Investigation of the Nematic-Isotropic Biphase in Thermotropic Main Chain Polymers. Homogeneity of the Pure Isotropic and Nematic Phases. Part III: NMR Study

The phase-separation process and the self-organization of the textures in the biphase region of a thermotropic liquid crystalline polyester sample [poly(4,4'-dioxy-2,2'-dimethylazoxybenzene-dodecanedioyl)] were studied by polarizing light microscopy both during the heating from the fully anisotropic phase to the biphase region and during the cooling from the isotropic phase to the biphase region. The phase separation occurs as a consequence of chain segregation according to the chain length. The phase-separation process is found to be the same for both thermal procedures, but the self-organization of the textures is found to strongly depend on thermal history. The domain structure depends on the thermal history under the heating and cooling cycles employed in this work. The special heating process used in this work developed a fractionation of molecular species in space according to their molecular length which caused a memory effect in the structure evolution during a subsequent cooling process, giving rise to a unique domain structure as described in the text.

show abstract

“…At 123 °C a fully anisotropic phase is observed. This temperature is about 10 °C lower than that obtained in the fresh sample.…”

Section: Resultscontrasting

confidence: 60%

Phase-Separation Process and Self-Organization of Textures in the Biphase Region of Thermotropic Liquid Crystalline Poly(4,4'-dioxy-2,2'-dimethylazoxybenzene-dodecanedioyl). 1. A Study on the Athermal Conditions

Nakai¹,

Wang²,

Hashimoto³

et al. 1994

Macromolecules

View full text Add to dashboard Cite

show abstract

“…Crystalline polymers such as linear polyethylene can be fractionated into high- and low-molecular-weight components by isothermal crystallization in the biphasic region after cooling from the homogeneous melt and side chain liquid crystalline homopolymers can be fractionated by isothermal ordering in the biphasic region for several hours. Both experimentalists − and theoreticians − conclude that the biphasic region of liquid crystalline homopolymers is due to selective partitioning of different chain lengths between anisotropic and isotropic domains (or two different anisotropic domains) and that the breadth of the transition reflects the molecular weight distribution of the sample.…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, both main-chain and side chain liquid crystalline homopolymers can be fractionated by isothermal ordering in the biphasic region for several hours. Both experimentalists − and theoreticians − conclude that the biphasic region of liquid crystalline homopolymers is due to selective partitioning of different chain lengths between anisotropic and isotropic domains (or two different anisotropic domains) and that the breadth of the transition reflects the molecular weight distribution of the sample. Although some of the theories take partial flexibility into account, they are based on a distribution of rod lengths, which should not vary as a function of molecular weight when the mesogen (rod) is attached as a side chain to the polymer backbone. − In addition, the broad transitions observed by DSC are observed under dynamic conditions, not isothermal conditions that force phase segregation of individual chains with different transition temperatures.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Molecular Architecture on the Thermotropic Behavior of Poly[11-(4‘-cyanophenyl-4‘‘-phenoxy)undecyl acrylate] and Its Relation to Polydispersity

1998

View full text Add to dashboard Cite

Contrary to theoretical predictions on rodlike molecules (mixture of axial ratios) and previous experimental speculations on side chain liquid crystalline polymers (mixture of molecular weights), the breadth of the isotropization transition of poly[11-(4‘-cyanophenyl-4‘‘-phenoxy)undecyl acrylate] is not broadened by polydispersity in chain length alone. Instead, it is broadened by the limited miscibility of a mixture of branched structures. SCLCPs and their mesogenic side chains can therefore be treated as mixtures of random coils and monodisperse rods. This was demonstrated by comparing the thermotropic behavior of linear and three-arm star poly[11-(4‘-cyanophenyl-4‘‘-phenoxy)undecyl acrylate]s prepared by atom-transfer radical polymerization (ATRP), and their binary blends and unmixed composites. The biphasic region of linear polymers with pdi = 1.15−1.49, and of their binary mixtures, is extremely narrow. Although 3-arm star polymers with pdi = 1.11−2.20 also exhibit extremely narrow isotropization transitions, binary mixtures of the star polymers with significant differences in branching density have limited miscibility and broad isotropization transitions. The broad isotropization transition of unfractionated poly[11-(4‘-cyanophenyl-4‘‘-phenoxy)undecyl acrylate] prepared by standard radical polymerization indicates that it also contains a mixture of branched structures due to chain transfer to polymer at high monomer conversion. 11-(4‘-Cyanophenyl-4‘‘-phenoxy)undecyl acrylate is the most highly functionalized monomer to be polymerized by ATRP, and the resulting 3-arm star polymers are the first star polymers synthesized by ATRP.

