The effect of hydrogen bonding addends on the dilute solution viscosity of poly(acrylamide) and unionized poly(acrylic acid) and poly(methacrylic acid)

Abstract

Abstract The effect of various addends on the specific viscosity of dilute aqueous unionized poly(methacrylic acid) (PMA) solutions, unionized poly(acrylic acid) (PAA) solutions, and poly(acrylic acmide) (PAAm) solutions was investigated. The addition of sodium and lithium chloride decreases the specific viscosity of PMA and PAA but leaves PAAm unaffected. The addition of ethanol to aqueous unionized PMA causes a decrease in specific viscosity up to 15% of the addend and an increase at higher alcohol content. The specific viscosity of PAA is increased and that of PMA decreased by ethanol. Urea and acetic acid addition decrease the specific viscosity of PMA and increase that of PAA. Urea does not affect the specific viscosity of PAAm. Guanidine hydrochloride addition decreases the specific viscosity of PMA. Perfluorooctanoic acid addition increases and caprylic acid decreases the specific viscosity of PMA, whereas neither of them affects PAA. It is assumed that the specific viscosity is a measure of the degree of intramolecular bonding. The results are discussed on the basis of a model which considers separately the effect of the addend on the polymer and on water. It is shown that for intramolecular bonding to decrease, ( f A / f W )exp {−(Δμ ° A − Δμ ° W )/ kt } must be larger than unity. In this expression, which represents the effectiveness of addend in replacing water on the chain, f A and f W are the activity coefficients of addend and water, respectively, and (Δμ ° A − Δ ° W ) is the free energy change when addend replaces water on the chain. Results from the literature are included in the discussion.