A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

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<ul><li><p>A novel type of Si-containinn</p><p>Ya</p><p>Istanbul University, Engineering Faculty, Chemical Engineering Department, Chemical Technologies Group,</p><p>tric breakdown strength, moisture uptake and solubility properties of the lms were also investigated.</p><p>their mechanical properties rapidly deteriorate above</p><p>8090 C and thermal degradation takes place at tem-peratures above 200 C [4]. Researches focused onimproving the thermal stability of PU have attempted</p><p>in various ways. The most accepted approach for the</p><p>0014-3057/$ - see front matter 2004 Elsevier Ltd. All rights reserved.</p><p>Koeln, Institute fur Physikalische Chemie, Luxemburger</p><p>str.116, D-50939 Cologne, Germany. Tel.: +49 221 470 4485/</p><p>+90 212 591 2479; fax: +49 221 470 7300/+90 212 591 1997.</p><p>E-mail addresses: hdeligoz@istanbul.edu.tr, H.Deligoz@</p><p>uni-koeln.de (H. Deligoz).</p><p>European Polymer Journal 41</p><p>EUROPEANPOLYMER 2004 Elsevier Ltd. All rights reserved.</p><p>Keywords: Poly(urethane-imide); Poly(amic acid); Thermal imidization; Dielectric properties</p><p>1. Introduction</p><p>Polyurethane (PU) is a versatile polymer and can be</p><p>easily prepared by a simple polyaddition reaction of pol-</p><p>yol, isocyanate and a chain extender. PUs have excellent</p><p>abrasion resistance and some properties of both rubber</p><p>and plastics [13]. They are becoming increasingly</p><p>important as engineering materials. Unfortunately, the</p><p>conventional PUs are known to exhibit poor thermal</p><p>stability which limits their applications. For example,* Corresponding author. Present address: Universitat zu34320 Avclar-Istanbul, Turkey</p><p>Received 31 March 2004; received in revised form 4 November 2004; accepted 5 November 2004</p><p>Available online 13 January 2005</p><p>Abstract</p><p>A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two dierent methods. In the rst</p><p>method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of</p><p>diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyro-</p><p>mellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP)</p><p>to form Si-containing modied polyimide directly. In the second method, PU prepolymer was reacted with diaminodi-</p><p>phenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally,</p><p>the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modied</p><p>polyimide. Cast lms prepared by second method were thermally treated at 160 C to give a series of clear, transparentPUI lms. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 C which is higherthan degradation temperature of conventional PU, conrming that the introduction of imide groups improved the ther-</p><p>mal stability of PU.</p><p>To characterize the modied polyimides and their lms, TGA, FTIR, SEM and inherent viscosity analyses were car-</p><p>ried out. The dielectrical properties were investigated by the frequencycapacitance method. Dielectric constant, dielec-synthesis, characterizatio</p><p>Huseyin Deligoz *, Tuncerdoi:10.1016/j.eurpolymj.2004.11.007g poly(urethane-imide)s:and electrical properties</p><p>lcnyuva, Saadet Ozgumus</p><p>(2005) 771781</p><p>www.elsevier.com/locate/europolj</p><p>JOURNAL</p></li><li><p>Buckhards method (mp: 147 C) [27]. Toluene diisocya-nate (TDI, mixture of 2,4- and 2,6-isomer), diaminodi-</p><p>772 H. Deligoz et al. / European Polymer Journal 41 (2005) 771781improvement of thermal stability of PUs is a chemical</p><p>modication in the structure by introducing thermally</p><p>stable heterocyclic polymers like polyimides [513].</p><p>Polyimides (PI) are the most important members of het-</p><p>erocyclic polymers with remarkable heat resistance and</p><p>excellent mechanical, electrical, chemical and durability</p><p>properties. The term of polyimides is used for a vari-</p><p>ety of polymers containing the imide structure in the</p><p>backbone. PI has been used widely in the microelec-</p><p>tronic industry as a dielectric layer because of its low</p><p>dielectric constant and high dielectric strength [1416].