Synthesis and characterization of novel

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REACTIVE & FUNCTIONAL POLYMERS

Reactive & Functional Polymers 67 (2007) 503–514

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Synthesis and characterization of novel polyurethanes based on 4,40-[1,4-phenylenedi-diazene-2,1-diyl] bis(2-carboxyphenol) and 4,40-[1,4-phenylenedi-diazene-2,1-diyl] bis(2-chlorophenol) hard segments q A.V. Raghu a, G.S. Gadaginamath a, N.T. Mathew b, S.B. Halligudi b, T.M. Aminabhavi a,* a

Center of Excellence in Polymer Science, Karnatak University, Dharwad 580 003, India b Catalysis Division, National Chemical Laboratory, Pune 411 008, India

Received 26 April 2006; received in revised form 23 December 2006; accepted 25 February 2007 Available online 12 March 2007

Abstract Eight novel polyurethanes (PUs) based on 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-carboxyphenol) and 4,40 -[1,4phenylenedi-diazene-2,1-diyl]bis(2-chloro- phenol) as hard segments with four diisocyanates viz., 4,40 -diphenyl-methane diisocyanate, toluene 2,4-diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate were prepared. Structural and thermal characterization of the segmented PUs were determined by FT-IR, UV spectrophotometry, fluoroscence spectroscopy, 1H NMR, 13C NMR spectroscopy and DTA/TGA analysis. All the PUs contain domains of semi-crystalline and amorphous structures, as indicated by X-ray diffraction. PUs were soluble in polar aprotic solvents like N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF) and dimethylsulfoxide (DMSO). Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Polyurethanes; Hard segments; Azo polymers; Fluorescence; Phase separation; Spectroscopy; Morphology; Thermal properties

1. Introduction Azo polymers have many special properties [1]. In search of new materials for optical applications, such as reversible optical storage and nonlinear q *

This article is CEPS communication #120. Corresponding author. Fax: +91 836 2771275. E-mail address: [email protected] (T.M. Aminabhavi).

optical (NLO) devices, azo polymers have attracted much attention [2,3]. The photosensitive properties of polymers are a consequence of the resonant reversible photoisomerization with respect to the azobenzene group. The NLO chromophore can be dispersed into a polymeric matrix or it can be introduced on the main chain or even it can be attached as a side group. Polymers containing azobenzene moieties have been employed in holography due to

1381-5148/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2007.02.003

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their high sensitivity and reversibility [4–13]. Optical properties of the azo-functionalized polymers are mainly influenced by the polymer backbone, structure of the azo-chromophore in addition to the linkage between backbone and the azo-chromophore [14,15]. Many polyurethanes (PUs) and polyureas were found to be insoluble in common organic solvents due to their rigid backbones [16,17], thereby inhibiting their applications due to difficulty in processing. In order to overcome such difficulties, the polymer structure modification is necessary, wherein one can introduce the bulky or asymmetric groups on the polymer backbone or incorporate non-coplanar structural units on the main polymer chain [18–21]. In our previous research [22,23], Schiff base PUs have been prepared using 2,20 -{ethane-1,2-diylbis (nitrilomethylylidene)}diphenol, 2,20 -{hexane-1,6-diylbis(nitrilo-methylylidene)}diphenol, 2,20 -{1,4-phenylenebis[nitrilomethylylidene]}diphenol and 2.20 -{4, 40 -methylenedi-2-methyphenylene-1,10 -bis[nitrilomethylylidene]}diphenol with different diisocyanates. In this study, we extend these protocols for the synthesis of other PUs based on bis-azo groups containing diols like 4,40 -[1,4-phenylenedi-diazene2,1-diyl]bis(2-carboxyphenol) and 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-chloro-phenol) as hard segments with 4,40 -diphenylmethane diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). The bis-azo diols were prepared according to the published report [24]. The structures of 3,30 -[1,4-phenylenedi-diazene-2,1-diyl]bis(6-hydroxybenzoic acid) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-chlorophenol) were established by Fourier transform infrared (FT-IR) spectroscopy, 1H NMR and 13C NMR spectral data. The synthesized PUs were further characterized by UV–Vis, fluorescence, FT-IR, 1H NMR, 13C NMR, DTA/TGA and X-ray diffraction techniques. Results of this study are discussed in terms of their structure-morphology based considerations. 2. Experimental 2.1. Materials 4,40 -Diphenylmethane diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI), hexamethylenediamine and dibutyltin diaurate (DBTDL) were purchased from Aldrich (Milwaukee, WI,

USA) and were used without further purification. p-Phenylenediamine, salicylic acid, o-chlorophenol, NaNO2, Na2CO3, NaOH, acetone, carbon tetrachloride, ethyl acetate, dioxane, xylene, ethyl methyl ketone, toluene, n-hexane, chloroform, carbon disulfide, tetrahydrofuran, dimethyl formamide (DMF), dimethylsulfoxide (DMSO), N-methyl-2pyrrolidone (NMP), dimethylacetamide (DMAc), acetic acid and hydrochloric acid were all are of analytical reagent (AR) grade samples purchased from s.d. fine chemicals, Mumbai, India. All the solvents were purified before use by following the standard procedures.

