Liquid crystalline polymers copolymerization

It is worthy to note at this point that the polymerization of mesogenic monomers with chiral moieties does not necessarily result in polymers with the chiral liquid crystalline phase. For example, Finkelmann (1982) reported that homopolymers of chiral monomers yielded only smectic mesophases. On the other hand, copolymerization of chiral monomers with different spacers or of a chiral monomer and a nematic monomer has been proven effective and convenient for synthesizing chiral liquid crystalline polymers. 

This review introduces the method of active ester mtheris, and discusses its application to the preparation of a variety erf specialty polymers, including amphiphilic gels, graft copolymers, and side chain reactive and liquid crystalline polymers. The polymerization and copolymerization of activated acrylates by solution and suspension techniques are discussed, and polymer properties such as comonomer distribution, molecular weights, C-NMR spectra and gel morphology are reviewed. Potential applications of these polymers are also highlighted, and the versatility of active ester synthesis as a new dimension of creativity in macromolecular chemistry is emphasized. 

Table IV summarizes the results of polymerization experiments. In all cases enantiotropic liquid crystalline polymers were obtained. The homopolymers exhibit smectic phases. Contrary to our expectations smectic polymer phases are obtained also by copolymerization of the monomers in which the spacer length is n = 2 H2 = 6 and n = 6 n2 = 12. A similar result was published recently by Shibaev et al. (l)y based on...

Although it is diffucult to homopolymerize MAH it can be easily copolymerized with numerous vinyl monomers. Such copolymers have achieved technical importance as coatings, glues, adhesives, thickeners, resins, and engineering plastics. In recent literature these polymers were also investigated as side-chain liquid-crystalline polymers [965], ArF-or 193nm-photoresists [966-972]. 

Twisted oriented structures can be expressed, for example, by the addition of chiral dopants. This also applies to liquid crystalline polymer, but because the heat treatment is performed in an open system as described above (one film interface is the alignment substrate and the other interface is with air) an added low molecular weight chiral dopant does not distribute homogeneously within the film after the heat treatment, which made the control of the orientadmi difficult. This problem was solved by copolymerizing a chiral unit into the Uquid crystalline polymer. By this copolymerization of a chiral unit, the twisted orientadmi structure is stable and it is possible to be cmitroUed by the film thickness. Furthermore, by changing the ratio of chiral/non-chiral units, films having the desired twisted orientation and pitch can be produced. 

Aromatic polyesters that do not contain any flexible structural units are often nonmeltable or extremely high melting polymers that cannot be processed. Copolymerization is a way to obtain processable wholly aromatic polyesters The Tm versus copolyester composition curve is a U-shaped curve exhibiting a minimum that is generally well below the Tm of corresponding homopolymers. Liquid crystalline aromatic polyesters, for instance, are usually copolymers.72 An example is Ticona s Vectra, a random copolyester containing 4-oxybenzoyl and 6-oxy-2-naphthoyl units in ca. 70 30 mol ratio. This copolymer melts at ca. 

In contrast to the substituted PPO s, It Is theoretically possible to obtain the same substituted PECH s by homopolymerization of the corresponding mesogenic oxirane, or by its copolymerization with epichlorohydrin. We have attempted these polymerizations in order to better interpret the thermal behavior of the more complicated copolymers that we have obtained by polymer analogous reactions. Homopolymerization would be instructive because the incorporation of nonmesogenic units into liquid crystalline homopolymers doesn t as a rule change the type of mesophase obtained (5). 

Statistical copolymerization of SCLC-monomers with non-liquid crystalline monomers leads to dilution of the mesogenic units in the polymer, and (below a critical value) to the loss of the LC behavior of the polymer [47]. 

To obtain amphiphilic polymers, different concepts are conceivable to introduce amphiphilic moieties into the polymer backbone. They are schematically summarized in Figure 5. Polymers of type A and B can be realized, if a polymerizable group is introduced into the hydrophobic group (type A) or hydrophilic group (type B) of a conventional surfactant, which exhibit the liquid crystalline state in solution. Copolymerization of a hydrophilic and a hydrophobic comonomer yields amphiphilic copolymers of type C. According to the convention, these polymers may be called "amphiphilic side-chain polymers"... 

