M. E. Cagiao

Aromatic polymers obtained by precipitation polycondensation: 4. Synthesis of poly(ether ketone ketone)s☆

Abstract 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.

Influence of filler structure on microhardness of carbon black–polymer composites

The microhardness, H, of carbon black–polycarbonate and carbon black–low-density polyethylene composites was investigated. Two types of microadditives with different average particle sizes were employed. It has been shown that the morphology of the polymeric matrix conspicuously influences the hardness dependence of the composites with volume concentration of filler, ϕ. The microhardness of the carbon black–polycarbonate composites shows a steplike behavior with respect to carbon black content, while the H value of the carbon black–low-density polyethylene composite linearly increases with increasing ϕ. The influence of filler structure on the microhardness of the carbon black–polymer composites is also discussed. Results favor the concept that a smaller carbon black particle size (smaller aggregate diameters and interaggregate distances) enhances the microhardness of the composites.

Aromatic polymers obtained by precipitation polycondensation: 5. 1H and 13C n.m.r. study of poly(ether ketone ketone)s

Abstract High molecular weight, linear aromatic poly(ether ketone ketone)s with different iso-/tere-isomer repeating unit ratio ( 100 0 , 50 50 , 0 100 ) have been studied by 1 H and 13 C n.m.r. spectroscopy. The polymers were obtained in particle form by precipitation electrophilic Friedel-Crafts acylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4-phenoxybenzoyl)benzenes. Conventional 1 H and 13 C n.m.r. spectroscopy shows para -substitution in the diphenyl ether fragments of the main chain. Analysis of the expanded 1 H n.m.r. spectra for the ring proton resonances reveals defect meta - and ortho -structures. The amount and isomer ratio of these defect structures depend on the polymer structure and preparation path. The low field of 1 H n.m.r. spectra of polyketones based on ‘small monomers’ (diphenyl ether and iso- and terephthaloyl chlorides) were found to show additional minor signals corresponding to a different type of defect structure. A possible mechanism of formation of these defect structures is discussed.

Study of the morphology of semicrystalline poly(ethylene terephthalate) by hydrolysis etching

Abstract Semicrystalline poly(ethylene terephthalate) was hydrolysed in water at 180°C under elevated pressure and subsequently treated with ethanol, following the etching process first developed by Miyagi and Wunderlich. The weight loss, the wide-angle X-ray scattering and the molecular weight were measured as a function of etching time. It was found that even at the end of the etching process not all the amorphous material could be removed by the hydrolysis treatment. By comparing the obtained results with those derived from an elaborate small-angle X-ray scattering study and with wide-angle X-ray scattering measurements, it was concluded that only those amorphous regions lying outside of the lamellar stacks were removed. Subsequently, the lamellar stacks themselves were attacked. It was also found that at the very beginning of the hydrolysis process additional crystals were formed in the material.

Structure–microhardness correlation in blends of nylon 6/nylon 66 monofilaments

The microstructure (crystallinity, long spacing) and the micromechanical properties (microhardness H) of two series of nylon 6 and nylon 66 monofilaments and their blends were investigated as a function of annealing temperature TA and uniaxial deformation in a wide composition range. In case of the homopolymers, the gradual rise of microhardness with TA is interpreted in the light of the increasing values of the crystallinity a and the hardness of the crystals Hc. The depression of the hardness values of the blends from the additive behavior of the hardness of individual compo- nents is discussed in the basis of the crystallinity depression of one component by the second one and viceversa. Finally, the influence of drawing and pressing the blends at 130°C which leads to a hardness increase is also explained in the light of an increase in the Hc value of nylon 66 due to orientation.

Influence of chlorosulfonation on the surface mechanical properties of lamellar polyethylene

SummaryThe hardening of lamellar polyethylene (PE) as a consequence of a controlled chlorosulfonation treatment has been studied using the microindentation technique. The hardness of the polymer turns out to be a linear function of the density of treated PE. The rate of increase is larger for samples with higher crystallinity. This increase is related to the hardening of crystal lamellae due to the surface attachment of electron dense groups. The latter impede the slippage of crystals and substantially reduce the rate of creep of the material under the contact pressure applied.

Micromechanical studies on binary and ternary blends of polyethylene, polypropylene, and polyamide 66: Influence of the compatibilizer

The microhardness H of PE/PP/PA blends prepared by one-Step and two-step mixing processes was determined. The microhardness of the blends was markedly affected by the composition. Results reveal that the presence of compatibilizers induces a remarkable decrease in the H of the blends. It is shown that the large deviation of H from the additivity law of the single components is mainly due to the depression of the crystal hardness values of polymer crystals. However, the decrease in crystallinity of the individual components in each blend also has to be considered. Comparison of experimental and calculated H data and analysis of DSC results in all the blends suggest that the surface free energy of the crystals increases as a consequence of the blending process. Results are discussed in light ofthe changes occurring in the defective boundary surface of the crystals. Finally, a linear relationship between the hardness H and the yield stress σ y , as well as between H and the Youngs modulus E, are found. The deviation of the H/ σ y and the H/E ratios from the theoretical predictions are discussed in the light of the strain rate used and the compatibilizer effects on the blend structural properties.

Melting of Gelatin Crystals below Glass Transition Temperature: A Direct Crystal-Glass Transition as Revealed by Microhardness

Abstract In the present paper the effect of crystallization conditions on the melting temperature (Tm ) of chemically cross-linked gelatin is studied by means of differential scanning calorimetry (DSC) and microhardness (H) measurements as extension of our recent findings (Ref. [11]). A rather unusual situation when polymer crystals melt below the glass transition temperature (Tg ) is confirmed by DSC. This is highlighted on dry gelatin which is characterized by relatively high, and close to each other, Tg and Tm values (217 and 230°C, respectively). By depressing Tg , using water as plasticizer, rather imperfect crystallites are obtained which melt well below the Tm of dry gelatin. It is shown that H increases with temperature mostly due to the drying out of the room-conditioned gelatin. In the 160–180°C range H reaches values of about 390MPa. In this temperature range the imperfect crystallites melt (according to DSC), however without formation of a typical liquid phase (since H remains constant). It is...

Hydrolysis etching of crystalline and amorphous poly(ethylene terephthalate): Influence of molecular weight and microstructure

Abstract The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180°C are less perfect and the lamellar stacks in...

THE ROLE OF DOUBLE-HELIX FORMATION IN WATER DIFFUSION AND AGING OF INJECTION-MOLDED STARCH*

Native potato starch has been processed without the use of any additive. Moldings of initial high strength and ductility have been achieved. However, mechanical properties change with time. Thermogravimetric experiments at different temperatures show that aging takes place in three different steps. The first is characterized by a strong formation of double helices (as revealed by wide-angle X-ray scattering [WAXS]) in parallel with strong water loss. Hardness, strength, and elongation at break increase in this time range: Double helices act as reinforcing elements. When the yield elongation is surpassed, double helices are unraveled, providing a higher elongation at break. With further aging (drying), due to a shrinking process, a temporary reduction of double helices, causing a resoftening, seems to take place. In a third step, the starch moldings become quite brittle due to the lack of molecular mobility. At room conditions, it takes approximately 1 year (beginning of range 3) to lose the good mechanical properties. It is proposed that the mechanical behavior of starch moldings is controlled by a molecular network that consists of singlehelix molecules bound by double helices within an amorphous structure. *Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th birthday.