show abstract

“…For thermotropic main-chain liquid crystalline (LC) polymers, chemical heterogeneity, such as (i) the sequence distribution of rigid segments and their compositional variation and (ii) polydispersity of molecular mass (or chain length), is the origin of polydispersity in chain flexibility ( polyflexibility ). They are the main factors making the anisotropic−isotropic phase transition of such polymers more complex than that of low molecular weight liquid crystals. − A biphase region, wherein the anisotropic liquid phase coexists with the isotropic liquid phase, is developed transiently during the nematic−isotropic transition. For thermotropic LC polymers, the biphase region exists in a certain temperature interval even at thermal equilibrium.…”

Section: Introductionmentioning

confidence: 99%

“…For thermotropic LC polymers, the biphase region exists in a certain temperature interval even at thermal equilibrium. Formation of the biphase is ascribed to the partitioning of molecules with different chain flexibilities between the two phases. − For various statistical LC copolyesters, a broad biphase region was detected 1,2 and its formation was primarily explained by the polyflexibility, or more precisely by a polydispersity, of persistence lengths (factor i). , In contrast, the biphase behavior of the LC polymers with a chemically more regular structure appears in a somewhat narrower temperature interval, because it is primarily ascribed to the polyflexibility due to the polydispersity in molecular mass (factor ii). − In such LC polymers, macromolecules are partitioned within the isotropic and anisotropic phases according to their chain length; namely, a fraction of shorter chains cannot be incorporated into the nematic phase and is expelled from the nematic phase to form isotropic domains in which the molecules are expected to be essentially in a random coil conformation. On the other hand, another fraction of relatively longer chains remains in the anisotropic phase with an extended-chain conformation.…”

Section: Introductionmentioning

confidence: 99%

Phase-Separation Processes and Self-Organization of Textures in the Biphase Region of Thermotropic Liquid Crystalline Poly(4,4‘-dioxy-2,2‘-dimethylazoxybenzene−dodecanedioyl). 2. A Study of the Isothermal Conditions

et al. 1996

View full text Add to dashboard Cite

The isothermal phase-separation process and the self-organization of textures in the biphase region of a thermotropic liquid crystalline polyester were investigated in situ by using polarizing light microscopy. When the test temperature was rapidly raised from room temperature to the temperature corresponding to the biphase region (T-jump) or rapidly lowered from a temperature corresponding to the isotropic phase to that corresponding to the biphase region (T-drop), the phase separation occurs as a consequence of chain segregation according to the chain length: the chain species shorter than the average length gradually separate from the anisotropic phase to form the isotropic phase. The phase-separated textures transiently formed in the biphase region depend strongly on the thermal processes: in the case of the T-jump the coarsening of texture involves the diffusion−coalescence of isotropic drops in the anisotropic matrix, while in the case of the T-drop it involves the diffusion−coalescence of anisotropic drops in the isotropic matrix. For both cases growth of the radius of the drop R with the annealing time t obeys approximately the same power law, R(t) ∼ t 1/3, over the time scale covered in this experiment. The coarsening mechanism is discussed in the text.

show abstract

Investigation of the Nematic-Isotropic Biphase in Thermotropic Main Chain Polymers. Homogeneity of the Pure Isotropic and Nematic Phases. Part III: NMR Study

Cited by 10 publications

References 12 publications

Phase-Separation Process and Self-Organization of Textures in the Biphase Region of Thermotropic Liquid Crystalline Poly(4,4'-dioxy-2,2'-dimethylazoxybenzene-dodecanedioyl). 1. A Study on the Athermal Conditions

Phase-Separation Process and Self-Organization of Textures in the Biphase Region of Thermotropic Liquid Crystalline Poly(4,4'-dioxy-2,2'-dimethylazoxybenzene-dodecanedioyl). 1. A Study on the Athermal Conditions

The Effect of Molecular Architecture on the Thermotropic Behavior of Poly[11-(4‘-cyanophenyl-4‘‘-phenoxy)undecyl acrylate] and Its Relation to Polydispersity

Phase-Separation Processes and Self-Organization of Textures in the Biphase Region of Thermotropic Liquid Crystalline Poly(4,4‘-dioxy-2,2‘-dimethylazoxybenzene−dodecanedioyl). 2. A Study of the Isothermal Conditions

Contact Info

Product

Resources

About