結合ポリマーMEH-PPVVにおける秩序-乱雑の移行
Anna Köhler1, Sebastian T Hoffmann, Heinz Bässler
1Organic Semiconductors, Experimental Physics II, Department of Physics and Bayreuth Institute of Macromolecular Science, University of Bayreuth, Bayreuth 95440, Germany. anna.koehler@uni-bayreuth.de
Journal of the American Chemical Society
|June 20, 2012
まとめ
ポリ・・・p-フェニレン・ビニレン (MEH-PPV) の青と赤の相間の移行は,重要な現象である. この相変遷は204Kで起こり,電子安定化とエントロピー損失によって引き起こされます.
科学分野:
- マテリアルサイエンス 材料科学
- ポリマー化学のポリマー化学について
- 物理化学 物理化学
背景:
- ポリ (p-フェニレン・ヴィニレン) (MEH-PPV) は,青と赤の相がはっきりしている.
- これらの相間の移行を理解することは,ポリマーの性質を制御するために不可欠です.
研究 の 目的:
- MEH-PPVの青から赤の段階への相変化を調査する.
- この移行を重要な現象として定量的に記述する.
主な方法:
- MEH-PPVをメチルテトラヒドロフラン (MeTHF) で様々な温度と濃度で研究するために,吸収と光スペクトロスコーピーを用いた.
- クーンエクシトンモデルは,スペクトルデータを分析し,有効な結合長さを決定するために適用されました.
主要な成果:
- 青色から赤色への相変遷は,第2次相変遷であり,臨界温度 (T (c)) は204Kであった.
- T (c) 未満では,MEH-PPVが赤色相を形成し,有効結合長さの増加 (約. 10回繰り返す単位) と,より秩序ある形状である.
- 室温で存在する青色相は,より短い有効結合長 (約. 5 繰り返し単位) は,無秩序な形状を示す.
結論:
- 段階移行は,電子安定化エネルギーとエントロピー損失のバランスによって制御されます.
- 赤相形成には集積が必要ですが,電子状態は主に連鎖内です.
- この研究は,温度誘発の相変化によるMEH-PPV形態制御の定量的な理解を提供します.
さらに関連する動画
関連する概念動画
Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)
Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
Cationic Chain-Growth Polymerization: Mechanism
The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
Anionic Chain-Growth Polymerization: Mechanism
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.
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...
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...
Polymer Classification: Crystallinity
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Polymer Classification: Stereospecificity
Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...


