Secondary Crystallization of Isotactic Polystyrene

When isotactic polystyrene (i-PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i-PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk-crystallized i-PS. Electron microscopic studies of surface replicas of i-PS support this view.

Laminates on the basis of polypropylene and process for preparing such laminates

The invention accords to a laminate at least consisting of a first layer from a mixture of at least a propylene polymer and an ethylene-vinylalcohol copolymer and a second layer from at least one propylene polymer, the first layer at least consisting of a mixture of 60-99 parts by weight of a substantially crystalline propylene polymer and 1-40 parts by weight of an ethylene-vinylalcohol copolymer, the second layer at least consisting of a substantially crystalline propylene polymer, the said ethylene-vinylalcohol copolymer having a melting temperature at atmospheric pressure which is at most equal to and not more than 30K lower than the melting temperature at atmospheric pressure of the one of the substantially crystalline propylene polymers used having the highest melting temperature, and the laminate having been subjected to multi-axial stretching to a degree of at least twice in at least 2 directions at a temperature which at most equals the melting temperature of the one of the substantially crystalline propylene polymers used having the highest melting temperature and to a process for preparing such a laminate

Processing of intractable polymers using reactive solvents: 1. Poly(2,6-dimethyl-1,4-phenylene ether)/epoxy resin

A new processing route for poly(2,6-dimethyl-1,4-phenylene ether) (PPE), an intractable polymer on account of its thermal and oxidative sensitivity, was explored. PPE can be dissolved at elevated temperatures in epoxy resin and these solutions can then be processed at temperatures as low as 175°C. For solutions of PPE with a molecular weight of 10, 20 and 30 kg mol-1, the phase diagram and the flow curves in the homogeneous region were determined. The upper critical solution temperature (UCST) cloud point curves intersect the glass transition-composition lines at a PPE content of 70 wt%. Below this composition, thermoreversible gelation is observed upon cooling which prevents complete phase separation. Curing of the homogeneous solutions, using diethyltoluene diamine, resulted in virtually complete phase separation. In the composition range that was studied (30–70 wt% PPE), the chemically induced phase separation is accompanied by phase inversion, yielding a final morphology of epoxy spheres dispersed in a PPE matrix. Thus, after processing, the (reactive) solvent is converted into a dispersed phase. The mechanical and thermal properties of the final materials, such as toughness and glass transition temperature, are dominated by the continuous PPE matrix

Processing in intractable polymers using reactive solvents: 3. Mechanical properties of poly(2,6-dimethyl-1,4-phenylene ether) processed by using various epoxy resin systems

The rather intractable polymer poly(2,6-dimethyl-1,4-phenylene ether) (PPE) can easily be processed by using epoxy resin as a reactive solvent. In this reactive solution processing technique, PPE is dissolved in epoxy resin at elevated temperatures and processed. After processing, the epoxy resin is polymerized and phase separation accompanied by phase inversion is initiated and the reactive solvent is subsequently integrated in the final material. In this paper, attention was focused on the possibility of tuning the properties of the in situ polymerized dispersed epoxy phase. A solvent system was studied which consisted of epoxy resins and diamine curing agents, based on bisphenol and poly(propylene oxide). Both resins could be used as a solvent for PPE and the resulting processable solutions exhibited upper critical solution temperature behaviour. Upon increasing the poly(propylene oxide) content in the reactive solvent system the properties of the dispersed phase could be varied gradually from non-ductile glassy to completely rubbery, and consequently the properties of the PPE/epoxy could be controlled over a broad range. The presence of a non-ductile glassy dispersed phase (with yield stress yield stress of PPE) resulted in an increase in the yield stress of the material and was shown to constrain yielding of the PPE matrix. Reduction of the yield stress of the dispersed phase facilitated ductile deformation of PPE in tensile loading but resulted additionally in a reduction in toughness. After changing the properties of the dispersed epoxy phase to completely rubbery a substantial increase in toughness was obtained. Interestingly, the rubber with the lowest level of adhesion proved to be the most efficient impact modifier for PPE

Liquid-crystalline main-chain polymers with a poly(p-phenylene terephthalate) backbone. 3. Drawing, structure development and ultimate mechanical properties of films of the polyester with dodecyloxy side chains

Soln.-cast films of poly(p-phenylene 2,5-didodecyloxyterephthalate) were characterized by x-ray diffraction, DSC and mech. measurements. Three different structures, in which the main chains are arranged in layers sepd. by the interdigitating side chains, could be distinguished. In the as-cast films these layers are parallel to the film surface. Upon drawing, the backbones of the chains orient parallel to the drawing direction, while most of the parallel orientation of the layers with respect to the film surface is maintained. At room temp. the Young's moduli of the less-ordered phases, termed A and Lf, are approx. 15 GPa, which is rather low in comparison with the value of almost 30 GPa found for the third modification, termed B. However, below the b-relaxation at .apprx. -20 Deg the moduli of all three phases are of the same order of magnitude. At -175 Deg they are in line with the theor. predicted modulus of 50 GPa. [on SciFinder (R)