The most intensively developed materials, however, are the azobenzene-containing side chain LC polymers, which show a unique combination of liquid crystallinity and photochromic behavior in a single macromolecule, whereas copolymerization of comonomers with different functionality allows fine tuning of phase behavior, photo-optical properties, and other parameters to the requirements of a particular application. Starting from the first publications of Eich et work in that area has been done by several research... 

The following protocols (6-10) describe the synthesis of some cholesterol-based acrylates and their photopolymerization in an aligned cholesteric phase. The protocols utilize a modification of a system previously described by Shannon. 5 6 ip ie absence of a diacrylate comonomer, the cholesteric phase produced initially on copolymerization is not stable and reverts to a smectic phase on a single cycle of heating and cooling. In the presence of the diacrylate the first-formed phase is stable. This is one example of how crosslinking can stabilise the liquid crystal phase in liquid crystalline elastomers, others include, the so-called, polymer-stabilized liquid crystals and those described in the later protocols. 

The other and most popular way is to copolymerize the flexible segment into the polymer main chains. De Gennes (1975) predicted that incorporation of both a rigid and a flexible segment in the repeating unit should afford semi-flexible polymers exhibiting thermotropic liquid crystallinity,... 

Side chain liquid crystalline and nonlinear optical polymers (e.g. 37 and 38), which are conventionally produced by multi-step processes, are also available very easily via active ester synthesis. A unique feature of the active ester method for this purpose is that a single activated polymer intermediate can be used for the synthesis of any number of macromolecular structures, all by a simple single-step reaction pathway. Synthesis of such polymers by copolymerization of the... 

In conclusion then, we have synthesized a series of extended-chain, aromatic polyazomethlnes under on-degradatlve conditions. Fusible, tractable polymers were obtained by use of unsymmetrlcally placed substituents, copolymerization, and/or limited proportions of flexible chain units. Many of the polymers yield liquid crystalline melts which were spun Into oriented, high tenacity, high modulus fibers. The fibers were further strengthened by heat treatment. The ease of preparation of the aromatic polyazomethlnes and the outstanding tenacity and modulus range of the fibers make these products excellent candidates for use as reinforcing fibers In resins and rubber. 

B. Synthesis of Liquid-Crystalline Hybrid Polymers Using POSS as a Component of Copolymerization ... 

Sadron et al. (l) prepared lyotropic liquid crystalline systems using polymers and a polymerizable solvent and attempted to fix the mesomorphic structure by polymerizing the monomeric solvent. Bouligand et al. (2) attempted to prepare liquid crystalline substances with fixed structure by copolymerizing mono- and bifunctional mesomorphic monomers. However neither group investigated the phase conditions of the monomers or of the monomer and polymer. In both cases identical homogeneous phases were assumed before and after polymerization. 

Electrochemical homopolymerization of poly(aniline-N-alkylsulfonates) (alkyl = propyl, butyl and pentyl) in acetonitrile containing 0.1 M NaC104 and 5 % (v/v) 0.3 M HCIO4 was carried out by Rhee et al. [144]. The polymers were prepared on a platinum electrode by cyclic voltammetry (0.0 to 1.0 V vs Ag/AgCl) or potentiostatic techniques (1.0 V). These polymers were found to form liquid crystalline solutions in water. The conductivity of poly(aniline-N-propanesulfonic acid) and poly(aniline-N-butanesulfonic acid) was reportly 9 x 10 and 6 x 10 S/cm, respectively. Electrochemical polymerization of orthanilic acid, metanilic acid and sulfonic acid and their copolymerization with aniline in dimethyl sulfoxide containing tetrabutyl ammonium perchlorate were carried out by Sahin et al. [145]. These polymers and copolymers were found to be soluble in water, dimethyl sulfoxide and N-methylpyrrolidinone. The conductivity of orthanilic acid, metanilic acid and sulfonic acid was reportly 0.052,0.087 and 0.009 S/cm, respectively. The conductivity of copolymers for these three isomers of aminobenzene-sulfonic acid was reported as 0.094, 0.26 and 0.033 S/cm, respectively. Sahin et al. [146] have also prepared the copolymers of these three isomers with aniline in acetonitrile containing fluorosulfonic acid (FSO3H). The copolymers were found to be soluble in water, dimethyl sulfoxide and N-methylpyrrolidinone. 

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