Kinetics of mesophase formation and crystallization in poly(diethylsiloxane)

Abstract

A c d m y of Science of the USSR, Moscow, USSR SynopsisOptical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsi1oxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 pm thick in the temperature range 293-307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular t o the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (It is equal to 1.75 +_ 0.05). which corresponds to t h e two-dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of t h e isotropic melt w a s shown to bc temperature-dependent. This is likely to he connected with a change in the number of nuclei with temperature. T h e crystallization of polymer from t h e mesomorphic state occurs with retention of the optical texture of the .sample. T h e process proceeds not as a sporadic crystallization of individual mesomorphic lamellac but a s a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystalliz. ing lamellae.

Thermotropic Mesophases in Element-Organic Polymers

“…On the contrary, the morphology of PDES and PDPS resembles more the morphology of crystalline polymers 22,35). The colorless transparent PDES melt becomes turbid during the mesophase appearence.…”

“…Information about the kinetics of mesophases formation in polymers is very scarce at present, although it is quite obvious that such a study may throw additional light '0> The isotherm of crystallization at 276 K is also shown 22,35) on the nature of the mesomorphic states. A complex kinetic study of the formation ofmesophase in PDES published recently 35) included the measurements ofthe linear growth rates of the lamella-type mesophase domains and the calorimetric overall kinetics of the mesophase formation.…”

“…A complex kinetic study of the formation ofmesophase in PDES published recently 35) included the measurements ofthe linear growth rates of the lamella-type mesophase domains and the calorimetric overall kinetics of the mesophase formation.…”

“…Photomicrographs of a PDES sampIe in the transmitted light between crossed Nicol prisms (below) and the surface ofthe same sampIe in reflected light (above) at different stages of formation of the mesophase at 305 K35) …”

Kinetics of Nonisothermal Transformations of Thermotropic Hydroxyethyl Cellulose Acetate

“…The value of n is genegally close to 1 from 400 K to 420 K. It has been shown above that the relationship between k(T) and dF(T)/dT is descripted by Equation (6). Then, k ( T ) at any temperature can be calculated from equation above and the half-time of transformation r1,2 can also be obtained from the Equation (7).…”