Kenncorwin H. Gardner

Time-resolved X-ray study of poly(aryl ether ether ketone) crystallization and melting behaviour: 1. Crystallization

Time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) experiments using synchrotron radiation were made in order to study the isothermal crystallization behaviour of poly(aryl ether ether ketone) (PEEK). Two types of long period (LB and LMC), the scattering invariant Q, and the linear degree of crystallinity within the lamellar stacks xCL were estimated from the Lorentz-corrected plot and the correlation function. As a result, the average lamellar thickness lC was calculated as the product of LMC and xCL during crystallization at temperatures of 230–310°C. The bulk degree of crystallinity (by weight), ψC, was determined by WAXD. It was found that both long periods decreased, Q increased and lC remained approximately constant with time. The decrease in the long period was explained by the lamellar insertion within the lamellar stacks, whereas the increase in Q was attributed to the increase in the bulk-volume degree of crystallinity xC, rather than xCL. In addition, the values of the long period and of Q were found to increase with temperature as a result of the thicker lamellae. Finally, our results support the model of two populations in lamellar thickness, namely the primary lamellae which are developed first in bundle-like stacks, and the narrower, secondary lamellae (as a small fraction) that are inserted later between the primary lamellae under various spatial restrictions.

Structure, crystallization and morphology of poly (aryl ether ketone ketone)☆

Abstract The structure, crystallization and morphology of poly (aryl ether ketone ketone)s (PEKKs) prepared from diphenyl ether (DPE), terephthalic acid (T) and isophthalic acid (I) and having different T/I ratios have been investigated. As prepared, these copolymers can be thought of as consisting of ‘phthalate diads’ containing -DPE-T-DPE-T-(TT) and/or -DPE-T-DPE-I-(TI). Melt-crystallized PEKKs (all T/I ratios) form a structure similar to that observed in other poly(aryl ether ketone)s (form 1; a = 0.769 nm, b = 0.606 nm and fibre axis c = 1.016 nm). However, depending on composition, both TT and TI crystals were observed. All PEKK materials grow in the form of spherulites having negative birefringence. The incorporation of isophthaloyl moieties is observed to increase the chain flexibility and decrease the rate of crystallization. The equilibrium melting temperatures of various PEKKs were estimated using the Hoffman-Weeks approach, and showed a linear correlation with the meta isomer content. In contrast to other poly(aryl ether ketone)s, a form 2 crystalline modification ( a = 0.393 nm, b = 0.575 nm and c = 1.016 nm) can be induced either by exposure to solvents or by cold crystallization. The two crystalline modifications differ from each other in the placement of the chains and, consequently, the interchain interactions.

Time-resolved X-ray study of poly(aryl ether ether ketone) crystallization and melting behaviour: 2. Melting

Abstract Heating measurements of amorphous and isothermally crystallized (260–320°C) samples were carried out using time-resolved small-angle X-ray scattering (SAXS) to study the melting behaviour of poly(aryl ether ether ketone) (PEEK). In the amorphous sample, the scattering maximum became detectable after the cold crystallization, with the peak position qmax decreasing with temperature. The latter was also seen in crystallized samples. Two types of long period (LB and LMC) were determined, by using Braggs law and the correlation function, respectively. These values are inversely proportional to qmax, and therefore they all increased with temperature. In the crystallized samples, two stages of increase in the long period were found: below the lower melting temperature of the double endotherms (Tm1, determined by d.s.c.), the increase was small, while above Tm1, both of the long periods increased rapidly. In addition, the invariant Q was found to increase with temperature but reached a maximum near the onset temperature of the last endotherm. These results were consistent with the hypothesis of sequential melting of lamellar bundles consisting of two populations of thickness. In the crystalline specimens, the increase in Q was mainly due to the thermal expansion, whereas in the amorphous sample, the larger increase in Q was additionally attributed to the broad cold crystallization.

Ester interchange reactions in poly(ethylene terephthalate): observation using smallangle neutron scattering☆

Abstract Ester interchange reactions have been studied in poly(ethylene terephthalate) (PET) by means of small-angle neutron scattering (SANS). Cast film PET samples containing 20 wt% deuterated PET chains were prepared at low temperature. The SANS molecular weight of the as-prepared specimen agrees with the g.p.c. value and the molecular dimensions are close to the unperturbed value. Samples were then annealed at temperatures of 150°C–300°C at times from 10–600 min. If ester interchange occurs in a blend sample, block copolymer chains are formed with the blocks consisting of protonated and deuterated sequences. The SANS Mw obtained from these samples is an apparent Mw, the Mw of the blocks, and is lower than the g.p.c. value. Ester interchange is shown to be rapid in the melt and also to take place at a slower rate at temperatures 15°C below Tm, in general agreement with previous studies. An apparent clustering effect at elevated temperatures is also reported.

