End-on and side-on nematic liquid crystal dendrimers

L Pastor, J Barberá, M McKenna, M Marcos… - …, 2004 - ACS Publications
L Pastor, J Barberá, M McKenna, M Marcos, R Martín-Rapún, JL Serrano, GR Luckhurst
Macromolecules, 2004ACS Publications
A group of nematic materials based on poly (propyleneimine) dendrimers (PPI) containing
two types of mesogenic subunits were synthesized. The presence of different types of
mesogenic group, the topology of the attachment to the core (end-on and side-on), and the
chemical nature of the linking connection to the PPI scaffold (imine or amide) were used to
tailor the mesomorphic properties. The materials were characterized by a variety of
techniques including 1H, 13C NMR spectroscopy, GPC, MALDI− TOF MS, DSC, POM, and X …
A group of nematic materials based on poly(propyleneimine) dendrimers (PPI) containing two types of mesogenic subunits were synthesized. The presence of different types of mesogenic group, the topology of the attachment to the core (end-on and side-on), and the chemical nature of the linking connection to the PPI scaffold (imine or amide) were used to tailor the mesomorphic properties. The materials were characterized by a variety of techniques including 1H, 13C NMR spectroscopy, GPC, MALDI−TOF MS, DSC, POM, and X-ray diffraction. The crystalline state, when it exists, was found to be suppressed for most of the materials once they had undergone the first transition to the isotropic phase. The majority of the compounds exhibited glass transitions near to or lower than room temperature and an accompanying wide temperature range mesophase. All of the side-on dendrimers synthesized exhibit a nematic mesophase whereas end-on dendrimers exhibit different mesophases depending on the length of the terminal chain of the mesogenic unit (nematic for n = 2, 4, 5). The 2H NMR technique was used to investigate the symmetry of the nematic phase formed by the side-on dendrimers (G = 3). These studies revealed that the symmetry of the nematic phase is uniaxial. They also allow the investigation of the orientational order of the phase and the rate of field-induced director alignment.
ACS Publications
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