Ha, D. T. H., H. Linh, and L. V. Tuyen. ‚ÄúSynthesis of Pour Point Depressant Additives for Production and Transportation of High-Paraffin Bach Ho Crude Oil Based on Ester of Poly-Triethanolamine‚ÄĚ. Petrovietnam Journal, Vol. 5, May 2013, pp. 26-35, http://www.pvj.vn/index.php/TCDK/article/view/662.