BUSCADOR RECOLECTA

A high molecular weight, linear aromatic poly(ether ketone ether ketone ketone) (PEKEKK) has been synthesized by electrophilic Friedel-Crafts acylation condensation of 1,4-diphenoxybenzophenone with terephthaloyl chloride. The syntheses were performed as precipitation polycondensations, and the polyketones were obtained in particle form. The viscosity (molecular weight), shape and size of these particles were found to be strongly dependent on the reaction conditions. For low monomer concentration, highly ordered needle-like particles were also obtained. The chemical structure of the polymers obtained was confirmed by 1H and 13C NMR spectroscopy, and para-substitution in aryl fragments of the main chain was identified. Analysis of the expanded 1H NMR spectra for the ring proton resonances reveals defect mefa- and ortho-structures. The amount and isomer ratio of these defect structures depend on the monomer concentration used., Peer reviewed

High molecular weight aromatic poly(ether ketone ketone)s were synthesized by the Friedel-Crafts polyacylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4- phenoxybenzoyl)benzenes. Depending on the monomers used for polycondensation, polyketones of regular structure with different iso-/tereisomer repeating unit ratio (100/0, 50/50, 0/100) in the main chain were obtained. Polymers of each repeating isomer unit were prepared in two different ways. All the polymer syntheses were performed as precipitation polycondensations and the resulting polymers were obtained in particle form. The influence of reaction conditions and preparation route on the polymer properties were examined. The monomer concentration and monomer stoichiometric ratio were found to affect the polymer viscosity. The size and shape of the polyketone particles obtained were also found to be governed by reaction conditions and preparation route., Peer reviewed

High molecular weight, linear aromatic poly(etherketoneketone)s with differentiso-/tere-isomer repeating unit ratio (100/0,50/50/0,0/100) have been studied by 1H and 13Cn.m.r.spectroscopy. The polymers were obtained in particle form by precipitation electrophilic Friedel–Crafts acylation condensation of iso-and terephthaloyclhlorideswithdiphenyl ether,1,4-and l,3-bis(4-phenoxybenzoyl) benze.ConvwentionallH and 13Cn.m.r. spectroscoy shows para-substitution in the diphenylether fragments of the mainchain. Analysis of th eexpanded 1Hn.m.r.spectra for the ring proton resonances reveals defect meta-and orthostructures. The amount and isomer ratio of these defect structures depend on the polymer structure and preparationp ath.Thelow field of 1Hn.m.r.spectra of polyketones based on ‘small monomers’(diphenylether and iso- and terephthaloylchlorides)were found to show additional minor signals corresponding to a different type of defect structure.A possible mechanism of formation of these defec tstructures is discussed., Peer reviewed

The dielectric properties of chitosan films with a degree of deacetylation of 86% have been investigated in the frequency range of 103-106 Hz covering a broad range of temperatures from -150 to 150 °C. The variation of the dielectric properties with temperature has been associated with two dielectric processes: (a) a local relaxation attributed to the presence of hydrogen-bonded water appearing at low temperatures (b) a conduction process related to water molecules which becomes desorbed upon heating at T > 80 °C. Isothermal dielectric experiments have been performed in order to follow, in real time, the occurrence of both, the water sorption and desorption processes. © Steinkopff Verlag 1997, Peer Reviewed

The cold crystallization of amorphous films of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends, with different composition, prepared by co-precipitation from solution followed by melt-pressing for 2 min at 280°C and quenching in ice water, was followed by measuring the microhardness, H, in real time as a function of crystallization temperature and time. An analytical model was derived, relating properties of the individual components to the blend microhardness based on an Avrami-type equation to account for the crystallization of the components upon heating. Fitting of the model to the experimental results revealed a two-step hardening process of the blends. The degree of transesterification of the blends, can be estimated with this model. Finally, a removal of the physical ageing, inducing a decrease in H of PET in the blend, was observed upon heating above its glass transition temperature. ©1997 Chapman & Hall, DGICYT (Grant PB94-0049), Spain, and to NEDO's International Joint Research Programme, Japan. Fond National Suisse de la Recherche Scientifique, Peer Reviewed

5 pags., 6 figs., Syntheses of aromatic polyketones in the form of particles were performed using a very small monomer concentration (0.05 mol/1) by the precipitation polycondensation method. Some of these particles present highly ordered elongated needle‐like structures (whiskers) particularly for the all‐para polyketone samples. The use of isophthaloyl instead of terephthaloyl for the same low monomer concentration produces, in addition to the globular particles, bundles of ribbon‐like structures. The average size of the needle‐like particles is 1−5 μm in width and 150−250 μm in length. The factors controlling the morphology texture and size of the whiskers and ribbons are shown to be the polymer structure and the reaction conditions. Formation mechanisms are discussed., Grateful acknowledgement is due to DGICYT, Spain, for the support of this investigation (grant PB94- 0049). One of us (M.G.Z.) also thanks the Ministerio de Education y Ciencia, Spain, for tenure of a sabbatical grant (SAB95-0253) during his research work in Madrid, Peer reviewed