2.2. Monomer synthesis 2.2.1. Preparation of 4,40 -[1,4-phenylenedi-diazene2,1-diyl]bis(2-carboxyphenol) [PDBCP] p-Phenylenediamine (5.40 g, 0.05 mol) was suspended in a solution containing ice-water (50 mL) and HCl (37%w, 20 mL, 0.27 mol). The solution was cooled to 5 °C in a water-ice bath. A solution of sodium nitrite (7.2 g, 0.102 mol) dissolved in water (30 mL) was then added to the above suspension for over 30 min at 5 °C, and the resulting solution was stirred at 0–2 °C for 1 h to obtain a clear yellow-brown solution. Thereafter, salicylic acid (15 g, 0.108 mol) was dissolved in hot solution (40 °C) of Na2CO3 (6 g, 0.0566 mol) taken in water (90 mL). To this solution, NaOH (8 g, 0.20 mol) was added and the mixture was cooled with ice to 5 °C. Half of the resulting salicylic acid solution was added to the prepared bis-diazonium salt under constant stirring so as not to exceed the reaction temperature beyond 5 °C within 45 min. The pH of the reaction was maintained at 7.5–8 by periodically adding 0.5 M Na2CO3 aqueous solution and the mixture was kept cold with crushed ice for 2 h. The dye was precipitated without salting by adjusting the pH to 6–7 by the addition of 10% of aqueous HCl. The crude dye was collected by vacuum filtration and purified by several recrystallizations using ethanol. Product yield was 16.5 g (80%). FT-IR and NMR assignments of these compounds are given below. FT-IR (KBr): 3238, 3006, 2860, 1662, 1612, 1577, 1483, 1463, 1444, 1325, 1294, 1249, 1209, 1122, 893 and 759 cml. 1 H NMR (DMSO-d6, TMS): d, 6.70–8.00 (m, Ar–H), 11.48 (br, 2H, phenolic-OH) and 13.60 (br, 2H, carboxyl OH).

A.V. Raghu et al. / Reactive & Functional Polymers 67 (2007) 503–514 13

C NMR (DMSO-d6): 113.39, 117.46, 119.49, 130.67, 135.93, 161.60 (Ar carbons) and 172.31 (carboxyl C@O carbons). The reaction Scheme 1 displays the formation of 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-carboxyphenol) based on the above cited spectral assignments.

+ N2Cl

+ ClN2

Conc HCl

NH2

H2N

505

diazonium salt

p-phenylene diamine

Cl OH o-chloro phenol

Cl

2.2.2. Preparation of 4,40 -[1,4-phenylenedi-diazene2,1-diyl]bis(2-chlorophenol) [PDBClP] 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-chlorophenol) was obtained from p-phenylenediamine (5.40 g, 0.05 mol) and o-chlorophenol (13.90 g, 0.108 mol) under the same conditions described above. Yield 16 g (76%) and m.p. 75–78 °C. FTIR and NMR assignments of these compounds are given below. FT-IR (KBr): 3375, 3307, 3199, 2925, 1620, 1512, 1450, 1386, 1309, 1261, 1124, 831 and 719 cml. 1 H NMR (DMSO-d6, TMS): d, 6.60–7.20 (m, 10H, Ar–H) and 11.79 (br, 2H, phenolic-OH). 13 C NMR (DMSO-d6): 113.91, 117.85, 118.31, 129.36, 134.84 and 162.63 (Ar carbons). The reaction Scheme 2 displays the formation of 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-chlorophenol) as per the spectral assignments suggested above.

HO

N

Scheme 2. Preparation of 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-chlorophenol).

COOH OH N N

HOOC

COOH O

HO N N

HOOC

CH3

CH2

NH2 sodium nitrite

CH3

C H2

H2 C

H2 C

C H2 (HDI)

(IPDI)

C H2

Cl OH N N

+

N

HO

O N N

Cl

HOOC

N CH 3

CH 2

COOH

N N

(MDI)

N N

n

O where R =

HO

H H N N CO CO R

N

COOH

OH salicylic acid

O=C=N - R - N=C=O

N

Cl

+ N2Cl

diazonium salt

p-phenylene diamine

(2,4-TDI) H2 C

Scheme 3. Reaction pathways for the formation of PUs (i.e., PU1 to PU-4).

