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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
Published on: September 26, 2016
Structure-property correlations in polypropylene from metallocene catalysts: stereodefective, regioregular isotactic
Claudio De Rosa1, Finizia Auriemma, Annunziata Di Capua
1Dipartimento di Chimica, Università di Napoli Federico II, Complesso Monte S. Angelo, Via Cintia, 80126 Naples, Italy.
Journal of the American Chemical Society
|December 23, 2004
Summary
New metallocene catalysts create tailored polypropylenes with tunable properties. Controlling regio-errors (rr defects) in isotactic polypropylene allows for precise adjustments in mechanical behavior, from stiff plastics to flexible thermoplastics and strong elastomers.
Area of Science:
- Polymer Chemistry
- Materials Science
- Catalysis
Background:
- Metallocene catalysts enable precise control over polymer microstructure.
- Isotactic polypropylene's properties are influenced by stereoregularity and defects.
- Regio-errors (rr defects) impact polypropylene's polymorphic behavior and mechanical characteristics.
Purpose of the Study:
- To synthesize isotactic polypropylenes with varying degrees of stereoregularity using novel C(1)-symmetric indenyl-ansa-dithienocyclopentadienyl-based zirconocenes.
- To investigate the effect of regio-errors (rr defects) on the polymorphic behavior and mechanical properties of polypropylene.
- To establish a relationship between defect concentration, polymorphic form, and material properties.
Main Methods:
- Synthesis of MAO-activated C(1)-symmetric indenyl-ansa-dithienocyclopentadienyl-based zirconocenes.
- Polymerization of propylene to produce isotactic polypropylenes with controlled molecular weights and stereoregularity.
- Analysis of polymorphic behavior (crystallization of gamma and disordered forms) and mechanical properties as a function of rr defect concentration.
Main Results:
- The presence of rr defects induces crystallization of the gamma form and intermediate disordered modifications.
- A linear relationship was found between the amount of gamma form and the average length of isotactic sequences.
- Polypropylene samples with 3-4% rr defects exhibit high melting points (130-160°C) and act as stiff-plastic materials.
- Samples with 4-6% rr defects show lower melting points (115-120°C) and behave as flexible thermoplastic materials.
- Samples with 7-11% rr defects have melting points of 80-110°C and function as high-strength thermoplastic elastomers.
Conclusions:
- Tailored design of metallocene catalysts allows fine-tuning of polypropylene chain microstructure.
- Control over rr defects enables the production of polypropylenes with a spectrum of properties, bridging stiff plastics and elastomers.
- This approach facilitates the development of novel polypropylene materials with desired intermediate properties for specific applications.
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