Cucurbit[6]uril dimer induces supramolecular polymerisation of a cationic polyethylene glycol derivative

Abstract

Recently, we reported the synthesis of two new dimeric cucurbit[6]uril compounds (1 and 2). Herein, we describe the ability of compound 1 to undergo supramolecular polymerisation when combined with polyethylene glycol (PEG) derived divalent guests 3_MW (MW = 300, 1000, 3350, 10,000). Interestingly, we find that the shorter PEG-derived guests 3₃₀₀, 3₁₀₀₀ and 3₃₃₅₀ lead to low degrees of oligomerisation based on the diffusion coefficients obtained by diffusion-ordered spectroscopy measurements. In contrast, when 1 was combined with the longest PEG-derived guest 3_10,000, we observed the formation of a supramolecular polymer with a degree of oligomerisation of at least 36. We observe that the supramolecular polymer 1_n·(3_10,000)n undergoes a slow decrease in its degree of oligomerisation to 22 over the course of 14 days controlled by the slow dissociation rate constant of the hexanediammonium unit of 3_10,000 from the CB[6]-sized cavity of 1.

Keywords::

• cucurbituril
• supramolecular polymer
• polyethylene glycol
• DOSY

Acknowledgements

The authors thank the National Science Foundation (CHE-1110911 to L.I.), the Department of Education (P200A090105, GAANN fellowship to J.B.W.) and the University of Maryland (University Fellowship to J.B.W.) for financial support.

Notes

^1. For the molecular weights of 3_MW we used the average molecular weight of the PEG oligomer minus two OH groups plus the weight of the two ⁺H₃N(CH₂)₆NH₂ + arms; MW(3₃₀₀) = 500, MW(3₁₀₀₀) = 1200, MW(3₃₃₅₀) = 3550, MW(3₁₀₀₀) = 10,200.