|||||||||||||| USOO56633A United States Patent (19) 11 Patent Number: 5,166,313 Archibald et al. 45) Date of Patent: Nov. 24, 1992 (54) DIAMANTANE MODIFIED RIGID-ROD Attorney, Agent, or Firm-Norton R. Townsley; POLY BENZAZOLE AND METHOD OF Thomas N. Giaccherini MANUFACTURE 57 ABSTRACT 75) Inventors: Thomas G. Archibald, Sacramento; Aslam A. Malik, San Dimas; Kurt The present invention comprises diamantane groups Baum, Pasadena, all of Calif. interspersed among benzothiazole groups, benzoxazole groups or benzimidazole groups. This constitutes a rig 73) Assignee: Fluorochem, Inc., Azusa, Calif. id-rod polymer with stable cycloaliphatic groups inter 21 Appl. No.: 693,166 spersed into the aromatic-heteroaromatic backbone of the rods. The presence of the aliphatic groups decreases 22 Filed: Apr. 29, 1991 crystallinity by adding disorder to the rods thus mini 51) Int. Cl....................... C08G 73/18; C08G 73/22; mizing interactions between the heteroaromatic groups. CO8G 75/32 The interspersed aliphatic groups act as insulators and 52 U.S. Cl. .................................... 528/344; 528/176; thus permit greater relative protonation. Also, the re 528/183; 528/190; 528/337; 528/342 duced conjugation of the aromatic-heteroaromatic rings 58 Field of Search ............... 528/344, 337,342, 190, reduces the color of the polymers. The preferred 528/176, 183 method of manufacturing this improved rigid-rod poly (56) References Cited mer is by condensation of dimethyl diamantanecarboxy late with 2,5-diamino-1,4-benzenedithiol, 1,2,4,5-tet U.S. PATENT DOCUMENTS raaminobenzene, or 4,6-diamino-1,3-benzenediol. 3,464,957 9/1969 Driscoll ............................... 528/344 Primary Examiner-Harold D. Anderson 11 Claims, 3 Drawing Sheets U.S. Patent Nov. 24, 1992 Sheet 1 of 3 5,166,313 FIG FIG 2 DAMANTANE / BENZOHAZOLE POLYMER FILM ABSORBANCE SPECTRUM N METHANESULFONIC ACID - PBT FILM 3OO 5OO 7OO 900 U.S. Patent Nov. 24, 1992 Sheet 2 of 3 5,166,313 FG 4 U.S. Patent Nov. 24, 1992 Sheet 3 of 3 5,166,313 X F. G. 5 N IO,N H H X FG 6 5,166,313 1. 2 heteroaromatic rings, would reduce the color of the DAMANTANE MODIFIED RIGID-ROD POLY rigid rod polymers. BENZAZOLE AND METHOD OF MANUFACTURE SUMMARY OF THE INVENTION STATEMENT OF GOVERNMENT INTEREST 5 The present invention is a rigid-rod polymer with reduced intermolecular interactions. It comprises dia The Government has rights in this invention pursuant mantane groups interspersed among benzothiazole to Contract F33615-89-C-5630 awarded by the Depart groups, benzoxazole groups or benzimidazole groups. ment of the Air Force. This constitutes a polymer with stable cycloaliphatic BACKGROUND OF THE INVENTION 10 groups interspersed into the aromatic-heteroaromatic backbone of the rods. The presence of the aliphatic The present invention relates to the field of polymers groups decreases crystallinity by adding disorder to the and more particularly to the field of rigid-rod polymers. rods thus minimizing interactions between the In 1981, the U.S. Air Force sponsored research into heteroaromatic groups. Interspersed aliphatic groups new structural materials having low density, high 15 act as insulators and thus permit greater relative proton strength, and high modulus. This research was reported ation. Also, the reduced conjugation of the aromatic in Macromolecules, 1981, 14, pp. 909-954. These new heteroaromatic rings reduces the color of the rigid rod materials were formed by condensing tetrafunctional polymers. benzene derivatives with aromatic p-dicarboxylic acids The preferred method of manufacturing this im to give heteroaromatic rings. The resulting polymers 20 proved rigid-rod polymer is by condensation of di are known as rigid-rod polymers. One rigid-rod poly methyl diamantanecarboxylate with 2,5-diamino-1,4- mer, polybenzothiozole (PBT), is formed by the con benzenedithiol, 1,2,4,5-tetraaminobenzene, or 4,6- densation of 2,5-diamino-1,4-benzenedithiol with ter diamino-1,3-benzenediol. ephthalic acid in polyphosphoric acid. Another, poly An appreciation of other aims and objectives of the benzoxazole is formed by the condensation of 4,6- 25 present invention and a more complete and comprehen diamino-1,3-benzenediol with terephthalic acid. A sive understanding of it may be achieved by referring to third, polybenzimidazole is formed by the condensation the accompanying drawings and by studying the fol of 1,2,4,5-tetraaminobenzene with terephthalic acid. lowing description of a preferred embodiment. Rigid-rod polymers were found to exhibit liquid crystal line behavior in solution, suggesting potential uses as BRIEF DESCRIPTION OF THE DRAWENGS nonlinear optical materials or in molecular composites. FIG. 1 is a structural representation of the diaman Several theoretical and structural studies on these mate tane molecule showing the 4,9 and 1,6 functional posi rials have been published. See for example, Wolfe, J. F. tions. "Polybenzothiazoles and Oxazoles', Encyclopedia of FIG. 2 is a comparison of the absorbance spectra of Polymer Science and Engineering 1988, 11, 601. 