</p><p>Moreover, PI can be used as lms, gas separation mem-</p><p>branes with high permeability and surface coating mate-</p><p>rials [14,16].</p><p>Although they have some superior properties as</p><p>listed above, their applications are limited since they</p><p>have high Tg and Tm values. In other words, processing</p><p>of PIs is dicult and has many problems. An eective</p><p>way for improving solubility and processibility of PI is</p><p>the introduction of some exible groups which come</p><p>from either the diamine or the dianhydride component</p><p>(ether, carbonyl, etc.) into the polymer backbone [17].</p><p>Another possible choice is the preparation of some</p><p>copolymers such as poly(ether-imide) [12], poly(urea-</p><p>imide) [18], poly(amide-imide) [19], poly(urethane-</p><p>imide) [513].</p><p>PIs are typically chosen for high temperature applica-</p><p>tions such as coating materials and insulators for elec-</p><p>tronic parts [16]. This is due to their good thermal</p><p>stability, their high planarization, low leakage current</p><p>density, high dielectric breakdown strength, good pro-</p><p>cessibility and high glass transition temperatures. The</p><p>method generally used for lowering the dielectric con-</p><p>stant, is the incorporation of uorine atoms or other</p><p>groups into the polyimide backbone [20,21]. Another</p><p>alternative is the copolymerization of PIs with other</p><p>polymers [20]. There is only one literature that gives lim-</p><p>ited information on the electrical properties of PUIs [22].</p><p>Various attempts have been made to prepare</p><p>poly(urethane-imide) (PUI). Reaction of an isocyanate</p><p>terminated PU prepolymer with acid dianhydride is</p><p>the most widely utilized method (direct method) [5</p><p>12]. Another method is blending of an isocyanate termi-</p><p>nated PU prepolymer with poly(amic acid) [5,6,9,12,13].</p><p>Intermolecular DielsAlder (DA) reaction of 4-methyl-</p><p>1,3-phenylenebis(2-furanyl carbamate) with various</p><p>bismaleimides is also reported to give poly(urethane-</p><p>imide) [2325]. Recently, it was reported that an imide</p><p>function was introduced into PU backbone through a</p><p>dierent synthetic strategy. This route involves reaction</p><p>of an amine telechelic PU prepolymer with dianhydride</p><p>and cyclodehydration of the intermediate polyamic acid</p><p>in a sequential way [8]. Ghatge and Jadhav have re-</p><p>ported that preparation of Si-containing polymers can</p><p>lead to an improvement of the thermal stability of thepolymers due to incorporation of a siliconcarbon bondphenylether (DDE), diaminodiphenylsulfone (DDS),</p><p>pyromellitic dianhydride (PMDA) and benzophenone</p><p>tetracarboxylic dianhydride (BTDA) were used as re-</p><p>ceived from Merck, Germany. N-Methyl pyrolidone</p><p>(NMP) and dimethyl acetamide (DMAc), were supplied</p><p>from Merck-Germany and then were puried by distilla-</p><p>tion under reduced pressure, and NMP was stored over</p><p>5 A molecular sieve. Methylene chloride (MeCl2) was</p><p>used as received from Merck-Germany, toluene was</p><p>used as received from Carlo Erba-Italy and petrol ether</p><p>was used as received from Riedel de Haen.</p><p>2.2. Reactions</p><p>2.2.1. Preparation of PU prepolymer</p><p>Reaction was carried out in a 250 ml ve necked</p><p>round bottomed ask equipped with a thermometer,</p><p>condenser, magnetic stirrer, oil bath and nitrogen</p><p>inletoutlet system. TDI (0.13 mol) was added onto di-</p><p>phenyl silane diol (0.065 mol) and reacted for 9 h at</p><p>80 C under nitrogen atmosphere. TDI and DSiD weremixed vigorously. After 1 h, 100 ml toluene was added</p><p>to the mixture. The temperature was kept constant atin the polymer backbone [26]. Moreover, although there</p><p>are lots of paper on the synthesis of PUI, no study has</p><p>been reported on dielectric properties of Si-containing</p><p>PUI by now.