Solution Properties of Poly(N-isopropylacrylamide) in Water

Abstract

ABSTRACT:Various molecular parameters characterizing the solution properties of poly(Nisopropylacrylamide) (in the range of molecular weight from 13.8 to 910 x l<f) in water at 20"C and the temperature dependence of them in the range of 20°C to 30.6'C were determined with static and dynamic light scattering technique. (Modified) Flory's fifth power law of excluded volume effect predicts well the temperature dependence of the chain dimension. It is shown that this polymer molecule behaves as a flexible coil from the molecular weight dependence of these parameters and the relation between the interpenetration function and expansion coefficients. The unique thermal behavior of this solution, temperature of phase change being independent of molecular weights and concentrations at least in the range of I wt%, should be mainly attributed to the hydrated structure.KEY WORDS Poly(N-isopropylacrylamide) / Light Scattering / Solution Properties / Hydration / It is well-known that non-ionic water soluble polymers exhibit. unusual behavior. That is, the solution property often differs significantly from that of other polymers in nonpolar organic solvents. 1 The reasons for this are still not well understood. Of course the hydrophobic interaction may play an important role. Aqueous solutions of relatively simple synthetic polymers which undergo phase transition around at 31 °C on heating have attracted particular attention due to similarity with the denaturation of proteins in aqueous systems.Previously, Heskins and Guillet 2 studied the solution properties of poly(N-isopropylacrylamide) (PNiPAM) in water which shows the phase transition on heating the solution. Although the qualitative features of their results were acceptable, they only studied one unfractionated polymer sample, the polydispersity of which was quite broad. Moreover, they reported nonproportional relation bePolym. J.. Vol. 22, No. I. 1990 tween intrinsic viscosity arid partial specific volume. On the other hand, Chiantore et al. 3 reported quite unacceptable results of viscosity massurements using unfractionated samples. These peculiar results are considered due to the use of unfractionated samples. Recently, one of the authors established an effective procedure for molecular weight fractionation of this polymer. 4 As reported in our previous papers, 5 • 6 the phase transition of aqueous PNiPAM solution is quite sensitive, reversible and reproducible to the thermal stimulation. The phase transition takes place as the temperature reaches about 31 °C, contrary to Heskins, almost independently of molecular weight and concentration in the experimental range. This newly observed behavior is quite different from that of the usual polymer solution, where the temperature of the phase change significantly depends on molecular weight and concentrations. Such a phase diagram suggests that the main reason for the phase 15

Microcalorimetric Study of Aqueous Solution of a Thermoresponsive Polymer, poly(N-vinylisobutyramide) (PNVIBA)

“…For samples of several hundreds kDa and concentrations over 0.05 (w/v)%, these dependences are practically unobservable and will give almost flat phase diagrams. 26 Compared with PNIPAM, PNVIBA gives larger ∆H and ∆S , but the size of the cooperative domain is similar. The difference in T t is only 15% in absolute temperature scale, but this larger ∆H value will result in the sharper transition in turbidimetric measurements, which is very important for practical applications.…”

Constructing the Phase Diagram of an Aqueous Solution of Poly(N‐isopropyl acrylamide) by Controlled Microevaporation in a Nanoliter Microchamber

“…To our knowledge, there is a lack of phase diagrams for most polymers, which is mainly due to two reasons: 1) lack of sufficient amount of narrowly distributed polymer samples with different chain lengths; and 2) an extremely long time required for a viscous polymer solution to reach its phase equilibrium, especially when the concentration is high. Phase transition of solutions of thermosensitive polymers, such as PNIPAM, which exhibits a lower critical solution temperature (LCST), has been widely investigated by various experimental techniques, including IR spectroscopy, [1] 1 H NMR spectroscopy, [2] viscometry, [3,4] fluorescence, [5] turbidimetry, [6] light scattering, [7] and calorimetry. [8] These studies of the phase transition behavior were generally carried out in conventional reaction vessels with volume of 1 mL or more.…”

Chemical and thermo‐responsive characterisation of surfaces formed by plasma polymerisation of N‐isopropyl acrylamide

“…In aqueous solution, poly(NIPAAm) exhibits an LCST of around 32°C. 7 However, once grafted to a surface, the constraining effect of the substrate can alter the characteristics of the transition, limiting the degree of swelling of the hydrogel 8 -10 and subsequently the extent of the contact angle change measured at the interface. The temperature at which this VPT occurs may be controlled by the addition of hydrophilic or ionisable co-monomers 10 -13 allowing a degree of control to the properties of the gel.…”