Unusual phase behaviour of a new liquid-crystalline side group polymer

Wolff, Dietmar; Čačković, H.; Krüger, Hartmut; Rübner, Joachim; Springer, Jürgen

doi:10.1080/02678299308027769

Cited by 24 publications

(18 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The transition temperatures appear strongly dependent on the polymerization degree, the glass (Tg), the smectic-nematic (T SM ) and the nematic-isotropic transition temperatures (Ti) of the series diminishing with the decrease of chain length (Figure 7). In particular, the Ti and T SM values of Star(M6A)-2 to Star(M6A)-24 increase from 124 to 150 C and from 78 to 94 C (Table 1) approaching the maximum values of 152 and 97 C, respectively, found for poly(M6A) with M w ¼ 74;000, obtained by AIBN-initiated free radical polymerization [16]. Interestingly, Star(M6A)-8 and Star(M6A)-24 show higher Tg than the corresponding linear derivative, this finding being attributable to the stiffness of aromatic core, which limits the free movements of one chain end, thus favoring the macromolecules to increase the extent of interchromophore interactions with respect to the related linear sample.…”

Section: Thermal Properties and Polarized Optical Microscopy Charactementioning

confidence: 74%

“…The monomer 4-x-methacryloyloxy-hexyloxy-4 0 -ethoxyazobenzene (M6A) was synthesized as previously reported [16]. THF was purified and dried according to the reported procedures [17] and stored under nitrogen.…”

Section: Methodsmentioning

confidence: 99%

“…Figure 6 reports, as an example, the first cooling and the second cycle heating curves for the sample Star(M6A)-8. The smectic (S A1 ) and nematic (N) liquid-crystalline phases have been identified by the observation of their typical optical texture by POM and confirmed by comparison of their DSC traces with that one of poly(M6A), extensively studied by DSC, POM, and X-ray diffraction [16]. Indeed, the LC texture and the thermal properties of Star(M6A) homopolymers are in agreement with those of poly(M6A) with the expected differences in the transition temperatures values ( Table 2).…”

Section: Thermal Properties and Polarized Optical Microscopy Charactementioning

confidence: 99%

“…All the derivatives have been characterized by usual spectroscopic techniques and their liquid-crystalline behavior investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). With the aim to investigate the structureproperty relationships of these systems, they have been compared with the analogue linear polymer [Poly(M6A)] with M w ¼ 74000, M w =M n ¼ 1:9, previously reported in the literature [16] (Figure 1) and obtained by AIBN free radical polymerization of the corresponding monomer. Synthesis is by ATRP 791 EXPERIMENTAL Physico-Chemical Measurements 1 H-and 13 C-NMR spectra were obtained at room temperature, from 5-10% CDCl 3 solutions, using a Varian NMR Gemini 300 spectrometer.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Synthesis by ATRP and Properties of Liquid Crystalline Three-Armed Star Polymers Containing Azobenzene Chromophores

Angiolini

Benelli

Giorgini

et al. 2007

International Journal of Polymeric Materials

View full text Add to dashboard Cite

Atom Transfer Radical Polymerization (ATRP) has been applied to synthesize liquid crystalline methacrylic polymers having three-arms star structure, starting from a central core of C 3 symmetry. By just changing the duration of the polymerization process, macromolecules having distinct average chain lengths with low polydispersity values and well defined end-groups have been obtained. All the obtained star-shaped polymers, characterized by differential scanning calorimetry and polarized optical microscopy, exhibit smectic and nematic liquid-crystalline phases on heating, with transition temperatures strongly dependent on the average polymerization degree, and high clearing points. The comparison of these systems with the analogous linear derivatives pointed out higher glass transition temperature values, although they are characterized by lower average polymerization degree. Such behavior can be attributed to the stiffness of the aromatic core, which limits the free movement of chain ends.

show abstract

Section: Thermal Properties and Polarized Optical Microscopy Charactementioning

confidence: 74%

Section: Methodsmentioning

confidence: 99%

Section: Thermal Properties and Polarized Optical Microscopy Charactementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Synthesis by ATRP and Properties of Liquid Crystalline Three-Armed Star Polymers Containing Azobenzene Chromophores

Angiolini

Benelli

Giorgini

et al. 2007

International Journal of Polymeric Materials

View full text Add to dashboard Cite

show abstract

“…4-Alkoxy-4'-hydroxyazobenzenes 2 were obtained from 4-acetamidophenol 1 using standard methods of *Author for correspondence; e-mail: bubnov@fzu.cz alkylation, diazotation and coupling (using phenol or o-cresol) [16]. Mesogenic phenols 3 were obtained by esterification of 2 with 4-methoxycarbonyloxybenzoic acid chloride in dry pyridine followed by ammonolysis by 30% ammonia solution at room temperature for 3 h in a mixture of ethanol and acetone (1/1).…”

Section: Synthesismentioning

confidence: 99%

New ferroelectric liquid crystalline materials with an azo group in the molecular core

et al. 2004

View full text Add to dashboard Cite

Six series of new liquid crystalline materials with an azo group (NLN) located in different parts of the mesogenic core of the molecule have been synthesized and their physical properties studied. The chiral segments of these materials are based on alkoxypropionate or alkyllactate units. It has been found that lateral methyl substitution on a phenyl ring in the molecular core disturbs the packing of the molecules. As a result smectic phases disappear and the phase transition temperatures decrease. In addition, shifting the NLN group closer to the chiral centre of the molecule leads to the disappearance of the ferroelectric SmC* phase. For the compounds which show the ferroelectric SmC* phase, the temperature dependence of the spontaneous polarization, the spontaneous tilt angle, the helix pitch length and the complex permittivity has been studied. The effect of shifting the azo group in the molecular core on the physical properties is discussed.

show abstract

Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

Barberá

Giorgini

Paris

et al. 2008

Chemistry A European J

View full text Add to dashboard Cite

The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL), it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. The effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates.

show abstract

Unusual phase behaviour of a new liquid-crystalline side group polymer

Cited by 24 publications

References 14 publications

Synthesis by ATRP and Properties of Liquid Crystalline Three-Armed Star Polymers Containing Azobenzene Chromophores

Synthesis by ATRP and Properties of Liquid Crystalline Three-Armed Star Polymers Containing Azobenzene Chromophores

New ferroelectric liquid crystalline materials with an azo group in the molecular core

Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

Contact Info

Product

Resources

About