Polymer Journal, Vol. 27, No. 7, pp 664-672 (1995) Synthesis and Thermotropic Properties of Polyurethanes Prepared from 2,5-Tolylene Diisocyanate and 2,6-Bis(w-hydroxyalkoxy )naphthalenes Jong Back LEE, Takashi KATO, and Toshiyuki URYU* Institute of Industrial Science, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan (Received October 12, 1994) ABSTRACT: A series of thermotropic polyurethanes containing no mesogenic unit were synthesized by polyaddition of a para-type diisocyanate such as 2,5-tolylene diisocyanate (2,5-TDI) with 2,6-bis(w-hydroxyalkoxy)naphthalenes (BHNm: HO(CH2 )mOC10H 6 O(CH2 )mOH; m is the carbon number in the hydroxyalkoxy group). Intrinsic viscosities of the polymers were in the range of 0.27---0.48 dL g- 1. The thermal properties of these polymers were studied by differential scan­ ning calorimetry, thermogravimetric analysis, polarizing microscopy, and X-ray diffractometry. Polyurethane 2,5-TDI/BHNm's (m=5, 6, 8, 11) prepared from BHNm and 2,5-TDI having methyl substituent on the phenylene unit exhibited monotropic liquid crystallinity. For example, poly­ urethane 2,5-TDI/BHN8 with [IJ]=0.30 exhibited a mesophase from 139 to lll°C on cooling. However, in the series of polyurethanes prepared by polycondensation of 1,4-phenylene di­ isocyanate (1,4-PDI) with BHNm, no explicit mesomorphic behavior was observed by DSC measurement and polarizing microscopic observation. KEY WORDS Thermotropic Polyurethane / 2,5-Tolylene Diisocyanate / 1,4-Phenylene Diisocyanate / Hydrogen Bonding/ Polyurethanes are a distinct class of mate­ In the previous paper, we reported the syn­ rials with industrial importance. 1 Induction thesis and thermotropic properties of a series of mesomorphic behavior for polyurethanes of liquid-crystalline polyurethanes by poly­ have attracted much attention. Iimura and addition reaction of such para-substituted di­ co-workers first reported thermotropic poly­ isocyanates as 2,5-tolylene diisocyanate (2,5- urethanes prepared by polyaddition of 3,3' - TDI) and 1,4-phenylene diisocyanate (1,4- dimethyl-4,4' -biphenyldiyl diisocyanate with PDI) with 4,4'-bis(w-hydroxyalkoxy)biphenyl (X,<.a-alkanediols. 2 Tanaka and Nakaya synthe­ or 1,4-bis( w-hydroxyalkoxy)benzene. 21 •22 sized several polyurethanes by polyaddition of In this study, we synthesized a new series of diols containing mesogenic units with various polyurethanes by the polyaddition of para­ diisocyanates. 3 •4 MacKnight and coworkers substituted diisocyanate monomers, i.e., 2,5- reported thermotropic properties of poly­ TDI and 1,4-PDI, with 2,6-bis(w-hydroxyal­ urethanes based on meta-type 2,4- or 2,6- koxy)naphthalenes. Thermal properties were tolylene diisocyanate. 5 - 12 Other research examined for these polyurethanes using differ­ groups have also reported the preparation and ential scanning calorimetry (DSC), X-ray dif­ the physical properties of liquid-crystalline fractometry and polarizing microscopy. polyurethanes consisting of rigid or mesogenic units in the main chain. 13 - 20 * Corresponding author. 664 Thermotropic Polyurethanes EXPERIMENTAL dropwise to the BHNm solution under a dry nitrogen atmosphere at room temperature. Materials Then, after the reaction mixture was stirred at Diisocyanate monomers, i.e., 1,4-phenylene 80°C for 24 h, it was poured into methanol to diisocyanate (1,4-PDI) and 2,5-tolylene diiso­ precipitate the polymer. The precipitated cyanate (2,5-TDI), were kindly supplied by polymer was treated with boiling methanol, Mitsui Toatsu Co., Ltd. These compounds filtered, and then dried under vacuum at 60°C were used without further purification. overnight. Yield: 85-93%. Anal. Calcd for l,4-PDI/BHN5 (C28H 32Nr Monomer Synthesis 0 6)": C, 68.28; H, 6.55; N, 5.68. Found: C, 2, 6- Bis( w-hydroxyalkoxy )naphthalenes 68.25; H, 6.56; N, 5.65. Calcd for 2,5-TDI/ (BHNm; m=2, 3, 5, 6, 8, 11) were synthesized BHN2 (C23H 22N 2 0 6)n: C, 65.39; H, 5.24; N, by the reaction of 2,6-dihydroxynaphthalene 6.63. Found: C, 65.34; H, 5.20; N, 6.65. with w-halogenated alkanols. A mixture of sodium hydroxide (5.4 g, 0.13 mol), 2,6-dihy­ Measurements droxynaphthalene (5.1 g, 0.032mol), and w­ 1 H NMR spectra were obtained in dimethyl bromo- or chloro-1-alkanol (0.13 mol) in 150 sulfoxide-d6 (DMSO-d6) by a JEOL JNM GX- mL of ethanol was refluxed for 12 h, and then 270 spectrometer. Infrared spectra were ob­ poured into cold water. The precipitate was tained by a Perkin Elmer FT/IR 1600 spectro­ filtered and recrystallized from isopropyl alco­ meter. Viscosities were measured on the poly­ hol. Yield 50-86%. mp: 187-189°C (m=2), mer solution in dichloromethane~trifluoroace­ 148-150°C(m=3), 126-127°C(m=5), 125- tic acid (4: I, v/v) mixture with an Ubbelohde 1260C (m=6), 117-119°C (m=8), 121- viscometer at 25°C. Differential scanning 1230C (m= 11). 