Synthesis and Preliminary Characterization of Some Polyester Rotaxanes

Abstract

A series of polyester rotaxanes containing polysebacate backbones [decamethylene, tri(ethyleneoxy), and 1,4-butylene] and ethylene oxide-based crown ethers [30-crown-10,42-crown-14,60-crown-20, and bis(p-phenylene)-34-crown-101 was synthesized via step growth polymerizations using diacid chloride-diol and transesterification reactions. The polyrotaxanes were purified by multiple reprecipitations in good solvents for the crown ethers, and the physical linkage of the crown ether to the polymeric backbone was confirmed by a variety of experiments, including hydrolysis, NMR, GPC, and VPO. Up to 55 wt % macrocycle was incorporated, depending on the size and shape of the macrocycle and the feed ratios employed. In all cases, the solubilities of the polyrotaxanes were strongly influenced by the cyclic component; enhanced solubilities in polar solvents were observed relative to the simple parent polysebacates. Mark-Houwink K and a values were also strongly affected by rotaxane formation; in the case most thoroughly investigated, K decreased by almost 2 orders of magnitude and a doubled. Interpretation of this observation is complicated by the changes in solubility. Thermal behavior was also affected. In the tri-(ethyleneoxy) system, Tg is lowered in the rotaxanes; in the 60-crown-20 system, the macrocycle crystallized! The poly(buty1ene sebacate) 60-crown-20 and 42-crown-14 systems also possessed two crystalline phases, a crown ether phase and a poly(buty1ene sebacate) phase. These exciting result demonstrate the mobility of the macrocycle along the polyester backbone in melt and solution states, allowing aggregation and crystallization without dethreading.

Polyrotaxanes: Past, present and future

“…7). All of the cunent polysebacate rotaxanes except that from 30-crown-I0 (only 1.5 mass %) displayed DSC melting transitions for both the crown ether and the backbone.…”

“…6) and polyesters (Ref. 7). In all of these syntheses the cyclic component, the crown ether, comprised a major, if not the sole, component of the solvent for polymerization, in an attempt to achieve high incorporation rates of the threaded macrocycles into the resuitant polymer.…”

Continuous beds (monoliths): stationary phases for liquid chromatography formed using the hydrophobic interaction-based phase separation mechanism

“…Self-assembly of the polyrotaxanes and their characterization was recently reviewed by Harada [62]. Polyrotaxanes can be formed as side chain or main chain polyrotaxanes [63]. They can be formed with the macrocyclic molecules mechanically interlocking in the crosslinked linear polymer network as insoluble solids (for instance, gels) [64].…”

Synthesis, dynamic mechanical, and solid-state NMR spectroscopy of crown-ether-based linear aliphatic polyurethane rotaxanes

“…This clean mixture was obtained from the crude reaction mixture following a series of extractions. Since it has been shown repeatedly that 18c6 will not thread a polymethylene chain 26,27) , the 18c6/36c12 mixture was used without further purification.…”