Monomers, mesogenic copolymerization

If a mesogenic monomer is copolymerized with a nonmesogenic monomer, the mesophase is observed above a minimum concentration of the mesogenic monomer. For example, neither poly (methyl meth-acrylate)-co-[6-[4 -(4"-cyanophenylazo)-phenoxy]hexyl methacrylate]) DP 35, pdi =1.35) nor poly (methyl methacry late)-co-[6-[4 -(4"-n-butoxyphenoxycarbonyl)-phenoxy]hexyl methacrylate] DP 69, pdi =1.12) (Scheme 36) prepared by metal-loporphyrin-initiated copolymerizations and containing 18-20 mol% of the mesogenic monomer exhibit the SmA mesophase of the corresponding SCLCPs [90]. 

Figure 10 Synthesis of LC polymers with mesogenic side groups (a) homopolymerization (b) copolymerization of different mesogenic monomers (c) copolymerization of mesogenic and nonmesogenic monomers (d) polymer analogous reaction A and B - functional groups.

The latter involves the synthesis of monomers containing LC (mesogenic) groups, with the subsequent homopolymerization or copolymerization with mesogenic or non-mesogenic compounds (Fig. 1), or the attachment of low-molecular crystal... 

Besides, it is possible by copolymerization of one and the same mesogenic monomer with non-mesogenic comonomers to vary the type and temperature range of the mesophase 36,37) (Table 2). It is seen from the table that using alkylacrylates with alkyl groups of different length (A-n) as comonomers and varying the ratio of components it is possible to shift the transition temperatures of a LC phase. 

Copolymerization of two mesogenic monomers is, at the present time, the only pathway to obtain polymers with cholesteric mesophase (see Part 4.4). On the other hand, only by copolymerizing smectogenic and nematogenic monomers and investigating the properties of copolymers in a broad interval of compositions, is it possible to establish the principles of formation of each type of mesophase. We demonstrate... 

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]. 

Fig. 16 Monomers used for block copolymerization containing laterally-attached mesogens...

It is also known that in side-chain LC polymers the copolymerization of optically active monomers with mesogenic monomers, in the same manner as the mixing of optically active compounds with nematic low molecular weight compounds, can induce the formation of a cholesteric mesophase. Therefore, it is expected that inclusion of chiral spacers in main chain liquid crystal polymers, which would be nematic... 

Copolymerize mesogenic monomers to form random copolymers with lower melting temperatures. 

The same authors prepared a series of liquid-crystalline polysiloxanes copolymerizing the nonionic mesogenic monomer cholest-5-en-3-ol(3P)-10-undecenoate 47 and the ionic mesogenic monomer potassium 2-allyloxy-5-cholesteryloxycar-bonyl-benzenesulfonate 48. 

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. 

Copolymerization of several mesogenic monomers of different sizes to give a random and more irregular structure (Figure 5.7b). 

The chiral nematic state, first observed in cholesteryl derivatives, was later detected in other chiral mesogens, and can also he induced hy adding small chiral molecules to a host nematic TCP. Chiral nematic LCPs have thus heen synthesized as side-chain polymers hy introducing a chiral unit in the tail moiety of mesogens or hy copolymerizing cholesterol-containing monomers with another potential mesogenic monomer. Examples [4] of these types are shown as structures (V) and (VI) ... 

The synthesis of polymers capable of entering into a chiral nematic phase initially proved difficult as many of the acrylate and methacrylate comb-branch polymers to which a cholesterol unit was attached as a side chain tended to give a smectic phase. This was overcome by either copolymerizing the cholesterol-containing monomers with another potential mesogenic monomer, or by synthesizing mesogens with a chiral unit in the tail moiety. Examples of both types are shown as structures VIII and IX. 

Although many controlled cationic polymerizations that have been developed [120], only mesogenic vinyl ethers have been used in an attempt to prepare well-defined SCLCPs by a cationic addition mechanism [121]. Nevertheless, these polymerizations (and copolymerizations) provide the most complete series of SCLCPs with the widest range of structural variables. As shown in Eq. (22), most of these monomers, includ-... 

Therefore, copolymerization of a mesogenic monomer with a nonmesogenic monomer whose homopolymer has a lower glass transition temperature can be used to both eliminate side-chain crystallization and to depress the glass transition tempera-... 

Copolymers. The second part of our model is concerned with the copolymerization of monomers with different spacers. In this case a statistical distribution of the centers of gravity of the mesogenic chain might be preferred even more. This prediction was tested with cholesteryl derivatives ... 

The expected preference of a statistical distribution of the mesogenic side chain has so far been only realized by the copolymerization in which n = 2 n.p = 12 and only if the monomer ratio is 1 1. Other compositions also led to smectic phases. The best proof for its cholesteric structure is its selective reflection of left-circular polarized light in the visible which indicates a left-handed cholesteric helix of the polymer. The structure has been established also by x-ray investigations (8). This copolymer is the first enantiotropic cholesteric polymer. 

In the swollen block copolymeric materials, the insoluble block of the polymer aggregates into microphase separated domains that in turn are dispersed in well-defined, spatially periodic supramolecu-lar structures.(18) While the morphologies of these structures are sometimes indistinguishable from textures assumed by thermotropic (and lyotropic) MLCs, these block copolymer phases are frequently more solid-like in their physical properties. Multiple interconnections between microphase separated domains tend to establish static, 3-dimensional, translationally ordered topologies in the materials. These aspects of the mesogenic block copolymers can be emphasized if, for example, multi-block copolymers — chains with several distinct monomer compositions along its contour length — are swollen,(19) Reference 20 provides a current entry to the literature of mesomorphic block copolymers. 

Copolymerization of several mesogenic monomers such as p-hydroxy-benzoic acid (PHB) or 2-hydroxy-6-naphthoic acid produces random copolymeric structures with depressed melting points. ... 

If the same nematic monomer but various mesogenic cholesterol-containing monomers are used for copolymerization (copolymer series 6-9, 10-13, and 14-16), the optical properties of copolymers are only slightly affected. The dependence of on the content of cholesterol-... 

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