2,2'-bis-[(3,4-dicarboxyphenoxy)phenyl]- 3,3-5,5 -tetramethyl-1,4-phenylenediisopropylidene

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1 Design and Synthesis of Novel Hydrogen-Rich Polyimides for Radiation Shielding David J. Hill and Dr. Robert A. Orwoll Department of Chemistry, College of William and Mary, Williamsburg, VA 23187, USA In space, there are several types of radiation, including solar radiation and galactic cosmic radiation (GCR), that can be harmful to both living beings and machines. The current radiation shielding available on spacecraft is insufficient to protect astronauts and sensitive equipment for long-duration space flight or extraterrestrial habitation, and terrestrial shielding techniques are too heavy to be practical for spacecraft. The use of polymers, specifically hydrogen-rich, aromatic polyimides, as radiation shielding provides a method of slowing radiation in space and preventing the damaging cascade of radiation that results from its collision with spacecraft. This research focuses on the development of novel aromatic-ether dianhydrides for use in polymerization with similarly structured diamines to produce hydrogen-rich polyimides for use as radiation shielding. Introduction One of the greatest hazards to the extended stay of humans and equipment beyond Earth s orbit is radiation. The surface of the Earth is relatively well shielded from extra-planetary radiation by the Van Allen radiation belts and the thick layers of the atmosphere. Beyond the Van Allen belts, however, there is very little protection from the particles and waves of radiation emitted by the sun and extra-solar events. Any manned mission to Mars or an asteroid, lunar settlement, or missions of or exceeding the length of SkyLab 4 (87 days in Low Earth Orbit) would receive high levels of radiation, which could cause physical damage, or in extended periods, become lethal. Therefore, in order to continue manned missions into space, adequate radiation shielding is necessary to protect vulnerable electronic, and more importantly, the human lives already at risk in these exploratory missions The danger from radiation takes many forms, and comes both from the Sun and as Galactic Cosmic Radiation (GCR) from beyond the solar system. One form is high energy electromagnetic waves, such as X-rays and gamma rays, while the majority of cosmic rays are in fact not rays at all, but atomic nuclei accelerated to very high speeds. When GCR, electromagnetic radiation, and other radiation particles smash into the aluminum and steel of the spacecraft, they create a cascade of particle collisions that, in the relatively small thickness of the spacecraft, simply results in a much larger number of radiation particles. The traditional solution to radiation shielding is erecting thick layers of lead and concrete, which eventually block harmful radiation. However, a spacecraft covered in lead and concrete would be too heavy to take off, so more innovative methods are required to provide shielding. It has been established that materials with high hydrogen contents are better radiation shields, because hydrogen produces the most Coulombic interactions per unit mass, which is what stops GCR. Large elements, like gadolinium, have very large neutron capture radii, and the incorporation of such elements into polymers will help to absorb neutron radiation. Finally, on a more tangible level, any radiation shielding put in place will need to be lightweight so as to not weigh down the launching craft, be mechanically

2 strong so that it can be installed for a variety of purposes, such as plumbing, insulation, and structural support, and have good thermal stability, so that it does not degrade in the wide range of temperatures that a spacecraft would experience. It is the combination of these properties that make polymers suitable radiation shields. Polyimides, as a class of polymers, are well known for their good mechanical properties and stability under thermal stresses upwards of 500ºC. Well-made polymer films of this type are also flexible, allowing for their use in a variety of parts of the spacecraft and extra-vehicular equipment like spacesuits. In general, polymers containing aromatic (benzene-containing) backbones are stronger on the macroscopic level but relatively hydrogen deficient, while aliphatic polymers (like polypropylene and polyethylene) have higher hydrogen contents, but are relatively weak and degrade easily. The goal of this research is to synthesize novel polymers that incorporate an aromatic backbone for strength, but are also relatively hydrogen rich, so as to better shield against radiation. R= a) b) c) d) e) i) Methods The general synthesis of these dianhydrides starts with a bisphenols core. Variations in the structure, substitution patterns, and substituent groups on these bisphenols allow for the incorporation of additional hydrogen via aliphatic chains and can affect the thermal properties of the subsequent polymers. The bisphenols (a) are converted to phenoxide salts, which react via nucleophilic aromatic substitution with 4-nitrophthalonitrile (b) to displace NO 2 and produce a tetracyano aromatic ether (c). This compound is then saponified in aqueous solution and acidified to produce the tetracarboxylic acid aromatic ether (d). This compound is reacted in acetic ii) iii) iv)

