Polystyrene segmental motions

The dynamic viscoelasticity and the thermal behaviour of films of Thermoelastic 125 cast from solutions in four solvents - toluene (T), carbon tetrachloride (C), ethyl acetate (E), and methyl ethyl ketone (M) — have been studied by Miyamato133 The mechanical loss tangent (tan 8) and the storage modulus E dependences exhibit two transitions at —70 °C and 100 °C which have been attributed to onset of motion of polybutadiene and polystyrene segments, respectively. The heights of the polybutadiene peaks on tan 6 curves decrease in the order C > T > E > M, while for polystyrene the order is reversed C < T < E < M. These phenomena have been related to the magnitude of phase separation of the polystyrene and polybutadiene blocks. 

CHARACTERISTIC TIME OF THE SEGMENTAL MOTION OF POLYSTYRENE IN SOLUTIONS AND MELT... 

On a basis of the Eqs. (54)-(56) it was calculated the activation energies of the segmental motion of polystyrene in diluted, concentrated solutions and melt, which consists of 55.4,49.4 and 133.0 kJ/mole, respectively. 

TABLE 7 Characteristic parameters of segmental motion of polystyrene in solutions and melt. 

Here, V is the volume of the sphere and // is the viscosity of the solvent As can be seen in Table 1.4, the Tj values of proteins such as bovine serum albumin and trypsin in aqueous solution He in the ns range and become larger with increasing molar mass. The proteins were labeled with fluorescent markers such as l-dimethylamino-5-sulfonyl-naphthalene groups (see Chart 1.10) [38], Segmental motions and molecular flexibiUty have been studied for various polymers, such as polystyrene and the Y-shaped immunoglobulins IgA and IgG. Relaxation times in the range of 10-100 ns were found. In these studies, the... 

Molecular motion in polymer solutions can have significant effects on the physical properties of the systems formed from these solutions. For example, the rates of drying polymer films can determine the film properties. We have shown that the drying of a polystyrene film from toluene solutions could be predicted with the knowledge of thermodynamic parameters, plus solvent diffusion data.(i) The ability of polymers to respond to changes in conditions is determined by die ability of the polymer and/or its segments to reorient. Solvent diffusion is also correlated to the segmental motions of the polymer chains.(2) The reason for this correlation appears to be that both molecules are coupled to the same fractional free volume. 

The presence of dissolved CO2 molecules in a polymer results in the plasticization of the amorphous component of the matrix. In this respect CO2 mimics the effect of heat but with the important distinction that the Tg is depressed. The extent of the Tg depression is dependent on the wt% of CO2 in the matrix. As previously mentioned, one of the characteristics of plasticization is the enhancement of segmental motion, which has been observed spectroscopically for the ester groups of PMMA [20] and the phenyl rings of polystyrene [21]. The consequential increase in free volume of the matrix has been studied by methods such as laser dilatometry [22], in situ FTIR spectroscopy [20], high-pressure partition chromatography [23], and inverse gas chromatography [24]. 

In all the above studies, the bulk chain motions are approximated by those of a rigid rotor. The validity of this approximation is underlined by a study of lithium polystyrene carboxylate in micellar form, undertaken by Raby et al [23]. They showed by electron microscopy that the micelles had a uniform diameter of 6.0 nm, and that near to room temperature their librational (segmental) motions were largely frozen, even though the micelles were still moving freely in the acetone solvent. They then converted the NMR determined value of Tr to a dynamic micellar diameter using the Stokes-Einstein equation, and thus obtained a value of 5.7 nm. This is satisfyingly close to the microscopy value. 

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