To clarify the effect of a molecular arrangement of long‐chain monomers on polymerizability, γ‐ray‐initiated postpolymerization of polymorphic crystals of octadecyl acrylate and the melt has been investigated. According to thermal, x‐ray, and infrared (IR) analyses octadecyl acrylate exhibit three crystalline modifications similar to, but different in transition behavior from, those of octadecyl methacrylate. The α‐form is stable in the range of 19–32°C (mp) and at lower temperatures the β‐form is stable, whereas the sub‐α‐form appears transiently in α → β transition. The monomer molecules in triclinic packing (α‐form) show little tendency to polymerize, whereas those in hexagonal packing (β‐form) have high polymerizability that increases with temperature. The polymerizability in the molten state at fairly high temperatures is rather low, however. Thus the polymerization rate, saturated conversion, and polymer molecular weight exhibit maxima just above the melting point of α‐form. It is concluded that the hexagonal packing of monomer molecules with particular orientation in the layered structure and rotational freedom around the molecular axis, together with some conformational freedom of functional group, is favorable to the polymerization reaction. In addition, the mechanism of polymerization in the layered structure is discussed, assuming a cone‐type distribution for the polymerization probability.

The tetragonal-to-cubic structural phase transition in pollucite (CsAlSi 2 O 6 ) was investigated using low-temperature X-ray powder diffraction in the temperature range of 93 to 298 K, and the lattice constants were refined with Rietveld analysis. It was found that CsAlSi 2 O 6 had a tetragonal phase with a space group of I4 1 /acd in the temperature range of 93 to 248 K, a = 1.36337(4) nm, c = 1.36988(6) nm at 248 K, and underwent a phase transition from tetragonal to cubic with a space group of Ia-3d in the temperature range of 248 to 273 K, a = 1.36645(3) nm at 273 K.

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