Polymer Journal, Vol. 38, No. 4, pp. 343–348 (2006) Controlled Oxidation of Dextran for Evolution of Polyether Segment Bearing Pendant Carboxyl Groups for Corrosion Inhibition Applications Kenichi OYAIZU,1 Aritomo YAMAGUCHI,2 Takamitsu HAYASHI,2 y Yukiaki NAKAMURA,2 Daisuke YOSHII,2 Yuji ITO,2 and Makoto YUASA1;2; 1Institute of Colloid and Interface Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjyuku-ku 162-8601, Japan 2Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda 278-8510, Japan (Received August 22, 2005; Accepted November 17, 2005; Published April 15, 2006) ABSTRACT: Partially oxidized dextran containing carboxyl groups was prepared as an environmentally benign organic corrosion inhibitor for mild steel. Introduction of carboxyl groups was accomplished by oxidation of dextran using sodium hypochlorite under basic conditions. The structure of the product was confirmed by spectroscopic meas- urements. GPC analysis revealed that oxidation of dextran proceeded without significant molecular-weight degradation. 1H NMR spectra revealed that up to 1.3 carboxyl groups per repeating unit were introduced into the polymer. The prod- uct showed moderate corrosion inhibition activity for mild steel, and biodegradability under conditions for cooling water systems. [DOI 10.1295/polymj.38.343] KEY WORDS Dextran / Oxidation / Polycarboxylate / Hypochlorite / Corrosion Inhibitor / Spectroscopy / New perspectives open up with developments to medical applications.13–24 Periodate oxidation of dex- utilize corrosion inhibition by water-soluble polycar- tran is known to give polymeric dialdehydes with the boxylates such as poly(acrylate) and related poly- elimination of formates.25–27 However, products from mers.1 These compounds inhibit corrosion of mild further oxidation with hypohalites,28 possibly poly- steel and stainless steel by adsorbing at the metal sur- meric dicarboxylates, have not been characterized yet. face through carboxyl groups, which also lead to ef- For applications to corrosion inhibitors, polycarbox- fective scale inhibition for calcium carbonate in cool- ylates with relatively low molecular weights are pref- ing water systems.2–6 Despite these practical benefits, erable because high molecular mass polymers would however, the utilization of these compounds is still remain a long period in water phase before adsorbing controversial, especially with regard to degradability onto the metal surface due to their low diffusivity.1 and environmental safety. One strategy to reduce the We chose dextran as a starting material because struc- potential environmental impact aims at the use of na- ture-defined oligomers are available, while various low ture-identical agents belonging to various groups of molecular-weight biomass residues would in principle organic acids. Here we report that partially oxidized be applicable. Applying the Besemer’s reaction condi- polysaccharides are environmentally benign corrosion tions,12 we aimed at obtaining a highly carboxyl-sub- inhibitors for steels. stituted polymer by controlled and uncatalyzed oxida- Oxidation of primary alcohol groups in polysaccha- tion of dextran with sodium hypochlorite (NaClO).29,30 rides to uronic acids has widely been investigated us- Regioselective oxidation of dextran at the C2 and C4 7–9 10,11 ing various oxidants such as NO2 and Pt/O2, but atoms, allowing the control of molecular mass, was the reaction is accompanied by substantial degradation successfully accomplished, providing a polyether seg- of the polymer and by non-selective oxidation. A sig- ment containing two carboxyl groups per repeating unit nificant increase in the selectivity was accomplished in the main chain. The choice of the oxidant, NaClO, by Besemer et al. using 2,2,6,6-tetramethyl-1-piperidi- is also based on the anticipation that eutrophication nyloxy as a mediator and hypochlorite/bromide as an of the cooling water containing the oxidized polysac- ultimate oxidant under basic conditions (pH 10–11).12 charide, which is intrinsically biodegradable and there- This reaction was exploited for determination of a fore nutritive, would be depressed by the sterilizing ef- small amount of primary alcohol groups as a defect in fect of the hypochlorite ion during the use of cooling dextran, a (1!6)- -D-glucan.12 At present, chemical water. The effect of corrosion inhibition was prelimi- modification of dextran is widely investigated for bio- narily investigated by corrosion weight loss tests. yTo whom correspondence should be addressed (Tel: +81-4-7124-1501, Fax: +81-4-7121-2432, E-mail: [email protected]). 