Cl

H2N

n

N

CH3 CH2

H H N N CO R CO

N

O

H3 C

O=C=N - R - N=C=O

+ N

N

(MDI)

+ ClN2

OH

4,4'-[1,4-phenylenddi-diazene-2,1-diyl]bis(2-chlorophenol)

2.3. Polymer synthesis

Conc HCl

N N

where R =

Typical general procedure used to synthesize PUs was carried out in a three-necked 100 mL round bottom flask equipped with a magnetic stirrer, condenser and dropping funnel under nitrogen atmosphere. The respective diols viz., 4,40 -[1,4phenylenedi-diazene-2,1-diyl]bis(2-carboxyphenol) and 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2chloro- phenol) were dissolved in dry DMF under

Cl

N

OH

4,4'-[1,4-phenylenddi-diazene-2,1-diyl]bis(2-carboxyphenol)

Scheme 1. Preparation of 4,40 -[1,4-phenylenedi-diazene-2,1-diyl]bis(2-carboxyphenol).

CH3

H3 C CH2

CH 3 (IPDI)

(2,4-TDI) H2 C

C H2

H2 C

C H2

H2 C

C H2

(HDI)

Scheme 4. Reaction pathways for the preparation of PUs (i.e., PU-5 to PU-8).

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dry nitrogen atmosphere with a constant stirring. Then, equimolar quantity of diisocyanates (MDI, TDI, IPDI or HDI) with respect to each azo-based diols taken in dry DMF was added to this solution over a period of 1 h. The reaction mixture was stirred continuously for 8 h at 80 °C, cooled, poured into distilled water and then filtered. The solid powder polymer obtained was washed with double distilled water and dried under reduced pressure at 30 °C. Chemical structures of PUs are shown in Schemes 3 and 4. 2.3.1. Preparation of poly[4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-carboxyphenyl) 4,40 -methylene diphenylene diurethane] (PU-1) PU-1 was prepared by taking MDI (2.502 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-carboxyphenol) (1.94 g, 0.01 mol) to yield 4.3 g (96.8%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3303, 3030, 2914, 2850, 1652, 1598, 1544, 1494, 1407, 1307, 1232, 1109, 852, 812 and 758 cml. 1 H NMR (DMSO-d6, TMS): d, 3.78 (s, Ar–CH2– Ar), 6.40–8.30 (m, Ar–H), 8.56 (br, –NH–COO–), and 10.10 (br, –COOH). 13 C NMR (DMSO-d6): d 40.36 (Ar–CH2–Ar carbon merged with DMSO-d6 methyl carbon peaks), 114.29 (Ar carbons ortho to –O–), 116.83 (Ar carbons ortho to –NH–), 118.47 (Ar carbons ortho to AN@NA), 119.39 and 119.98 (Ar carbons ortho to ACOOH and AN@NA), 128.86 (Ar carbons ortho to ACH2A), 130.24 (Ar carbons linked to ACOOH), 134.94 (Ar carbons linked to ACH2A), 135.73 (Ar carbons linked to ANHA), 137.71 (Ar carbons linked to AN@NA), 152.61 (Ar carbons linked to AOA), 161.37 (carboxyl carbonyl carbons) and 162.29 (urethane carbonyl carbons). 2.3.2. Preparation of poly[4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-carboxyphenyl), toluene 2,4diurethane] (PU-2) PU-2 was prepared by taking TDI (1.742 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-carboxyphenol) (1.94 g, 0.01 mol) to give a yield of 3.757 g (98%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3307, 3070, 2922, 2856, 1700, 1656, 1558, 1452, 1305, 1217, 871, 810 and 756 cml. 1 H NMR (DMSO-d6, TMS): d, 2.20 (s, –CH3), 6.30–8.80 (m, Ar–H), 9.07 (br, –NH–COO–) and 10.10 (br, –COOH).

