Macrocycles, 7. Cyclization of oligo- and poly(ethylene glycol)s with dibutyltin dimethoxide - a new approach to (super)macrocycles

Abstract

SUMMARY: When commercial oligo-or poly(ethylene glycol)s and dibutyltin dimethoxide were condensed in bulk with elimination of methanol, no linear polycondensates were obtained and tin-containing macrocycles were the only reaction products. In order to improve the hydrolytic stability, stoichiometric amounts of cthiobutyrolactone were inserted into the macrocyclic oligoethers, so that the Sn1O bonds were transformed into Sn1S bonds. The formation of monomeric (containing one Bu 2 Sn group) macrocycles was confirmed. The tin-containing macrocyclic polyethers were used as macrocyclic initiators for the ring-expansion polymerization of e-caprolactone. The resulting macrocyclic poly(ether-ester)s were isolated in the form of telechelic A-B-A block copolymers after precipitation into methanol.

Cyclic polymers: Synthetic strategies and physical properties

“…140 Hence, this preparation of tin-containing cyclic polyether is a TCP for two reasons. The polycondensation reaction is itself an equilibration and the cyclic reaction products are involved in an alkoxide exchange equilibration via DA-interaction.…”

“…First, two lactones were polymerized in a sequential manner, under conditions preventing transesterification. 231 Second, a cyclic Bu 2 Sn-containing polyether derived from poly(ethylene glycol) (Scheme 39, 1st eq) 140 from a polysiloxane (Scheme 49) 231 or from poly(tetrahydrofuran) diol (Scheme 50) 232 was used as ''macroinitiator,'' so that a cyclic poly(ether ester) was obtained. Polycondensation of such cyclic diblock copolymers yielded multiblock copolymers (Scheme 50, 2nd eq), which partially consist of cyclic species like all polycondensates of linear monomers (see Chapter 2).…”

Macrocycles, 16. Macrocyclic Dibutyltin Dicarboxylates via Thermodynamically Controlled Polycondensations

“…This conclusion is based on a comparison with, for example, cyclic tin-containing oligoethers. [11,12] In order to characterize the molar masses of products 6 a-h more accurately, the following analytical methods were applied: vapor pressure osmometry (VPO) in chloroform, classical mass spectrometry, fast-atom bombardment (FAB) mass spectrometry and MALDI-TOF mass spectrometry. The VPO data obtained from chloroform solutions (Table 1) were somewhat lower than those revealed by cryoscopic measurements reported by Andrews et al [13] on the basis of the Rast method.…”

“…More recently, Kricheldorf and coworkers [11,12] have studied the polycondensation of dibutyltin dimethoxide with monodisperse or polydisperse oligo(ethyleneglycol)s. Macrocycles of structure 3 (see Scheme 2) were obtained and no polymers regardless of the length of the oligo(ethylene oxide)s (up to M -n 2 000). [11,12] Considering thermodynamic control, it is obvious that entropy favors numerous cycles at the expense of one large polymer. Yet, again no indication of a Jacobson-Stockmeyer distribution of cyclic oligomers was found.…”

New Polymer Syntheses, 108. Controlled Degradation and In-Situ Functionalization of Polycarbonates by Means of Bu2SnO

“…Analogous results were obtained from various oligo-and poly(ethylene oxide) diols. [9] The reasons why in the case of poly(tin-alkylene oxide) the smallest possible macrocycles are thermodynamically favored over linear (or cyclic) polymers are twofold. Firstly, a population of strain-free cycles is favored over high-molecular weight polymers for reasons of entropy.…”