Volume changes for thermally induced transitions of block copolymers of propylene oxide and ethylene oxide in aqueous solution as model systems for hydrophobic interaction

Abstract

The expansibility of a nonionic water soluble polymer, a propylene oxide-ethylene oxide copolymer, in aqueous solution, was measured as a function of temperature between 2 and 80 °C. Volume changes were measured, with a dilatometer of novel design, to an accuracy of 0.1 pL. Values for the apparent molar volume, , and apparent molar expansibility, , of the polymer were obtained. A sharp transition with change in apparent molar volume was found to occur, indicating cooperativity. The value of this change increased with increasing propylene to ethylene ratio, at constant molar mass of the polymer. Typical values obtained for the increment in apparent molar volume and expansibility, per mole of monomer residue, were = 0.60 X 10"6 m3 mol"1, = 0.11 X 10"6 m3 mol"1 K"1, at propylene to ethylene ratio of 0.29:1, and = 3.82 X 10"6 m3 mol"1, = 0.42 X 10"6 m3 mol"1 K"1, at a propylene to ethylene ratio of 6.78:1. The increase in transition volume with increase in propylene to ethylene ratio was also associated with a decrease in the cloud point, which indicated an increase in hydrophobic interaction.

Temperature Study of Sound Velocity and Volume-Related Specific Thermodynamic Properties of Aqueous Solutions of Poly(ethylene oxide)–Poly(propylene oxide) –Poly (ethylene oxide) Triblock Copolymers

“…because of self-aggregation, as shown from results using The apparent specific volumes were calculated from denother techniques (7)(8)(9)(10)(11)(12). sity measurements using the following relation:…”

“…the above copolymers have the same POP/POE mass ratio but different relative molar masses and absolute POP con-The sharpness of the change in apparent specific expansibility is considered to indicate processes that are highly coopertent, e.g., 950, 1750, 2250, and 3250 amu for POP in F38, F68, F88, and F108, respectively. The results obtained in ative (12).…”

Volumes of aqueous block copolymers based on poly(propylene oxides) and poly(ethylene oxides) in a large temperature range: A quantitative description

“…As far we know, the first contributions were given by Williams et al [30] and Armstrong et al [18] who determined volumes of some EO a PO b EO a , at fixed composition, over a large temperature domain (ca. 275 K to 350 K).…”

“…This is not a general rule since a negative change of the heat capacity is obtained for these copolymers [27,29,32,33,35] in agreement with the hydrophobic desolvation which accompanies the micelles formation [37][38][39]. Scarce are the investigations of the thermodynamic properties (enthalpy [17,18], density [18][19][20][21][22][23]26,27,30], compressibility [20,21,26], expansibility [30] and heat capacity [26,27,29]) obtained from direct measurements. Most all of them are available at a few copolymer compositions in a very broad range of temperature and are generally analyzed from a qualitative view-point in spite insights at molecular level are evidenced by applying chemical models to the observed trends.…”

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants

“…The variation of their molecular characteristics (PPO/PEO ratio, molecular weight) allows these macromolecules to have optimum properties that meet specific requirements in different areas. Various techniques such as light scattering [5,6], fluorescence spectroscopy [7,8], nuclear magnetic resonance (NMR) [9], specific volume [10,11], and SANS [12,13] have frequently been used to gain new insight into the aggregation behavior of these systems. The results of these investigations clearly show that at low polymer concentration and low temperature, TBP dissolves in water as monomers.…”