**1. Introduction**

Originally there are three states of matter; solid, liquid and gas. The emergence of an exotic and extraordinary form of matter, which is known as liquid crystal has been considered as one of the major breakthrough in polymer science. Liquid crystal can be defined as an intermediate of solid (crystal) and liquid (Knight & Vollrath, 2002) where the molecules have the capabilities to flow like a liquid (mobility) as well as possessing the common property associated to solid, which is the degree of order (Doldeny & Alder, 1998). In addition, liquid crystal materials are self assembling by nature and can offer a very elegant and effective way of controlling and tuning the physical properties that ultimately define the self-organizing and self assembly process (Zhang et.al., 2008). One of the exciting developments involving this unique material is the introduction of liquid crystalline behavior in polyurethane elastomers (PUE) where the first of this kind was synthesized by Iimura in 1981 (Lin et.al., 2001).

Polyurethane [PU] is one of the most versatile class of polymeric materials known today. Wide variety of structural changes can be produced with the different hydroxyl compounds and isocyanates leading to a wide spectrum of properties and applications (Yeganeh et.al., 2007). It contains a high concentration of polar groups, in particular the urethane group, resulting from isocyanate-hydroxyl reactions. The interactions between these polar entities are of great importance in determining the properties of PU of all types (Lee et.al., 1999) besides the composition and characteristic of the polyol, diisocyanates and the additives utilized during the synthesis (Pachecho et.al., 2009).

High toughness, excellent wear and tear properties and good oil resistance are among the advantages displayed by PUE (Wright & Cumming, 1969). Moreover, not only they have good mechanical and physical properties, PUE are also benefited with biocompatibility

© 2012 Mohammed and Hamidi, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Mohammed and Hamidi, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

characteristics for biomedical applications (Barikani et.al., 2009). Despite all the great aforementioned properties, modifications and improvements are done to conventional PUE in order to meet the qualities in more advanced applications.

New Liquid Crystalline Polyurethane Elastomers

1H-NMR

Containing Thiazolo [5,4d] Thiazole Moiety: Synthesis and Properties 21

in a 500 ml round bottom flask fitted with condenser and left to be refluxed for 2h. Precipitates were obtained by pouring the hot mixtures to the cold water. Subsequently, the yield was filtered off and washed with ethanol followed by ether. The product obtained was dried at 70oC in a vacuum oven for 24 hours. Recrystallization from cyclohexanone was performed giving an orange-yellowish powder. Yield: 35% with melting point 364oC. Fourier transform infrared (FTIR; KBr, cm-1): 3492 (-OH), 1606 (C=N), 1596 (C=C), 855 (*p*-substituted benzene). 1H-NMR (400 MHz, DMSO-d*6* ppm): δH 7.12 (m, aromatic protons), 9.8 (s, -OH). Elemental

analysis: Found: C, 59.16; H, 3.28; N, 8.84, C16H10N2O2S2 Calc.: C, 58.89; H, 3.09, N, 8.59.

*2.2.2. Synthesis of 2,5-bis(4-hydroxy-3-methoxyphenyl) thiazolo [5,4d] thiazole (II)* 

4.03; N, 6.89, C18H14N2O4S2 Calc.: C, 55.95; H, 3.62, N, 7.25.

oven at 60o C.

**2.4. Measurements** 

*2.2.3. Synthesis of liquid crystalline polyurethane elastomers (LCPUE)* 

The same procedure was applied to the synthesis of 2,5-bis(4-hydroxy-3-methoxyphenyl) thiazolo [5,4d] thiazole except that 4-hydroxybenzaldehyde was substituted with vanillin. Orange-yellowish powder was obtained as the end product. Yield: 26% with the melting point of 259oC. Fourier transform infrared (FT-IR; KBr disc): 3534 cm-1 (OH), 1608 cm-1(C=N), 1510 cm-1 (C=C), 842 cm-1 (-CH out of plane). 1H-NMR (400 MHz, DMSO-d*6* ppm): δH 7.09 (m, aromatic protons), 9.5 (s, -OH) and 3.87 (s, OCH3). Elemental analysis: Found: C, 55.60; H,

Preparation of LCPUE was achieved by two steps solution polymerization reaction, where isocyanate terminated pre-polymer was synthesized initially in the first stage. To produce pre-polymer, 0.01 mol of PEG (Mw = 1000, 2000, and 3000) and 0.02 mol of MDI were mixed in 500ml of reactor flask equipped with condenser, thermometer, nitrogen inlet and mechanical stirrer. The mixture was allowed to be stirred and heated for 4h at 70oC in the presence of 15 ml of DMF as solvent and nitrogen gas was kept flowing to provide inert atmosphere. The reaction was followed by chain extension process, using either compound (I) or (II), where the chain extender was added dropwise within 1h to complete the formation of LCPUE. Subsequently, the temperature was increased to 100oC and the reaction continued for another 9 hr. The hot viscous solution was then poured into 200ml of cold water for precipitation, before subjected to filtration. Later, the filtered product was washed with ethanol several times and finally with ether, before being dried overnight in a vacuum

100mg mixture of samples and KBr (grounded) were pressed into translucent disc before being subjected to Nicolar Avatar Model 360 Fourier Transform infrared spectrometer

and 13C-NMR spectra were obtained using Bruker 400 MHz NMR spectrometer consuming DMSO-d*6* as solvent and TMS as internal standard. Thermal stability of LCPUE was determined by thermogravimetric analyzer (Perkin Elmer Pyris series 6) under nitrogen purge and with 10oC/min of heating rate and the heating was done up to 800oC. Liquid crystalline behavior was verified by means of differential scanning calorimetry (DSC) to

devices to obtain FT-IR spectra. Data was collected in the range of 4000-400cm-1.

Diisocyanates, polyol and low molecular weight diamine or diol (chain extender) are the basic building blocks of conventional PUE (Yeganeh & Mehdizadeh, 2009). In order to synthesize liquid crystal polyurethane elastomers (LCPUE), the low molecular weight diamine or diol used in conventional PUE was substituted with the mesogenic unit. Incorporation of geometrically anisotropic moieties (mesogenic unit) within polymer architecture can drive the formation of liquid crystalline phase from strictly steric repulsion considerations (Abe & Ballauf, 1991; Rowan & Mather, 2007). Furthermore, the insertion of mesogenic unit in the backbone of PUE will impart unique physical properties to the polymer and also improve its mechanical, optical and electrical characteristics (Jia et.al., 1996).

Various mesomorphic behaviors are exhibited with different types of mesogenic units in preparation of LCPUE. In this research work, mesogens consumed were thiazolo [5.4d] thiazoles based and it is known as an important class of biycyclic aromatic molecule comprising two fused thiazole rings (Knighton et.al., 2010). Thiazolothiazole rigid fused ring can enhance the rigidity of the polymer and the conjugation (Osaka et.al, 2007) which makes it a best candidate to be part of the hard segment in the LCPUE network. The hard segments consisted of either 2,5-bis(4-hydroxyphenyl) thiazolo-[5,4d] thiazole or 2,5-bis(4-hydroxy-3 methoxyphenyl) thiazolo [5,4d] thiazole and 4,4'- methylene diphenyl diisocyanate (MDI). As for the soft segments, polyethylene glycol (PEG) 1000, 2000 and 3000 were involved.

The ultimate aim of this work is to synthesize new LCPUE with the presence of thiazolo- [5,4d] thiazole as a chain extender. Study and analysis were carried out to determine the effects and consequences of the introduction of thiazolo-[5,4d] thiazole moiety and the influence of various lengths of polyols on the properties of LCPUE.
