Environmental and processing factors affecting the biostability of medical devices made from traditionally "stable" polymers, such as isotactic polypropylene (PP) and ultrahigh molecular weight polyethylene (UHMW-PE) , were analyzed and their undesirable degradation was related to performance of typical medical devices. Among the critical phenomena determining the biological performance of UHMW...

The role of liquid crystalline mesophases in polymer crystallization has seen increased attention following the observations of meta-stable liquid crystalline pre-ordering in the crystallization of isotactic polypropylene and other flexible polymers [1–7]. In addition to these recent observations, both in Nature and industry liquid crystal mesophases are used to create polymeric materials with ...

Ageing of polymers results from structural modifications at the molecular scale and kinetic modelling must be elaborated from analysis of the phenomenon at this scale. However, the change of mechanical properties results from modifications of structure at larger scale, especially the macromolecular scale (chain scission, crosslinking) and or at the macroscopic scale (skin-core structure linked ...

A new bis(indenyl)zirconocene bearing a pendant Si-Cl anchor has been grafted onto MCM-41, SBA-15, MCM-48 and a disordered mesoporous silica for the polymerisation of ethylene and propylene, producing polymers with very high molecular weights, low polydispersities and, in the case of polypropylene, higher levels of isotacticity than obtainable with analogous homogeneous systems.

The detailed structure and molecular mobility of nascent isotactic polypropylene (iPP) powder was investigated using differential scanning calorimetry, transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). The crystallinity of the nascent iPP powder is approximately 33%, which is much lower than that of melt-quenched or isothermally crystallized iPP. Peaks from the variab...