cyclic PEG, which can be used to optimize the preparation of such cyclic polymers. Initial results confirm that the impurities are cyclic dimers rather that linear or concatenanted dimers. In addition, CuAAC were applied for the PEGylation of solid surface, such as group IV elemental nanoparticles and carbon hard spheres, which verified the versatility of this reaction in the preparation of functional materials