Unusual Phase Behavior of a Mesogen-Jacketed Liquid Crystalline Polymer Synthesized by Atom Transfer Radical Polymerization

Abstract

A series of mesogen-jacketed liquid crystalline polymers, poly{2,5-bis[(4-butoxyphenyl)oxycarbonyl]-styrenes} (PBPCS), with a wide range of molecular weights (M n ) 1.24 × 10 4 -35.6 × 10 4 ) and narrow molecular weight distributions (M w /M n e 1.18) have been synthesized by atom transfer radical polymerization. The resulting polymers have been investigated by a combination of techniques including differential scanning calorimetry, polarized optical microscopy, and X-ray scattering. The samples with M n e 2.42 × 10 4 are isotropic. The samples with M n g 3.36 × 10 4 display a thermodynamically stable isotropic phase at lower temperature and a liquid crystalline (LC) phase at higher temperature. The phase behavior shows a phenomenon quite similar to the reentrant isotropic phase. These transitions are correlated with the rheological properties measured as a function of temperature. The rheological behavior of the polymer in the isotropic phase and in the LC phase has been studied as well. On the basis of these experimental observations, a generalized phase diagram is constructed for the polymers showing the influence of the molecular weight on the phase transition temperature. It is illustrated that LC phase is formed through a global change of the whole molecule from the coiled to extended chain conformation accompanied by an increase of the entropy. Higher entropy originating from the free mobilities of bulky side chains in LC phase has been proposed to be an important factor to stabilize the LC phase.

Synthesis and characterization of optically active helical vinyl polymers via free radical polymerization

“…In Figure 8(b), a ring pattern at 2θ = 4.39° ( d ‐spacing of 2.01 nm) was present, which exhibited an isotropic intensity distribution. Considering the similar X‐ray results reported previously,57–59 we proposed the supramolecular columnar nematic phase for the sample studied, following the same mechanism of LC phase formation.…”

Thermoreversible Order−Order Transition of a Triblock Copolymer Containing a Mesogen‐Jacketed Liquid Crystalline Polymer with a Re‐Entrant Phase Behavior

“…These results are in agreement with the WAXS results. From our previous report, the LC phase is a hexatic columnar nematic (Col hn ) phase. Therefore, PBPCS in the triBCP is amorphous and the triBCP is a coil−coil−coil one at low temperatures.…”

“…The T g of PS cannot be observed mainly because it is a minor component in the triBCP. For D 120 S 100 B 120 , a small endothermic peak is found at 175 °C during the heating process which is attributed to the amorphous−LC transition of the PBPCS block . The exothermic peak at 156 °C during cooling proves that the transition is reversible.…”

“…In this work, we used poly{2,5‐bis[(4‐butoxyphenyl)‐oxycarbonyl]styrene} (PBPCS) as a rod block to synthesize a new kind of ABC rod−coil−coil triBCP. PBPCS is an MJLCP with a re‐entrant phase behavior . For PBPCS with a molecular weight (MW) above 3.36×10 4 g mol −1 , its conformation changes from coiled to worm‐like when the temperature increases above its LC phase formation temperature ( T LC ) at which it goes through an amorphous−LC phase transition.…”

Synthesis and properties of mesogen‐jacketed liquid crystalline polymers containing bistolane mesogen

“…The columnar nematic phase (ϕ N ) is one of the most often observed phase structures in these MJLCPs 26. Higher‐ordered liquid crystalline (LC) structures, such as hexatic columnar nematic phase (ϕ HN ) and hexagonal columnar phase (ϕ H ) have also been observed 25–29. However, the rod‐like chain shall not be the only molecular shape of MJLCPs.…”