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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
Published on: November 27, 2015
Interchain coupled chain dynamics of poly(ethylene oxide) in blends with poly(methyl methacrylate): coupling model
1CNR-IPCF, Dipartimento di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy. ngai@df.unipi.it
The Journal of Chemical Physics
|November 25, 2011
Summary
Poly(ethylene oxide) chain dynamics in blends show a crossover from Rouse model behavior at short times to slower, coupled relaxation at longer times. This transition, observed via neutron scattering and simulations, offers a simpler explanation than previous models.
Area of Science:
- Polymer physics
- Materials science
- Condensed matter physics
Background:
- Poly(ethylene oxide) (PEO) chain dynamics in poly(methyl methacrylate) (PMMA) blends exhibit deviations from the Rouse model at longer timescales.
- Previous explanations, like the random Rouse model (RRM), proposed broad distributions of monomer friction coefficients.
- However, simulations suggest a narrower distribution than predicted by the RRM.
Purpose of the Study:
- To propose a simpler explanation for the observed crossover in PEO chain dynamics.
- To highlight the general nature of relaxation crossovers in interacting systems.
Main Methods:
- Analysis of quasielastic neutron scattering data.
- Molecular dynamics simulations of PEO/PMMA blends.
- Comparison of experimental data with theoretical models (Rouse model, RRM).
Main Results:
- PEO chain dynamics follow the Rouse model at short times (< 1-2 ns) but deviate at longer times.
- A crossover from independent to coupled many-body relaxation is observed at a characteristic time t(c).
- This crossover phenomenon is consistent across different polymer systems, including entangled homopolymers and PEO in PMMA blends.
Conclusions:
- The observed crossover in PEO dynamics provides a simpler explanation for deviations from the Rouse model.
- This crossover reflects a general principle of relaxation in interacting systems, transitioning from independent to coupled behavior.
- The findings emphasize the importance of intermolecular interactions and constraints in polymer dynamics.
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