The viscosities and densities of several mixt~lres of dimethyl s~llphoside and \\rater have been meas~~red a t 25', 45", and 65" C. Heats of mixing and refractive indices a t 25' C are also reported. The results indicate there is strong association of the two liquids which [nay be attributed to hydrogen bonding. IYTRODUCTIONThe widespread application of dimethyl sulphoxide (Di\lISO) as a solvent, plasticizer, and chemical iilterinediate has led to its large-scale production in recent years. In spite of the increased use of this compound its physical properties do not appear to have been studied extensively.DMSO is a colorless, non-toxic liquid which boils a t 189' C and freezes a t 18.5' C. I t is coillpletely miscible with water and is strongly hygroscopic, but little has been reported about the behavior of DLIISO-H20 mixtures (I). During the course of a recent investigation on the solution properties of amylose dissolved in DIMSO, it was fouild that water alters the viscosity of amylose-DMSO solutions in such a manner as to suggest a strong interaction between DMSO and I-120.Many binary liquid systeins exhibit non-linear viscosity isotherms which pass through a minimum. However, a smaller group possess a maximum, indicating some form of liquid-liquid interaction, and the DMSO-H20 system was found to belong to this latter class.Viscosities and densities of 14 mixtures have been ~neasured a t 2s0, 45', and 65' C while refractive indices and heats of mixing have been deterinined a t 25' C. EXPERIMENTAL SolventsDNISO, supplied by Crown Zellerbach Corporation, was carefully dried by refluxing for 24 hours over CaO. I t was left in contact with this drying agent for about 10 days with occasioilal shaking and then fractionally distilled under reduced pressure. The middle fraction, with boiling point approximately 68' C a t 6-7 inm pressure, was collected and used in all physical measurements. The purity of this fraction was determined by analysis for water using two independent methods.LeBel and Goring (I) have suggested a method using infrared spectroscopy in which the height of the 01-1 absorption peak a t 3500 cm-I is measured and can be related to the water concentration in the sample. The method was calibrated using mixtures up to 0.5Y0 water but no peak was detected in the distilled DMSO used in this investigation.Analysis for water by the Karl Fischer (2) technique indicated that there was less than 0.0170 water present in the DMSO. ViscosityThe viscometer used was a Cannon-Ubbelohde inodel designed to have negligible

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Various fluorescence techniques and cloud point measurements have been used to study the effects of altering the hydrophilic/hydrophobic balance in a series of N-isopropylacrylamide (NIPAM)/N,N-dimethylacrylamide (DMAC) statistical copolymers upon the smart thermal responses of these systems in dilute aqueous solution. As expected, incorporation of DMAC into the polymer structure raises its lower critical solution temperature to an extent dependent upon DMAC content. However, use of such a hydrophilic modifier reduces the magnitude of the collapse transition that characterizes the macromolecule's thermal response. In PNIPAM, the LCST is associated with a conformational transition between a coil and a globule. However, introduction of DMAC derivatives into the polymer expands its “globular” form into a much more open structure that progressively loses its capacity for solubilization of organic guests. Consequently, although copolymerization with more polar monomers can be used to raise the LCST of NIPAM-based thermoresponsive polymers, the value of this approach will be limited in applications requiring switchable carrier/release properties.