Constrained polymer chain behavior observed in their non-stoichiometric cyclodextrin inclusion complexes

Abstract

Much has been learned from inclusion compounds (IC’s) formed between guest polymers and host cyclodextrins (CDs) [polymer-CD-ICs] by examining the properties of the fully covered guest polymers, as well as those coalesced neat bulk samples of guest polymers obtained upon removal of the host CDs. However, what can be gained from studying the properties of the restrained unthreaded portions of polymer chains that “dangle” from non-stoichiometric (n-s)-polymer-CD-IC’s? We attempt to assist in answering this question by observing (n-s)-polymer-CD-IC’s formed between amorphous atactic-poly(methyl methacrylate) (PMMA) and γ-CD, as well as the IC formed between a synthesized poly(e-caprolactone)-poly(propylene glycol)-poly(e-caprolactone) (PCL-PPG-PCL) triblock copolymer and β-CD, which was presumed to have threaded and unthreaded PPG and PCL blocks. Though our (n-s)-PMMA-γ-CD-IC samples were found to exhibit extremely heterogeneous behaviors, glass transition temperature increases of up to 27 °C above that of neat PMMA were observed. X-ray diffraction data indicates modest γ-CD crystallinity at partial coverages of PMMA, with a crystal structure similar to that of the IC with full coverage. On the other hand, XRD, DSC and FTIR data revealed an almost total disruption of PCL block crystallinity upon complexation of PCL-PPG-PCL with β-CD, suggesting either partial threading and coverage of the PCL blocks by β-CD or their partial mixing with the PPG blocks covered with β-CD.