3 anhydride to extract water and effect a ring closure to produce the dianhydride (e) 1. Several different syntheses were attempted before arriving at this synthesis, including the reaction between the bisphenol salt and 4-fluoro-N-phenylphthalimide 2 (followed by hydrolysis to produce (d)), and between the bisphenol salt and 4- fluorophthalic anhydride 3 without success. To ensure that the correct product was being prepared in the reaction sequence, 2,2-Bis[4- (3,4-dicarboxyphenoxy)phenyl] propane dianhydride (e.iv) (known as BPADA or UDA) was used as a model compound, as it is commercially available and can be produced by this synthetic route. This allows for the comparison of data from samples of known purity to the experimental results. 2,2-Bis[4-(3,4-dicyanophenoxy) phenyl]propane In a 100mL flask, 5.00g (0.022mol) of Bisphenol A (a.iv) was combined with 6.062g (0.044mol) of K 2 CO 3, 45mL of DMF, and 15mL of toluene. The mixture was heated to reflux (160ºC) under dry N 2 with a Dean-Stark trap to remove water azeotropically. The reaction mixture was then allowed to cool to 60ºC and 7.59g (0.044mol) of 4-nitrophthalonitrile was added. The reaction was stirred for 24 hours. The reaction was then cooled to room temperature and poured onto 150mL of water, precipitating a reddish-brown solid that was filtered. This solid was washed with methanol and water and dried at 100ºC, yielding 9.36g (89% yield); mp = 185º - 187ºC. 2,2-Bis[4-(3,4-dicarboxyphenoxy) phenyl]propane 6.50g (0.0116mol) of KOH was dissolved in a mixture of 40mL of H 2 O and 40mL of EtOH. This solution was added to 9.36g (0.0195mol) of 2,2-Bis[4-(3,4- dicyanophenoxy) phenyl]propane in a 100mL flask. The mixture was refluxed (112ºC) for 24 hours until a clear solution was produced. The solution was then cooled to room temperature and acidified with HCl to a ph = 1. This precipitated a yellow solid, which was filtered, washed with water, and dried. The acid produced was not characterized in detail but was used directly in the synthesis of 2,2-Bis[4-(3,4- dicarboxyphenoxy) phenyl]propane dianhydride. 2,2-Bis[4-(3,4-dicarboxyphenoxy) phenyl]propane dianhydride Boiling acetic anhydride was added to the acid compound until full dissolution was achieved. Refluxing was continued for one hour, and the solution was cooled to room temperature, then to -1.0ºC. A light brown solid was precipitated and dried at 100ºC, yielding 3.91g (34% total sequence yield); mp = 180º-183ºC, and a mixture melting point with stock UDA melted from 178º 183ºC. IR analysis (KBr) showed absorptions at 1845cm -1 (assym. C=O), 1782cm -1 (sym. C=O), cm -1 (aromatic C=C), and 1280cm -1 (C-O-C). 2,2'-bis-[(3,4-dicarboxyphenoxy)phenyl]- 3,3-5,5 -tetramethyl-1,4-phenylenediisopropylidene In a 500mL flask, 26.57g (0.066mol) of tetramethyl bisphenol P (a.ii), 22.85g (0.132mol) of 4-nitrophthalonitrile, and 27.36g of K 2 CO 3 were combined in 135mL of DMF and 45mL of toluene. The mixture was stirred at 60ºC for 24 hours. The reaction was then cooled to room temperature and poured onto 700mL of water, precipitating a yellow solid that was filtered. This solid was washed with methanol and water and dried at 100ºC. The crude product was then recrystallized in acetonitrile, yielding 29.40g (68% yield); mp = 200º-202ºC. IR analysis (KBr)

