KINETICS AND MECHANISM OF PHOTOINDUCED POLYMERIZATION BY α,α-DIMETHOXY-α-PHENYL ACETOPHENONE

α,α-dimethoxy-α-Phenyl acetophenone (DMPA) is an efficient and thermally stable photoinitiator. Here its spectral characteristics in the transient state were shown. The transient species were identified as a benzoyl radical and a dimethoxyi benzyl radical that played a primary initiation role in polymerization. The kinetics and mechanism of the bulk polymerization of MMA were investigated. The exponent of DMPA concentration and k_p/k_1~(1/2) value were found to be 0.5 and 0.066 mol(-1/2)l~(1/2)s~(-1/2), respectively. The existence of oxygen led to obtain the polymer with higher molecular weight, which can be attributed to the occurrence of the subsequent polymerization induced by active polymer end group. In the photocrosslinking reaction, the dependence of DMPA content on initial rate has been found. A principal reason is that the sample contained higher percentage of DMPA has higher light-absorbed efficiency. In solid film, higher concentration of DMPA is permitted to be used because there is little excited state self-quenching effect in the rigid medium.

KINETICS AND MECHANISM OF PHOTOINDUCED POLYMERIZATION BY α,α-DIMETHOXY-α-PHENYL ACETOPHENONE

 α,α-dimethoxy-α-Phenyl acetophenone (DMPA) is an efficient and thermally stable photoinitiator. Here its spectral characteristics in the transient state were shown. The transient species were identified as a benzoyl radical and a dimethoxyi benzyl radical that played a primary initiation role in polymerization. The kinetics and mechanism of the bulk polymerization of MMA were investigated. The exponent of DMPA concentration and k_p/k₁^1/2 value were found to be 0.5 and 0.066 mol(-1/2)l^1/2s^-1/2, respectively.The existence of oxygen led to obtain the polymer with higher molecular weight,which can be attributed to the occurrence of the subsequent polymerization induced by active polymer end group.In the photocrosslinking reaction,the dependence of DMP A content on initial rate has been found.A principal reason is that the sample contained higher percentage of DMPA has higher light-absorbed efficiency.In solid film,higher concentration of DMP A is permitted to be used because there is little excited state self-quenching effect in the rigid medium.