Abstract:
Disclosed is a liquid crystal monomer compound represented by formula (1): ##STR1## wherein n is an integer of from 2 to 18, X is direct bond, --(C═O)--O--, --(C═O)--NH-- or --N═N--, R 1  is hydrogen or a lower alkyl group, and R 2  is hydrogen, a cyano group or a methoxy group, as well as a liquid crystal polymer derived therefrom.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a novel liquid crystal monomer compound and a liquid crystal polymer obtained therefrom. 
     BACKGROUND OF THE INVENTION 
     Various polymers having liquid crystal characteristics have already been developed. Such polymers generally have the mesogen group represented by formula: ##STR2## wherein X represents a direct bond, --(C═O)--O--, --(C═O)--NH-- or --N═N--, R represents hydrogen, cyano group or methoxy group; 
     present in the polymer backbone (main chain type liquid crystal polymer) or in the side chain (side chain type liquid crystal polymer). 
     Although the mesogen group shown above is introduced into the polymer via various bonds (e.g. ester bond), few polymers having urethane bond have been reported. 
     In the main chain type liquid crystal polymer having a higher molecular weight, hydrogen bond characteristics of the urethane bond are considered to serve to bend the terminal of the molecule, whereby reducing the interaction of the mesogen group. Similar tendency is suspected also in the cases of side chain type liquid crystal polymers. Therefore, there are few studies on liquid crystal polymers having urethane bonds in their side chains. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a side chain type liquid crystal polymer having urethane bonds in the polymer backbone as well as to provide monomer compounds to form such polymers. A liquid crystal polymer having (meth)acrylic main chain and acyl urethane bonds in their side chains is a novel compound. 
     Accordingly, the present invention provides a liquid crystal monomer compound represented by formula (1): ##STR3## wherein n is an integer of from 2 to 18, X is direct bond, --(C═O)--O--, --(C═O)--NH-- or --N═N--, R 1  is hydrogen or a lower alkyl group, and R 2  is hydrogen, a cyano group or a methoxy group. 
     The present invention also provides a liquid crystal polymer represented by the formula (2): ##STR4## wherein m is an integer of 2 or more, n, X, R 1  and R 2  are the as mentioned above, as well as a liquid crystal polymer obtained by polymerizing one or more of the liquid crystal monomer compounds represented by formula (1). 
     DETAILED DESCRIPTION OF THE INVENTION 
     The monomer compound (1) according to the present invention may be easily synthesized at a high yield by reacting an alkanoyl isocyanate represented by formula (3): ##STR5## wherein R 1  is as defined above, with an active hydrogen containing compound having a mesogen group represented by formula (4): ##STR6## wherein n, X and R 2  are defined as above. 
     The alkanoyl isocyanate (1) has already been provided by the present inventors, and detailed in Japanese Kokai Publication Sho 60(1985)-115557 (corresponding U.S. Pat. No. 4,925,982) and the like. R 1  in the alkanoyl isocyanate is hydrogen or a lower alkyl group (preferably having 1 to 4 carbon atoms), with hydrogen and a methyl group being preferred. 
     The active hydrogen containing compound (4) having mesogen group employed in the present invention is known per se. Generally, the compound (4) can be obtained readily by reaction a biphenyl compound with a compound represented by Y(CH 2 ) n  Z (wherein Y and Z, same or different, are a halogen atom or an OH group, n=2 to 18), for example α-halogeno-ω-hydroxyalkane, α,ω-dihalogenoalkane or α,ω-dihydroxyalkane (e.g. 2-chloro-1-ethanol). 
     The reaction between the alkanoyl isocyanate (3) and the active hydrogen compound (4) may be conducted at a temperature of -20° to 100° C. in an inert solvent. An amount ratio of the compound (3) to the compound (4) may be one equivalent of the compound (3) to 0.5 to 1 equivalent of compound (4). The compound obtained was subjected to a standard work up and then purified by, for example, recrystallization. Generally, the: obtained product is solid, thus, it is suitable to be recrystallized. 
     The inert solvents employed in the reaction include aliphatic hydrocarbons such as pentane and hexane; aromatic hydrocarbons such as benzene, toluene and xylene; alicyclic hydrocarbons such as cyclohexane and cyclopentane; halogenated hydrocarbons such as chloroform, dichloromethane, dichlorobenzene and bromobenzene; ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, diisopropyl ether, THF (tetrahydrofuran), anisole and diphenyl ether; nitriles such as acetonitrile and benzonitrile; amides such as dimethylformamide N-methylpyrrolidone; nitrobenzene; dimethyisulfoxide. The solvent may be selected in view of the solubility of the reactants. 
     The obtained compound may be polymerized independently by conventional methods such as radical polymerization, or copolymerized using 2 or more monomers, whereby yielding a polymer. The polymerization may be conducted at a temperature of 0° to 150° C. in an inert solvent as listed above in the presence of a polymerization initiator. The polymerization initiator includes an azo initiator such as 2,2&#39;-azobisisobutylonitrile (AIBN) and 2,2&#39;-azobis(2,4-dimethyivaleronitrile); a peroxide initiator such as benzoyl peroxide, di-t-butyl peroxide and t-butyl perbenzoate; and a photopolymerization initiator, such as benzophenone, acetophenone and benzoin. 
     When liquid crystal characteristics of the polymers obtained as described above has been examined, thermotropic liquid crystal characteristics are found in spite of the presence of the urethane bonds. The liquid crystal monomer compounds according to the present invention may also be employed as a useful reactant for the polymers described above. It is, of course, that the monomer compounds themselves can be used in other applications. 
     The polymers obtained according to the present invention can be processed and formed into various shapes, such as films, fibers and thin films, in addition to being used as the material for the liquid crystals. They may also be modified widely by employing general modification methods in the field of polymers, such as copolymerization, blending and alloy formation. 
    
