Oxyethylene spacer

Figure 16 Loss tangent (tanS) at 3 Hz, as a function of temperature for a series of main chain thermotropic polyesters having oxyethylene spacers.

Crosslinked poly(styrene) beads (20) were prepared with contain Ru(bpy)2+ anchored at oligo(oxyethylene) spacer group 50). Vigorous stirring was needed for the suspended complex (20) to sensitize the photoreduction of MV2+ in the presence of... 

FIGURE 7.9 Variation of the transition entropy AS ilR with the number of constituent atoms (n) of the spacer BCBOn (CBA-n) [Emsley et al., 1984] and MBBE- [Kobayashi, 2004 Abe et al., 2007]. While the former comprises PM-type spacers, the latter includes a POE-type spacer. Note that the oxyethylene spacers of MBBE-x are expressed by the number of constituent atoms. The oxygen atoms of the ether linkage located at both chain terminals are not counted in n. 

Furuya, H., Iwanaga, H., Nakajima, T., and Abe, A., Nemahc conformation of oxyethylene spacers involved in main-chain hquid crystals, Macromol. Symp., 192, 239-250 (2003). 

Jeon In-Yup., Tan Loon-Seng, Baek Jong-Beom. (2007). Synthesis of Linear and Hyperbranched Poly(esterketone)s Containing Flexible Oxyethylene Spacers. 

FIGURE 15 Phase diagram of MBBE with oxyethylene spacer of different length data after Abe etal. (2005) ( ) ( ). ... 

The phase transitions depend significantly on spacer length, as has been demonstrated for oligo-oxyethylene spacers.Closer coupling between the mesogenic groups and the polymer backbone tends to make the system more sensitive to the mechanical deformation, at least in the case of methylene groups in the spacer. ... 

Sulfated and sulfonated ethoxylated cholesterol surfactants have been synthesized and studied by Meissner et al. [8]. The oxyethylene spacers consisted of three and four units. The investigated surfactants all formed lamellar phases upon addition of water at room temperature. The sulfonate variants displayed a richer phase behavior with hexagonal or micellar cubic phases at water concentrations higher than those of the lamellar phases. 

This type of polymer support seems to be an interesting alternative to conventional polystyrene because the simple procedures for the experimental work-up of the Merrifield synthesis can be applied and simultaneously quasi-homogeneous reaction conditions are attained by reason of the hydrophilic poly(oxyethylene) spacer group. 

Although the liquid crystalline phase of most polybibenzoates usually undergoes a rapid transformation into a three-dimensional crystal, the introduction of oxygen atoms in the spacer of polybibenzoates has been used to prevent or to slow down this transformation. The dynamic mechanical behavior of polybibenzoates with 2, 3, or 4 oxyethylene groups in the spacer (PDEB, PTEB, and PTTB, respectively) is determined by the composition of the spacer [24], as discussed in this section. 

The presence of three oxyethylene units in the spacer of PTEB slows down the crystallization from the meso-phase, which is a very rapid process in the analogous polybibenzoate with an all-methylene spacer, P8MB [13]. Other effects of the presence of ether groups in the spacer are the change from a monotropic behavior in P8MB to an enantiotropic one in PTEB, as well as the reduction in the glass transition temperature. This rather interesting behavior led us to perform a detailed study of the dynamic mechanical properties of copolymers of these two poly bibenzoates [41]. 

Note 3 Examples of polymer backbones are polyacrylates, polymethacrylates, and polysiloxanes the spacers are usually oligomethylene, oligo(oxyethylene), or oligosiloxane. 

Steady-state fluorescence spectra are obtained for dilute solutions of 16 aromatic polyesters with the repeating unit ABm. The chromophore, A, is isophthaloyl or phthaloyl, and the flexible spacer, B, Is methylene or oxymethylene. The number of methylene units Is 2 - 6, and the number of oxyethylene 1 - 4. Results obtained are interpreted within the frame of the RIS method. 

Fluorescence is measured in dilute solution of model compounds for polymers of 2,6-naphthalene dicarboxylic acid and eight different glycols. The ratio of excimer to monomer emission depends on the glycol used. Studies as functions of temperature and solvent show that, in contrast with the analogous polyesters in which the naphthalene moiety is replaced with a benzene ring, there can be a substantial dynamic component to the excimer emission. Extrapolation to media of infinite viscosity shows that in the absence of rotational isomerism during the lifetime of the singlet excited state, there is an odd-even effect In the series in which the flexible spacers differ in the number of methylene units, but not in the series in which the flexible spacers differ in the number of oxyethylene units. 

Polymers of this type have been prepared with various mesogenic units connected by oligomers of poly(ethylene oxide), PEO, and it is possible in some cases to use spacers having a broad distribution of molecular weights instead of a monodisperse molecular species. It shoxxld be noted that each oxyethylene unit adds three bond lengths to the spacer, so the comparison of polymers with different types of spacers should be between spacers having the same numbers of atoms in the spacer chain. 

Most main chain liquid crystalline polymers are composed of mesogenic units linked by spacers with varying degrees of flexibility, such as repeated methylene, oxyethylene, or siloxane groups, etc., in order to reduce the... 

FIGURE 7.2 Variation of the phase-transition temperatures, Tcn and Tni, of MBBE-x as a function of the number of oxyethylene units (x) in the spacer. 

Abe, A., Hiejima, T., Kobayashi, Y, Zhou, Z., and Nakafuku, C., Thermodynamic characteristics of chain molecules in the nematic state PVT studies of main chain liquid crystal comprising a long oxyethylene-type spacer. Macromolecules, 40,1746-1753 (2007). 

Hiejima, T., Seki, K., Kobayashi, K., and Abe, A., Orientational and conformational characteristics of oxyethylene-type spacers involved in dimer hquid crystals, 7. Macromol. Sci., B42, 431 39 (2003). 

Semirigid-rod LC monomers contain spacers consisting of methylene units with five to 10 carbons or oxyethylene units between mesogen and reactive... 

Naka, Y. Yu, H. F. Shishido, A. Ikeda, T. (2009) Photoalignment and Holographic Properties of Azoberizene-Containing Block Copolymers with Oxyethylene and Alkyl Spacers. Mol. Cryst. Liq. Cryst, 2009, 513,131-141. 

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