Intrinsic viscosity of aminoacetalized polyvinyl alcohol sulfate in 1/10 N potassium sulfate solution

Abstract

The intrinsic viscosity of the sulfate of aminoacetalized polyvinyl alcohol (Am‐PVA) in N/10 K2SO4 solution has been studied to disclose the influence of the number of ionic substitutents on the intrinsic viscosity of the polymer. The number of ionic substitutents is easily changed by controlling the degree of aminoacetalization, which is determined by a selection of the conditions of aminoacetalization. β‐Cyclohexylamino n‐butyraldehyde dimethylacetal, CH3(C6H11NH)CH·CH2·CH(OCH3)2, and β‐cyclohexylamino‐n‐propylaldehyde dimethylacetal, (C6H11NH)CH2·CH2·CH(OCH3)2, were used as aminoacetals. The aminoacetalization reaction was carried out in a system of aminoacetal, polyvinyl alcohol (PVA), sulfuric acid, and water. The reaction product was purified by dialysis, and the degree of aminoacetalization was estimated from the nitrogen content as given by the semimicro Kjeldahl method. The PVA was used unfractionated and its degree of polymerization, as determined by the viscosity method, was found to be between 900 and 2400. The solution viscosity was measured in an Ostwald viscometer designed to reduce the kinetic energy term for which a correction was made. It was first ascertained that the viscosity in N/10 K2SO4 solution was not influenced by the rate of shear in the range of our experiment. The intrinsic viscosity was found from linear extrapolation, a linear relation between ηsp and c, being well realized in the concentration range from 1.5 to 9 g./l. The intrinsic viscosity increased with the degree of aminoacetalization in an S‐shaped fashion. Compared to the same degree of aminoacetalization, Sakurada‐Houwink's equation [η] = KPa was found to hold well at each degree of aminoacetalization, and the index a was found to increase with the degree of aminoacetalization. The volume expansion α3 of the polymer in the solution was estimated from [η]M/[η]θM0 according to Flory's theory, in which M is the molecular weight of the sulfate of Am‐PVA, M0 the molecular weight of each original PVA, [η] the intrinsic viscosity of the sulfate of Am‐PVA, and [η]θ is the mean intrinsic viscosity of each original PVA in Flory's unperturbated state. The viscosity in a mixture of acetone (35.2%) and water (64.8%) was used for [η]θ, its value being calculated from [η]θ = 1.06 P1/2, having reference to Sakurada's report. Then (α5 − α2/M1/2) was calculated and plotted against the degree of aminoacetalization x. It was found that these points fall on one curve, independently of the degree of polymerization of the original PVA. When [(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0 was plotted against x in a log‐log scale (we are subtracting the value [((α5 − α3)/M1/2]0 for PVA) it was found that a linear relation between them holds well independently of the degree of polymerization of PVA. The empirical formula [(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0 = Axn was thus obtained. In both Am‐PVA's n is 1.45, but A differs slightly. When the ionic strength is constant, {[(α5 − α3)/M1/2]x − [(α5 − α3)/M1/2]0} should be proportional to x2/(M/r 20)3/2...

Dilute polyelectrolyte solutions: recent progress and open questions

“…The cross-over between [ η ] ∼ f 0 to [ η ] ∼ f 1.1 can in principle be used to obtain an estimate of the molar mass of the electrostatic blob, but we have been unable to get consistent values from this. Similar behaviour can be observed in the data of Matsumoto and Eguchi for polyvinyl sulfate, 416 as shown in Fig. S8 (ESI†).…”

“…Matsumoto and Eguchi 399 reported diluted viscosity data for aminoacetalyzed polyvinyl alcohol with different fractions of charged groups in salt-free water. As 0.1 M K 2 SO 4 is a near theta solvent for the uncharged polymer, 416 we expect water to be a marginally good solvent for the backbone and x T c x el . The c* values normalised by N 2 are plotted as a function of the fraction of charged groups in Fig.…”

“…Data for different degrees of polymerisation and added salt concentrations show the same scaling exponent, which indicates that the exponent is independent of the number of electrostatic blobs in a chain. Matsumoto and Eguchi's 416 intrinsic viscosity data, discussed in the ESI † (Section S4), display a weaker scaling of [Z] p f 0.7 . At very low degrees of ionisation, the [Z] p f 1.1 scaling breaks down as the polymer chains approach their neutral polymer dimensions.…”

“…103 The scaling of other parameters with the charge fraction, particularly A 2 , is of interest to understand the nature of the electrostatic excluded volume, but the available data [551][552][553][554] do not allow for any systematic conclusions to be drawn, particularly in the low charge fraction limit. The Huggins coefficient of a PVA polyelectrolyte in excess added salt was shown to be a decreasing function of charge fraction, 416 see Fig. S8 (ESI †).…”

“…For several systems, the ratio k D /(A 2 M w ) was independent The Huggins and Kraemers coefficients of polyelectrolytes are discussed in the ESI † (Section S5). Briefly, an analysis of literature data 111,141,210,299,416,[531][532][533][534][535][536] revealed that: (1) increasing the charge fraction leads to a large increase in k H in salt-free solutions and a modest decrease in k H for solutions in excess salt; (2) the Huggins coefficient shows a non-monotonic dependence on the added salt concentration; (3) k H decreases with increasing N until it reaches a constant value, which appeared to be similar to that of neutral polymers; (4) introducing hydrophobic groups leads to a large increase in k H if the added salt concentration is sufficiently high.…”