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Tacticity of Poly(vinyl alcohol) 577 methyl radicals with ethylene.13 The very small fraction of ethyl branches for which there is ,3C evidence may be introduced via the extension of the Roedel mechanism described by Willbourn;1 this must now be regarded as a reaction of (13) A.

A new type of monomer, called Imprinter, combined with its copolymerization with a stimulisensitive monomer, allows gels with receptor sites of reversible affinity to be created. Imprinter-Q is a dimeric monomer that has two cationic groups linked by a 1,2-glycol bond, which is easily cleavable. Weakly cross-linked gels have been prepared using Imprinter-Q, N-isopropylacrylamide, and cross-linker N,N′-methylenebis(acrylamide). After breaking the 1,2-glycol link, the members of each cationic pair are close together, and they can capture target molecules via a multiple-point electrostatic interaction. The higher affinity of these gels for disodium nitroisophthalate (NPA) or dipotassium naftalenedicarboxylate (NDC) in comparison with control gels, which were prepared with randomly distributed cationic groups, proved that the gels prepared with Imprinter-Q memorized the position of the pairs of cationic groups after swelling and reshrinking. Although the efficient adsorption was expected to depend on the correspondence between the spacing of the two juxtaposed cationic groups of the gel and the spacing of the two anionic groups of the adsorbate, it was found that NPA and NDC (carboxyl spacing 60% longer than in NPA) are adsorbed with similar efficiency. The control gels experienced difficulty in forming pairs, and their affinity for NPA or NDC decreased exponentially as a function of cross-linker concentration. In contrast, the topological constrains were completely absent in the imprinted gels, showing that memorization had been achieved. This "conformational imprinting effect" was tested for several concentrations of Imprinter-Q and permanent cross-linkers.

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