    
     EXAMPLES 
     The present invention is further described in the following examples, which are not intended to limit the present invention. 
     Reference Example 1 
     Synthesis of 4-hydroxy-4&#39;-methoxybiphenyl (EBm) from 4,4&#39;-dihydroxybiphenyl 
     120 ml of water and sodium hydroxide (14.00 g, 0.35 mol) were placed in a conical flask and dissolved. 4,4&#39;-Dihydroxybiphenyl (28.00 g, 0.15 mol) was then added and heated to reflux for 2 hours with stirring using a condenser. Dimethyl sulfate (14.5 ml, 0.15 mol) was added dropwise over about 40 minutes. After addition, the mixture was heated while stirring for 2 hours, and then allowed to cool and filtrated. The filter cake was transferred into 700 ml of water, which was then heated to boiling temperature, and filtrated while still keeping warm. The filtrate was kept at 70° C., and 20% hydrochloric acid was added. White precipitation: formed was washed extensively. Recrystallization from ethanol yielded 4&#39;-methoxy-4-hydroxybiphenyl (13.17 g, Yield: 48.0%). 
     Reference Example 2 
     Synthesis of 4&#39;-methoxy-4-hydroxyethoxybiphenyl from 4&#39;-methoxy-4-hydroxybiphenyl 
     4&#39;-Methoxy-4-hydroxybiphenyl (24.08 g, 0.123 mol) was dissolved in ethanol (180 ml), and aqueous solution (36 ml) of potassium hydroxide (8.36 g, 0.141 mol) was added and heated to reflux for 1 hour. 2-Chloro-1-ethanol (11.96 g, 0.149 mol) was added dropwise over about 30 minutes, and the mixture was heated while stirring at reflux for 23 hours. After the reaction was completed, 180 ml of water was added and ethanol was distilled off. White precipitation formed was filtrated and washed successively with 5% warm aqueous solution of KOH and water, and then dried. Recrystallization from ethanol yielded 4-[2-(N-methacryloyl)carbamoyloxyethoxy]biphenyl. 
     Reference Examples 3 to 7 
     The compounds listed below were synthesized similarly as in Reference Examples 1 or 2. 
     Reference Example 3: 4-hydroxyhexyloxy-4-methoxybiphenyl (HBm) 
     Reference Example 4: 4-hydroxyethoxybiphenyl (EB) 
     Reference Example 5: 4-hydroxyhexyloxybiphenyl (HB) 
     Reference Example 6: 4-hydroxyethoxyazobenzene (EA) 
     Reference Example 7: 4-hydroxyhexyloxyazobenzene (HA) 
     In Reference Example 3, 6-chloro-1-hexanol was employed instead of 2-chloro-1-ethanol employed in Reference Example 2, and 4-hydroxybiphenyl was employed in Reference Example 4 instead of 4&#39;-methoxy-4-hydroxybiphenyl employed in Reference example 2. 4-Hydroxybiphenyl and 6-chloro-1-hexanol were employed in Reference Example 5 instead of 4&#39;-methoxy-4-hydroxybiphenyl and 2-chloro-1-ethanol employed in Reference Example 2, respectively. In Reference Examples 6 and 7, azobenzene compounds were: employed instead of biphenyl compounds employed in Reference Examples 4 and 5. Characteristics, melting points and yields of the compounds synthesized are shown in Table 1. 
     
