Cooperative Character of the Relaxation Processes in a Side-Chain Liquid Crystalline Polymer

Abstract

Side-chain liquid crystalline polymers (SCLCP) are complex materials that exhibit peculiar relaxation processes. Particularly, the assignment of the α-relaxation has been controversial. In this work, its attribution to the segmental dynamics within the backbone is strengthened, despite possibly being highly influenced by special modes of motions within the mesogenic groups in the sidechains. The discussion is based on results obtained by dielectric relaxation spectroscopy, TSDC, DSC, DMA, and TMA. It was found that the motion within the spacers may influence the α-process dynamics, broadening the distribution of relaxation times. The analysis of the fragility locates the α-process in the fragile region of the fragile/ strong Angell scale. The δ-relaxation of SCLCPs is cooperative and is found to have similar features to the α _c -relaxation seen in flexible semicrystalline polymers.

Key Words:

• Glass transition
• Liquid crystalline polysiloxane
• Relaxation dynamics

Acknowledgments

Fruitful discussions with Prof. José L. Gómez Ribelles (Univ. Politécnica de Valencia) and the valuable comments of Prof. Phillip Geil (Univ. of Illinois) are both acknowledged. Financial support for this work was provided by FCT-Foundation for Science and Technology, through the POCTI and FEDER programmes.