part of the price rise is due to US propane exports, which have been and will continue to increase. This year EPD added 7.5 m B/mo export capacity, and will likely add more. Targa just ramped up to 3 m B/mo export capacity in october, and plans to add 2 m B/mo more capacity by 3Q14. Other projects include new pipelines (oneok's Sterling line as an example) shipping NGL's to the gulf coast for export. RBC energy estimates propane exports will reach 15 m B/mo by 2018
fortunately, propylene exports have also been rising
the huge corn crop, harvested late due to weather -and in need of post harvest drying- contributed to recent demand for propane; the demand from corn farmers has now abated but the home-heating seasonal demand for propane is likely to keep price high through winter
eia lists propane prices which have jumped to $1.30/ ga last week (up from ~1.17 end of nov, and 1.10/ga week of oct 9) , but where do you find propylene prices- I can only find occasional mentions (like Platt said yesterday the dec delivery price of polymer grade propylene 73.5 cents/lb - highest since feb '13- up from the 67.5 c/lb that isis cited oct 9) with expectation of 5 c/lb increase in spot price in jan.
seems like proplyene price is NOT outpacing propane, at least from the limited data I mention above