Architectural studies of macromolecules: Syntheis and mass spectral characterization of linear, cyclic, and star polyesters
Description
Cyclic polyesters are of interest, as cyclic topology imparts unique physical properties when compared to linear analogs. The production of high purity cyclic poly(epsilon-caprolactone) (PCL) is achieved by copper catalyzed 'clicking' of &agr;-azido-&ohgr;-alkyne functionalized linear PCL through a cycloaddition reaction resulting in no change of mass of the polymer. Through development of improved methods of calibration, end group mass calculation, and metastable byproduct characterization, the structure of the linear precursor and cyclic products could be defined by MALDI-TOF MS, as well as GPC and NMR. For the first time, MALDI methods were developed to show that the hydrolytic degradation of cyclic PCL is retarded when compared to its linear counterpart, while simultaneous monitoring of the degradation by GPC showed an initial increase in solution volume for the cyclic PCL, offering potentially intriguing material and biomedical applications. Cyclic architecture caused no appreciable change in thermal degradation temperature. Tm and Tc are also consistently higher for cyclic PCL. The gas-phase ion volume, as observed by drift time in ion mobility spectrometry-mass spectrometry (IMS-MS) is smaller for cyclic PCL than linear PCL, and thus IMS-MS is a powerful technique for confirming change in architecture where there is no m/z difference. To this end, a library of various polyester architectures (linear, cyclic, star, and dendrimer) were examined via IMS-MS to correlate architecture to drift time, and IMS-MS is shown to be a powerful tool to elucidate architecture of polymers with respect to molecular weight