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Related Concept Videos

Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
Determination of Molar Masses of Polymers I01:24

Determination of Molar Masses of Polymers I

Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
Characteristics and Nomenclature of Copolymers01:24

Characteristics and Nomenclature of Copolymers

Copolymers are the products obtained from the polymerization of multiple monomer species. So, in a polymer chain itself, there can be multiple repeating units that come from different monomers. The process of synthesizing a polymer from different monomer species is called copolymerization. When two monomers are involved, the polymer is known as a bipolymer. Polymers with three and four monomers are termed terpolymers and quaterpolymers, respectively. Figure 1 depicts the copolymerization of...
Polymer Classification: Architecture01:14

Polymer Classification: Architecture

Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...

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Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering
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Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering

Published on: December 21, 2017

An oligomer study on small band gap polymers.

Bram P Karsten1, Lucas Viani, Johannes Gierschner

  • 1Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands.

The Journal of Physical Chemistry. A
|October 2, 2008
PubMed
Summary

Small band gap polymers enhance solar cell efficiency by absorbing more sunlight. This study shows longer polymer chains reduce the band gap, improving light absorption and energy conversion.

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Area of Science:

  • Materials Science
  • Organic Electronics
  • Photovoltaics

Background:

  • Small band gap polymers are crucial for increasing the energy conversion efficiency of polymer solar cells.
  • Enhanced absorption of sunlight is a key factor in improving photovoltaic performance.

Purpose of the Study:

  • To investigate the optical and electrochemical properties of small band gap oligomers with alternating donor and acceptor units.
  • To understand how chain length affects the band gap and electronic properties of these materials.

Main Methods:

  • Combined experimental and theoretical study.
  • Synthesis of well-defined, lengthy oligo(5,7-bis(thiophen-2-yl)thieno[3,4-b]pyrazine)s.
  • Analysis of optical absorptions (ground state, excited state, radical cation, dication) and electrochemical properties.

Main Results:

  • Optical absorptions shift to lower energy with increasing chain length.
  • Band gap reduction is primarily due to an increase in the highest occupied molecular orbital (HOMO) level.
  • Singlet-triplet splitting (S 1-T 1) decreases significantly with increasing chain length, indicating delocalized electronic states.

Conclusions:

  • Alternating donor-acceptor small band gap oligomers show promise for efficient solar energy conversion.
  • Chain length is a critical parameter for tuning the electronic and optical properties.
  • Delocalization of HOMO and lowest unoccupied molecular orbital (LUMO) over multiple units is key to reduced band gaps and improved performance.