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...

KEY WORDSPoly(methacrylamide) / Intramolecular Hydrogen Bonding / Secondary Structure / Circular Dichroism / The photoprocesses of polymers differ from those of isolated low-molecular-weight analogues 1: excitation energy can be transported in the polymer through the pendant chromophores as in crystals or concentrated solutions of low-molecular-weight analogues 2 • Excitation energy, however, can be trapped as excimers (excited dimers) which are formed with pairs of chromophores suitably situated for their formation along the polymer chain. The chromophore interactions in the excited state, i.e., excitation energy transport and trapping, are affected by the stereoregularity and conformation of the main chain 3 as well as by the steric hindrance introduced in the side chain. 4 While it is not fully understood how these structural differences actually affect energy migration and excimer formation, one may be able to enhance the former and suppress the latter if one properly controls the orientation of the chromophores along the polymer chain. If this is possible, "a molecular wire" will be obtained which allows efficient one-dimensional transport of excitation energy along the polymer chain. Studies along this line have been carried out using polypeptides where side-chain chromophores are arranged at regular intervals along the helical main chain. 5 Previously, we have prepared poly(L-glutamines) where naphthalene chromophores are introduced in the side chain via amide linkage and examined how the sidechain structure affects the hydrogen bonding interactions among the side-chain amide groups and subsequent ordering of the side-chain chromophores. 6 In the present study we prepared isotactic and atactic polymethacrylamides, i.e., poly(l-naphthylmethyl methacrylamide) (1) and poly[(S)-1-(1-naphthyl)ethyl methacrylamide] (2), where naphthalene chromophores are likewise introduced in the side chains via amide linkage and examined how the stereoregularity and the side-chain structure affect the hydrogen bonding interactions among the side-chain amide groups and the subsequent orientation of the side-chain chromophores.