从聚合物分子量及聚合动力学参数计算链转移常数

CALCULATION OF CHAIN TRANSFER CONSTANTS FROM THE MOLECULAR WEIGHTS OF POLYMERS AND THE KINETIC PARAMETERS OF POLYMERIZATION

在研究自由基聚合反应动力学时,将单体浓度、引发剂浓度和溶剂浓度之间的摩尔比相对固定,并使之同步改变,由此获得一系列的R_p值。从时间—聚合转化率关系各直线部分截取转化率低于0.10质量分数、相对偏差小于±0.010质量分数的聚合物,测定它们的数均相对分子质量,于是关系式: 1/ _n=R_t/R_p+∑R_(tr)/R_p被简化为1/ =R_t/R_p+K链终止方式可从附表中判定。从1/ =k_1/K_p^2·R_p/c^2(M)+K(双基终止),1/ =k'_1/K_p·1/c(M)+K(单基终止)、或1/ =1/2·fk_dk_(prt)/(K_1·K_2)·c(I)/c^2(M)+K(初级自由基终止)计算出k_t/k_p^2·k_1'/k_p或1/2·fk_dk_(prt)/(k_1·k_p)值,并在各给定的实验条件下得C_1、C_s和C_M值。本文详细地阐述了1/ =K和1/ ≠K条件下计箅C_I、C_s和C_M值的实例。并由此佔价链转移反应机理。

In present paper, a simple experimental design using to calculate the chain transfer constants was introduced. In a study on the relation between the reaction time and the polymer conversion concerning the kinetics radical polymerization, the initial concentrations of monomer, initiator, and solvent were made in a fixed molar ratio and varied simultaneously, a series of values of polymerization rate (R_p) may be obtained. The polymer samples were selected with the same conversion level (±0.5％) and less than 10％ on yield from the R_p straight lines. From which the number average molecular weights were determined, the equation 1/ _a=R_1/R_p+∑R_(tr)/R_p is thus simplified to 1/ _n=R_t/R_p+K.If the chain radicals terminated by bimolecular reaction, the equation 1/ _2=(k_1/k_p^2)·(R_p/c^2(M))+K is derived, the value k_t/k_p^2 may be calculated and the chain transfer constants C_I,C_S and C_(M ) thus be evaluated, respectively, under each series of experimental condition. Some examples with regard to the calculation of chain transfer constants and the evaluation of chain transfer mechanism have been discussed.