Open Journal of Polymer Chemistry, 2011, 1, 1-9 doi:10.4236/ojpchem.2011.11001 Published Online November 2011 (http://www.SciRP.org/journal/ojpchem) Organosoluble and Thermally Stable of Benzazole- Containing Poly(Imide-Urea)s: One-Pot Synthesis and Characterization Hojjat Toiserkani1,2* 1Department of Chemistry, College of Sciences, Hormozgan University, Bandar Abbas, Iran. 2College of Oil Engineering, Hormozgan University, Bandar Abbas, Iran. E-mail: *[email protected] Received October 12, 2011; revised November 10, 2011; accepted November 18, 2011 Abstract The preparation of new types of poly(imide-urea)s (PIUs) with high thermal stability and improved solubility was investigated. Three series of aromatic poly(imide-urea)s (PIUOa-c, PIUSa-c, and PIUNa-c) bearing pen- dent benzoxazole, benzothiazole or benzimidazole rings were prepared by one-pot polycondensation reaction of three bis(imide-carboxylic acid)s, 2-[3,5-bis(N-trimellitimidoyl)-phenyl]benzoxazole (1O), 2-[3,5-bis(N- trimellitimidoyl)-phenyl]benzothiazole (1S), or 2-[3,5-bis(N-trimellitimidoyl)-phenyl]benzimidazole (1N) with various kinds of aromatic diamines (a-c). The effects of the benzazole pendent groups on the polymer properties such as solubility and thermal stability were investigated by comparison of the polymers. All of the resulting polymers exhibited excellent solubility in common polar solvents. The glass transition tem- perature of the polymers determined by DSC thermograms were in the range 192˚C - 236˚C. The tempera- tures at 10% weight loss from their TGA curves were found to be in the range 390˚C - 441˚C in nitrogen. Keywords: Poly(Imide-Urea)s, Structure-Property Relation, Thermal Properties, Benzazole Pendent Groups 1. Introduction molecular asymmetry into the polymer backbone [5-19]. Among these approaches, the method of incorporating Aromatic polyimides (PIs) are well known as materials bulky, rigid benzazole hetero rings as pendent groups of high performance were developed in the early 1960s into the polymer backbone has become very attractive and since then have been of great technological impor- [20-23]. The advantages of this method include two main tance because of their outstanding thermal stability and parts: (1) close chain packing and intermolecular interac- chemical resistance, together with their balanced electric tions of the resulting polyimide are restricted, and this and mechanical properties [1,2]. Because many of them results in relatively high polymer solubility, and (2) the are insoluble and infusible, however, their applications in main chain rigidity of the polyimide can be maintained some fields were limited. It is well known that the poor by restricting the segmental mobility, in addition, these properties of PIs have a close connection with its chemi- benzazole hetero rings are thermally stable, and these cal composition and chain structure, in other words, the allow the polyimide to have a high glass-transition tem- chemical composition and chain structure of PIs will be a perature (Tg) and excellent thermal properties. head ingredient leading them to infusible within proc- As reported in our previous publications [22,23], three essing temperature and insoluble in organic solvents. bis(imide-carboxylic acid)s, 2-[3,5-bis(N-trimellitimi- Thus, incorporating new functionalities to make polyim- doyl)-phenyl]benzoxazole (1O), 2-[3,5-bis(N-trimelliti- ides more tractable without decreasing their many desir- midoyl)-phenyl]benzothiazole (1S), and 2-[3,5-bis(N-tri- able properties has become one important target of mellitimidoyl)-phenyl]benzimidazole (1N) were synthe- polyimides’ chemistry [3,4]. So far, many efforts on sized via a two-stage procedure that included the con- chemical modifications of polyimides structure have densation reaction between 2-aminophenol, 2-amino- been made to enhance their processability and solubility thiophenol, or m-phenylenediamine and 3,5-diamino- while other advantageous polymer properties are retained benzoic acid in the presence of polyphosphoric acid either by introducing flexible linkages, bulky groups, or (PPA) in 190˚C, followed by their reaction two mole Copyright © 2011 SciRs. OJPChem 2 H. TOISERKANI equivalents of trimellitic anhydride in refluxing glacial 2.3. Synthesis of Poly(Imide-Urea)s (PIUs) acetic acid, and were used to prepare aromatic poly(amide- imide)s containing benzazole hetero rings pendent The general procedure to prepare the poly(imide-urea)s groups in the backbones. is as follows: into a 50 mL two-neck round-bottom flask Because of the bulky heat-resistant structure of the equipped with a drying tube-capped reflux condenser, components 1O, 1S, and 1N as pendent groups, the result- magnetic stirrer, and dropping funnel were placed bis ing polymers exhibited reduced chain-packing efficiency (imide-carboxylic acid) 1O (0.172 g, 0.30 mmol) in and intermolecular interactions such as hydrogen bond- DMSO (2.0 mL). Then, DPAP (0.7 mL) and triethyl- ing. Therefore, several organosoluble poly(amide-im- amine (0.8 mL) were added to the initial contents of the ide)s with moderate Tgs and high thermal stability could flask. The final mixture was stirred 2 h at about 10˚C and be achieved by the incorporation of the benzazole pen- then for 3 h at 70˚C until evolution of nitrogen gas dent units in the main chain. These results prompted us stopped. 