A series of homopolymer polypropylenes (PPs), within a weight-average molecular weight (M w ) range of 100-1600 kg/mol, were manufactured as dumbbell microspecimens. The effects of the molecular weight and shearinduced crystallization on the mechanical properties and morphology were studied to gain a better understanding of the structure-property relationship. The results showed that the crystallinity decreased from 50 to 41% and the lamellar thickness increased as M w increased. Tensile tests demonstrated that the stiffness and especially the tensile strength rose to extremely high values (Young's modulus ¼ 2400 N/mm 2 , stress at 30% strain ¼ 120 N/mm 2 ). Furthermore, the strain hardening effect was strongly affected by the lamellar thickness and highly oriented superstructures. Dynamic mechanical analysis demonstrated that the mobility of the molecular chains depended on M w and on the lamellar thickness. In addition, the viscoelastic properties of unannealed and annealed samples indicated further the existence of shishkebab structures caused by shear-induced crystallization during injection molding.

Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight ($\overline M _{\rm w}$) were studied. A series of homopolymer PP in a wide $\overline M _{\rm w}$ range from 101 000 to 1 600 000 g · mol−1 was polymerised in a liquid pool (LP) under defined conditions. The LP‐PP with a well‐known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection‐moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi‐static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750 000 s−1. In addition, the present crystallisation time of the high‐molecular‐weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear‐induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300 000 s−1. Above this shear rate level, shish kebab structures are favourably formed. The shear‐induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid‐state properties of the analysed LP‐PP samples. With a tensile strength up to 100 N · mm−2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature.True strain–stress behaviour of moulded the LP‐PP samples of different molecular weight.magnified imageTrue strain–stress behaviour of moulded the LP‐PP samples of different molecular weight.

The influence of molecular weight and comonomer content on the mechanical properties of several melt‐processable polytetrafluoroethylene (MP PTFE) materials is studied. Additionally, a comparison of mechanical properties including tensile properties and their dependence on environment as well as fatigue life of PTFE, MP PTFE and perfluoroalkoxy copolymer (PFA) is made. PTFE homopolymer and PTFE copolymers exhibit considerably different mechanical properties. The small strain deformation behaviour up to yielding correlates with the degree of crystallinity and comonomer content, whereas the large strain deformation was found to depend on intercrystalline connections, such as tie molecules and chain entanglements. The special role of these elements in determining the fatigue life and sensitivity to environmental stress cracking is also demonstrated.

A new melt‐processable PTFE material is presented and characterized that provides new and economical solutions in polymer technology while bridging the gap between perfluorinated PTFE and fluorothermoplastic materials such as perfluoroalkoxy resins. Thermal transitions, MW and MWD, and microstructures of the melt‐processable PTFE materials are investigated and compared to standard PTFE, modified PTFE, and PFA materials. The influence of the polymerization type used for the preparation of the melt‐processable PTFE (emulsion and suspension polymerization) on the MWD and the comonomer distribution are discussed.

For the first time, blends of melt processable polytetrafluoroethylene (MP PTFE) with polyetheretherketone (PEEK) in the MP PTFE/PEEK ratio of 100/0, 80/20, 50/50, 20/80, and 0/100 w/w were prepared and characterized. MP PTFE/PEEK blends are attractive materials due to the combination of low coefficient of friction and universal chemical resistance of MP PTFE with good wear resistance and mechanical strength of PEEK while maintaining high thermal stability of both. Miscibility, phase morphology, and mechanical properties of the new MP PTFE/PEEK blends were investigated. To improve their end-use properties, an attempt of reactive compounding with the electron beam irradiated MP PTFE (e-beam MP PTFE) was made. The reactive compounding was done in two steps, that is, the preparation of a masterbatch (MB) consisting of e-beam MP PTFE/PEEK (50/50 w/w) and subsequent melt blending of MP PTFE/ PEEK with varying concentrations of MB. The e-beam irradiation of MP PTFE carried out in air atmosphere and at room temperature with a dose of 50 kGy results in its chain scission associated with formation of ACOF and ACOOH functional groups. Such modified MP PTFE can be used to compatibilize MP PTFE/PEEK blends. Reactive compatibilized blends exhibit improved phase morphology and mechanical properties. Especially for MP PTFE/PEEK 50/50 blends, a great improvement of almost 250% in strain at break, 40% in stress at break, and more than 600% in toughness was achieved. the very high melt viscosity of PTFE its processing is limited to, for example, sintering process, whereas MP PTFE, characterized by lower melt viscosity, can be processed by the conventional melt processing methods. Consequently, only PTFE blends with less than 30 wt % (weight percent) of PTFE can be produced by a melt extrusion process otherwise only a compression moulding process is possible. 5 Moreover, due to the high melt viscosity of PTFE, melt blending of PTFE powder in polymer matrix results in filler-matrix morphology. The tendency of the PTFE powder to agglomerate and a lack of an adhesion between PTFE phase and the polymer matrix are responsible for the reduced mechanical properties of PTFE blends. In contrast to PTFE blends, in MP PTFE blends, the lower viscosity of MP PTFE enables its better dispersion and distribution within the polymer matrix. Thus, in comparison with PTFE blends, better mechanical performance for MP PTFE blends is expected.