Efficient Capacitance Computation for Three-Dimensional Structures Based on Adaptive Integral Method

The invention provides a novel preparation process of a polycondensation type polymer, an excellent polymer which is represented by lactic acid and the preparation process of the polymer, a polycondensation agent used for the preparation process, and an intermediate. Specifically, the invention provides a preparation process of the polycondensation type polymer, for example, polyamide, polyimide, polythioester and polyester, comprising bonding a carboxyl group comprising compound with an active hydrogen group comprising compound in the presence of haloiminium salt. The invention provides excellent polylactic acid having a controlled D/L-isomer ratio in the repeating structural units and preparation process of polylactic acid, and further provides a haloiminium salt compound used for the preparation process and an intermediate compound of acid chloride.