Liquid Crystalline Polymers. 15. Synthesis and Thermal Behavior of Some Aromatic Polyethers Containing Different Spacers

Abstract

A series of aromatic homo-and copolyethers containing 6, 7 or 8 methylenic groups as spacers are presented. The polymers were synthesized by phase-transfer catalysis and they were characterized by using 1 H-NMR, polarized light microscopy, differential scanning calorimetry and thermogravimetric analyses. All copolymers have low molecular weight, situated within the oligomer domain. They have high transition temperatures except for the case when bent or semi-flexible bisphenols were used as comonomers. Only 4,4 1 -dihydroxyazobenzene-based polymers showed liquid crystalline properties with a mesophase range over 50 2 C, and with the clearing temperatures situated near their thermal decomposition limit. The insertion of kink or flexible bisphenols was not favorable to mesophase formation (it induced too high a disorder in the system), but it lowered the transition temperatures, as expected. Few exceptions occurred in the case of bisphenol A and 4,4 1 -dihydroxybenzophenone. The biphasic nature of these copolyethers is most probably due to both the polydispersity and the chemical heterogeneity of the samples. Some of the semi-crystalline copolymers may exhibit virtual mesophase that can be uncovered by increasing their molecular weight or by raising the free energy of the isotropic liquid state.

Study of the nanostructuration capacity of some azopolymers with rigid or flexible chains

“…This assumption is based on previously published thermal studies focused on the azobenzene structures. [34][35][36] The same azopolyimide polymeric structure (e) was reported also in references 24,31 showing only one thermal degradation step. This thermal decomposition profile can be probably explained by taking into account the different molecular weight values.…”

Thermal behavior of some aromatic copolyethers containing a propylenic spacer

“…Details concerning the synthesis procedure have been previously reported [1][2][3]. Polymers' thermostability was investigated using thermo-dynamic methods run on a MOM-Budapest apparatus.…”

“…The trans-cis transition will significantly influence some of the polymer properties, such as dipole-moment, inter-chain interactions, etc., with direct influence on the supramolecular order degree. Our previous work focused on the study of liquid crystalline polymers (LCP) containing mesogenic groups in the main chain, such as azobenzenic units [1][2][3][4][5][6]. But, due to the presence of the mesogenic groups in the main-chain, high transition temperatures values were observed.…”

The Non-isothermal Degradation Process of some Polyethers and Azo-polyethers

“…For liquid crystalline (LC) polymers with mesogenic groups in the main chain, it is very important to know the limits of the thermal stability, taking into consideration the high values of the temperature transitions. Due to the fact that there are not many reported studies [6][7][8][9][10][11] concerning the thermal stability of the aromatic polyethers, we decided to extend the thermal investigation to polyethers without LC properties.…”