Radical SCLCP

A block copolymer consisting of a SCLCP-block of monomer XXVII with a laterally-attached mesogenic unit, and butyl-acrylate, was synthesized using a combination of ROMP and atom transfer radical polymerization (ATRP) (Fig. 16) [81]. 

ROMP of the SCLCP block was carried out with the Grubbs -initiator 6 in a monomer to initiator ratio of about 25. The polymerization was terminated by reaction with 4-(2-bromopropionyloxy)-but-2-enyl 2-bromopropionate, leading to a macroinitiator for ATRP. The radical polymerization was carried out with CuCl, 4,4 -di(n-nonyl)-2,2-bipyridine, and butylacrylate (BA), giving a poly-XXVII-fo-BA copolymer. The homopolymer of poly-XXVII had a narrow PDI of 1.06, while the diblock copolymer showed a PDI of 1.32. 

Unil recently, most side chain liquid crystalline polymers (SCLCPs) were prepared by either hydrosilations of mesogenic olefins with poly(methylsiloxane)s or by free radical polymerizations of acrylates, methacrylates and chloroacrylates [1,2]. Both routes involve chain polymerizations, either directly or prior to a polymer analogous reaction. Chain polymerizations involve the four elementary reactions shown in Scheme 1 [3], In contrast to step polymerizations,... 

Free radical polymerization of a vinyl monomer, e.g., acrylate, methacrylate, or styrene derivative, has been widely used to produce NLO single-component SCLCPs. This type of monomer is suitable as it is relatively easy to prepare and the conditions for free radical polymerization of acrylates, methacrylates, and styrene derivatives have been well documented. There are, however. 

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).

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