2,6-Diaminopyridine (a) (0.032 g, 0.30 mmol) to use bis(imide-carboxylic acid) monomers (1O, 1S, and in DMSO (2.5 mL) was added dropwise to the initial 1N), and to study the properties of the poly(imide-urea)s reaction mixture, and the final mixture was heated for 12 obtained by direct polycondensation of them with aro- h at 90˚C. The viscous polymer solution obtained was matic diamines (a-c). trickled on stirred methanol to give rise to a crude pre- cipitate, which was collected by filtration, washed thor- HOOC COOH oughly with methanol, hot water, and ether, respectively, O O and dried under reduced pressure at 40˚C to afford 0.103 a as dark brown powder. N N g (51%) of PIUO The inherent viscosity of the poly(imide-urea)s ob- O O tained in N,N-dimethylacetamide (DMAc) was 0.22 dL/g, measured at a concentration of 0.5 g/dL at 30˚C . N X=O –1 X 1O FT-IR (KBr, cm ): 3352, 3190 (br, m), 1778 (sh, w), X=S 1S 1724 (sh, s), 1677 (sh, s), 1616 (sh, m), 1595 (sh, w), 1502 (sh, m), 1449 (sh, m), 1349 (sh, s), 1206 (sh, w), X=NH 1 N 1163 (sh, w), 1096 (sh, m), 1035 (sh, w), 924 (sh, w), 1 893 (sh, w), 763 (sh, w), 725 (sh, m), 675 (sh, w). 1 H-NMR (DMSO-d6; δ, ppm): 8.81 ppm (4H of ureylene 2. Experimental linkages), 7.44 - 8.46 ppm (separate peak blocks, 16H of aromatic rings). Elemental analysis: calculated for 2.1. Materials C36H20N8O7 (676)n: C, 63.72%; H, 2.27%; N, 16.51%. Found: C, 63.21%; H, 2.24%; N, 16.09%. Diphenyl azidophosphate (DPAP) purchased from Merck The above one-pot polyaddition reaction was chosen and used as received. Dimethyl sulfoxide (DMSO, as a procedure for preparation of the other PIUs. Merck) and triethylamine (TEA, Merck) were purified by distillation under reduced pressure over calcium hy- 2.4. Measurements dride and stored over 4-Å molecular sieves. 2,6-Diami- nopyridine (a, Merck) was purified by sublimation be- Inherent viscosities (ηinh) of polymers were determined fore use. Aromatic diamines including 5-(2-benzoxazo- for solution of 0.5 g/dL in DMAc at 30˚C using a le)-1,3-phenylenediamine (b, mp 226˚C - 230˚C), and Canon-Fenske viscometer. 1H-NMR spectra were re- 5-(2-benzothiazole)-1,3-phenylenediamine (c, mp 167˚C corded on a Bruker AV-500 FT-NMR spectrometer in -171˚C) were prepared in our laboratory according to the DMSO-d6 at 25˚C with frequencies of 500.13 MHz. method previously reported [22]. FT-IR spectra were recorded on a Bruker Tensor-27 spectrometer for the measurement of infrared absorption 2.2. Synthesis of the Monomer spectra for monomers and polymers. The spectra of sol- ids were obtained using KBr pellets. Melting points (mp) Bis(imide-carboxylic acid) monomers 1O, 1S, and 1N were were determined with a Buchi 535 melting point appara- synthesized by the condensation of 5-(2-benzoxazole)-1,3- tus. Thermogravimetric analyses (TGA) was conducted phenylenediamine, 5-(2-benzothiazole)-1,3-phenylenediamine, with a Du Pont 2000 thermal analysis under nitrogen and 5-(2-benzimidazole)-1,3-phenylenediamine, with two atmosphere (20 cm3/min) at a heating rate of 20˚C /min. mole equivalents of trimellitic anhydride in glacial acetic Differential scanning calorimeter (DSC) was recorded on acid, respectively, according to our previous works [22,23]. a Perkin Elmer pyris 6 DSC under nitrogen atmosphere Copyright © 2011 SciRes. OJPChem H. TOISERKANI 3 3 (20 cm /min) at a heating rate of 20˚C /min. (1N) with various aromatic diamines (a-c). As shown in Scheme 1, bis(imide-carboxylic acid) 3. Result and Discussion monomers, 1 were converted to bis(imide-carbonyl azide) components, 2 using DPAP in DMSO as the reaction 3.1. Synthesis and Characterization solvent. The thermal decomposition of the in situ ob- tained bis(imide-carbonyl azide) 2 via Curtius rearran- Bis(imide-carboxylic acid) monomers such as 1O, 1S, and gement gave the corresponding diisocyanates 3. In con- 1N were synthesized by the condensation reaction be- tinuation of this reaction, compounds 3 have been re- tween the appropriate aromatic diamine, 5-(2-benzoxa- acted with various aromatic diamines (a-c) to prepare the zole)-1,3-phenylenediamine, and 5-(2-benzothiazole) final benzazole-based poly(imide-urea)s (PIUs).