Solutions of hyperbranched aromatic polyamides

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Properties and morphology of segmented copoly(ether urea)s with uniform hard segments

Block copoly(ether urea)s with uniform hard blocks consisting of two urea groups possess appealing elastomeric properties. The crystal structure of a model bisurea illustrates the formation of long stacks of hydrogen-bonded urea groups. Thermal anal. of these polymers demonstrates the reversible melting of the hard blocks, causing the material to flow. The low glass transition temp. ensures excellent low-temp. flexibility. The morphol. of the material consists of long stacks of assocd. hard blocks embedded in the soft phase. Elongation of the materials demonstrates their highly elastic behavior, with a strain at break ranging from 1000 to 2100%. During tensile testing, irreversible deformation and reorganization of the hard blocks occur, resulting in a significant amt. of tensile set. These well-defined polymers proved to be superior compared to a less-defined analog having a polydisperse hard block

A small angle X-ray scattering study of sizes and shapes of poly(benzyl ether) dendrimer molecules

The structure of a series of poly(benzyl ether) dendrimers was derived from small angle X-ray scattering (SAXS) experiments of highly diluted solutions. The form factor contribution of the uncorrelated macromolecules contains information on their size and shape and reveals that they attain a globular structure. Electron distributions, calculated form the scattering data point towards an ellipsoidal shape with a rather uniform distribution of the electron density and hence the monomer subunits within the macromolecules

An experimentally validated model for quiescent multiphase primary and secondary crystallization phenomena in PP with low content of ethylene comonomer

While crystallization behavior of isotactic polypropylene homopolymers had been subject to a wide range of experimental and modeling studies, this is not the case for propylene-ethylene random copolymers (PPR). This class of polymers offers up to now significant challenges, both from an experimental as well as a modeling perspective. The ethylene incorporation in the propylene chains, as well as the distribution of this comonomer, has a marked effect on the crystallization kinetics. Moreover, the presence of these defects causes a clear separation between primary crystallization (i.e. space filling) and subsequent secondary crystallization (increase of crystallinity in filled space) within the spherulitic skeletons, particularly subsequent at high primary crystallization temperatures. In this work, the underlying mechanism is first quantified by means of a combination of in-situ WAXD and SAXS experiments, as well as ex-situ WAXD experiments and calorimetric measurements. Based on these experiments an extended model framework is presented, capable of predicting multiphase non-isothermal crystallization kinetics as well as the final crystallinity as a function of the applied thermal conditions relevant for processing. The chemical composition distribution (CCD) of the ethylene comonomer serves as critical input to parameterize the model. Optical microscopy- and DSC experiments are used for parameterization of the primary crystallization model. The model developed in this study is, in principle, applicable to all polypropylenes, ranging from homo-polymers to random copolymers with variable comonomer content and/or CCD but, so far, only applied and validated on one PPR. To validate the model and the parameters for a given PPR, several non-isothermal and isothermal experiments (the latter followed by subsequent cooling) are conducted over a wide range of crystallization temperatures and cooling rates. The good match between experiments and model predictions demonstrates the power of the newly developed framework. The final crystallinity, the amount of α- and γ-phase, and the ratio between primary and secondary crystallization can be predicted as a function of the time-temperature history. To the best knowledge of the authors, it is the first time that such a direct connection with the CCD is incorporated in a crystallization model. Consequently, the model offers a new tool to bridge the gap between chemical structure and resulting product properties, which now has come one step closer for PPR systems

Complex melting of semi-crystalline chicory (Cichorium intybus L.) root inulin

When concentrated solutions (30–45% by weight) of inulin (degree of polymerization 2–66, number average degree of polymerization 12) are cooled at 1 °C/min or 0.25 °C/min from 96 °C to 20 °C, suspensions of semi-crystalline material in water are formed. A thermal nucleation process was detected by optical microscopy: the 8-like shaped crystallites resulting from primary nucleation at higher temperature are larger than those resulting from secondary nucleation at lower temperature. Differential scanning calorimetry (DSC) thermograms display melting profiles with three to four partly overlapping endotherms that vary as a function of concentration, cooling rate during crystallization and storage time at 25 °C of the crystallite suspension. Recrystallization during melting was observed. The wide-angle X-ray scattering patterns of the samples at 25 °C correspond to those of the hydrated crystal polymorph. The structural changes during melting indicated the existence of a single crystal polymorph throughout melting. A periodicity of 95 Å, arising from alternating regions of different electron density, is detected in the small angle X-ray scattering patterns at 25 °C. The stepwise increase of the long period upon heating is related to the existence of two types of lamellar stacks: one with a higher long period, resulting from the primary nucleation and thus crystallized at high temperature, and a second one with a smaller long period, formed by crystallization at lower temperature. The lamellae formed at low temperature melt at a lower temperature than those formed at high temperature, explaining the existence of the two DSC-endotherms