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

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali‐soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam‐explosion method, and alkali‐soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non‐Newtonian property at relatively smaller γ than the former solution did. Spin‐lattice relaxation time T1 (by 13C‐NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra‐ and intermolecular hydrogen bondings at the C6 position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra‐molecular structure of the solid is at least partly reserved in the above solutions.

ABSTRACT:The gelation of an aqueous (aq) solution of the sodium salt of carboxyethylcellulose (NaCEC: total degree of substitution <(F~=0.39) by contacting several aqueous metal chloride solutions was investigated visually and by 13 C NMR analysis. Diffusion of acidic Ti 3 + and Al3+ into aq NaCEC solution was found to produce CEC gel with high dimensional stability, slightly loosing the original transparency of aq NaCEC solution. Purple Ti 3 + ion was proved to diffuse slower than proton ion. Ca2+ was also found to produce CEC gel having a little weaker dimensional stability than those obtained by Ti3+ and Al3+. It was also affirmed that deuterated hydrogen chloride solution was significantly opaque. Any diffusion of Na+ and K + into NaCEC solution produced no gel and aq NaCEC solution remained as solution phase. Analysis on the chemical shift and the half value width of 13 C NMR peaks obtained for_ the CEC gel phases in comparison with those of the peaks for the original NaCEC solution revealed that only Al3+ and Ti 3 + produced considerable broadening and splitting of the peaks responsible for the carboxyethyl substituent, but DC! only resulted in a peak shift towards a higher magnetic field with no peak broadening. Chemical shift of C1 carbon, constituting backbone of NaCEC, of the CEC gels gave different values from gel to gel, showing some difference in configuration of /J-glucoside linkage of these CEC gels. Several possible gelation mechanisms were proposed to explain the roles of the cation species and pH value of their solutions used for contacting the aqueous NaCEC solution.KEY WORDS Carboxyethyl Cellulose / Gelation / 13 C NMR Analysis / Metal Chloride / Some aqueous (aq) solutions of naturally occurring polysaccharides and proteins have been known often to show gelation under rather specialized conditions 1 : An aq solution of agarose becomes a temperature-reversible (thermotropic) gel 2 and carrageenan in water was reported to make gel under the existence of cations (Cs+, Rb+, K +, NH 4 +). 3 An aq solution of casein becomes gelatinous by addition of some enzymes 4 . Some anionic cellulose derivatives such as cellulose sulphate and carboxymethylcellulose are also known to produce gel under the coexistence of polyvalent cations 5 • Gelation of aq solutions of these cellulose derivatives has been believed to be brought about by ionic cross-linking of polyvalent metal cations 6 • However, no direct evidence experimentally supporting this hypothesis has been presented up to now.In this article, we attempt to disclose a gelation mechanism of an aq solution of sodium salt of carboxyethylcellulose (N aCEC) as an typical anionic cellulose derivative by analysing the changes in chemical shift of 13 C NMR peaks and in their peak line width of the CEC phases obtained by diffusing various metal cation solutions into aq NaCEC solution. 259

An attempt has been made to explain the solubility behavior of sodium carboxyethyl cellulose (NaCEC) towards water and aqueous sodium hydroxide (aq. NaOH) in terms of supermolecular structure, i.e. degree of breakdown of intramolecular hydrogen bonding related to the degree of substitution. For this purpose, five NaCEC samples with «F» ranging from 0.03 to 0.0.39 were prepared in homogeneous aqueous media and subjected to CP/MAS 13C NMR and deuteration IR measurements. Existence of O3H…O'5 intramolecular hydrogen bonds in solid water‐insoluble NaCEC was first confirmed using both CP/MAS NMR and deuteration IR. This fact strongly suggests that for cellulose derivatives with relatively low «F» the solubility of the derivative in water or aq. NaOH is mainly governed by the considerable destruction of intramolecular hydrogen bonds. These findings are consistent with our previous conclusions [Polym. J., 16 (1984) 857] that the solubility of pure cellulose solid in aq. NaOH is mainly governed by the destruction of intramolecular hydrogen bonds.

The Belousov−Zhabotinsky (BZ) reaction was investigated to understand how the direction of traveling waves (TWs) is determined in a spherical field. A cation-exchange resin bead loaded with the catalyst of the BZ reaction was placed on a glass plate coated with silicone greases with different surface densities. TWs were generated at the contact point between the bead and glass plate for a lower density silicone grease, and at the upper half of the bead for a higher density silicone grease. In addition, TWs were generated in the middle section of the bead, which was sandwiched between two parallel glass plates coated with a high-density silicone grease. The experimental results were qualitatively reproduced by numerical calculations. These results are discussed in relation to the adsorption of Br 2 into the silicone grease as the source of the inhibitor.