35 the diamentane/benzothiazole polymer and PBT in methanesulfonic acid through the visible region. The high intermolecular attraction and degree of FIG. 3 is a structural representation of the 4,9. molecular order of rigid-rod polymers, which results in diamantane/benzothiozole polymer. their excellent mechanical properties, also makes these FIG. 4 is a structural representation of the 1,6- materials insoluble in everything except strong acids. diamantane/benzothiozole polymer. Dissolution of rigid rods in acid occurs by protonation FIG. 5 is a structural representation of the 4,9- of the heteroatoms but is limited by charge delocaliza diamantane/benzoxazole polymer. tion along the chain resulting in fewer protonations. FIG. 6 is a structural representation of the 4,9- Processing is therefore difficult. Attempts have been diamantane/benzimidazole polymer. made to improve the solubility characteristics by insert 45 ing pendant groups on the polymer chain, or small nun DETAILED DESCRIPTION OF THE bers of flexible groups into the chain. These changes PREFERRED EMBODIMENT usually resulted in improved processability at the ex There are two major requirements for aliphatic com pense of the thermal stability and mechanical proper ponents to be used in rigid-rod polymers: the aliphatic ties. 50 group must have thermal stability comparable to that of Rigid-rod polymers could potentially be useful as the aromatic-heteroaromatic segment and it must have molecular reinforcement for composites or for optical symmetry to allow linear connection (a cantenation applications, for example aircraft windshields. Molecu angle of 180') to the heteroaromatic segments. lar reinforcements are similar to macroscopic chopped Hydrocarbons containing the adamantane and dia fiber reinforcements. The advantage of molecular rein 55 mantane cage structure are unusually stable. Polymers forcements is that interfacial adhesion problems are based on 1,3-diethynyladanantane and 1,6- and 4,9-die minimized or eliminated so that fracture toughness, thynyldiamantanes have been previously studied. It has impact resistance and dimensional stability are in been found by TGA analysis that adamantane-based proved. The use of rigid-rod polymers for optical appli materials start to decompose around 475 C., whereas, cations has been hampered by the inherently dark col the diamantane analogues, decompose around 520' C. ors of the polymers which result from their highly con Unlike adamantane, diamantane has parallel connecting jugated backbones. bonds that are needed for use as a linking group in If a method could be found to reduce the high inter rigid-rod polymers. molecular interactions of rigid-rod polymers it would FIG. 1 is a structural representation of the diaman be a great advance in the field. Reducing the intermo 65 tane molecule. Diamantane is named because its carbon lecular attraction would add disorder to the rods, per atoms are arranged in six-membered-ring chair struc mit greater relative protonation, enhance processability tures similar to the structure found in diamond. Dia and, by reducing conjugation of the aromatic mantane has two axes of symmetry which makes it 5,166,313 3 suitable for incorporation into rigid-rod polymers. The hydrocarbon contains 6 bridge carbons and 8 bridge head carbons. Of the bridgehead carbons, two are "api cal" (4 and 9 positions) and groups at these positions oppose one another by an angle of 180. Similarly (i. - G Binor-s - b. s. bridgehead carbons on the girdle are opposing at the l and 6 positions. Thus, diamantane derivatives function alized at the 1,6- and 4,9-positions posses geometry suitable for incorporation into rigid-rod polymers. By 10 Tetrahydrobinor-s - G contrast, the bridgehead positions in adamantane are at an angle of 109 and cannot be used. For incorporation into the polymer chain, dimethyl 4,9-diamantanedicarboxylate was reacted with 2,5- diamino-1,4-benzenedithiol at polymer concentrations 15 either above (anisotropic polymerization) or below (isotropic polymerization) the critical concentration to Aluminum chloride-mediated isomerization of tet give white polymers. The diamantane modified rigid rahydrobinor-s in refluxing methylene chloride gave rod polymers exhibited nematic behavior above the diamantane in 50 to 82% yield. Diamantane crystallized critical concentration, and both stir-opalescence in solu 20 from the reaction mixture and was purified by an ace tion and birefringence in polymer dopes were observed. tone wash to give material that was pure by nmr and gle The intrinsic viscosity of the polymer in methanesul analysis. fonic acid at 30° C. and a concentration of 0.25 g/dL 4,9-Dibromodiamantane. Diamantane (50 g, 0.26 was 10.2 dll/g. The diamantane modified rigid-rod 25 mol) was added over 1 h to bromine (200 mL) at 0°C. Aluminum bromide (5.4g, 0.02 mol) was added and the polymer was cast from methanesulfonic acid and the mixture was stirred at 0° C. for 3 hand at ambient tem absorption spectrum showed no absorption in the visi perature for 16h.