Synthesis SCLCP

Cho et al. described the synthesis and polymerization of 4,8-cyclododeca-dien-l-yl-(4 -methoxy-4-biphenyl) terephthalate VIII [54,55]. Polymerization was carried out with WCl4(OAr)2/PbEt4. The double bonds in the polymer backbone were subsequently hydrogenated with H2/Pd(C), leading to a SCLCP with a fully saturated hydrocarbon backbone. This polymer system had a very flexible polymer backbone but a stiff connection between the main chain and the mesogenic unit. The distance between two adjacent side chains was about 12 methylene units. This very flexible main chain allowed the polymer to organize into a LC mesophase. Both polymers - the unsaturated and the saturated -showed smectic liquid crystalline mesophases with almost the same transition temperatures (see Table 5). 

Komiya et al. described the living ROMP synthesis of AB-type block copolymers that contain side chain liquid crystalline polymer blocks and amorphous blocks [62]. Norbornene (NBE), 5-cyano-2-norbornene (NBCN) and methyl-tetracyclododecene (MTD) were used for the amorphous polymer blocks, while I-n (n=3,6) were used for the SCLCP block (see Fig. 9). Initiator 1 was used for the ROMP. Block copolymers with monomer ratios from 75/25 to 20/80 (amor-... 

There have been two main approaches toward the synthesis of SCLCPs containing NLO mesogenic groups ... 

A controlled free radical polymerization technique was also used, namely, atom transfer radical polymerization (ATRP), to synthesize ATE on the basis of ABA triblock copolymers (Fig. 11.3b) (Cui et al., 2004). The triblock copolymer was designed to have a rubbery midblock of poly(n-butyl acrylate) (PnBA) and two end blocks of poly 6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate) (PAzoMA) that is azo-SCLCP. For synthesis, a dibromo initiator, namely, l,l -biphenyl-4,4 -bis(2-bromoisobutyrate), can first be used to prepare the dibromo PnBA macroinitiator, which is then used to polymerize the azobenzene methacrylate monomer to yield the two end blocks of PAzoMA. This ATE is different from azo-SCLCP-grafted SBS. It is a thermoplastic elastomer, in which... 

Figure 11.3. Two methods for the synthesis of azobenzene thermopiastic eiasto-mers (a) grafting of an azobenzene-containing side-chain iiquid crystaiiine polymer (azo-SCLCP) onto the thermoplastic styrene-butadiene-styrene (SBS) tribiock copoiymer using radical polymerization, and (b) tribiock copoiymer composed of a rubbery centrai block and two azobenzene SCLCP end blocks synthesized using atom transfer radical polymerization (ATRP).

However, there is an enormous number of possible polymer backbones that can be used for generating SCLCPs, but only a small selection have been widely used in the synthesis and evaluation of SCLCPs. In general, poly(siloxanes) and poly(aciylates) constitute the vast majority of SCLCPs. The reported role of the spacer group is to decouple the effects of the backbone from those of the mesogenic side chains. Accordingly, the backbone should not influence the mesomorphic properties of SCLCPs. However, decoupling is... 

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