STAR-SHAPED POLYMERS BY LIVING CATIONIC POLYMERIZATION .4. SELECTIVE HOST GUEST INTERACTION OF SMALL MOLECULES BY AMPHIPHILIC STAR-SHAPED POLYMERS OF VINYL ETHERS

Amphiphilic star-shaped block polymers (1) of vinyl ethers, prepared by living cationic polymerization, were found to interact with small organic molecules (guests) with polar functional groups. The occurrence of the host-guest interaction was judged from reduction of the C-13 NMR spin-lattice relaxation time (T1) of the guest molecules upon mixing with the host polymer 1 in CDCl3 at 30-degrees-C. With star polymer 1a, {H[-CH2CH(OCH2CH2OH)]m-[CH2CH(OiBu)]n}f-(core) (m = 10, n = 29, f = 8 arms/molecule), for example, the T1 of the aromatic carbons of benzoic acid (3) and methyl 3-hydroxybenzoate (5) decreased but those of ethyl benzoate (7) and n-pentylbenzene (8) remained unchanged. Thus, 1 could interact specifically with the guests carrying functional groups that are capable of forming hydrogen bonds with the hydroxyl groups of 1. Similar host-guest interactions were also observed for amphiphilic heteroarm star polymers, where two sets of homopolymer arm chains (hydrophilic and hydrophobic) were attached onto a single core. The host-guest interaction is also selective; when an equimolar mixture of 3 and 8 was brought into contact with 1a in CDCl3,3 interacted with la, whereas 8 was not complexed. The T1 of 3 also decreased with the increasing mole ratio of the hydroxyl groups in 1 to the guest molecule.