Study on Alkaline Hydrolysis of Polyacrylamide by 13C NMR

Abstract

ABSTRACT:Alkaline hydrolysis of a polyacrylamide sample was performed in aqueous sodium hydroxide (Na0H) solutions at various Na0H concentrations to investigate the effects of hydrolysis conditions on the sequence distribution of the hydrolyzed products. For this purpose, 13 C NMR spectra for the aqueous solutions of the products were measured, in order to determine the sequence distribution based on carboxyl (on acrylic acid residue) and carbamoyl (on acrylamide residue) carbon peak assignments. It was first found that the specific concentration of aqueous sodium hydroxide solution gives a product with a sequence distribution greatly differing from the conventional product whose sequence distribution is almost completely alternative of acrylic acid and acrylamide residues. Under the other hydrolysis conditions employed here, the products with almost alternative sequence distribution were found to be commonly produced. Possible hydrolysis mechanisms are discussed based on the structures of aq Na0H solutions.KEY WORDS 13 C NMR / Polyacrylamide / Alkaline Hydrolysis/ Sequence Distribution / Many studies have been carried out on the alkaline hydrolysis of the carbamoyl group in polyacrylamide (PAA) to carboxyl group. Moens et al. 1 investigated the process of alkaline hydrolysis as change in electric conductivity of the system by measuring the increase of negative charge due to conversion of the carbamoyl group to the ionic carboxyl group. Gunari et al. 2 analyzed its kinetics by measuring the viscosity of the aqueous (aq) solution of hydrolyzed PAA, because the viscosity varied in proportion to the degree of hydrolysis of PAA. Moens et al. 1 and Gunari et al. 2 speculated that the carbamoyl group was not randomly hydrolyzed and the carbamoyl group in the acrylamide (A) monomer unit adjacent to the acrylic acid (B) monomer unit produced by alkaline hydrolysis of PAA was strongly resistant to further alkaline hydrolysis, finally leading to the formation of * To whom all correspondence should be addressed.ABABAB type polymer. This kind of autoretarded reaction has already been proposed by Fuoss et al.3 in the case of quaternization of poly(4-vinylpyridine) by alkyl halide. Higuchi et al. 4 supported the above speculation on the hydrolysis model of PAA using experimentally determined rate constants of hydrolysis of A unit in AAA, ABA, and BAB sequences. Halverson et al. 5 directly measured the 13 C NMR spectra of the alkaline solution of PAA, in which PAA was hydrolyzed to the desired degree. Here, note that they used a hydrolysis media consisting of water and sodium chloride (0. 75 mol 1 -i) or isopropanol (2 wt%) and stoichiometrical amount of sodium hydroxide (NaOH) (0.23--0. 7 mol) for the desired hydrolysis degree of PAA using the polymer solution with its concentration of 5 and 9 wt%. They analyzed carbonyl carbon peaks for A and B monomer units and suggested that 1101

Improved rheological properties and stability of multiwalled carbon nanotubes/polymer in harsh environment

“…Based on Table , the viscosity ratio is significantly reduced for all polymers at alkali solution (pH = 11) due to a high degree of hydrolysis in the presence of OH − ions. Earlier studies investigated the mechanism of PAM hydrolysis at either alkaline or acidic conditions . The alkali or acidic environments assist the process of hydrolysis as shown in Figure .…”

Polyampholyte polymer as a stabiliser for subgrade soil

“…Figure 10 plots the 13 C-NMR spectrum of the anionic HPAM. Delta peaks at 34-36, 42-44 ppm, representing the methylene and methine carbon signals, respectively, are seen, but also observed is the signal at δ = 180.23 ppm (Halverson et al 1985, Yasuda et al 1988) from the carbonyl carbon attached to the amine group (as in Figure 9) and the carbonyl signal, δ = 183.55 ppm, from the carboxylate sodium ion group (Feng et al 2002). Figure 11 displays the 13 C-NMR spectrum of the cationic PAMTAC with peaks at δ = 22.…”

Lignin‐g‐poly(acrylamide)‐g‐poly(diallyldimethyl‐ ammonium chloride): Synthesis, Characterization and Applications

“…The FTIR spectra of unmodified lignin, P(AM)‐g‐P(DADMAC), and lignin‐g‐P(AM)‐g‐P(DADMAC) copolymer prepared under optimal conditions is shown in Figure . Both lignin and lignin‐g‐P(AM)‐g‐P(DADMAC) have absorption bands at 1266 and 1140 cm −1 , attributed to the C−O and C−H stretching frequency of the guiacyl unit, respectively . The characteristic aromatic stretching bands of the lignin skeleton are also observed at 1591, 1510, and 1425 cm −1 .…”

“…When the reaction was conducted at pH 5, the lignin copolymer had an average charge density of −0.04 meq g −1 . When the reaction was conducted at higher pH values, the hydrolysis of the acrylamide and degradation of the quaternary ammonium ring group of DADMAC would occur . In other words, the decrease in positive charge density is attributed to 1) the hydrolysis of the acrylamide monomer as the amide groups could be converted to carboxylic acids groups and 2) the loss of the quaternary ammonium groups in the DADMAC monomer.…”

“…When the reaction wasc onducted at pH 5, the lignin copolymerh ad an average charged ensity of À0.04 meq g À1 .W hen the reaction was conducted at higher pH values, the hydrolysis of the acrylamide andd egradation of the quaternary ammonium ring group of DADMAC would occur. [35,36] In other words,t he decrease in positive charge density is attributedt o1 )the hydrolysis of the acrylamide monomer as the amide groups could be converted to carboxylic acids groups and 2) the loss of the quaternary ammonium groups in the DADMAC monomer.T he amount of acrylamide added to the reactionm ixture had an insignificant effect on the overall charged ensity of the resulting copolymer,a st he dosageo facrylamide wasi ncreased from 0.35 to 1.4 mol L À1 , but the charge density of the lignin copolymer increased slightly from 0.39 to 0.52 meq g À1 ,r espectively. [33] Although acrylamide is an eutral monomer and does not contribute to the overall charge density of the lignin copolymer,t his slight increasei nc harge density is associated with the fact that acrylamide most probably helped cross-linked DADMAC to lignin.…”