Studies on poly (urethane?urea) s based on zinc salt

Studies on poly (urethane?urea) s based on zinc salt

(Parte 1 de 3)

Studies on poly(urethane–urea)s based on zinc salt of mono[hydroxyethoxyethyl]phthalate a Division of Environmental and Chemical Engineering, The Research Institute of Industrial Technology,

Engineering Research Institute, Chonbuk National University, Chonju 561-756, South Korea b Department of Chemistry, Anna University, Chennai 600 025, India c Department of Chemistry, Merit International Institute of Technology, Ootacamund, The Nilgiries 643 002, India

Received 28 February 2003; received in revised form 24 June 2003; accepted 21 July 2003

Abstract

Zinc containing poly(urethane–urea)s having ionic links in the main chain were synthesized by the reaction of hexamethylene diisocyanate or tolylene-2,4-diisocyanate with 1:1 mixture of zinc salt of mono(hydroxyethoxyethyl) phthalate and each of the bisureas such as hexamethylene-bis(x,N-hydroxyethylurea), tolylene-2,4,-bis(x,N-hydroxyethylurea), hexamethylene-bis(x,N-hydroxypropylurea) and tolylene–2,4-bis(x,N-hydroxypropylurea) using di-n-butyltin dilaurate as catalyst. These polymers were characterized by FT-IR, 1H NMR and 13C NMR spectroscopy, elemental analysis, solubility test, viscosity measurement and X-ray diffraction analysis. Thermal properties of the polymers were determined by differential scanning calorimetry and thermogravimetric analysis. 2003 Elsevier B.V. All rights reserved.

Keywords: Zinc salt of mono(hydroxyethoxyethyl)phthalate; Ionic monomer; Bisureas; Poly(urethane–urea)s; Thermal studies

1. Introduction

Urethane-based materials are of commercial interest in many applications owing to their abrasion resistance, low temperature flexibility, high strength and aging and chemical resistance. There are various ways of combining polyols and diisocyanates in order to produce tailor-made polyurethanes [1,2]. The proper combination of these and other reagents results in versatile polymers, which have wide range of applications as foams, elastomers, coatings and elastomeric fibers [3–6].

Poly(urethane–urea)s are a class of very important copolymers. They are composed of a class of elastomers exhibiting superior extensibility, toughness and extensively used ranging from textile fibers to medical prosthesis [7,8]. Introduction of urea group into the polymer backbone is expected to improve the solubility of the polymer without decreasing the thermal stability significantly. High

Reactive & Functional Polymers 57 (2003) 23–31 w.elsevier.com/locate/react

*Corresponding author. Fax: +82-063-270-2306. E-mail address: jayakumar77@yahoo.com (R. Jayakumar).

1381-5148/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2003.07.001 modulus polyurethane–urea elastomer has many practical applications;the most important are in the automotive industry [9,10].

Incorporation of metal and functional groups into the polymers have emerged and find wide applications as aqueous thickeners, impregnates, coatings, textile seizers, adhesives [1,12], additives [13], resins [14,15], catalysts [16] and in the biomedical field [17,18]. Ionic diols containing ionic linkages between COO and M2þ are of our interest. They are very important starting materials for the synthesis of ionic polymers in which the metal is incorporated into the backbone of the polymer. Metal containing polymers with ionic links formed between COO and M2þ in the backbone have already shown by us [19–25].

The present investigation is aimed at the synthesis and characterization of hexamethylene diisocyanate [HMDI] and tolylene-2,4-diisocyanate [TDI]-based poly(urethane–urea)s from zinc salt of mono(hydroxyethoxyethyl)phthalate [Zn[HEEP]2], hexamethylenebis(x,N-hydroxyethylurea)[HBHEU], tolylene-2,4,-bis(x,N-hydroxyethylurea) [TBHEU], hexamethylene bis(x,N-hydroxypropyl urea) [HB HPU] and tolylene-2,4-bis(x,N-hydroxypropylurea) [TBHPU].