                       TABLE 1______________________________________                               MeltingReference   Com-                        point  Yieldexample pound   n     x       R.sup.2                               (°C.)                                      (%)______________________________________2       EBm     2     Direct  OCH.sub.3                               179.1  52.1                 bond3       HBm     6     Direct  OCH.sub.3                               153.5  54.1                 bond4       EB      2     Direct  H     123.5  77.5                 bond5       HB      6     Direct  H      94.0  55.8                 bond          and                               105.96       EA      2     --N═N--                         H     104.5  79.17       HA      6     --N═N--                         H      89.3  40.2______________________________________ 
    
     Example 1 
     EB (1.00 g, 4.7×10 -3  mol) was dissolved in 50 ml of tetrahydrofuran and methacryloyl isocyanate (0.56 g, 5.0×10 -3  mol) was added while cooling to 0° C., and the mixture was stirred for 24 hours. The reaction mixture was poured into 300 ml of water, and the precipitation formed was filtrated and dried. Recrystallization from warm methanol at 40° C. yielded 4-[2-(N-methacryloyl)carbamoyloxyethoxy] biphenyl. 
     Examples 2 to 6 
     Except for using HB, EBm, HBm, EA and HA instead of EB employed in Example 1, similar procedure was conducted to obtain the compounds listed below. 
     UEB: 4-[2-(N-methacryloyl)carbamoyloxyethoxy]biphenyl 
     UHB: 4-[6-(N-methacryloyl)carbamoyloxyhexyloxy]biphenyl 
     UEBm: 4-[2-(N-methacryloyl)carbamoyloxyethoxy]-4&#39;-methoxybiphenyl 
     UHBm: 4-[6-(N-methacryloyl)carbamoyloxyhexyloxy]-4&#39;-methoxybiphenyl 
     UEA: 4-[2-(N-methacryloyl)carbamoyloxyethoxy]azobenzene 
     UHA: 4-[6-(N-methacryloyl)carbamoyloxyhexyloxy]azobenzene 
     Yields (amounts and rates) and melting points of the compounds obtained are shown in Table 2. Elemental analysis was conducted and the results are shown in Table 3. 
     