</p><p>In this work, for the rst time, Si-containing</p><p>poly(urethane-imide)s were synthesized by using two dif-</p><p>ferent methods. In the method 1, isocyanate terminated</p><p>PU prepolymer was directly reacted with tetracarboxylic</p><p>dianhydride. In order to prepare isocyanate terminated</p><p>PU prepolymer, diphenylsilanediol (DSiD) compound</p><p>was reacted with TDI. This method has some disadvan-</p><p>tages such as moisture sensitivity of the isocyanate</p><p>groups and side reactions such as the trimerization of</p><p>isocyanate compounds or amide formation. In the</p><p>method 2, reactions were carried out in two steps over</p><p>amine telechelic precursor and poly(amic acid) forma-</p><p>tion in order to avoid these problems. The chemical</p><p>and physical properties of Si-containing poly(urethane-</p><p>imide) lms produced by the direct method with those</p><p>obtained by the two step method are compared. Further,</p><p>preliminary studies on the electrical properties such as</p><p>dielectric constant and dielectrical breakdown strength</p><p>of silicon containing PUI lms have been carried out.</p><p>2. Experimental</p><p>2.1. Materials</p><p>Diphenylsilane diol (DSiD) was synthesized by C.A.80 C and the reaction was followed by the determina-</p></li><li><p>H. Deligoz et al. / European Polymer Journal 41 (2005) 771781 773tion of the NCO content with the dibutyl amine meth-</p><p>od [ASTM D1638-74] and found to be closed to the ex-</p><p>pected theoretical value. At the end of the reaction, the</p><p>PU prepolymer was puried by precipitation in petro-</p><p>leum ether, then ltered and dried in a vacuum oven</p><p>at 50 C for 4 h. Characterization of PU prepolymerwas carried out by FTIR spectroscopy, NCO end</p><p>group analysis and inherent viscosity. Results are given</p><p>in Table 1.</p><p>2.2.2. Preparation of Si-containing poly(urethane-imide)</p><p>lm by direct method (method 1)</p><p>The PU prepolymer was placed into a 100 ml three</p><p>necked round bottomed ask equipped with a thermom-</p><p>eter, magnetic stirrer, oil bath and nitrogen inletoutlet</p><p>system. PU prepolymer (1 g) was dissolved in dry</p><p>NMP under nitrogen atmosphere. An equivalent</p><p>amount of dianhydride (PMDA) (0.18 g) was added step</p><p>by step in 5 min by stirring at 0 C and temperature waskept at 0 C for 30 min. Then the temperature was in-creased stepwise to 40 C and held there for 2.5 h, subse-quently it was heated to 90 C for 2 h for evaluation ofcarbon dioxide. Finally the reaction mixture was heated</p><p>to 130 C and held there for 20 h. The brownish polymerwas precipitated by pouring the solution into cold water.</p><p>Precipitated polymer was ltered and washed twice with</p><p>methanol and dried in a vacuum oven at 110 C. Thesolution of the resulting mixture was spread onto a</p><p>well cleaned glass in order to obtain modied polyi-</p><p>mide lm. Then it was dried at 80 C for 5 h to removethe solvent. Finally free standing modied PI lm</p><p>Table 1</p><p>Formulation and viscosity of a prepolymer with isocyanate end</p><p>groups</p><p>Product DSiD</p><p>(mmol)</p><p>TDI</p><p>(mmol)</p><p>Isocyanate</p><p>content (%)</p><p>gred (dl/g)a</p><p>Calc. Theo.</p><p>I 130 60 13.9 14.9 0. 1</p><p>I: isocyanate end group having prepolymer.a 0.5 g/dl in NMP at 30 C.was obtained by immersing the glass plate into the boil-</p><p>ing water. The chemical structures are depicted in</p><p>Scheme 1.</p><p>2.2.3. Preparation of Si-containing poly(urethane-imide)s</p><p>by using amine telechelic precursors (method 2)</p><p> Preparation of diamine terminated PU. The sim-</p><p>ilar reaction system described in Section 2.2.2 was used.</p><p>Amine terminated PU was prepared by the reaction of</p><p>an equivalent amount of isocyanate terminated PU pre-</p><p>polymer with aromatic diamine in DMAc (isocyanate</p><p>amine equivalent ratio:1/2). Isocyanate terminated PU</p><p>prepolymer was added within 1 h into aromatic diaminesolution dissolved in DMAc. The reaction was carried</p><p>out at 10 C under nitrogen atmosphere. After the addi-tion of the PU prepolymer, the temperature was slowly</p><p>raised to 40 C and held at this temperature for another1 h to complete the reaction. Amine terminated PU pre-</p><p>polymer was isolated by precipitation in water, and then</p><p>it was ltered and dried at 60 C for 2 h in a vacuumoven. The product was characterized by FTIR spectros-</p><p>copy, amine content analysis and inherent viscosity</p><p>determination. The results are presented in Table 2</p><p>(Scheme 2).