| 1955 |
Nippon Petrochemicals Co., Ltd. (NPC) was founded as a 100% subsidiary of Nippon Oil Co., Ltd. and launched business related to petrochemicals. |
| 1957 |
Showa Denko K.K. (SDK) started business related to petrochemicals.Facilities for ethylene were completed for NPC and operation started at Kawasaki Complex. |
| 1969 |
Oita Complex was completed for SDK; facilities for polypropylene were completed and operation started in December. |
| 1989 |
Polypropylene facilities for Ukishima Polypro (UPP) were completed at the Complex of NPC. |
| 1993 |
The gas phase polypropylene facilities of SDK were completed in Oita. |
| 1995 |
Japan Polyolefin Co., Ltd.(JPO) was established, and the operations of SDK and NPC were transferred. |
| 1996 |
JPO and Montell (Currently known as LyondellBasell) jointly established Montell-JPO Co., Ltd. (MJC), and polypropylene business for automobiles were transferred to MJC from JPO. |
| 1999 |
Montell SDK Sunrise Ltd. (MSS) was established, and polypropylene business was transferred from JPO. |
| 2000 |
PolyMirae was estsblished in Korea as a joint venture with Daelim. |
| 2001 |
MSS changed its name to SunAllomer Ltd.(SUN) |
| 2002 |
SUN acquired 100% shares in UPP from NPC. |
| 2007 |
UPP transferred its whole business to SUN. |
| 2016 |
SDK and JX Nippon Oil & Energy Corporation acquired all shares of capital stock owned by LyondellBasell. |
| 2023 |
SDK transferred its shares to Resonac Holdings Co. |
| 2025 |
Resonac Holdings Co. transferred its shares to Crasus Chemical Inc. |
