Comparative Study of Photomechanical Effects in Linear and Star Azo-Polymers

Abstract

We investigated the influence of the polymer macromolecular geometry and chain length in azobenzene containing polymeric liquid crystals (azo-PLC). In particular we studied the photomechanical effects (photoinduced expansion and shrinking) on monodispersed azo-PLCs (polydispersity index 1.08–1.17) prepared from the same monomer and different molecular weights, both in linear and 3-arm star conformation.

The characterization has been carried out in thin films by high resolution null ellipsometry for a simultaneous and independent determination of both mechanical and optical properties (e.g., thickness and refractive index). The measurement system has been set up in a pump probe configuration for a real time characterization of the photoinduced dynamics. The effect of coupling introduced by the polymer star configuration is discussed.

Keywords:

• azobenzene
• photomechanical effect
• polymeric liquid crystals
• star polymers

PACS:

• 61.30.V
• 78.66

Acknowledgments

This work has been financially supported by MIUR (PRIN 2007) and University of Bologna (CLUSTERCAT-Strategic project 2006).

Notes

^a Determined by SEC in THF at 25°C.

^b Average polymerisation degree for linear macromolecules and for each branch of the star shaped derivatives calculated by values.

^c Obtained from the second DSC heating cycle under nitrogen at 10°C/min heating rate. g (glass), S (smectic A1), N (nematic), I (isotropic) phases.

^d Calculated by  = Conversion·(M _M6A/M _BMPB)·MW _M6A + MW _BMPB, where M _M6A and M _BMPB are the initial amounts in moles of monomer and trifunctional initiator and MW _M6A and MW _BMPB are their molecular weights, respectively.