1H NMR (dimethyl sulfoxide­ calorimetry (DSC) measurements were per­ d6): BHN2, b 3.72 (4H, m), 4.02 (4H, t), 4.82 formed on a Mettler DSC 30 at a scanning rate (2H, t), 7.72-7.03 (6H, m); BHN3, b 1.89 (4H, of 20°C min - 1 . The maximum point of the en­ m), 3.56 (4H, m), 4.07 (4H, t), 5.54 (2H, t), dotherm was taken as the transition temper­ 7.70-7.01 (6H, m); BHN5, b 1.82-1.37 (12H, ature. A polarizing microscope equipped with m), 3.39 (4H, m), 4.00 (4H, t), 4.32 (2H, t) a Mettler FP82 hot stage was used for visual 7.71-7.00 (6H, m); BHN6, b 1.80-1.22 (16H, observation. X-ray diffraction measurements m), 3.36 (4H, m), 4.00 (4H, t), 4.21 (2H, t), of the samples placed on a CN23 l 1B 1 ther­ 7.70-7.00 (6H, m); BHN8, b 1.79-1.20 (24H, mal control were carried out with a Rigaku m), 3.37 (4H, m), 4.02 (4H, t), 4.16 (2H, t), RINT X-ray 2000 system using Ni-filtered 7.72-7.02 (6H, m); BHNI I, b 1.80-1.09 Cu-Ka radiation. The thermogravimetric anal­ (40H, m), 3.32 (2H, t), 4.00 (4H, t), 7.68-7.01 ysis was performed by a Shimadzu DT-40 at (6H, m). a heating rate of I0°C min - 1 in air. Polymer Synthesis RESULTS AND DISCUSSION The polyurethanes were synthesized by a polyaddition reaction according to the method The general synthetic route and the structure described in the literature. 21 ·22 The solution of of 2,5-TDI/BHNm and 1,4-PDI/BHNm poly­ BHNm (2.87mmol) in 15mL of dry N,N­ urethanes are given in Scheme 1. A series of dimethylformamide (DMF) was placed in a polyurethanes 2,5-TDI/BHNm's and 1,4-PDI/ three-neck round bottom flask. The diisocya­ BHNm's were synthesized by the polyaddi­ nate, 2,5-TDI or 1,4-PDI (2.87mmol), dis­ tion reaction of equimolar amounts of di­ solved in 15mL of dry DMF was added isocyanates and 2,6-bis(w-hydroxyalkoxy)- Polym. J., Vol. 27, No. 7, 1995 665 J.B. LEE, T. KATO, and T. URYU 2 HO(CH2)m·X + HO-(°"\,-;\ naphthalenes. These polyurethanes contained '=C)-oH X=Br, Cl no mesogenic core unit in the main chain like m=2, 3, 5, 6, 8, 11 the thermotropic polyurethanes prepared from NaOH 2,5-TDI and 1,4-bis(w-hydroxyalkoxy)ben­ zenes. 22 The reaction was allowed to proceed in dry DMF at 80°C under a dry nitrogen atmosphere for 24 h. The results of the polymerization for 2,5- ocN-QNCO TDI/BHNm and 1,4-PDI/BHNm are given in 1,4-PDI (R=H) Tables I and II, respectively. The yields were 2,5-TDI (R=CH3) 87-92%. The intrinsic viscosities of the polymers were measured in the mixture of dichloromethane and trifluoroacetic acid ( 4 :1, v/v) except for 1,4-PDI/BHN2 which was 1,4-PDI/BHNm (R=H) insoluble in the mixture solvent. The viscosities 2,5-TDI/BHNm (R=CH3) for 2,5-TDI/BHNm and 1,4-PDI/BHNm were Scheme 1. Synthetic route of 2,5-TDI/BHNm and 1,4- in the range of 0.27-0.42dLg- 1 and 0.31- PDI/BHNm polyurethanes. 0.48dLg-1, respectively. Table I. Polyaddition reaction of 2,5-tolylene diisocyanate (2,5-TDI) with 2,6-bis(w-hydroxyalkoxy)naphthalenes (BHNm)" Carbon number Diisocyanate BHNm Yield [11Jh Polymer of alkylene chaind m g (mmol) g (mmol) % dLg- 1 2,5-TDI/BHN2 2 0.500 (2.87) 0.712 (2.87) 87 0.27 2,5-TDI/BHN3 3 0.510 (2.93) 0.808 (2.93) 90 0.25 2,5-TDI/BHN5 5 0.508 (2.92) 0.968 (2.92) 87 0.32 2,5-TDI/BHN6 6 0.500 (2.87) 1.033 (2.87) 92 0.32 2,5-TDI/BHN8 8 0.506 (2.91) 1.209 (2.91) 89 0.30 2,5-TDI/BHN 11 11 0.500 (2.87) 1.435 (2.87) 88 0.42 ·80°C, 24h, solvent: DMF (20mL). blntrinsic viscosity measured on dichloromethane-trifluoroacetic acid (4: I, v/v) solution at 25°C. Table II. Polyaddition reaction of 1,4-phenylene diisocyanate (1,4-PDI) with 2,6-bis(w-qydroxyalkoxy)naphthalenes (BHNm)• Carbon number Diisocyanate BHNm Yield [11Jh Polymer of alkylene chaind m g (mmol) g (mmol) % dLg- 1 l,4-PDI/BHN2 2 0.500 (3.13) 0.775 (3.13) 92 Insoluble l,4-PDI/BHN3 3 0.506 (3.16) 0.873 (3.16) 88 0.33 l,4-PDI/BHN5 5 0.505 (3.16) 1.048 (3.16) 91 0.36 l,4-PDI/BHN6 6 0.508 (3.18) 1.143 (3.