SYNOPSISPoly(ethylene-2,6-naphthalenedicarboxylate)(PEN) has been prepared from commercial dimethyl-2,6-naphthalenedicarboxylate (DM-2,6-NDC) and ethylene glycol (EG) according to the well-known transesterification/polycondensation route. P E N fibers, intended for industrial yarn applications, were obtained by melt spinning and drawing high molecular weight PEN. The properties of these yarns were measured in detail and compared with those of P E T industrial yarns. The development of molecular orientation in the spinline is more pronounced for PEN than for PET. Because the yield stress is lower, P E N yarns can more easily be drawn. Breaking tenacities of PEN yarns are comparable with those of P E T yarns, but the modulus is much higher and the thermal shrinkage is lower. Therefore, P E N yarns have a better dimensional stability than PET yarns. In addition, it was demonstrated that the thermal resistance of P E N yarns is better. 0 1995 John Wiley & Sons, Inc.

SYNOPSISThe results of a study of the relation between a number of mechanical properties of poly (ethylene terephthalate) ( P E T ) yarns and their physical structure are presented. The relation was studied on a set of 295 drawn yarn samples, resulting from an exceptionally large variety in process conditions applied. The size of this experiment offered a unique opportunity to study the property-structure relation more extensively than ever before. Therefore, our understanding of the mechanical properties could be enriched with several new insights. A selection of seven yarn properties has been investigated. Five of them have been derived from the stress-strain curves and the remaining two are shrinkage and shrinkage force. The physical structure has been described with a set of five, statistically selected, parameters. Most of the yarn properties could very well be described in terms of these structure parameters. This description was performed by means of an artificial neural network, ANN. The type of calculation is completely naive, i.e., without any specific mathematical formulation for the relation concerned. The fitting results have been translated into physical aspects related to the well-known molecular two-phase model. The practical importance of a good physical understanding of yarn properties is that the essential possibilities and impossibilities of combinations of properties can far more easily be surveyed and understood. As a result, the efficiency of process developments can be substantially improved.

SYNOPSISA method has been developed for measuring infrared spectra during the mechanical deformation of yarns. This rheooptical technique was applied to study the molecular processes that take place along the stress-strain curve of PET yarns. The results were combined with data obtained from size exclusion chromatography (SEC) and tensile measurements a t elevated temperatures. The results indicate that the first modulus maximum marks the breakdown of the amorphous entanglement network and the start of molecular uncoiling by gauche + trans transitions. In addition, stress develops on the crystals and particularly on tie molecules with a short contour length in the amorphous domains. Ultimately, molecular fracture of taut-tie molecules causes the modulus to pass through a second maximum. The chain ends of broken molecules recoil by trans + gauche transitions. Local stress accumulation will lead eventually to yarn rupture. 0 1993 John Wiley & Sons, Inc.

Frontier molecular orbital theory has been applied to the [4 + 2]‐cycloaddition of singlet oxygen, to mono‐ and dimethylnaphthalenes and to a number of other polycyclic aromatic compounds. Semilogarithmic plots of rate constants versus second order perturbation energies are found to be linear. The good correlations are due partly to the fact that singlet oxygen is such a small dienophile.

Abstract. In a two step reaction, hexamethylbenzene consumes two molecules of singlet oxygen to form epidioxy hydroperoxide 3. The first step involves a [4 + 2]-cycloaddition, which is followed by an ene-reaction. The structure of the intermediary endoperoxide 2 has been established spectroscopically. Pentamethylbenzene reacts in the same way with singlet oxygen, albeit much more slowly. Two epidioxy hydroperoxides are formed in this case.