SOLID-STATE POLYMERIZATION OF LONG-CHAIN VINYL COMPOUNDS .2. EFFECT OF MOLECULAR ARRANGEMENT ON POLYMERIZABILITY OF OCTADECYL ACRYLATE

In the reported experiments, to clarify the effect of a molecular arrangement of long-chain monomers on polymerizability, gamma -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 alpha -form is stable in the range of 19-32 degree C (mp) and at lower temperatures the beta -form is stable, whereas the sub- alpha -form appears transiently in alpha yields beta transition. The monomer molecules in triclinic packing ( beta -form) show little tendency to polymerize, whereas those in hexagonal packing ( alpha -form) have high polymerizability that increases with temperature. It is concluded that the hexagonal packing of monomer molecules with particular orientation in the layered structure and rotational freedom around the molecular 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.