MCLC polymers

MCLC Polymers. Creed et al. [21-27] have studied MCLC polymers such as 1 in which an aryl cinnamate chromophore is connected by polymethylene... 

The photo-Fries rearrangement of polymers such as 1 leads to yellowing, an undesirable behavior for many potential applications. The photochemistry of analogous MCLC polymers has been reported [30] in which the alkoxyphenyl ester groups of 1 have been replaced by 4,4 -franj-disubstituted cyclohexyl... 

Navarro [36] has reported several soluble, low transition temperature MCLC polymers containing ortho- or para-linked units and cinnamates or phenylene-fcis-acrylates in the main chain. One series of cinnamate-containing polymers is shown as 9. Some of the polymers seemed to be partially crystalline in the solid state. All had N and/or S mesophases which were retained in the solid glasses upon cooling to room temperature. Some of the polymers underwent thermal degradation and cross-linking above 300°C. Irradiation ( max = 300 nm)... 

SCLC Polymers. There has been a series of papers on the synthesis and photochemistry of SCLC polymers containing the 4-alkoxyphenyl-4 -alkoxy-cinnamate chromophore, the same chromophore as that of the MCLC polymer, 1. Ritter and co-workers [37] were the first to examine the photochemistry of any SCLC cinnamate polymer. The DSC data reported for polymer 10 indicated the... 

Chang and co-workers [56,57] also reported studies of thermotropic MCLC polymers containing the para-PDA chromophore. Their motivation was also to develop two-dimensionally reinforced polymer materials. Aromatic copoly-... 

Ganghadara and Kishore [64-66] have published an interesting series of papers on the photochemistry of MCLC [64,65] and SCLC [66] polymers containing various bis(benzylidene)cycloalkanones as mesogens/chromophores and a tetra-ethylene glycol-derived flexible spacer to lower the transition temperatures. The MCLC polymers [64], 30, had N mesophases, identified by POM. Polymer 30a... 

Unfortunately, temperature dependent UV-Vis spectra of polymers, 31, were not reported. Films of the polymers were irradiated (medium-pressure Hg lamp) and the reactions monitored by UV-Vis and FTIR spectroscopy. Homopolymer, 31 (jc = 6), was irradiated at 120°C in the N phase. A gradual decrease in the main absorption band of the chromophore at 352 nm was observed and the film eventually became completely insoluble. Interestingly, no initial increase in absorbance was observed, as had been seen for a small molecule LC model and for MCLC polymers [64] 30 (vide supra) and previously attributed to disruption of... 

Horie and his co-workers [131-135] have made extensive use of fluorescence spectroscopy to probe the microstructures of MCLC polymers. The first such polymer to be studied [131,135] was the all aromatic, rigid rod polyester, 65, with long, flexible side-chains attached to a pyromellitic ester mesogenic group. 

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

Gdmez and Ostariz [55] also investigated PDA containing LC polymers with the idea of photochemically fixing LC phases and thereby improving their mechanical properties. MCLC copolymers, 24, were obtained that contained... 

Saeva mentions, in an early review [10] on LC materials and aspects of their photochemistry and photophysics, the irradiation of an unspecified stilbene containing polymer and changes in its physical properties. Creed et al. [25,61,62] have reported several observations of the photophysics and photochemistry of a rra/w-stilbene 4,4 -dicarboxylate containing MCLC polyester, 29, one of a series of such polymers with different spacers synthesized by Jackson, Morris, and coworkers [63]. This polymer is partly crystalline in the as cast state and has a N mesophase over a narrow temperature range (177-186°C). In solution, the structured UV-Vis absorption [62] and fluorescence [25,61] spectra are almost... 

Angeloni, Chiellini, and their co-workers [116-118] reported the synthesis and characterization of both MCLC and SCLC polymers containing the 4,4 -bisalkoxyazobenzene chromophore. These interesting materials photoisomerized in solution but their photochemistry in an LC mesophase was not reported. 

Ikeda et al. [54] studied the excimer-like fluorescence of phenylenediacry-late chromophores in MCLC polyesters of type 23. These results are discussed in Section III.B of this chapter. A correlation was noted between the excimer fluorescence lifetime and the AS values for mesophase formation. The less-ordered, more mobile mesophases had shorter excimer lifetimes presumably because of more facile nonradiative decay. Kurihara, Ikeda, and Tazuke [129,130] also studied the emission properties of SCLC polymers of type 64, containing the... 

Tsutsumi N, Yoshizaki S, Sakai W, Kiyotsukuri T. 1996. Thermally stable nonlinear optical polymers. MCLC S T, Section B Nonlinear Optics 15(1 4) 387 390. 

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