THE CRITICAL PROPERTIES OF THERMALLY UNSTABLE SUBSTANCES - MEASUREMENT METHODS, SOME RESULTS AND CORRELATIONS

Methods of experimental determination of critical constants of thermal ly unstable substances are treated, namely, the sealed ampoule (tube) method, the flow method, and the method of pulsed heating of probe. Re sults are given of measurement of the critical properties of n-alkanes , individual and industrial siloxanes, polyethylene glycols, glycerine , hydrogen peroxide. Results of computer simulation of the critical co nstants of chain molecules are discussed. Various methods of assessmen t of the critical properties of substances, consisting of chain molecu les, by the number n of links in the molecule are treated. The asympto tic behavior of the critical temperature T-c, critical pressure P-c, a nd critical density rho(c) in the limit of long chains is discussed. A conclusion is made that, for n much greater than 1 T-c similar to 1-n (-1/2), p(c) similar to n(-3/2), rho(c) similar to n(-1/2), the critic al temperature of infinitely long chain molecules is finite, and the c ritical pressure and critical density are equal to zero.