J Polym Res (2012) 19:9754 DOI 10.1007/s10965-011-9754-8 ORIGINAL PAPER Synthesis and trans-ureation of N,N’-diphenyl-4, 4′-methylenediphenylene biscarbamate with diamines: a non-isocyanate route (NIR) to polyureas Hsueh-Yung Chen & Wen-Chen Pan & Chao-Hsing Lin & Chun-Ying Huang & Shenghong A. Dai Received: 25 May 2011 /Accepted: 25 August 2011 /Published online: 22 February 2012 # Springer Science+Business Media B.V. 2012 Abstract A non-isocyanate route (NIR) of making polyureas Keywords Non-isocyanate route . Trans-ureation . of high molecular weight has been found through trans- Polyurea . N,N’-diphenyl-4,4′-methylenediphenylene ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscar- biscarbamate . N,N’-dimethyl-4,4′-methylenediphenylene bamate (4,4′-DP-MDC) with a variety of diamines and mixed biscarbamate . Diphenyl carbonate diamines. The preparation of 4,4′-DP-MDC was achieved readily by carbonylation of 4,4′-methylenedianiline (4,4′- MDA) with diphenyl carbonate (DPC) using organic acids as catalysts. It was found that the highest yield (99%) of pure Primary intermediate synthesized Specifications Abbreviation 4,4′-DP-MDC can be isolated in a toluene solution under mild N,N’-diphenyl-4,4′- Mw:438.47 4,4′-DP-MDC conditions co-catalyzed by benzoic acid and tertiary amine. methylenediphenylene ′ biscarbamate Trans-ureation of 4,4 -DP-MDC with aliphatic amines indi- N,N’-dimethyl-4,4′- Mw:314.34 4,4′-DM-MDC cated that the process is a highly solvent dependent process methylenediphenylene and was found to be extremely facile in dimethyl sulfoxide biscarbamate ′ (DMSO) at 80 °C and in tetramethylene sulfone (TMS) at 4,4 -diphenylmethanebis- Mw:372.42 [DPMHU] [(2-hydroxyethyl)urea] 140 °C in absence of any catalyst. Particularly, the most DMSO/80 effective polymerization process was developed using tetra- methylene sulfone (TMS) as the solvent under reduced pres- sure for concurrently distilling off phenol from the reaction mixture during the polymerization in a shifting equilibrium Introduction towards polyurea. However, this solvent-assisted trans- ureation was found to be in-efficient when N,N’-dimethyl- Polyurea and polyurea elastomers have been known to 4,4′-methylenediphenylene biscarbamate (4,4′-DM-MDC) possess many outstanding mechanical properties. Since intro- was used in a similar condition for comparison. Thus, an duced commercially in the 1970s, polyurea elastomers have efficient green-chemistry process has been developed based been widely applied in polyurethane-urea reaction injection on 4,4′-DP-MDC in making urea prepolymers, urea elasto- molding (RIM) processes [1–5] and spray-coating systems mers and urea plastics all in excellent yields without using [6–8] to harness their fast polymerization rates and outstand- reactive methylenediphenylene diisocyanate (MDI) or any ing mechanical properties. Currently, two important polyurea catalysts in the trans-ureation polymerizations. commercial markets are automotive and construction applica- tions [9–12]withfamiliarfinishedproductssuchasbumpers, fascia, waterproofing linings, thermal insulation materials, : : : : industrial flooring and sports facilities. However, due to the H.-Y. Chen W.-C. Pan C.-H. Lin C.-Y. Huang S. A. Dai (*) high reaction rates of diisocyanates such as methylenedipheny- Department of Chemical Engineering, lene diisocyanate (MDI) and diamines, the synthesis and pro- National Chung-Hsing University, Taichung, Taiwan cessing of polyurea and polyurea elastomers have been heavily e-mail: [email protected] dependent upon the assistance of RIM-machine or high- Page 2 of 11 H. Chen et al. pressure mixing equipments. Synthesis of polyureas in bulk polyureas in nature, high cost of di-tert-butyl tricarbonate and through more controllable step-wise manners has rarely been carbonyl biscaprolactam seems limiting their wide-spread reported and will be highly prized for polyurea formulation applications. development [13–16]. If the synthesis of polyurea can com- Since the 1980s, biscarbamates of methylenediphenylene pletely avoid using diisocyanates such as MDI or toluene diisocyanate (MDI) such as 4,4′-DM-MDC or N,N’-diethyl- diisocyanate (TDI) as the raw materials, it would become 4,4′-methylenediphenylene biscarbamate (4,4′-DE-MDC) have even more attractive because of the elimination of highly toxic been touted as the most important precursors for non-phosgene and reactive diisocyanates in the overall synthetic scheme. synthesis of MDI [21–23]. These bis-carbamates are synthesized (Scheme 1) by the condensation of mono-phenylcarbamate (Scheme 1)with Recently, non-isocyanate synthesis of polyurea and formalin. The mono-phenylcarbamates were prepared by oxida- polyurethanes has been explored with reactions of diamines tive carbonylations