Phase structures, transition behavior and surface alignment in polymers containing rigid rod-like backbones with flexible side chains, 3. The even-odd effect on phase transitions in combined liquid crystal polyesters

Ge, Jason J.; Honigfort, Paul S.; Ho, Rong‐Ming; Wang, Shy-Yeu; Harris, Frank W.; Cheng, Stephen Z. D.

doi:10.1002/(sici)1521-3935(19990101)200:1<31::aid-macp31>3.0.co;2-l

Cited by 20 publications

(19 citation statements)

References 16 publications

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“…Again, this endothermic process seems to involve two transition processesnarrow and broad. Furthermore, the fact that the onset transition temperature during heating is lower than that during cooling is also an indication that more than one transition process is involved. − On the other hand, the endotherm in the low-temperature region is relatively broad (∼63 °C). At a heating rate of 1 °C/min, the overall heat of transition is 1.6 J/g.…”

Section: Resultsmentioning

confidence: 99%

Interrelationships of Nanometer and Subnanometer Structures in a Polynorbornene Containing Second Generation Liquid-Crystalline Monodendrons as Side Groups

et al. 2002

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A series of polynorbornenes containing monodendrons as side groups [DPNB(n)] with different degrees of polymerization (n) were synthesized. These dendritic side groups were second generation monodendrons based on the AB 2 mesogenic monomer, 13-hydroxy-1-(4-hydroxyphenyl)-2-(4hydroxy-4′′-p-terphenylyl)tridecane building blocks. Although the mesogens were rodlike, the polymer samples were overall conformationally flexible and displayed liquid-crystalline (LC) behavior. Above n ) 20 in DPNB(n), both the transition temperatures and heats of transitions were independent of n. Therefore, a DPNB(40) was chosen as the representative polymer for this study. The polymer exhibited complicated phase transformation behaviors which were associated with two different length scales. During cooling, a nematic (N) phase, two smectic A (S A and S A m ) phases, and one hexatic B (S B h ) phase were observed. Among them, the N phase only appeared in a narrow temperature window of less than 2 °C. The S A m phase might be monotropic and metastable with respect to the S B h phase. The N phase was formed via the orientation order of the LC mesogens in the monodendrons of the side groups on the subnanometer scale. In addition to the molecular orientation order, both of the SA and S A m phases also possessed the ordered layer structures on the nanometer scale despite different layer spacings (5.35 nm vs 4.90 nm). In the S B h phase, the layer structure was much larger than those in both the SA and the S A m phases (8.84 nm), and its lateral molecular packing exhibited a two-dimensional hexagonal array on the subnanometer scale (a ) 0.52 nm and γ ) 120°). Interrelations of these nanometer and subnamometer structural formations in these phases were discussed.

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Section: Resultsmentioning

confidence: 99%

Interrelationships of Nanometer and Subnanometer Structures in a Polynorbornene Containing Second Generation Liquid-Crystalline Monodendrons as Side Groups

et al. 2002

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“…It has been found that phase behaviors of this series of polymers exhibit an interesting odd−even effect. PEFBPs( n = even) only possess LC phases, while for PEFBPs( n = odd) both LC and crystalline polymorphism have been identified. , Here, we report polymorphous structures and their phase relationships on one of this PEFBP series, of which a 4-cyanobiphenyl mesogen in each side chain is coupled with the aromatic backbone via seven methylene units, PEFBP( n = 7). Compared with those previous studies, , this polymer is the most difficult one to study since the methylene unit number in the side chains is the smallest.…”

Section: Introductionmentioning

confidence: 89%

“…PEFBPs( n = even) only possess LC phases, while for PEFBPs( n = odd) both LC and crystalline polymorphism have been identified. , Here, we report polymorphous structures and their phase relationships on one of this PEFBP series, of which a 4-cyanobiphenyl mesogen in each side chain is coupled with the aromatic backbone via seven methylene units, PEFBP( n = 7). Compared with those previous studies, , this polymer is the most difficult one to study since the methylene unit number in the side chains is the smallest. This results in not only a higher glass transition temperature ( T g ) and other transition temperatures but also a change of the coupling power between the 4-cyanobiphenyls and the backbones.…”

