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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
Published on: November 27, 2015
How long are the ends of polyene chains?
1Texas A&M University at Galveston, 5007 Avenue U, Galveston, Texas 77551, USA. schmalzt@tamug.edu
The Journal of Chemical Physics
|December 17, 2009
Summary
Conjugation in polyene chains shows that bond lengths stabilize in the middle but are affected by chain ends. Significant conjugation effects extend through six neighboring double bonds, providing extra stabilization energy.
Area of Science:
- Computational Chemistry
- Polymer Science
- Organic Chemistry
Background:
- Conjugation in polyene chains influences electronic and structural properties.
- Bond length alternation is a key characteristic of conjugated systems.
- Understanding chain-end effects is crucial for predicting polymer behavior.
Purpose of the Study:
- To investigate the length scale of conjugation interactions in all-trans polyene chains.
- To determine how chain length affects bond length alternation and stabilization energy.
- To quantify the influence of end effects on conjugated systems.
Main Methods:
- Computational modeling using MP2/cc-pVTZ level of theory.
- Optimization of geometries for polyene oligomers up to n=11 repeat units.
- Analysis of bond lengths, energy increments, and stabilization energies.
Main Results:
- Bond length alternation diminishes towards the center of polyene chains, approaching a constant value for infinite chains.
- End effects significantly influence bond lengths near the chain termini, even in long chains.
- Conjugation effects extend through approximately six neighboring double bonds, contributing about 8 kcal/mol stabilization energy per monomer.
Conclusions:
- The study establishes the length scale for conjugation interactions in polyenes.
- End effects play a significant role in the properties of finite conjugated chains.
- Computational methods provide valuable insights into the behavior of conjugated systems.
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