2. Experimental 2.1. Materials

Phthalic anhydride (BDH), diethylene glycol

(Fluka), di-n-butyltin dilaurate (DBTDL) (Fluka), ethanolamine (Aldrich), propanolamine (Aldrich) and zinc acetate of extra pure grades were used without any purification. HMDI and TDI (Fluka) were also used without prior purification. The solvents such as acetone, methanol, dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc), benzene, toluene, mcresol and chloroform were purified by standard procedures. Zn[HEEP]2 was synthesized as reported in our previous paper [23]. The structure of

Zn[HEEP]2 is shown in Fig. 1. Bisureas such as HBHEU, TBHEU, HBHPU and TBHPU were synthesized according to the reported method [20,21].

2.2. Synthesis of poly(urethane–urea)s

Zn[HEEP]2 (0.005 mol) and any one of the bisureas, HBHEU, HBHPU, TBHEU or TBHPU

(0.005 mol) dissolved in 200 ml of DMSO were added to a three necked flask fitted with a nitrogen inlet, a condenser and a dropping funnel. To this 2–3 drops of DBTDL was also added as catalyst. Then 0.01 mol of HMDI or TDI dissolved in 25 ml of DMSO was slowly added with constant stirring under nitrogen atmosphere for 25–45 min at 95 C. After the addition the mixture was kept under stirring at the same temperature for 4 h. Then 50 ml of DMSO was added to the mixture and the contents were filtered. The filtrate was poured into a large excess of vigorously stirred chloroform to precipitate the product. The product was further washed with acetone several times and dried at 60 C in vacuum. In the similar method, using

Zn[HEEP]2 and four different bisureas, eight zinc containing poly(urethane–urea)s were synthesized based on HMDI or TDI. The polymers were en- coded as Zn[HEEP]2-HMDI-HBHEU (I), Zn[HE EP]2-HMDI-HBHPU (I), Zn[HEEP]2-HMDI-TB HEU (I), Zn[HEEP]2-HMDI-TBHPU (IV), Zn [HEEP]2-TDI-HBHEU (V), Zn[HEEP]2-TDI-HB HPU (VI), Zn[HEEP]2-TDI-TBHEU (VII) and Zn [HEEP]2-TDI-TBHPU (VIII).

2.3. Measurements

The FT-IR spectra of the polymers were recorded on a Testscan Shimadzu FT-IR 8000 series spectrophotometer at room temperature using KBr pellets. The 1H- and 13C NMR and DEPT spectra of the polymers were recorded on a JEOL

GSX-400 MHz spectrometer using DMSO-d6 as

HO(CH ) O(CH ) OOC COOZnOOC COO(CH ) O(CH ) OH

Zn[HEEP] Fig. 1. Structure of Zn[HEEP]2.

24 R. Jayakumar et al. / Reactive & Functional Polymers 57 (2003) 23–31 solvent and tetramethylsilane (TMS) as internal standard. Thermogravimetric analysis (TGA) was performed with a Mettler-3000 thermal analyzer using 2 mg of the sample at a heating rate of 20 C/ min in air. Differential scanning calorimetric analysis (DSC) was carried out in a DSC V4.OB Dupont 2100 model differential scanning calorimeter at a heating rate of 10 C/min under a nitrogen atmosphere. Powder XRD patterns were collected on a Philips PW 1710 diffractometer using

CuKa radiation. A Perkin–Elmer 2400 carbon– hydrogen analyzer was used for elemental analysis.

The inherent viscosity ginh of the polymers in DMSO was determined in an Ubbelhode-viscom- eter at 40 C. The flow time for the solvent as well as the polymer solution (1.0 g/dl) was determined. The solubility of the polymers was tested in various polar and nonpolar solvents by taking 10 mg of the polymers in 2 ml of different solvents in a closed test tube and keeping them for 1 day.