13

C NMR (DMSO-d6, TMS): d 17.31 (–CH3 carbons), 104.73 (Ar carbons ortho to –O–), 107.17 (Ar carbons ortho to –O–), 110.67 and 111.88 (Ar carbons ortho to AN@NA on phenylene), 116.87 (Ar carbons ortho to AN@NA on salicyclic acid part), 119.62 (Ar carbons ortho to ACOOH), 125.71 (Ar carbons linked to ACH3), 129.94 (Ar carbons linked to ACOOH), 134.89 (Ar carbons linked to ANHA), 138.79 (Ar carbons linked to AN@NA), 152.57 (Ar carbons linked to AOA), 161.31 and 162.28 (urethane carbonyl carbons) and 171.96 (carboxyl carbonyl carbons). 2.3.3. Preparation of poly[4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-carboxyphenyl), isophorone diurethane])] (PU-3) PU-3 was prepared by taking IPDI (2.22 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-carboxyphenol) (1.94 g, 0.01 mol) to yield 3.757 g (98%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3361, 3048, 2918, 1700, 1654, 1558, 1477, 1379, 1299, 1232, 1153, 1064 and 761 cml. 1 H NMR (DMSO-d6, TMS): d, 0.86 (s, –CH3), 0.91 (s, –CH3), 0.98 (s, –CH3), 1.00–2.90 (isophorone protons), 5.55 and 5.82 (br, –NH–COO–) and 6.70–7.94 (m, ArAH). 13 C NMR (DMSO-d6, TMS): d 27.60 (–CH3 carbons), 29.93 (–CH3 carbons), 30.79 (–CH3 carbons), 31.53, 35.03, 35.86, 36.50, 43.44 (isophorone carbons), 46.69 (–NH–CH2– carbons), 47.15 (ANHACH@ ring carbons), 114.47 (Ar carbon ortho to AOA), 116.80 (Ar carbons ortho to AN@NA), 118.53 (Ar carbon ortho to AN@NA and ACOOH), 130.22 (Ar carbon linked to ACOOH), 134.71 (Ar carbon linked to AN@NA), 157.76 and 161.40 (urethane carbonyl carbons), 158.66 (Ar carbon linked to AOA) and 171.86 (carboxyl carbonyl carbon). 2.3.4. Preparation of poly[4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-carboxyphenyl), hexamethylene 1,6-diurethane] (PU-4) PU-4 was prepared by taking HDI (1.682 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-carboxyphenol) (1.94 g, 0.01 mol) to yield 3.737 g (97%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3330, 3126, 2931, 2858, 1700–1624, 1573, 1521, 1473, 1379, 1336, 1253, 1215, 858, and 763 cml.

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H NMR (DMSO-d6, TMS): d, 1.22 (m, ANH CH2ACH2A), 1.50 (m, ANHACH2ACH2ACH2A), 2.94 (m, ANHACH2A), 5.74–8.00 (m, ArAH and ANHACOOA protons), and 13.20 (br, ACOOH). Scheme 3 displays the chemical reactions during the formation of different PUs mentioned above. 1

2.3.5. Preparation of poly[4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-chlorphenyl) 4,40 -methylene diphenylene diurethane] (PU-5) PU-5 was prepared by taking MDI (2.502 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-chlorophenol) (2.10 g, 0.01 mol) to yield 4.3 g (97%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3379, 3307, 3043, 2934, 2847, 1647, 1605, 1559, 1414, 1305, 1233, 1114, 1114, 1021, 912, 834 and 752 cml. 1 H NMR (DMSO-d6, TMS): d, 3.77 (s, Ar–CH2– Ar, H), 6.30–8.20 (m, Ar–H), and 8.41 (s, –NH– COO–, H). 13 C NMR (DMSO-d6, TMS): d, 39.08 (Ar–CH2– Ar carbons merged with DMSO-d6 methyl signals), 114.25 (Ar carbons ortho to –O–, but not linked to chloro group), 118.23 (Ar carbons ortho to ANHA), 118.43 (Ar carbons ortho to AN@NA, but para to chloro group), 119.80 (Ar carbons ortho to AOA and linked to chloro group), 120.78 (Ar carbons ortho to AN@NA, but ortho to chloro group), 128.80 (Ar carbons ortho to ACH2A group), 134.58 (Ar carbons linked to ACH2A group), 138.09 (Ar carbons linked to ANHA), 143.92 (Ar carbons linked to AN@NA), 153.03 (Ar carbons linked to AOA) and 162.29 (urethane carbonyl carbons). 2.3.6. Preparation of poly[4,40 -{1,4-phenylenedidiazene-2,1-diyl}bis(2-chlorophenyl), toluene 2,4diurethane] (PU-6) PU-6 was prepared by taking TDI (1.742 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-chlorophenol) (2.10 g, 0.01 mol) to give a yield 3.757 g (98%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3286, 3037, 2920, 2856, 1700–1645, 1554, 1461, 1409, 1299, 1213, 825 and 750 cml. 1 H NMR (DMSO-d6, TMS): d, 2.17 (s, –CH3), 6.30–8.70 (m, Ar-H) and 8.92 (br, –NH–COO–). 13 C NMR (DMSO-d6, TMS): d 17.13 (–CH3 carbons), 112.69 (Ar carbons ortho to both –NH– groups), 114.32 (Ar carbons ortho to –OA, but meta to chloro), 118.95 (Ar carbons ortho to –O–, but

