Versatile Strategy for the Synthesis of Hyperbranched Poly(ε-caprolactone)s and Polypseudorotaxanes Thereof

A novel class of hyperbranched poly(epsilon-caprolactone)s (HPCLs) and polypseudorotaxanes (HPPRs) thereof was synthesized through the polycondensation of AB(2) type poly(epsilon-caprolactone) or polypseudorotaxanes macromonomers with alpha-thiol and omega-alkyne terminal groups (thiol is A unit, and each pi bond in alkyne is B unit) by using thiol-yne chemistry. Their molecular structures and physical properties were characterized in detail by FT-IR, NMR, time-of-flight mass spectrometry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. The molecular weights of HPCLs gradually increased over the irradiation time, while weight-average molecular weight grew faster than number-average molecular weight, resulting in broadening their polydispersities. The cross-linking side reaction occurred in the polycondensation of poly(epsilon-caprolactone) with alpha-thiol and omega-alkyne terminal groups (PA-PCL-SH); however, this side reaction was prohibited if PA-PCL-SH was completely threaded by alpha-cyclodextrin to form the rigid polypseudorotaxanes. Both the maximal melting point and the crystallization point of HPCLs gradually decrease with increasing their molecular weights, and they are in the order of PA-PCL-SH > HPCL-3 > HPCL-6 > HPCL-10 > HPCL-15 > HPCL-30 (the number within sample denotes the irradiation time used). Furthermore, the degree of crystallization of HPCLs decreases from 51.4% to 30.4% with increasing the molecular weights.