Thermal polymerization of DL‐α‐lipoic acid (LPA) in bulk without any initiator proceeded easily above the melting point of LPA. The molecular weight polymer determined by GPC was high. From the 1H NMR spectra of polymers, poly(LPA) obtained from polymerization of high purity LPA was to consist of cyclic structures, which was confirmed by ESI‐MS. Interlocked polymer consisting of poly(LPA) and dibenzo‐30‐crown‐10 entangled with each other was synthesized by the polymerization of LPA in the presence of dibenzo‐30‐crown‐10. From the DSC analysis of the polymers, glass transition temperature was estimated to be about −11 °C, but melting point was not observed, indicating that poly(LPA) is an amorphous polymer. By photodecomposition of poly(LPA), Mn was rapidly decreased at the early stage of the decomposition. After that, the Mn of the polymer kept and then was almost constant even for a prolonged reaction time. On the basis of the results, it would be presumed that poly (LPA) obtained form polymerization of high purity LPA includes an interlocked structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis and characterization of polymers obtained from polymerization of 1,4-dihydro-2,3-benzodithine (XDS) were investigated. The polymerization of XDS proceeded at reaction temperatures above the melting points of XDS to give polymers, and the molecular weight, which determined by GPC was high. From the structural analysis of poly(XDS), the polymer was found to have cyclic structure, in contrast to their linear polymer (poly(XDS-XDT) obtained from the polymerization of XDS in the presence of chain transfer thiol compounds such as , 0 -mercapto-o-xylene (XDT). From TGA and DSC measurements, poly(XDS) with benzene rings in the main chain is more thermal stable than the polymer obtained from the polymerization of 1,2-dithiane (DT). From dynamic viscoelastic measurements, poly(XDS) showed a rubbery plateau under the molten state even though poly(XDS) has no crosslinking system. The difference in solubility between poly(XDS) and poly(XDS-XDT) was also observed. On the basis of the polymer characterizations, it may be concluded that the poly(XDS) obtained from thermal ring-opening polymerization of XDS includes a polycatenane structure.KEY WORDS: Ring-Opening Polymerization / 1,4-Dihydro-2,3-Benzodithine / Cyclic Polymer / Polycatenane Structure / Cyclic Disulfides / Thermal Decomposition / Recently, much attention has been paid to topologically unique macromolecules containing a single cyclic and multicyclic polymer unit from the viewpoints of not only their distinctive properties that is different from linear polymers, but also elements of architecturally complex polymers and interlocked macromolecules such as polyrotaxanes and polycatenanes.1-11 Many studies on synthesis of cyclic polymers in the polymerizations have been also reported.12-26 Although efficient synthesis of rotaxanes and catenanes have been achieved, 27-37 a high molecular weight polycatenane which consists of only ring components has not been synthesized. Recently, Takata et al. reported that the Diels-Alder polymerization of [2]catenane bearing diene and dienophile moieties on each ring afforded a ''bridged polycatenane'' with a poly[2]catenane skeleton. 38 Many approaches have been reported to prepare polymers containing disulfide linkages in the main chain. [39][40][41][42][43][44][45][46] Ringopening polymerization of cyclic disulfide compounds is one method for synthesizing such polymers. Although many studies on the polymerizations of cyclic disulfides were reported since the second half of the 1940s, 39,40 the detailed structural analyses and characterizations of the resulting polymers have not been investigated for a long time. Recently, we reported the thermal polymerization of 1,2-dithiane (DT) and detailed structural analyses and characterizations of the resulting polymers. From analyses of the polymer, the cyclic structure was formed mainly by a backbiting reaction of propagating species. [44][45][46] We also reported that a polycatenane structure composed of interlocking system by entanglements with cyclic polymers was formed durin...