507

linked to chloro group), 120.30 (Ar carbons ortho to –NH–, but meta to –CH3), 120.57 (Ar carbons ortho to AN@NA group) 120.71 (Ar carbons ortho to AN@NA, but para to chloro), 129.00 (Ar carbons ortho to ACH3), 130.08 (Ar carbons linked to ACH3), 134.19 (Ar carbons linked to AN@NA of ArAOACl), 143.88 (Ar carbons linked to AN@NAAr), 152.98 (Ar carbons linked to AOA) and 162.29 (urethane carbonyl carbons). 2.3.7. Preparation of poly[4,40 -{1,4-phenylenedidiazene-2,1-diyl}bis(2-chlorophenyl), isophorone diurethane] (PU-7) PU-7 was prepared by taking IPDI (2.22 g, 0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-chlorophenol) (3.22 g, 0.01 mol) to yield 4.8 g (88%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3334, 2950, 2922, 1700–1652, 1554, 1514, 1469, 1396, 1307, 1224, 1112, 829 and 756 cml. 1 H NMR (DMSO-d6, TMS): d, 0.90 (s, –CH3), 0.98 (s, –CH3), 1.02 (s, –CH3), 1.00–3.00 (isophorone protons), 5.82 (br, –NH–COO– protons), 6.09 (br, –NH–COO– protons) and 6.80–8.30 (m, Ar protons). 13 C NMR (DMSO-d6, TMS): d 27.56, 29.87, 30.80 (–CH3 carbons), 34.99, 35.74, 36.11, 42.91, 46.40 47.04 (isophorone ring carbons), 53.01 (ring– CH2–NH–COO– carbons), 114.29 (Ar carbons ortho to –O–, but meta to chloro group), 116.80 (Ar carbons ortho –O– and liked to chloro), 118.47 (Ar carbons ortho to AN@NA), 120.27 (Ar carbons ortho to AN@NA and para to chloro), 127.92 (Ar carbons ortho to AN@NA and ortho to chloro), 129.80 (Ar carbons linked to AN@NA), 134.41 (Ar carbons linked to AN@NA of chlorophenol), 154.74 (Ar carbons linked to AOA), 155.64 (Ar carbons linked to AOA), 162.26 (urethane carbonyl carbon). 2.3.8. Preparation of poly[4,40 -{1,4-phenylenedidiazene-2,1-diyl}bis(2-carboxyphenyl), hexamethylene 1,6-diurethane] (PU-8) PU-8 was prepared by taking 1.682 g HDI (0.01 mol) and 4,40 -[1,4-phenylenedi-diazene-2,1diyl]bis(2-chlorophenol) (2.10 g, 0.01 mol) to yield 3.737 g (97%). FT-IR and NMR assignments are given below. FT-IR (KBr): 3323,3039, 2929, 2858, 1700-1627, 1566, 1512, 1481, 1404, 1301, 1232, 825 and 736 cml.

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1

H NMR (DMSO-d6, TMS): d, 1.22 (m, AN@CHACH2ACH2A, H), 2.87 (m, AN@CH CH2A, H), 3.66 and 3.78 (s, ArACH2AAr, H), 6.30–7.90 (m, ArAH) and 8.50 (br, –NH–COO–, protons). 13 C NMR (DMSO-d6, TMS): d 26.16 (–NH– CH2–CH2– carbons), 29.89 (–NH–CH2–CH2– CH2– carbons), 39.14 (–NH–CH2– carbons), 114.30 (Ar carbons ortho to –O– but meta to chloro), 118.56 (Ar carbons ortho to AN@NA), 119.30 (Ar carbons ortho to AOA and linked to cholro), 120.41 (Ar carbons ortho to AN@NA and para to chloro), 129.89 (Ar carbons ortho to AN@NA and ortho to chloro group), 143.29 (Ar carbons linked to AN@NA group) and 155.84 (urethane carbonyl carbons and Ar carbons linked to AOA). Scheme 4 displays the chemical reaction pathways for the formation of different PUs. 2.4. Characterization Melting points of the monomers were determined in open capillary tubes. UV–vis (Secomam, France) and fluorescence spectra (F-2000, Hitachi, Japan) were recorded for the monomers and PUs in DMF. FT-IR spectra were recorded on a Perkin– Elmer 881 spectrophotometer (Madison, WI, USA). 1H NMR and 13C NMR spectra in CDCl3 or DMSO-d6 were recorded on Bruker’s 300 MHz NMR spectrophotometer (Silberstreifen, Rheinstetten, Germany). Chemical shifts d, were measured by taking TMS as a reference liquid. Thermogravimetry (TGA) and differential thermal analysis (DTA) were recorded on a Perkin–Elmer Diamond analyzer (Shelton, CT, USA) from ambient temperature to 1000 °C under the nitrogen gas flow rate of 100 mL/min. The sample weighing about 5–11 mg was placed in a platinum crucible and DTA/TGA were recorded using a-alumina at the heating rate of 10 °C/min. The X-ray diffractograms of the PUs were recorded using Rigaku Geigerflex diffractometer (Tokyo, Japan) equipped with Ni-filtered ˚ ). Dried PUs were Cu Ka radiation (k = 1.5418 A spread on a sample holder and diffractograms were recorded in the angle range of 5–50° at the speed of 5°/min. 3. Results and discussion Polyurethanes of this study are novel and all were obtained in quantitative yields. Since bis-azo based