</p><p> Preparation of poly(urethane-amic acid) (PU-</p><p>AA). PU-AA was prepared by the reaction of an equiv-</p><p>alent amount of dianhydride with diamine terminated</p><p>PU prepolymer in DMAc at 10 C under nitrogen atmo-sphere (isocyanateamine equivalent ratio:1/2). An</p><p>equivalent amount of PMDA (0.064 g) was added into</p><p>diamine terminated PU (1.5 g) solution in DMAc for</p><p>2 h under nitrogen atmosphere. After the addition of</p><p>PMDA, the temperature was increased to 40 C andheld there for another 1 h to complete amic acid forma-</p><p>tion. The readily prepared amic acid (PU-AA) solution</p><p>was kept in a refrigerator to prevent the imidization</p><p>and hydrolysis reactions for long term usage. Polymer</p><p>was isolated by precipitation with methanol. The precip-</p><p>itated polymer was washed with methanol and dried</p><p>under vacuum at 60 C for 2 h. The dried PU-AA wascharacterized by FTIR spectroscopy.</p><p> Preparation of Si-containing poly(urethane-</p><p>imide) lm by cyclodehydration of poly(urethane-amic</p><p>acid). PU-AA solution was cast on a well cleaned glass</p><p>plate by doctor blade to form a thin lm. It was heated</p><p>in an oven under nitrogen atmosphere. The lms</p><p>obtained by method 2, were cured at 160 C for 10 hin order to remove solvent and to cure PAA. All pre-</p><p>pared lms were obtained as clear, light brown to yellow</p><p>colored and transparent. Thicknesses of all lms are in</p><p>the range of 530 lm. All chemical structures are shownin Scheme 2.</p><p>2.3. Measurements (instruments)</p><p>Inherent viscosities of modied polymers and inter-</p><p>mediates were determined for solutions of 0.5 g/dl in</p><p>NMP at 30 C with an Ubbelohde viscometer. Thermalanalyses were carried out with Linseis thermal analyzer</p><p>with a heating rate of 5 C/min in air. The sample masswas approximately 10 mg. Infrared spectra of the sam-</p><p>ples were recorded on a Perkin Elmer Spectrum 2000</p><p>model with an ATR (attenuated total reectance) unit</p><p>in the range of 4004000 cm1. Dielectric constantsand loss factors were measured using HP 4192 A LCR</p><p>meter Impedance Analyzer at various frequencies andat room temperature. After coating both surfaces of</p></li><li><p>+774 H. Deligoz et al. / European Polymer Journal 41 (2005) 771781CH3NCO</p><p>NCO</p><p>2</p><p>Toluene diisocyanatethe specimen lms with gold, the contacts were applied</p><p>using indium oxide. The dielectric constant were calcu-</p><p>lated from the measured capacitance data as follow:</p><p>e1 Cde0Awhere C is the capacitance, e1 is the dielectric constant,eo is the permittivity of the free space (8.85 1012</p><p>MKS unit), d is the lm thickness and A is electrode</p><p>Table 2</p><p>Formulation and viscosity of a prepolymer with amine end</p><p>groups</p><p>Product Precursor</p><p>(g)</p><p>DDE</p><p>(g)</p><p>DDS</p><p>(g)</p><p>Amine</p><p>content (%)</p><p>gred(dl/g)a</p><p>Calc. Theo.</p><p>A-1 I (1.5) 0.6 61.6 58.4 0.11</p><p>A-2 I (1.0) 0.5 52.4 54.5 0.12</p><p>A: amine end group having intermediates.a 0.5 g/dl in NMP at 30 C.</p><p>NH CO Si</p><p>polyurethane prepolymer w</p><p>Benz</p><p>- CO2at 90 OC for 2 hours and at 130 OC for 20 ho</p><p>Silicon contain</p><p>urs .</p><p>OCN</p><p>3HC</p><p>NH CO Si O CO NH</p><p>3HC</p><p>N</p><p>O</p><p>O</p><p>Scheme 1. Synthesis ofSi OHOH</p><p>O CO NH</p><p>Diphenylsilanediol</p><p>ith isocyanate end group</p><p>C</p><p>O</p><p>CC</p><p>C</p><p>OO</p><p>CH3</p><p>NCO</p><p>O Oarea. Dielectric breakdown strengths of the lms were</p><p>measured with an Electrotechnic Laboratorium D-7015</p><p>Insulation Breakdown Tester UH 270, Resolution</p><p>50 V for 2.5 kV and 100 V for 5 kV. Thicknesses of the</p><p>lms were measured with Mitutoyo Model, 025</p><p>micrometer with 0.001 mm r...</p></li></ul>