Ethylene, propylene, and styrene oxides have been polymerized by a range of metal halide catalysts, high molecular weight products being obtained from the two firstnamed. The limited quantitative evidence presented is consistent with the view that these polymerizations proceed by a coordinate propagation mechanism. The effective catalyst for this stage is essentially a metal alkoxide, formed in an initial cationic polymerization in which a small number of monomer units are attached to the metal atom. The propylene oxide polymers generally contain a fraction of crystalline material, but the proportion of this can be reduced practically to zero (with FeCl3 catalysis) by careful exclusion of water.
Specific volumes of crystalline polyethylenes precipitated from dilute solutions in tetralin have been determined by adjusting the density of the suspending medium to the point of null sedimentation under centrifugation. The densities of particles within a given sample are remarkably uniform, and degrees of crystallinity calculated from the density approximate 80 % for various conditions of preparation. The model of a regularly folded, or pleated, array is irreconciliable with so large a fraction of amorphous material. It is postulated that the amorphous material exists as layers on the (001) surfaces of the single crystal platelets, and consists of chain loops averaging about 20 carbon atoms in length connecting pairs of crystalline sequences running through the crystallite. The connecting crystalline sequences are not necessarily in juxtaposition within the growth plane.The dissolution temperature T, at which a finely divided crystalline sample dissolves in the solvent is an accurately determinable index of the stability of the crystalline phase. For single crystals Ts = 96°C in tetralin, which is substantially lower than T, = 110°C for meltcrystallized samples. The difference is attributed largely to the much smaller dimensions of the single crystals in the c-axis direction. The Ts for single crystals may be increased several degrees by digestion in tetralin at temperatures approaching T, ; annealing in the dry state raises T, to the value for meltcrystallized specimens. Platelets are presumed to be converted by annealing to the morphology characteristic of crystallization from the melt. The interfacial free energy calculated from the Ts for single crystals and their thickness is 70 ergs cm-2, or 1900 cal mole-1 of chains emerging from the (001) face of the crystal platelet.The disparity between T, values for melt-and solution-crystallized specimens diminishes with increase in the solution concentration. It remains significant, however, up to concentrations of 50 %. This is a serious source of error, hitherto unrecognized, in studies of polymer solubility or crystal-solution equilibrium.
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