diols are incorporated, their physical, chemical and thermal properties were substantially different than those containing aliphatic chains. 3.1. Solubility properties All the PUs were soluble in polar aprotic solvents such as N0 -methyl-2-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) as well as acidic solvents like m-cresol, con. H2SO4, but were insoluble in water, acetone, methanol, tetrahydrofuran (THF), carbon tetrachloride, ethyl acetate, dioxane, xylene, ethyl methyl ketone, toluene, n-hexane, chloroform and carbon disulfide. 3.2. Spectral data UV–vis and fluoroscence spectra of the bis-azo based monomers and PUs were determined using DMF as a solvent at ambient temperature. The absorption and emission spectral data of both the monomers and PUs are listed in Table 1. Bis-azo based diols show two absorption bands around 264 nm and 304 nm, which are attributed to p–p* transitions of benzene and trans isomer of AN@NA transition [25], respectively. In contrast, all the PUs showed a single absorption band in the region 270– 290 nm (high intensity), which is attributed to hypsochromic shift of the band due to azo-chromophore and bathochromic shift of p–p* transitions of benzene in the main PU chains. The emissions from these monomers and PUs were seen around 345– 396 nm upon excitation at 290 nm. Structures of both the monomers and PUs are characterized by NMR and FT-IR; of these, FTIR spectra showed a disappearance of both the phenolic hydroxyl group and the isocyanate group as

Table 1 Absorption and emission peaks different monomers and PUs Code

Absorption (emission) kmax (nm)

PDBCP PU-1 PU-2 PU-3 PU-4 PDBClP PU-5 PU-6 PU-7 PU-8

264, 304 (390) 298 (386), 291 (387) 296 (392) 299 (389) 270, 328 (396) 282 (373) 290 (370) 273 (354) 270 (369)

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well as the formation of several characteristic stretching vibrations due to NAH, C@O, N@N and CAH bonds shown in Figs. 1 and 2. In all the PUs, the sharp bands appearing between 3286 and 3379 cml are due to the presence of hydrogen bonded NAH group [26]. However, hydrogenbonded broad carbonyl groups [26] of urethane are shown in the region from 1652 to 1700 cm1. The azo (N@N) groups [27] have appeared in the region 1407–1450 cm1. NMR analysis revealed the disappearance of –OH and –NCO groups as well as the formation of urethane polymer chain. 1H NMR spectra of PUs have shown characteristic signals as shown in Figs. 3 and 4. Resonance peaks observed in the region 0.89–3.78 ppm correspond to methyl/methy-

lene/isophorone protons of the monomer as well as PUs. The resonance peaks of –NH–COO– protons of all the PUs appeared around 8.41–9.07 ppm, except those of the IPDI-based polymers. In IPDIbased PUs, –NH–COO– protons were observed around 5.55–6.09 ppm which are in conformity with the earlier report [28], but in the monomer, –OH protons were found to be around 11.48–11.79 ppm while the resonance peaks of –COOH protons were displayed in the region of 10.10–13.20 ppm. The aromatic protons showed signals between 6.3 and 8.8 ppm. 13 C NMR spectra of all PUs have shown the characteristic signals has shown in Figs. 5 and 6. The chemical shifts ranging between 17.13 and

Fig. 1. Representative FT-IR spectra of PDBCP based PUs (PU1, PU-2, PU-3 and PU-4).

Fig. 2. Representative FT-IR spectra of PDBClP based PUs (PU-5, PU-6, PU-7 and PU-8).

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Fig. 3. 1H NMR spectra of PU-1, PU-2, PU-3 and PU-4.

Fig. 4. 1H NMR spectra of PU-5, PU-6, PU-7 and PU-8.

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Fig. 5.

13

C NMR spectra of PU-1, PU-2, PU-3 and PU-4.

Fig. 6.

13

C NMR spectra of PU-5, PU-6, PU-7 and PU-8.

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Major weight loss transition (°C)

368 323 335 364 369 356 333 347

T50b

282–409 222–413 230–379 237–403 273–407 273–403 268–390 285–420

c

T1 is the lowest temperature endotherm; T2 is the intermediate temperature endotherm; T3 is the melting temperature endotherm.

Temperature at which 25% weight loss observed by TGA. Temperature at which 50% of weight loss occurred in TGA. Residual weight observed by TGA at 700 °C in N2.

