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The isothermal crystallization kinetics and morphology of the melt-crystallized optically active polyenantiomers, their blends, and the stereoblock form of poly(epichlorohydrin) have been investigated using polarized light video microscopy. The optically active polyenantiomers develop regularly banded spherulites, while the equimolar blend and the stereoblock polymer form nonbanded, coarser spherulites. The apparent morphological differences among the polymers suggest a stereospecific segregation at the growth front in an attempt to produce optically pure lamellae. The equilibrium melting temperature as determined by the classical Hoffman-Weeks method was found to be 411 ± 1 K for all of the polymers. Over the range of crystallization temperatures from the Tt (247 K) to Tm°, the spherulite radial growth rates of the 50:50 blend of the polyenantiomers are depressed relative to those of either of the optically pure components. A further marked reduction in growth rates is recorded for the stereoblock polymer. An analysis of the linear spherulite radial growth rates in terms of the Hoffman-Lauritzen treatment gave evidence of the development of larger folds, hence a rougher lamellar surface in the stereoblock poisoner than in the polyenantiomers.

b S Supporting Information P olymer-related content is increasingly being added to the undergraduate chemistry program curriculum in many departments. An experiment has successfully been incorporated into the undergraduate physical chemistry lab in which the phase transition of linear chain polymers from the disordered melt to the ordered, semicrystalline solid is examined. Low molecular weight poly(ethylene glycol) (PEG) crystallizes at room temperature forming spherical crystals called spherulites. The spherulites can grow large enough under the right conditions to be visible with the naked eye if a thin film of melted polymer is left to solidify on a glass surface. Sandwiching a film of melted polymer between standard, glass microscope slides, however, forces the solid into disc-shaped spherulites. The radii of the spherulites increase linearly with time if the sample is kept isothermal.This polymer crystallization experiment can be performed successfully using a polarized-light optical microscope equipped with a digital or video camera. (This is a standard piece of teaching equipment in most undergraduate geology departments and it may be feasible to borrow the equipment for the lab period.) Students measure the radial growth rates of disc-like crystals of polyethylene glycol and the results can be interpreted in terms of existing models of polymer crystallization kinetics. The experiment can be performed with or without the use of a temperature-controlled microscope hot stage, and both options are described with students' results. The experiment provides an opportunity to demonstrate and discuss the concepts of (i) nonequilibrium, kinetically controlled phase transitions; (ii) crystal growth; (iii) molecular weight effects on polymer crystallization; (iv) general polymer materials properties and applications; and (v) polarized light and birefringence. The experiment might also be adapted for use in a graduate-level course.At least two articles in this Journal describe polymer crystallization from the melt state and both contain an in-depth treatment of the background theory including the origin of the birefringence in the polymer spherulites. 1,2 Those articles are recommended reading for the instructor. A brief background theory describing the structural hierarchy within the spherulite crystals and the equations used to describe their kinetics of crystallization, with references, is contained in the Supporting Information. This material is presented to students in the form of a reading assignment prior to the lab and a discussion is held on the subject as part of a prelab lecture and demonstration. ' EXPERIMENTAL PROCEDURE EquipmentStandard microscope glass slides and glass coverslips are used to prepare the sample. A hot plate with surface temperature of 65°C is used to melt the PEG samples. As the temperature is relatively low, a simple beverage warmer plate (Radio Shack, Coffee/Beverage Warmer, model #61À8371) is used. A polarized-light microscope (Nikon Optiphot) is used to view the crystallization even...

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