6 pags., 9 figs., 2 tabs., The changes in the two axial long periods of injection moulded oriented linear polyethylene (PE) with a shish-kebab structure have been investigated as a function of temperature by ultra-small angle X-ray scattering (USAXS) using synchrotron radiation. The aim of the present study is to investigate the origin of both periodicities and to establish whether both scattering maxima are mutually related. The gradual transformation of the initial two long periods, L1 = 36.4 and L2 = 65.7 nm, measured at room temperature to the final single long period Lf = 120 nm at T = 130°C has been demonstrated on high molecular weight oriented PE samples. The detection of such high long periods (up to 150 nm for these samples) has been possible, for the first time, thanks to the use of the new high resolution USAXS beam line at the DORIS-bypass, DESY. On the other hand, low molecular weight PE shows, at room temperature, one long period corresponding to an oriented structure with a wide lamellar distribution. The coherently diffracting domains in the chain direction and the mean orientation of the lamellae derived from the azimuthal scanning of the SAXS profiles have also been examined as a function of temperature. The changes of the long period L1 with temperature are shown to be independent from the changes of the L2 periodicity. From the results it is concluded that the oriented shish-kebab structure, in the high molecular weight samples, consists of two separate populations of lamellar stacks with the layer normals parallel to the injection direction. During annealing only the thinner lamellae increase in thickness until they reach the size of the thicker ones at about T = 130°C. For higher temperatures than T = 137°C the scattering maxima vanish suggesting that the lamellae melt. Finally, after cooling from the melt the lamellae crystallize epitaxially on the preserved oriented shish fibrils and both stacking periodicities L1 and L2 appear again., The work was generously supported by CICYT, Spain (Grant PB94-0049). USAXS measurements at the DORIS-bypass, DESY, Hamburg, have been funded by the program Human Capital and Mobility, Access to Large Installations EC., Peer reviewed

11 pags., 7 figs., 2 tabs.-- Dedicated to Prof. Dr. F. J. Baltá Calleja on the occasion of his 60th birthday, 1,3‐Bis(4‐phenoxybenzoyl)benzene (1) shows a single melting peak at T1 = 120°C when rapidly crystallized from a methanol/benzene mixture (10:1 v/v) (sample A) and a double melting peak at T1 = 120°C and T2 = 130°C when crystallized slowly (overnight) (sample B). Slow recrystallization of 1 using ethanol instead of methanol induces the formation of large single crystals which only show a single melting peak at T2 = 130°C (sample C). Analysis of powder X‐ray diffractograms obtained for A, B and C samples clearly point out the coexistence of two crystalline phases in sample B: phase 1 (observed for sample A) and phase 2 (sample C). From optical microscopy and thermal (DSC) observations, it can be concluded that, upon heating, phase 1 melts at T1 and the molten material converts itself into phase 2 if some crystals of phase 2 are present. Single crystal structure determination of, both, phase 1 and 2 reveal conformational differences of the molecule in both phases which pack in an orthorhombic and a monoclinic unit cell, respectively., s.. Grateful acknowledgement is due to DGIC’YT, Spain, for thc sup- port of this investigation (grant PB94-0049). One of us (M.G.Z.) also thanks DGICYT for the tenure ofa Sabbatical Grant during his research work in Madrid., Peer reviewed

18 pags., 6 figs., 2 tabs., A numerical method of identification to derive the elastic properties of polymers from indentation experiments has been developed. Five different polymers were tested: amorphous and semi-crystalline polyethylene terephthalate (PET), semi-crystalline polyvinylidene fluoride (PVF2), a copolymer of polyvinylidene fluoride and trifluorethylene, P(VF2/F3E) 60/40, and high pressure crystallised polyethylene (PE). The elastic properties of the polymers are calculated by two methods. On the basis of finite element solution, a simple function relating the load to the indentation depth and elastic modulus is first obtained. The elastic properties are then derived from the load-indentation depth and elastic modulus is first obtained. The elastic properties are then derived from the load indentation depth experimental data (loading curve). A second method to determine the elastic properties is based on using the experimental data of the unloading curve. Elastic properties obtained from loading and unloading curves are in good agreement., The method of identification of elastic properties of polymers from microhardness tests was developed during the visit of the first author to the Institute of Structure of Matter, Madrid, sponsored by the TEMPUS project JEP 06154-94. The authors would like to thank the project co-ordinator Prof. Dr.-Ing. A.K. Bledzki (University of Kassel) for the opportunity to perform the present study successfully. Thanks are also due to DGICYT, Spain (Grant PB94-0049) for their generous support of this investigation.