Industrial methods for producing carbonyl dichloride consist of a two step process with reactors that are connected in series, an exact fine tuning of the reaction parameters and with a high degree of consistency with regard to reaction conditions. An error module determines a pressure error based on a difference between the target pressure and a pressure measured using a pressure sensor. The novel polymerisate is also useful as a dispersant in a pigment dispersion containing dispersible inorganic or organic pigment particles. Finally a gate electrode and a sourcedrain of the low temperature polysilicon thin film transistor are formed.