Section: Introductionmentioning

confidence: 89%

“…Molecular architecture of LCPs emerges to be one of important elements in achieving desired physical properties via soft-ordered structural formations. Among different structural designs in LCPs, one interesting approach is to introduce flexible side chains onto the rigid-rod-like backbones in polymers. − It has also been reported that in these comb-shaped LCPs mesogens can also be incorporated into the side chains. − Consequently, the characteristics of chemical structures of the main-chain and side-chain mesogens, such as azobenzene and azoxybenzene, − p -phenylene benzoate, , and biphenylene, − may influence the molecular packing, the order of mesophases, and sometimes even the formation of nanoscale suprastructures.…”

Section: Introductionmentioning

confidence: 99%

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Polymorphous Structures and Their Phase Relationships in a Main-Chain/Side-Chain Liquid Crystalline Polyester

Ruan

Zhang

et al. 2001

Macromolecules

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A series of specially designed polyesters consisting of aromatic main-chain/side-chain liquid crystalline (LC) polymers for flat-panel display applications have been synthesized via polycondensation of 2,2′-bis(trifluoromethyl)-4,4′-biphenyldicarbonyl chloride with 2,2′-bis{ω-[4-(4-cyanophenyl) phenyoxy]n-alkoxycarbonyl}-4, , where n is the number of methylene units in the side chains). For a PEFBP polyester of which a 4-cyanobiphenyl mesogen in each side chain is coupled with the aromatic backbone via seven methylene units, PEFBP(n)7), complicated polymorphism has been identified during its structural evolutions. On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, electron diffraction (ED), polarized light, and transmission electron microscopy (TEM) experiments, it is found that this polymer possesses three triclinic crystalline (K t1, Kt2, and Kt3) phases having the same symmetry but different unit cell dimensions, one highly ordered LC smectic phase having an orthorhombic (SKO) structure, and one nematic (N) phase. Both of the triclinic Kt1 and Kt3 structures are also confirmed by the ED results. Investigations of thermodynamic phase stability relationships indicate that when PEFBP(n)7) is crystallized from the N phase, the Kt1 phase forms. During heating, this Kt1 phase transfers to the Kt3 phase via reorganization and melting/recrystallization before it enters the N phase. However, when the sample is first cooled to below 130 °C to form the SKO phase, the Kt2 phase develops during heating. Further heating the Kt2 phase leads to a transformation to the Kt3 phase at high temperatures via, again, reorganization and melting/recrystallization. Nevertheless, no apparent transformation between the Kt1 and Kt2 phases is experimentally observed. Polarized infrared spectroscopy experimental results indicate that the aromatic polyester backbones and 4-cyanobiphenyl mesogens are parallel to each other and packed into one crystal unit cell. TEM observations show different morphological characteristics of the Kt1 and Kt3 phases. It is concluded that the Kt3 phase is the thermodynamically most stable phase, and the Kt1 and Kt2 phases are metastable. These two phases can be experimentally accessed only because the crystallization rate of the Kt3 phase is much slower than those of the Kt1 and Kt2 phases.

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“…In order to tune these properties, main-chain LC polymers, comprised of flexible alkylene spacers between rigid and controlled aromatic units, with various chemical structures and molecular architectures for both mesogenic groups and flexible spacers have been designed [1][2][3][4][5][6][7][8][9][10][11]. It is common to tailor LC stabilities by selecting different mesogenic groups, varying the location of the mesogens, and altering the lengths and types of flexible spacers in the LC polymers.…”

Section: Introductionmentioning

confidence: 99%

Structures and phase transformations of odd-numbered asymmetric main-chain liquid crystalline polyesters

Jeong

Knapp

et al. 2006

Polymer

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Phase structures, transition behavior and surface alignment in polymers containing rigid rod-like backbones with flexible side chains, 3. The even-odd effect on phase transitions in combined liquid crystal polyesters

Cited by 20 publications

References 16 publications

Interrelationships of Nanometer and Subnanometer Structures in a Polynorbornene Containing Second Generation Liquid-Crystalline Monodendrons as Side Groups

Interrelationships of Nanometer and Subnanometer Structures in a Polynorbornene Containing Second Generation Liquid-Crystalline Monodendrons as Side Groups

Polymorphous Structures and Their Phase Relationships in a Main-Chain/Side-Chain Liquid Crystalline Polyester

Structures and phase transformations of odd-numbered asymmetric main-chain liquid crystalline polyesters

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