of aniline (Asahi’ Process) or reductive with new intermediates. For example, Meijer used di-tert-butyl carbonylation (ARCO’sProcess)ofnitro-benzene.Boththese tricarbonate and diamine terminated poly(tetrahydrofuran) as carbonylations involved carbon monoxide and precious metal raw materials for making thermoplastic elastomers (TPEs) [17, catalyses. However, high dilution and high temperature thermol- 18] of urea segmented block copolymers. Another approach for ysis of biscarbamates in excess of 250 °C are both required for preparing polyureas without isocyanate chemistry was reported MDI generation. As a consequence, those severe conditions in Mtilhaupt’s studies [19, 20] where a carbonyl biscaprolactam make the overall process unattractive due to energy cost, safety served as a non-halogen building block that could convert the concerns and process difficulties. Except for isophorone diiso- terminal amine-groups of functional polymers into the cyanate (IPDI) productions, no commercial diisocyanates (MDI corresponding caprolactam-blocked isocyanates. Although or TDI) has been diverted to the biscarbamate process so far [24, these approaches appear to be non-isocyanate processes to 25]. Therefore, non-phosgene routes (NPR) to diisocyanates NH2 NO2 O aniline nitrobenzene + H H Pd/NaI formaldehyde Pt.Se NHCOOCH3 H2N NH2 4,4'-methylenedianiline N-methyl phenylcarbamate O O O + + O H H diphenyl carbonate formaldehyde O O O O H C CH O N N O 3 O N N O 3 H H H H N,N'-diphenyl-4,4'-methylene diphenylcarbamate(4,4'-DP-MDC) N,N'-dimethyl-4,4'-methylene diphenylcarbamate(4,4'-DM-MDC) pyrolysis non-isocyanate route to polyurea non-isocyanate route to polyurea O O O O R R N N N N OCN NCO N N N N n H H H H H H H H n polyurea 4,4'-methylenediphenyl diisocyanate polyurea high molecular weights low molecular weights excellent mechanical performance O O O O R R O N N O N N N N n H H H H H H n polyurethane polyurea Scheme 1 Overall scheme of NIR route to polyurea. (The solid-line portions are carried out successfully in the study) Non-Isocyanate Route (NIR) to Polyurea through DP-MDC Page 3 of 11 such as MDI or TDI have remained a long-term un-met goal yet Since improved synthesis for 4,4′-DP-MDC from car- to be achieved in the polyurethane/urea fields. bonylation reaction of 4,4′-methylenedianiline (4,4′-MDA) However, in a non-isocyanate route (NIR) to polyurea, with diphenyl carbonates have been accomplished recently the approach based on MDI-biscarbamates seems promising by Harada’s[33]andbyBosetti’s[34]studies,wehave because no high-temperature condition is required through initiated a feasibility study of NIR-polyurea process using trans-esterification or trans-ureation. In fact, several attempts 4,4′-DP-MDC and 4,4′-DM-MDC as key intermediates to have tried to use carbamates, or biscarbamates directly as react with diamines. Our present study has established precursors for polyurethane (PU) and polyurea synthesis that there are tremendous advantages of using 4,4′-DP- bypassing isolation of diisocyanate completely [26]. In MDC over 4,4′-DM-MDC in trans-ureation reaction in 2000, ring-opening isomerization of cyclic-urethane [27–29] making polyurea. Our results show that the polymeriza- and trans-esterification [30, 31] to make PU are notable exam- tion using 4,4′-DP-MDC and diamines can lead to high ples. However, both produce low molecular weight polymers. molecular weight polyurea in dimethyl sulfoxide (DMSO) Metal or Lewis acid catalyzed trans-esterifications of diols and or tetramethylene sulfone (TMS). This NIR trans- diamines with biscarbamates also have been studied in recent ureation process is efficient and is achieved in absence reports with some success [32]. of any catalyst. Experimental section Materials and reagents Materials and reagents Specifications Suppliers Abbreviation Concentrated hydrochloric acid 37% Tedia Con. HCl Formaldehyde 37% Tedia – 1,6-Hexanediamine analytical grade Acros 1,6-HDA m-Xylylenediamine analytical grade TCI m-XDA Isophorondiamine analytical grade Acros IPDA 4,4′-Diaminodicyclohexylmethane analytical grade Alfa H12MDA 4,4′-Methylenedianiline analytical grade Acros 4,4′-MDA 2-Aminoethanol analytical grade Tedia AE Tetramethylene sulfone analytical grade Acros TMS Dimethyl sulfoxide HPLC grade Tedia DMSO Amine terminated PPG-2000 Jeffamine D-2000, Mw: 2000 Huntsman PPG-DA-2000 Amine terminated PPG-230 Jeffamine D-230, Mw: 230 Huntsman PPG-DA-230 Polyether diamine based on a predominantly PEG backbone Jeffamine ED-2003, Mw: 2000 Huntsman PEG-DA-2000 1,8-Diamino-3,6-dioxaoctane Jeffamine EDR-148, Mw: 148 Huntsman DADO N-Methyl-2-pyrrolidinone analytical grade Mallinckrodt NMP Diphenyl carbonate analytical grade Acros DPC Pyridine analytical grade Tedia – 1,4-diazabicycle[2, 2, 2]octane