Cationic Ring-Opening Photopolymerization of Long-Chain Epoxides in the Rotator Phase: Confirmation, Mechanism, and Combination

Rotator-phase photopolymerization has been developed
in the field
of free-radical addition polymerization since the photopolymerization
in the rotator phase was first proposed, and other mechanisms urgently
need to be extended. Herein, four long-chain glycidyl ethers were
synthesized, and their polymorphic behavior was studied by differential
scanning calorimetry and X-ray diffraction. Among all, the octadecyl
glycidyl ether (OGE) and the hexadecyl glycidyl ether (HGE) are proven
existing rotator phases. The cationic ring-opening photopolymerization
of the OGE in the rotator phase was achieved, and the highest conversion
reached 68.6% at 30 °C, which is even higher than that of liquid-state
photopolymerization at adjacent higher temperatures (27.2% at 40 °C).
The mechanism was discussed and explained with the aid of a molecular
dynamic simulation. In order to further develop the cationic ring-opening
photopolymerization in rotator phases at relatively low temperatures,
three types of long-chain compounds were chosen to separately blend
with the OGE to construct binary systems. The conversion of the OGE
at 20 °C (17% in the pure OGE system) could be obviously improved
in all binary systems, and the maximum conversion could reach 56%.
Subsequently, the interactions of different long-chain compounds on
the OGE and the effect on polymerization behavior are both discussed.