                                           TABLE 2__________________________________________________________________________   Reaction                 (I)    Com-   condition                        MeltingExam-    pound   (III)    (IV)     Temp.                         Time                            Yield                                Yield                                    pointple (I) n × R.sup.2 g/mol            R.sup.1 g/mol                     °C.                         h  g   %   °C.__________________________________________________________________________1   UEB 2-H      CH.sub.3 0   24 3.77                                49.2                                    154.7   5.05/2.36 × 10.sup.-2            3.69/2.42 × 10.sup.-22   UHB 6-H      CH.sub.3 0   24 4.11                                60.2                                     84.3   4.84/1.79 × 10.sup.-2            2.28/2.05 × 10.sup.-23   UEBm   2-OCH.sub.3            CH.sub.3 0   24 3.36                                43.9                                    162.4   5.26/2.15 × 10.sup.-2            2.63/2.37 × 10.sup.-24   UHBm   6-OCH.sub.3            CH.sub.3 0   24 4.44                                49.4                                    129.4   6.56/2.18 × 10.sup.-2            2.89/2.60 × 10.sup.-25   UEA 2 N═N H            CH.sub.3 0   24 6.79                                46.4                                    152.7   10.02/4.14            5.04/4.53 × 10.sup.-26   UHA 6 N═N H            CH.sub.3 0   24 11.22                                81.8                                    114.2   10.01/3.35 × 10.sup.-2            4.18/3.76 × 10.sup.-2__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________      Value of elementalExample    analysis   Calculated value                            ChemicalNo.  Compound      C   H  N   C   H  N   structure__________________________________________________________________________1    UEB   70.03          5.88             4.20                 70.14                     5.89                        4.31                            C.sub.19 H.sub.19 NO.sub.42    UHB   72.53          7.36             3.59                 72.42                     7.13                        3.67                            C.sub.23 H.sub.27 NO.sub.43    UEBm  67.71          6.04             3.86                 67.59                     5.96                        3.94                            C.sub.20 H.sub.21 NO.sub.54    UHBm  70.14          7.05             3.33                 70.05                     7.10                        3.40                            C.sub.20 H.sub.29 NO.sub.55    UEA   64.42          5.57             11.90                 64.58                     5.42                        11.89                            C.sub.19 H.sub.19 N.sub.3 O.sub.46    UHA   67.12          6.48             10.36                 67.46                     6.55                        10.26                            C.sub.23 H.sub.27 N.sub.3 O.sub.4__________________________________________________________________________ 
    
     Example 7 
     UEB (1.0 g, 3.0×10 -3  mol) and azobisisobutyronitrile (0.02 g, -1.22×10 -4  mol) were dissolved in 1,4-dioxane and polymerization was conducted for 24 hours at 60° C. under argon atmosphere. Then, the reaction mixture was poured into methanol, filtrated to obtain polymer PUEB. 
     Examples 8 to 12 
     Except for using UHB, UEB, UHBm, UEA and UHA instead of UEB employed in Example 7, similar procedure was conducted to obtain polymers, whose molecular weights (Mw and Mn) and P (Mw/Mn) are shown in Table 4. 
     
                       TABLE 4______________________________________Example   Polymer  Mn         Mw    P______________________________________ 7        PUEB     5500        8500 1.55 8        PUHB     12500      18000 1.44 9        PUEBm    3600        6500 1.8110        PUHBm    6000        7700 1.2811        PUEA     9000       12200 1.3612        PUHA     7600       11500 1.51______________________________________ 
    
     Example 13 
     Polymer PUHB thus obtained was examined by DSC and polarization microscope for its thermodynamic properties and liquid crystal characteristics. As a result, the melting point of the polymer during the course of heating (Tm) and the isotropic fluidization phase transition temperature (Ti) were revealed to be 97.1° C. and 126.6° C., respectively. Examination by a wide angle X-ray diffractometry at room temperature revealed diffraction peaks at 28Θ=7.60°, 19.82° and 23.60°, indicating that the polymer had a high performance as a liquid crystal. 
     Examples 14 to 18 
     Similarly to Example 13, the physical parameters of the polymers obtained in Examples 7 and 9 to 12 were examined, and the results are shown in Table 5. 
     
                       TABLE 5______________________________________           Phase           transition       Transition           temperature      enthalpy           (°C.)     (J/g)Example  Polymer  Tm         Ti    ΔHM                                    ΔHi______________________________________13     PUEB                136.4         19.5414     PUHB      97.1      126.6 8.25    25.4515     PUEBm    139.7      156.6 10.70   33.1516     PUHBm               136.317     PUEA     128.7      140.3 7.7      4.1318     PUHA                (126.7)       44.58______________________________________