343 K. OYAIZU et al. 4 4 1:7 Â 10 , Mw ¼ 1:9 Â 10 (Mw=Mn ¼ 1:1). EXPERIMENTAL Products with lower degree of oxidation were pre- pared by the oxidation of the same amount of dextran Materials and Measurements (1.0 g, 6.2 mmol unit) with less amounts of NaClO Dextran (ICN Biomedicals Inc., MW ¼ 1:5{2 Â (17 mmol (2) or 9.4 mmol (3)) added at a time and re- 104), aqueous NaClO (Wako Chem., available chlo- acted for 24 h under the same conditions. Analytical 1 rine 5%), sodium hydroxide, and D-glucuronic acid data for 2: Yield: 29 wt %. H NMR (D2O, TMSP, were used as received. Poly(acrylic acid) (PAA) with ppm): 4.96 (m, 1H), 4.63–3.51 (m, 4.44H). GPC: 4 4 a molecular weight of Mn ¼ 4500 and a copolymer of Mn ¼ 1:8 Â 10 , Mw ¼ 2:0 Â 10 (Mw=Mn ¼ 1:1). 1 acrylic acid and 2-acrylamido-2-methyl-1-propanesul- Analytical data for 3: Yield: 20 wt %. H NMR (D2O, fonic acid (co-PAA) with a molar composition of 75/ TMSP, ppm): 4.97 (m, 1H), 4.64–3.51 (m, 4.88H). 4 4 25 and a molecular weight of Mn ¼ 4500 were pre- GPC: Mn ¼ 1:9 Â 10 , Mw ¼ 2:1 Â 10 (Mw=Mn ¼ pared as previously reported.1 GPC measurements 1:1). were performed using Shimadzu LC-10AT equipped with a UV detector (Shimadzu SPD-10A) and Shodex Characterization of the Product Protein KW-804. Fluorescein isothiocyanate-dextran A working curve was prepared using absorbance at 5 À1 from Sigma-Aldrich (MW ¼ 2:82 Â 10 and 4:64 Â 1730 cm (C=O) in the IR spectra for aqueous mix- 5 5 4 10 ), catalase (1:0 Â 10 ), albumin (8:0 Â 10 ), myo- tures of dextran ((C6H10O5)n) and D-glucuronic acid 4 4 globin (1:65 Â 10 ), and cytochrome c (1:2 Â 10 ) (C6H10O7) with various molar fractions. The amount were used as molecular-weight standards. The eluent of carboxyl groups in the product was roughly esti- À1 was a 0.1 M phosphate buffer prepared from KH2PO4 mated by the absorbance at 1595 cm (C=O), assum- (>99:5%) and K2HPO4 (>99:5%) which were ob- ing that absorbances for carboxylic acid and carboxyl- tained from Wako Chem. and used as received. The ate were identical. detection wavelength was 280 nm. NMR spectra were The effect of corrosion inhibition was preliminarily obtained using JEOL 300 MHz JNM-AL300 spec- investigated by corrosion weight loss tests of carbon trometer with 3-(trimethylsilyl)propionic-2,2,3,3-d4 steel using tap water at 35 C for 7 d with constant acid sodium salt (TMSP) from Sigma-Aldrich as an stirring in an open vessel. Analytical data for the tap internal standard. IR spectra were obtained using water: pH 7.4, electric conductivity ðRTÞ¼172 mS/ JASCO FT/IR-410 spectrometer and a KBr pellet cm, and hardness = 58 mgCaCO3/L. The metal sam- or a CaF2 cell with an optical path length of 20 mm. ple employed was a pretreated plate of mild steel JIS Lyophilization was carried out using a Kyowa Trio- SS 400 with a dimension of 30 Â 50 Â 1 mm,4 which master II A-04 freeze-drying system. was polished with emery papers and washed thor- oughly with H2O, CH3OH, and acetone under ultra- Preparative Methods sonic irradiation. Then, the metal plates were immers- Oxidation of dextran was carried out with various ed into solution (1 L) containing various inhibitors. amounts of NaClO at room temperature. In a typical The corrosion rate, v, was defined as the rate of de- procedure, to a 100 mL aqueous solution of dextran crease in the weight of metal plates during exposure (1.0 g, 6.2 mmol unit) containing NaOH (0.1 N) was to corrosive atmosphere. The corrosion rate was ob- added the aqueous NaClO (25.6 mL, 1.28 g, 17 mmol). tained from v ¼ w Á AÀ1tÀ1 where w was the loss of The resulting solution was stirred for 24 h at room weight in mg, A was the surface area of the sample temperature. In order to force the reaction to proceed, in dm2, and t was the period of exposure to the atmo- the same amount of NaClO (17 mmol) was added sphere in day, and thus expressed by a unit of again to the solution, which was then kept stirring mgÁdmÀ2 dayÀ1 which was abbreviated as mdd.2 The for further 2 d. The polymeric product with a molecu- corrosion rate of the steel in the absence of inhibitors lar weight of more than 5000 was fractionated by ul- (i.e. blank test) was normalized by averaging the trafiltration on a polyethersulfone membrane (Milli- results of several independent experiments, which 2 pore) and purified by dialysis in H2O using seamless were in the range of ð1:3 Æ 0:2ÞÂ10 mdd as shown cellulose tubing (UC24-32-100) from Sanko Chem. in Table I. Lyophilization of the aqueous solution afforded the product 1 as a white powder. Yield: 88 wt %. IR (KBr, RESULTS AND DISCUSSION À1 cm ): 1614 (C=O), 1417, 1308, 1246, 1147, 1107, 1 1078, 1041, 1020, 914, 887, 808, 642.