Giuseppe Ferrara

Phase transition II → I in isotactic poly-1-butene: wide- and small-angle X-ray scattering measurements

Phase transition II → I in isotactic poly-1-butene was studied by wide- and small-angle X-ray scattering in order to follow the change of crystallinity and of the characteristic parameters of the lamellar stacks over time. Small-angle X-ray scattering experimental patterns were analyzed by a fitting method with the profiles calculated from some theoretical distribution models of the lamellar thickness. The mathematical evaluation of small-angle X-ray scattering patterns provided crystallinity values which were compared with those obtained by wide-angle X-ray scattering, in order to obtain information on the lamellar stacks organization. The transition nucleation seems to be localized on lamellar distortion points and the transition itself involves the rearrangement of lamellae and of lamellar stacks.

Small- and wide-angle X-ray scattering analysis of Ziegler–Natta catalysts: structural disorder, surface area and activity

Abstract An analysis was carried out of some Ziegler–Natta catalysts precursors by small- and wide-angle X-ray scattering in order to get information on the crystallites dimensions, structural disorder and surface areas. The results were correlated with catalytic activities in polymerization of propylene. It was shown that the structural variations, which mainly influence the catalytic activity, are associated with the rotational disorder of the Cl–Mg–Cl triple layers and that the crystallites dimensions and surface areas play a determinant role in the same activity. Furthermore it was shown that the surface areas of the examined samples, determined by BET, are less meaningful than the data obtained by small-angle X-ray scattering, probably for the presence of intra-particle closed pores and/or microporosity.

High-performance liquid chromatographic determination of some of the hydrolytic decomposition products of poly(α-hydroxyacid)s

Abstract An HPLC procedure is described for the separation and identification of some hydrosoluble by-products resulting from the hydrolytic degradation of poly(α-hydroxyacid)s having biomedical interest: poly( l -lactide), poly( dl -lactide), poly-(glycolide) and poly(lactide-co-glycolide). Peak identification was performed by comparing the respective retention times with those of pure standards. It was observed that optimum shape and separation of peaks are considerably affected by the composition of the mobile phase, consisting of acetonitrile (A) and a 0.006 M K2HPO4 buffer (B), and, in particular, its pH and A:B ratio, which had to be adjusted to around 5.8 and 75:25 (v/v), respectively. Under the investigated experimental conditions (aqueous suspension, 100°C for 12 h under stirring), poly( l -lactide) is quite stable, poly(glycolide) degrades easily to glycolic acid, whereas poly( dl -lactide) and poly( dl -lactide-co-glycolide) exhibit intermediate behaviour. Upon hydrolytic decomposition, these poly(α-hydroxyacid)s yield not only the corresponding acids, but also their linear dimers and, possibly, trimers, tetramers and higher oligomers.