Narrow polydisersity cyclic poly(caprolactone) was synthesized by cyclization of linear R, ω-functionalized poly(caprolactone). The linear precursors were prepared via ring-opening polymerization from an azido-functionalized initiator, followed by end group modification to attach a terminal alkyne. Click coupling afforded the cyclic polymer in high yields and provided linear and cyclic poly(caprolactone) with exactly identical molecular weight distributions. The thermal and acid-catalyzed degradation of analogous linear and cyclic poly(caprolactone) samples were investigated to determine the effect of architecture.

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While amphiphilic block copolymers have demonstrated their utility for a range of practical applications, the behavior of cyclic block copolymers remains largely unexplored due to limited synthetic access. To investigate their micelle formation, biocompatible cyclic amphiphilic poly(ethylene glycol)-polycaprolactone, c-(PEG-PCL), was synthesized by a combination of ring-opening polymerization (ROP) and click chemistry. In addition, exactly analogous linear block copolymers have been prepared as a control sample to elucidate the role of polymer architecture in their self-assembly and acid-catalyzed degradation.

Novel nanocomposites were prepared by blending linear or cyclic poly(ε-caprolactones) with two types of chemically modified carbon nanotubes (CNTs). The low-polydispersity cyclic PCL samples (C-PCLs) were synthesized by click chemistry with a number-average molecular weight (M n) of 22 kg/mol. Linear analogues (L-PCLs) with the same M n value were also prepared. Two types of CNTs were employed (with 1% w/w content): single wall CNTs functionalized with octadecylamine (SWNT-ODA) and multiwall carbon nanotubes grafted with linear PCL chains (i.e., MWNT-g-PCL prepared by ring-opening polymerization on previously functionalized MWNTs with a composition of 10% MWNT and 90% L-PCL). The nanocomposites were characterized by transmission electron microscopy (TEM), polarized light optical microscopy (PLOM), and differential scanning calorimetry (DSC). A nucleating effect was detected in both PCLs when SWNT-ODAs were employed. However, in the case of MWNT-g-PCL, the nanofiller nucleated L-PCL but caused an unexpected antinucleation effect on C-PCL. Another interesting behavior displayed by this novel C-PCL/MWNT-g-PCL nanocomposite (composed of 90% C-PCL, 9% L-PCL, and 1% MWNTs) was not only a reduction in nucleation density and in T c temperatures during cooling from the melt, as expected for an antinucleating agent, but also a decrease in spherulitic growth rate and in overall isothermal crystallization kinetics as compared to C-PCL. The results were explained by realizing that new topological effects were created upon mixing the grafted L-PCL chains within MWNT-g-PCL with C-PCL molecules. When these linear chains come into contact with cyclic PCL chains, a threading effect is produced that dramatically affects chain dynamics by forming a transient entanglement network. As a consequence, cyclic molecules relax and diffuse more slowly than anticipated, decreasing both nucleation and growth kinetics. Results on linear and cyclic PCL blends are also presented here, and they support our explanation of the unexpected antinucleation effect reported for C-PCL/MWNT-g-PCL nanocomposites.

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An extra dimension of polymer analysis: ion mobility spectrometry-mass spectrometry (IMS-MS) separates ions according to their size in the gas phase, allowing differentiation of linear and cyclic polymeric isomers. This analytical technique is a rapid and sensitive method for assessing cyclic polymer purity in one step. As highly pure cyclic polymers are crucial for adequately assessing architecture dependent properties, IMS–MS offers great promise in the characterization of this unique class of polymers.