The thermal degradation of poly(oxycarbonylpentamethylene), (poly-E-caprolactone), (3), was investigated at 220°C and 80 mm Hg under nitrogen. 3 was found to be thermally much more stable than poly(oxycarbonylethylene), (poly-8-propiolactone), (l), although it decomposed faster than poly(oxycarbonyl-1,l-dimethylethylene), (polypivalolactone), (2). The reaction was of the first order with a rate constant of k=6,2.10-4 min-' and proceeded via a "zipper mechanism" to yield monomeric E-caprolactone. ZUSAMMENFASSUNG:Der thermische Abbau von Poly(oxycarbonylpentamethylen), (Poly-~-caprolacton),(3), wurde bei 220°C im Stickstoffstrom bei 80 mm Hg untersucht. Dabei wurde gefunden, dalj 3 thermisch wesentlich stabiler als Poly(oxycarbonylathylen), (Poly-b-propiolacton), (l), ist, obwohl es schneller als Poly(oxycarbony1-I ,I-dimethylathylen), (Polypivalolacton), (2), abgebaut wird. Die Reaktion verlief nach der 1. Ordnung mit einer Geschwindigkeitskonstanten von k=6,2. min-* unter Bildung von monomeren 8-Caprolacton.

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.

Since Johnson's finding in poly(N-vinylcarbazole) (PVCz)l of a high-energy trap, which he referred to as a second excimer, considerable interest has been aroused in the nature of the high-energy trap and its relationship to the normal low-energy e~c i m e r .~-~ Despite the obvious implication that bulky pendant chromophores, in general, may cause second-excimer-like trap formation, no work along this line has been reported to our knowledge. This might be partially due to the finding of Johnson' and Keyanpour-Rad et al.5 that other carbazole-containing polymers do not afford second excimer emission. This implies that among various vinyl aromatic polymers, only PVCz fulfills the strict geometric requirements for formation of the high-energy trap and subsequent emission.In the present communication we present evidence that polymers having sterically hindered naphthalene chromophores do, in fact, form second-excimer-like high-energy traps in a film and to a lesser extent in fluid solution.The monomer 2-tert-butyl-6-vinyhaphthalene (tBVN), its homopolymer (PtBVN, M, = 79000), and its copolymer with styrene (P(tBVN-co-St), 8 mol % in tBVN content,

The effects of the pendant group structure on intramolecular singlet energy migration and excimer formation in poly(2-naphthylmethyl methacrylate) (PNMMA), poly[l-(2-naphthyl)ethyl methacrylate] (P-1-NEMA), poly[2-(2-naphthyl)ethyl methacrylate] (P-2-NEMA), and poly[3-(2-naphthyl)propyl methacrylate] (P-3-NPMA) were examined by fluorescence quenching experiments in deaerated 2-methyltetrahydrofuran. Introduction of steric hindrance near the naphthalene chromophore (P-1-NEMA) or of a polymethylene bridge between the polymer main chain and the naphthalene chromophore (P-2-NEMA and P-3-NPMA) was found to reduce excimer formation but retard energy migration as well, suggesting that more specific chromophore arrangement along the polymer chain is desirable for selective promotion of energy migration and suppression of excimer formation. In film, these polymers exhibited little monomer emission; extensive emission from excimer (PNMMA, P-2-NEMA, and P-3-NF'MA) or that from a second-excimer-like trap (P-1-NEMA) indicates efficient trapping of excitation energy at these trap sites. The formation of the higher energy trap in P-1-NEMA film is discussed in terms of the conformational constraints, Le., increased chromophore separation and chain rigidity, imposed by the pendant group structure.

IntroductionThe photoprocesses of aromatic chromophores introduced in polymers differ, in many aspects, from those of low-molecular-weight analogues '). In solution, they may be regarded as covalently-bonded chromophore aggregates and possess unique photophysical as well as photochemical properties, e. g., intramolecular excitation energy migration and photosensitizati~n~*~). . Chromophores introduced in the side chains of helical polypeptides, in particular, are arranged at regular intervals and can be further oriented rigidly by side-chainhide-chain and/or side-chain/main-chain interactions. In fact, induced circular dichroism (CD) is often observed when aromatic chromophores are bound to the side chains of helical polypeptides4-'). Sisido et al.,for example, prepared poly(L-1-and L-2-naphthylalanines) and observed strong CD signals indicative of exciton coupling in the 'B, band of the naphthalene chromophore in trimethyl phosphate solution and attributed them to rigid orientation of the naphthalene chromophores along the helical polypeptide chain4x5). Ueno et al. ' ), on the other hand, examined induced CD in the 'B, band of poly(y-1-naphthylmethyl Lglutamate) and its dependence on the solvent composition in the mixed solvents of dichloromethane and hexafluoroisopropyl alcohol, but found no concrete evidence for exciton coupling. The flexible ester linkage, as well as the long spacer chain between the chromophore and the main chain, apparently causes looser chromophore orientation and thus weaker interaction among the chromophores. c=o NH