Peculiar behavior of the ester carbonyl vibrational modes in anisotropic aliphatic and semi-aromatic polyesters.

The current work reports on a systematic study related to the vibrational modes of the ester carbonyl group in drawn polyesters. We have observed and try to explain how the presence of aromatic units in the molecular structure substantially affects the respective elements of the Raman tensor in contrast to the dipole moment derivative vector which is only marginally influenced. The work is based on the collection of polarized Raman spectra and FTIR dichroism measurements on the one hand and on DFT calculations on the other. The experimental data were obtained from uniaxially stretched aliphatic and semi-aromatic polyesters. The calculations were applied on relevant oriented oligomers and allowed the extraction: (i) of reliable Raman/FTIR vibrational spectra and (ii) the components of the dipole moment derivative and Raman tensor of the vibrational modes and in particular the ones involving the ester carbonyl group. Experimental data indicate that the intensity of the ester carbonyl band is considerably enhanced in the Raman spectra of semi-aromatic polyesters, which results from a considerable enhancement of the related coupling coefficient. Furthermore, the angles of the principle Raman tensor axis are rotated so that the element of the tensor with the greatest value is oriented towards the direction designated by the segment. The latter explains the peculiar experimentally indicated anisotropy, through the ester carbonyl stretching, for the case of semi-aromatic polyesters, which is totally different with that observed in the aliphatic ones.

The effect of the molecular orientation on the release of antimicrobial substances from uniaxially drawn polymer matrixes.

A new method of controlled release of low molecular weight biocides incorporated in polymer matrixes is described. The molecular orientation of uniaxially drawn biocide doped polymer films is suggested as a significant parameter for controlled release monitoring. Triclosan, a well-established widespread antibacterial agent, has been incorporated into high density polyethylene (HDPE) films that have been subsequently uniaxially drawn at different draw ratios. The molecular orientation developed was estimated utilizing polarized mu-Raman spectra. Biocide incorporated polymer films, drawn at different draw ratios, have been immersed in ethanol-water solutions (EtOH) and in physiological saline. The release of Triclosan out of the polymer matrix was probed with UV-Vis absorption spectroscopy for a period of time up to 15 months. In all cases, although the film surface of the drawn samples exposed to the liquid solution was higher than the undrawn one, the relevant release rate from the drawn specimens was lower than the non-stretched samples depending on the molecular orientation developed during the drawing process. A note is made of the fact that no significant molecular orientation relaxation of the polyethylene films has been observed even after such a long time of immersion of the drawn films in the liquid solutions.

Incorporation of low molecular weight biocides into polystyrene-divinyl benzene beads with controlled release characteristics.

Triclosan and phosphonium salt biocides have been separately incorporated into polystyrene-divinylbenzene (PS-DVB) beads by suspension polymerization. Ultraviolet (UV) absorption measurements have been used to monitor the release of these low molecular weight biocides out of the PS-DVB beads immersed in water-ethanol mixtures and in physiological saline. The release of the biocide agents is strongly dependent on either the DVB or/and the antimicrobial composition ratio in the beads. An increase of biocide incorporation in the PS/DVB beads was accompanied by a corresponding enhancement of its concentration in liquid mixtures. On the contrary, higher cross-linking densities hindered the biocide migration out of the beads by diminishing its release rate into either the aqueous ethanol solutions or the natural serum. Moreover, Fourier transform Raman (FT-Raman) spectra and Attenuated Total Reflectance Infrared (ATR-FTIR) measurements of the PS-DVB-Triclosan and PS-DVB-phosphonium salt beads, before and after their immersion in water-ethanol solutions, gave a similar qualitative evidence of the biocide release.

Molecular orientation of poly(ethylene terephthalate) and poly(butylene terephthalate) probed by polarized Raman spectra: a parallel study.

Poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) samples uniaxially drawn above Tg and beyond the yield point exhibit significant differences in their molecular orientation behavior as probed by polarized Raman spectra. The quasi-amorphous PET samples, drawn close to the Tg, manifest considerable molecular orientation development; however, when drawn above Tg + 30 degrees C, they exhibit significant molecular orientation relaxation. The semi-crystalline PBT samples maintain prominent molecular orientation even when drawn 110 degrees C above Tg. The drawing process, in PET samples, when resulting in molecular orientation, is accompanied by a gauche-trans transformation of the glycol linkage and a concurrent initiation of crystallinity development. In PBT specimens, it gives rise to a coexistence of alpha- and beta-type crystalline phases. Phase alpha is predominant at high draw temperatures, i.e., Tg + 110 degrees C, while phase beta dominates at low draw temperatures, i.e., Tg + 10 degrees C. PBT samples, with beta-phase predominance, left at relevant draw temperatures without stress, exhibit a beta-alpha phase change though no molecular orientation relaxation occurs. A note is made of the fact that complete molecular orientation analysis of PBT segments utilizing the depol method gives more reliable results than the simplified analysis assuming a cylindrical tensor for the 1614 cm(-1) symmetric stretch of the para-disubstituted benzene ring of PBT. In this context, segments of PBT specimens rich in alpha-phase exhibit higher molecular orientation than those with beta-phase predominance.