Thermal Properties of the Polyamide from 2-Methylpentamethylenediamine and Dodecanedioic Acid

The polyamide from 2-methylpentamethylenediamine and dodecanedioic acid (MPMD-12) has been studied by differential scanning calorimetry, dynamic mechanical analysis, dielectric analysis, X-ray crystallography, and simultaneous small and wide-angle X-ray scattering using synchrotron radiation. The polymer exhibits polymorphism which is shown to be associated with the incorporation of the branched diamine. At relatively low temperatures, the crystal structure is similar to the gamma form which has been found in many other polyamides. At higher temperatures, a new delta form appears in which the diamine moiety adopts a bent conformation. In this form, the chains follow a zig-zag pattern with two chemical repeats units per crystallographic repeat with a shortening of about 10% along the c-axis.

Crystal morphological investigation in thin films of poly(aryl ether ketone ketone) having a meta-linkage

The lamellar crystal morphology of thin films of poly(aryl ether ketone ketone) having a meta-linkage (PEKK(I)) is observed under transmission electron microscopy (TEM), utilizing samples with different thermal histories and preparation procedures. After isothermal crystallization from the melt, a double endothermic behaviour can be found through differential scanning calorimetry (d.s.c.) experiments. Partial melting of PEKK(I) can be obtained by heating the samples to a temperature between these two endotherms. By comparing the TEM morphological observations of the samples before and after partial melting, it can be shown that edge-on lamellar crystals, having different thermodynamic stabilities, form during isothermal crystallization. After partial melting, only the type of lamellar crystal exhibiting the higher thermodynamic stability remains. Small angle X-ray scattering (SAXS) results exhibit a change in the long period of the lamellar crystals before and after the partial melting process. For the solution-induced crystallization of PEKK(I), only a single endotherm exists in the d.s.c. observations. After annealing at high temperatures, however, a double endothermic behaviour appears. This also results in a decrease in the long period observed by SAXS. The double population of the lamellar crystals is difficult to observe in TEM, since the lamellar crystals in these thin film samples possess a random, rather than an edge-on, orientation. Detailed TEM imaging for observing these lamellar crystals is discussed.

Amyloid character of self-assembling proteins based on adenovirus fiber shaft sequences

Fibrous proteins found in natural materials such as silk fibroins, spider silks, and viral spikes increasingly serve as a source of inspiration for the design of novel, artificial fibrous materials. The fiber protein from the adenovirus has previously served as a model for the design of artificial, self-assembling fibers. The fibrous shaft of this protein consists of 15-amino-acid sequence repeats that fold into a triple β-spiral motif in their native context. Recombinant proteins based on multimers of simplified consensus shaft repeats were previously reported to form self-assembling fibrils from which filaments could be spun. Here, we describe the structural characterization of these fibrils; X-ray fiber diffraction, Raman spectroscopy, and Congo Red binding strongly suggest an amyloid-type structure for these fibrils, with β-strands arranged perpendicular to the fibril axis. This amyloid structure is distinct from the native β-spiral fold, and similar to amyloid structures formed by short, synthetic peptides corresponding to shaft sequences. We discuss implications for the rational design of novel fibrous materials, based on crystal structure information and knowledge of folding and assembly pathways of natural fibrous proteins.

Pressure-volume-temperature properties of polymethacrylates: anomalous behaviour in the melt

Abstract Pressure-volume-temperature measurements have been performed for a series of polymethacrylates. Samples of poly(ethyl methacrylate) that have been pressed and quenched show densification between 100 and 150°C which disappears up to 200°C. Samples which have been heated above 200°C appear not to show this effect on reheating. Densifications similar to the above are also observed for the propyl and butyl polymethacrylates. Densification is not seen for poly(methyl methacrylate) nor for polyacrylates. Several other initial observations were made using other techniques. D.s.c. peaks are seen in this region which depend on the thermal history. The rheology is very dependent on thermal history. Some small changes in X-ray patterns are produced by thermal treatments. These observations could be interpreted as suggesting that polymethacrylates can be partially crystalline.