299

a

248, 295 292, 343

T3 (°C) 363 329 368 373 375 353 326 334

b

T2 (°C)

346 281 304 331 342 332 300 321

92 77 77 67 92 77 141 128

T25a

T1 (°C)

Table 3 Thermal properties of PUs

Code

Decomposition temperature (°C)

Table 2 Different melting endotherms of PUs from DTA/TGA

PU-1 PU-2 PU-3 PU-4 PU-5 PU-6 PU-7 PU-8

21 10 4 4 18 17 4 8

Residual weight loss at 700 °C (%)c

Thermal behavior of all the PUs was studied in nitrogen using DTA/TGA. These data are presented in Tables 2 and 3, while the curves are displayed in Figs. 7 and 8. The existence of multiple endotherms has been documented on thermal characteristics of the segmented PU block copolymers [29–31]. Koberstein and Galambos [32] suggested that the origin of multiple endotherms in PUs is dependent upon the specimen preparation procedure. Martin et al. [33] suggested that five endotherms observed were possibly due to the melting of various hard segment length populations. On the other hand, van Bogart et al. [34] identified three endothermic transitions associated with the ordering of MDI/BDO hard segments in materials subjected to the third thermal cycle. Blackwell and Lee [35] studied the multiple melting in MDI-based PUs that have been oriented and thermally annealed. Recently, Raghu et al. [22,23] observed 2–5 endothermic transitions associated with the hard segmented PUs and polyureas. In the light of these reports, it is obvious that the melting behavior of PUs is highly dependent upon the procedure adopted for sample preparation. Indeed, the origin of multiple melting peaks are inherently different for materials prepared under varying conditions. In the present paper, we observed multiple melting phenomena in identical PUs prepared from only

PU-1 PU-2 PU-3 PU-4 PU-5 PU-6 PU-7 PU-8

3.3. Thermal properties

327 290 260 319 316 312 273 300

On set temperature (°C)

53.01 is due to aliphatic and isophorone carbons. Resonance signals observed in the region between 114.29 and 155.64 ppm are due to aromatic carbons. Peaks observed in the region from 155.84 and 171.96 ppm were ascribed to urethane and carboxyl carbonyl carbons.

Polymer

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endotherms. The lowest endotherms (T1) in the region of 67–141 °C was due to local restructuring of hard-segment units within the hard microdomains, which are considered to be the glass transition temperature, Tg of the PUs. However, the intermediate temperature endotherms (T2) were observed around 245–393 °C, which were associated with the destruction of long-range order of the unspecified nature of the PU. Higher temperature endotherms (T3) observed in the range 326–375 °C can be generally ascribed to melting of the microcrystalline regions within the hard microdomains. Weight loss data from TGA for all the PUs are presented in Table 3. These results suggested that 25% and 50% weight loss had occurred in the temperature range of 281–346 °C and 323–368 °C, respectively. PUs have the onset temperature range from 260 to 327 °C. The curves showed a major weight loss between 222° and 420 °C, but the residual weight remaining at 700 °C was 4–21%. This variation in weight loss was due to the differences in the structure of hard segments of PUs. TGA data indicated that the MDI-based PUs exhibited good

Fig. 7. DTA thermograms of PU-1 to PU-8.

Fig. 8. TGA tracings of PU-1 to PU-8.

hard segments of the main chain. DTA data of PU1, PU-2, PU-5, PU-6 and PU-8 showed two endothermic peaks, while PU-7 displayed three endotherms, but PU-3 and PU-4 exhibited four

Fig. 9. X-ray diffactograms of PU-1 to PU-8.

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thermal stability when compared to other diisocyanate based PUs, which is attributed to the presence of biphenyl on the main chains. 3.4. X-ray diffraction X-ray diffraction curves of the PUs are shown in Fig. 9. The crystalline form of hard segments depended upon their structure as well as on the crystallization conditions [36]. PU-1, PU-3 and PU-4 were amorphous in nature, while PU-8, PU-2, PU5, PU-6 and PU-7 displayed the semi-crystalline nature. Semi-crystallinity decreased in the order: PU-8 < PU-7 < PU-5 < PU-6 < PU-2. These results are in close agreement with our earlier report [22,23]. This could be due to variations in the cis and trans structural units of the bis-azo base backbone of the main PU chain. 4. Conclusions Novel PUs based on 4,40 -[1,4-phenylenedidiazene-2,1-diyl]bis(2-carboxyphenol) and 4,40 [1,4-phenylenedi-diazene-2,1-diyl]bis(2-chlorophenol) with MDI, 2,4-TDI, IPDI and HDI were synthesized. The structures of monomers and PUs were confirmed by UV–visible, fluorescence and FT-IR spectra in addition to NMR studies. All the PUs were soluble in polar aprotic solvents and showed fluoroscent properties. TGA indicated that the onset temperature of all the PUs were more than 260 °C, while the curves showed a major weight loss between 222 and 420 °C. DSC displayed multiple endotherms that are in good agreement with the reported data. Semi-crystalline and amorphous nature of the PUs developed were confirmed by X-ray diffraction studies. Acknowledgments The authors thank the University Grants Commission, New Delhi, India (Grant No. F1-41/ 2001/CPP-II) for a major support to establish Center of Excellence in Polymer Science. References [1] S. Xie, A. Natansohn, P. Rochon, Chem. Mater. 5 (1993) 403. [2] D. Eaton, Science 253 (1991) 281. [3] A. Nataneohn, P. Rochon, J. Gosselin, S. Xie, Macromolecules 25 (1992) 2268. [4] D.Y. Kim, S.K. Tripathy, L. Li, J. Kumar, Appl. Phys. Lett. 66 (1994) 1166.