4 showed absorptions at 2232cm -1 (C N), cm -1 (aromatic C=C), and 1245cm -1 (C-O-C). Elemental analysis calculated for C 44 O 2 N 4 H 38 (654.57): C, 80.71%; H, 5.85%; N, 8.56%. Found: C, 80.22%; H, 5.85%; N, 8.49%. 2,2'-bis-[(3,4-dicarboxyphenoxy)phenyl]- 3,3-5,5 -tetramethyl-1,4-phenylenediisopropylidene dianhydride The target molecule of this project (e.ii) was prepared by adding the acid compound to 400mL of Ac 2 O and refluxing for 24 hours. The solution was then reduced to a total volume of 100mL and cooled to room temperature, then -1.0ºC. A solid was collected, filtered, and recrystallized in Ac 2 O, then dried under vacuum, yielding 16.25g (35% total yield). Thermal analysis by DSC shows a change in heat capacity centered around 105ºC. IR analysis (KBr) showed absorptions at 1854cm -1 (assym. C=O), 1778cm -1 (sym. C=O), cm -1 (aromatic C=C), and 1282cm -1 (C-O-C). 1 H NMR (CDCl 3, ppm): δ = 7.94 (2H, d), δ = 7.39 (2H, d), δ = 7.19 (6H, m), δ = 7.01 (4H, s), δ = 2.05 (12H, s), δ = 1.70 (12H, s). Elemental analysis calculated for C 44 H 38 O 8 (694.77): C, 76.06%; H, 5.51%. Found C, 75.93%; H, 5.55%. Discussion The synthesis of dianhydrides of this type, with the conscious incorporation of aliphatic substituents for increased hydrogen content, will broaden the range of compounds that can be polymerized with similarly structured diamines to produce hydrogen polymers suitable for radiation shielding in space. This synthesis relies primarily on previous research 1, but some modifications have been made. The initial reaction is traditionally done with a Dean- Stark trap, but as can been seen in the synthesis of (c.ii), this is not required to effect the reaction, as the quantity of water theoretically produced ( 1mL) is insignificant in scale of this reaction. In the saponification step (to produce [d]), 6 equivalents of KOH were used. This is a departure from previous work, which has suggested using only 2 equivalents of KOH. While the hydroxide is technically catalytic in the addition of water to the nitrile, the resulting carboxylic acid will be deprotonated and quench the base. Therefore, it is desirable to have an excess of base, and there are no other base-sensitive groups on these molecules. References 1 Hsiao, Sheng-Huei and Yu, Chou-Huan. Aromatic Poly(ether imide)s Bearing Isopropylidene or Hexafluoroisopropylidene Links in the Main Chain. Polymer Journal, 29:11, (1997). 2 Zhang, Min; Wang, Zhen; Ding, Mengxian. Process for preparation of diether type benzenetetracarboxylic dianhydrides. Faming Zhuanli Shenqing, 13 (2006). 3 Williams, Frank J., III. Aromatic ether anhydrides and products made thereby. Patent 3,850, Nov Bibliography Bate, Norah. Monomer and Polyimide Production for Radiation Shielding Purposes in Manned Space Exploration. BS Thesis. Williamsburg: College of William and Mary, Mewaldt, R. A. "Cosmic Rays." Rigden, John S, Carl T Tomizuka and Roger H Stuewer. Macmillan Encyclopedia of Physics. Charlottesville: Simon & Schuster Macmillan, Wald, Matthew L. "Mars Mission's Invisible Enemy: Radiation." The New York Times 9 December 2003.

5 Acknowledgments The authors would like to thank Dr. Richard Kiefer and other members of the lab for their assistance. They graciously acknowledge the financial support from NASA via the VSGC.

Supporting Information

Supporting Information Anion Conductive Triblock Copolymer Membranes with Flexible Multication Side Chain Chen Xiao Lin a,b, Hong Yue Wu a, Ling Li a, Xiu Qin Wang a, Qiu Gen Zhang a, Ai Mei Zhu a, Qing