Effects of Side-Chain Structure and Solvent on Intramolecular Hydrogen Bonding in Isotactic Poly(methacrylamide)s

Abstract

ABSTRACT:Intramolecular hydrogen bonding in isotactic poly(methacrylamide)s, i.e., poly[(S)-1-phenylethyl methacrylamide] (1) and isotactic poly[(S)-1-(1-naphthyl)ethyl methacrylamide] (2), was examined by IR, 1 H NMR, and CD in non-hydrogen bonding and hydrogen bonding solvents and in mixtures thereof. Isotactic 1 was found to form intramolecular hydrogen bonds more extensively than isotactic 2; the former even forms a stable hydrogen-bonded structure in a hydrogen bonding solvent, i.e., dioxane, suggesting that the phenyl groups as well as the methyl groups in the side chains provide adequate steric effects for stabilization of the hydrogen-bonded structure. Formation, in solution, of helical structures of one prevailing handedness with specific chromophore orientation is suggested. The hydrogen-bonded structures were found to break down on addition of a helix-breaking solvent, trifiuoroacetic acid.KEY WORDS Poly(methacrylamide) I Intramolecular Hydrogen Bonding I Solvent Effects I Circular Dichroism IAs part of our continuing study of control of side-chain chromophore orientation in polymers to devise "molecular wires" capable of transporting excitation energy and charge one-dimensionally along the polymer chain, 1 • 2 we have previously prepared isotactic poly(methacrylamide)s, i.e., poly(l-naphthylmethyl methacrylamide) and poly[(S)-1-(1-naphthyl)ethyl methacrylamide], and showed that they undergo extensive intramolecular hydrogen bonding among the side-chain amide groups in non-hydrogen bonding solvents such as chloroform and 1 ,2-dichloroethane (EDC) while the corresponding atactic ones do so only partially. 3 Accordingly, isotactic and atactic poly[(S)-1-(1-naphthyl)ethyl methacrylamide] were found to give markedly different circular dichroic (CD) spectra in EDC; rather strong Cotton effects observed with isotactic poly[(S)-1-(1-naphthy1)-ethyl methacrylamide] suggest the formation of a regular secondary structure, e.g., a one-handed helix, leading to a specific side-chain orientation. A high isotacticity was found to be required for extensive formation of intramolecular hydrogen bonds and hence formation of the regular secondary structure. It was also found that the methyl groups, introduced in the side chains to provide chiral centers in poly[(S)-1-(1-naphthyl)ethyl methacrylamide], have favorable steric effects on the stability of the hydrogen-bonded structure.In the present study we examined the dependence of intramolecular hydrogen bonding on the solvent and on the side-chain chromophore structure using isotactic poly[(S)-1-phenylethyl methacrylamide] (1) as well as isotactic poly[(S)-1-(1-naphthyl)ethyl methacrylamide] (2). Isotactic 1 was found to form intramolecular hydrogen bonding even to a larger extent than isotactic 2. We also found that isotactic 1 forms stable intramolecular hydrogen bonds even in a hydrogen bonding solvent, i.e., dioxane, suggesting that the phenyl t To whom correspondence should be addressed. 910groups as well as the methyl groups in the side chains provide adequate ster...

Secondary Structure and Side-Chain Chromophore Orientation of Isotactic Poly(methacrylamide)s in Solid Film

“…The positive peak at ca. 230 nm, which we assigned to the n-n * absorption band of the side-chain amide groups in the fully hydrogenbonded structure in solution, 11 however, is weaker than that in EDC. As the IR spectrum suggests, some of the fully hydrogen-bonded structures are destroyed during film formation.…”

Observation of optical activity in polythiourethane obtained by the controlled cationic ring‐opening polymerization of chiral cyclic thiourethane derived from serine

“…This is the accurate design strategy of nature for constructing biopolymers with specific functionality. The well‐integrated nature of biopolymers has prompted many researchers to develop synthetic polymers with controlled high‐order structures, including poly(triphenylmethyl methacrylate),1 polyisocyanides,2 polyacetylene derivatives,3 polypeptides,4 and poly(methacrylamide)s 5. For example, isotactic poly(methacrylamide)s and poly( N ‐propargyl carbamate)s3(c) have been reported to possess helical conformations that are stabilized by the intramolecular hydrogen bonds between the NH groups and the carbonyl groups.…”

“…This type of polyadditions does not seem appropriate for constructing polyurethanes and polythiourethanes with highly ordered structures because AA chiral monomers inherently possess neither head nor tail. To solve this problem, we developed polyurethanes and polythiourethanes with controlled chirality in the main chain by self‐polyaddition5 and ring‐opening polymerization,6 respectively.…”

Supramolecular Helix–Helix Block Copolymers

“…Similarly the amide carbonyl CO stretch ranges from 1660 to 1620 cm −1 with lower wavenumbers denoting a more hydrogenbonded structure. 61,62 Homopolymer Ba-Poly-3 shows an amide N−H stretch at 3448 cm −1 with a broad shoulder around 3370 cm −1 and a carbonyl CO stretch at 1652 cm −1 suggestive of a partially intrachain hydrogen-bonded structure (Figure S41). Poly(isocyanide), HW-Poly-1, contains side chains with ester linkages and therefore does not utilize intrachain hydrogen bonding for helix stabilization.…”