[5] K.G. Yager, Ch.J. Barrett, Curr. Opin. Solid State Mater. Sci. 5 (2001) 487. [6] K. Munakata, K. Harada, M. Itoh, S. Umegaki, T. Yatagai, Opt. Commun. 191 (2001) 15. [7] N.K. Viswanathan, S. Balasubramanian, J. Kumar, S.K. Tripathy, J. Macromol. Sci.-Pure Appl. Chem. A 38 (2001) 1445. [8] S.K. Tripathy, D.Y. Kim, L. Li, J. Kumar, CHEMTECH (May) (1998) 34. [9] X. Meng, A. Natansohn, P. Rochon, Polymer 38 (1997) 2677. [10] T.S. Lee, D.-Y. Kim, L.X. Jiang, I. Li, J. Kumar, S.K. Tripathy, J. Polym. Sci. Chem. 36 (1998) 283. [11] Ch.-J. Chang, W.-T. Whang, Ch.-Ch. Hsu, Z.-Y. Ding, K.Y. Hsu, S.-H. Lin, Macromolecules 32 (1999) 5637. [12] E. Schab-Balcerzak, F. Grabiec, D. Sek, A. Miniewicz, Polym. J. 35 (2003) 851. [13] S. Yang, l. Li, A.L. Cholli, S.K. Tripathy, J. Macromol. Sci. Pure Appl. Chem. A 38 (2001) 1345. [14] H. Saadeh, A. Gharavi, L. Yu, Macromolecules 30 (1997) 5403. [15] W.N. Leng, Y.M. Zhou, Q.H. Xu, Z. Liu, J. Polym. 42 (2001) 9253. [16] A.V. Raghu, G.S. Gadaginamath, T.M. Aminabhavi, J. Appl. Polym. Sci. 98 (2005) 2236. [17] A.V. Raghu, G.S. Gadaginamath, N.N. Mallikarjuna, T.M. Aminabhavi, J. Appl. Polym. Sci. 100 (2006) 576. [18] H.-J. Lee, M.-H. Lee, M.-Ch. Oh, S.G. Han, Polym. Bull. 42 (1999) 403. [19] S. Akimoto, M. Jikei, M. Kakimoto, High Perform. Polym. 12 (2000) 197. [20] Ch.-P. Yang, S.-H. Hsiao, J.-H. Lin, J. Polym. Sci. Chem. 31 (1993) 2995. [21] J.P. Chen, A. Natansohn, Macromolecules 32 (1999) 3171. [22] A.V. Raghu, G.S. Gadaginamath, S.B. Halligudi, T.M. Aminabhavi, J. Polym. Sci. A 6032–6046 (2006) 44. [23] A.V. Raghu, G.S. Gadaginamath, N.T. Mathew, S.B. Halligudi, T.M. Aminabhavi, J. Appl. Polym. Sci., 2007, in press. [24] G.M. Simu, S.A. Chicu, N. Morin, W. Schmidt, E. Sisu, Turk. J. Chem. 28 (2004) 579. [25] D.Y. Shen, S.K. Pollack, S.L. Hsu, Macromolecules 22 (1989) 2564. [26] K. Ueno, J. Am. Chem. Soc. 79 (1957) 3205. [27] M. Mahkam, M.G. Assadi, R. Zahedifar, M. Ramesh, S. Davaran, J. Bioact. Compat. Polym. 19 (2004) 45. [28] A. Prabhakar, D.K. Chattopadhyay, B. Jagadeesh, K.V.S.N. Raju, J. Appl. Polym. Sci. A 43 (2005) 1196. [29] R.W. Seymour, S.L. Cooper, Macromolecules 6 (1973) 48. [30] T.R. Hesketh, J.W.C. van Bogart, S.L. Copper, Polym. Eng. Sci. 20 (1980) 190. [31] C.H.M. Jacques, in: D.K. Klempner, K.C. Frisch, (Eds.), Polymer Alloys, Plenum Press, New York, 1977. p. 287. [32] J.T. Koberstein, A.F. Galambos, Macromolecules 25 (1992) 5618. [33] D.J. Martin, G. Meijs, P.A. Fgunatillake, S.J. McCarthy, G.M. Renvvick, J. Appl. Polym. Sci. 64 (1997) 803. [34] J.W.C. van Bogart, D.A. Bluemke, S.L. Cooper, Polymer 22 (1981) 1428. [35] J. Blackwell, C.D.J. Lee, Polym. Sci. Polym. Phys. Ed. 22 (1984) 769. [36] Z. Petrovic, J. Ferguson, Prog. Polym. Sci. 16 (1991) 695.