Investigation on dual properties of photosensitive thermotropic liquid‐crystalline poly(benzylidene‐ether)s containing alkanones and methylene spacers in the main chain

Abstract

Thermotropic main chain liquid‐crystalline poly (benzylidene‐ether)s were synthesized by Claisen‐Schmidt polycondensation reaction of 4,4′‐diformyl‐2,2′‐dimethoxy‐α,ω‐diphenoxyalkanes with acetone, cyclopentanone, and cyclohexanone. The diformyl precursors were synthesized from 4‐hydroxy‐3‐methoxybenzaldehyde with dibromoalkanes of varying spacer lengths. The structure of monomers and polymers was confirmed by elemental analyses, Fourier‐transform infrared, 1H NMR, and 13C NMR spectral analyses. The thermal properties were studied by thermogravimetric analysis and differential scanning calorimetry. Thermogravimetric analysis (TGA) data revealed that the polymers were stable up to 285 °C and start degrading thereafter. Cyclopentanone‐containing polymers are more stable than cyclohexanone‐ and acetone‐containing polymers. The self‐extinguishing property of the synthesized polymers was studied by calculating the limiting oxygen index values using Van Krevelen's equation. The influence of the length of methylene spacer on phase transition was investigated using differential scanning calorimetry (DSC), and it was proved that the isotropic temperature decreases with an increase in the length of the spacer. Polarized optical microscopic study showed that cyclohexanone‐containing polymers exhibit nematic threadlike and nematic droplet texture. The photolysis of liquid‐crystal poly(benzylidene‐ether)s revealed that the Entgegen, Zusammen (EZ) photoisomerization proceeds in the system. The band gap energy was calculated from absorption spectra and is in the range of 3.05–3.37 eV and proved that the length of spacers has a significant influence on their absorption and emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis, thermal, and photocrosslinking studies of thermotropic liquid crystalline poly(benzylidene‐ether)esters containing α,β‐unsaturated ketone moiety in the main chain

“…The olefinic protons appeared as a singlet around 7.7 ppm in all the polymers as in the monomer. This indicated the existence of E configuration38, 42, 43 in the backbone of the polymers. The singlet peaks appearing at 2.85 to 2.95 ppm and 1.72 to 1.90 ppm correspond to β and γ methylene protons of cyclohexanone respectively 41.…”

Photoactive poly(hydroxyl-amino ether)s based on 4-methyl-cyclohexanone and 4-tert-butylcyclohexanone moieties in the main chain: synthetic methodology and characterization

“…As shown in Table 3, the char residue values of these polymers at 600 °C are high. The limiting oxygen index (LOI) values of all polymers which calculated by using the char residue values, obtained from TGA curves in Van Krevelen's equation [63,66,67] are higher than the threshold in irradiation time and intensity of δ−δ* absorption of the cyclobutane increases. The degree of photocrosslinking can be calculated by using the following equation [69]: Degree of photocrosslinking = (1 _ A t / A o ) × 100 Where A o is the absorbance at λ max before UV irradiation, A t is the absorbance at time t. The photocrosslinking degrees of the polymers after UV irradiation for 30 minutes were 14%, 11%, 67% and 55% corresponding to P1b, P1d, P2b and P2d.…”

Synthesis, spectral and thermal characterization of polyester derived from 1,1-bis(4-hydroxyphenyl)cyclohexane

“…This type of observation was well reported by various research groups. [36][37][38] The aromatic polyesters are found to be more stable than the aliphatic polyesters. Among the aromatic polyesters, the polymer containing terephthaloyl units showed a higher stability and char yield when compared with the polyester derived from isophthalic acid.…”