3. Results and discussion 3.1. Synthesis

The synthesis of metal containing poly(urethane–urea)s were carried out in DMSO. In other solvents such as dioxane, toluene, xylene, acetone, nitrobenzene and anisole, both Zn[HEEP]2 and bisureas were insoluble and the polyaddition re- action did not proceed smoothly. The reaction of diisocyanates with diols catalyzed by DBTDL took place via the formation of ternary complex between the catalyst and the reagents [26]. During the synthesis of polymers, the mole ratio of diiso- cyanate:diol (Zn[HEEP]2 and bisureas) was taken as 1:1 to avoid the formation of crosslinkages. The crosslinked product formed if any was filtered off after stirring the product with excess of DMSO to dissolve the linear polymer. The dissolved linear polymer was reprecipitated by the addition of nonsolvents. The yield was generally high. The HMDI-based polymers showed higher yield than TDI-based polymers. This may be due to the higher reactivity of HMDI than TDI when DBTDL was used as a catalyst. In the case of TDI, the 2- and 4-positions are sterically hindered due to the presence of methyl group and hence the coordination of metal catalysts to TDI would be lesser than that to HMDI. The yield obtained was between 75% and 92%. The synthesis data of poly(urethane–urea)s are given in Table 1. The reactions involved in the synthesis of poly(urethane–urea)s are shown in Scheme 1.

The polymers are soluble in polar solvents like

DMSO, DMF, DMAc and m-cresol, but insoluble in methanol, ethanol, acetone, ethyl methyl ketone, chloroform, carbon tetrachloride, n-hexane, benzene, toluene, xylene, tetrahydrofuran, ethyl acetate and dioxane. The polymers are polar in nature. Hence, the solubility of the polymers increases with increase in polarity of the solvents.

In zinc containing poly(urethane–urea)s the zinc content is lesser than the value calculated based on equal reactivity of Zn[HEEP]2 and bisureas. But the values of carbon and hydrogen contents are slightly higher than the calculated values. This may be due to the lower reactivity of

Zn[HEEP]2 towards the diisocyanates when compared to the bisureas. The results of the elemental analysis of poly(urethane–urea)s are presented in Table 2.

3.2. Characterizations

3.2.1. FT-IR spectra

The FT-IR spectra of HMDI-based polymers show the –NH stretching absorption band between 3335–3332 cm 1. The C–H asymmetrical and symmetrical stretchings due to the methylene group are

Table 1 Yields and viscosity values of the polymers

Polymer Yield (%) Inherent viscosity (ginh)

Reaction temperature¼95 C and reaction time¼5h .

R. Jayakumar et al. / Reactive & Functional Polymers 57 (2003) 23–31 25

observed between 2931 and 2857 cm 1. The carbonyl stretching of the urethane, urea and ester groups show a peak at 1687–1685 cm 1. The carboxylate ion of the zinc salt gives two broad peaks between 1624 and 1472 cm 1. This confirms the presence of ionic linkage in the polymer. These bands were not found in metal-free analogues of these polymers. The C–H out of plane bending vi- brationofaromaticsystemshowsapeakat772–770 cm 1.

The FT-IR spectra of TDI-based polymers show a peak at 3306–3290 cm 1 due to –NH stretching. The C–H asymmetrical and symmetrical stretchings due to the methyl and methylene groups are observed between 2921 and 2852 cm 1. The peak at 1691–1684 cm 1 is attributed to the

Table 2 Elemental analysis data of the polymers

Polymer Analytical data found (calculated)

Scheme 1. Synthesis of zinc containing poly(urethane–urea)s.

26 R. Jayakumar et al. / Reactive & Functional Polymers 57 (2003) 23–31 carbonyl stretching of urethane, urea and ester groups. The carboxylate ion shows two peaks in the range from 1643 to 1461 cm 1. The C–H out of plane bending vibration of aromatic system shows a peak at 752–746 cm 1.

3.2.2. 1H NMR spectra

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