Crystalline Elastomers 2014-2016

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Schermata 2015-10-09 alle 13.35.28
Novel polyolefin based elastomers with tailored stiffness from metallorganic catalysis (CRYSTALLINE ELASTOMERS)

CRYSTALLINE ELASTOMERS project aims at developing low cost innovative elastomers based on polyolefins that present increased stiffness, with respect to conventional elastomers, thanks to the presence of non-negligible level of crystallinity. The novelty of this project is the definition of a new class of materials, the “crystalline elastomers”, which are characterized by a combination of mechanical properties typical of crystalline materials (high mechanical strength and stiffness) and of elastomers (ease of deformability, ductility and perfect elasticity). According to basic knowledge of polymer science, these properties are considered irreconcilable in the same material, so that a basic principle of polymer physics sanctions that an elastomer cannot be highly crystalline.

It is worth recalling that elasticity can develop in crystalline materials only if crystals play an active role in the elastic recovery through various mechanisms, such as occurrence of polymorphic transition of a metastable form into a more stable form during recovery (enthalpic elasticity) or reversible textural transformations. Various polymeric materials based on polyolefins and copolymers of olefins, such as propylene, ethylene, etc., have shown these characteristics and have interesting properties of crystalline elastomers.

Semicrystalline homo- and copolymers of ethylene, propylene and other a-olefins (including cyclic olefins) as well as copolymers with various chain microstructures and molecular architectures (e.g. random and block-copolymers and/or multiblock copolymers) will be synthesized. To this aim the more advanced synthetic strategies will be used, based on catalytic systems composed of transition metals complexes which allow for a better control over stereoregularity, regioregularity and comonomer distribution. In particular, stereoregular homopolymers as well as block or multiblock copolymers will be basically prepared through “living” and “chain shuttling” polymerization catalysis.

The structure and the morphology of these materials will be studied using different techniques, as X-ray diffraction, calorimetry, solution NMR, FT-IR, optical microscopy, Transmission and Scanning Electron Microscopy (TEM and SEM) and Atomic Force Microscopy (AFM). Dynamic Mechanical Thermal Analysis in bending and stretching mode will allow to study the segmental relaxation as a function of chain architecture. In situ time-resolved Wide Angle and Small Angle X-ray Scattering with synchrotron radiation and neutrons will be used for studying these stress induced structural transformations and crystallization kinetics of crystallizable segments under a variety of conditions including controlled cooling rate, temperature jumps or by effect of pressure.

These studies will allow understanding the relationships between the structures of the metallorganic catalysts and the synthetic strategy used for the preparation of the polymers, the molecular and the crystalline structure of the obtained materials and the final end-use material properties, with particular reference to the links between molecular and crystalline structure, solid-state mechanical and viscoelastic properties, crystallization ability, chain dynamic, as a function of molecular architecture fixed in the polymerization step.

The final goal is to establish the rules of synthetic retro-design i.e. the rules that for any given set of desired properties and end use applications allow identifying the best molecular architecture and the most suitable synthetic approach (including the catalysts to be utilized, the synthetic method, polymerization temperature and pressure) for preparation of the targeted polymeric material.

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Ti rispoderemo al piu' presto. Grazie per averci contattato

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