Spacer groups polymers with flexible

Polymers with flexible spacer groups. Polymers obtained by precipitation or by casting films from solutions were found to be amorphous as shown by X-ray and microscopical observations. The DSC data revealed that on heating up the samples for the first time a stepwise increase of the specific heat occurred which could be attributed to a glass transition. Thus at room temperature the as received samples were in the isotropic glassy state, apparently no liquid crystalline solutions exist. 

Polymers with flexible spacer groups. Smectic or nematic polymers were obtained depending on the nature of the substituent R in the case of polymers 1 (Table 2). It has to be pointed out that the structures at temperatures above the glass transition temperatures are equilibrium structures, since thermodynamically stable liquid crystalline phases exist. This is in contrast to most systems studied until now where only liquid crystalline structures were obtained ... 

Figure 6. General structure for phosphazenes with mesogenic side groups. Example is a mixed substituent polymer (VII) where R represents the trifluoroethoxy group and the mesogen with flexible spacer is represented by the curlicue and rectangular box.

The first generation NLO polymers were side chain polymers, usually made by copolymerisation of a monomer bearing the chromophore bridged by a flexible spacer group with a co-monomer, commonly methacrylates. This is a flexible process allowing a wide range of co-polymers to be made. A typical example of this type of polymer is the methyl methacrylate azo dye co-polymer (5.9). 

Polymers with 6H4SNSNSC6H4- or -C6H4SNSNS CeUiSNSNSCeUi segments separated by flexible spacer groups have also been synthesized. These insulators are converted to semiconductors (see Semiconductors) when doped with Br2. 

Figure 1. Structures of liquid crystalline polymers (LCPs) (A) rigid rod LCP [25, 65] (B) main chain LCP with flexible spacer [26] (C) side group LCP with flexible spacer [27] (D) combined main/side group LCP [28] (E) side group LCP without flexible spacer or mesogen jacketed LCP [29], (F) well-defined three-arm star [30] (G) LC dendrimer [33].

Finally, it is possible that side chains in polymers with very long side chains occur in mesomorphous structures, whereas the main chain is amorphous below the glass transition temperature, and behaves like a normal liquid above it. This type of behavior is observed when the movements of the main and side chains are decoupled by flexible spacer groups joining them together. An example of this is a poly(methacrylate) with the monomeric unit ... 

Figure 2. Schematic of liquid crystalline order formation in polymers with mesogenic side groups decoupled from the main chain by a flexible spacer...

The polymers were formed by condensation of 4,4dihydroxy-benzene and 2,2 -dimethyl-4,4 dihydroxyazoxybenzene with various diacid chlorides acting as flexible spacer groups Polydisperse homopolymers and copolymers, sharp fractions of homopolymers and mixtures of polydisperse polymers with a low mass mesogen were investigated. Supercooling at the mesophase-isotropic and solid-mesophase transitions, sharpness of the nematic-isotropic transition (range of N+I biphase), polymer crystallization from the mesophase melt, and enhancement of crystallinity upon addition of a low mass nematic, were studied. 

Polymers studied by these groups all have flexible spacers, meaning the mesogenic jacket effect is smaller than it is in our P -n and PA-n polymers in winch no spacers are incorpcn ated. As a matter of fiu t, all the pofymers with flexible spacers have... 

The main-chain and side-chain polymers as well as the classical small-molecule liquid crystals consist essentially of one-dimensional molecules (rods). Low molar mass compounds of two-dimensional discshaped molecules were discovered by Chandrasekhar (1977) to possess liquid crystallinity. They were referred to as discotic liquid crystals. Later research has involved the synthesis and characterization of polymers with discotic moieties connected via flexible spacer groups. 

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