乙醇/水介质中丙烯酰胺的分散聚合动力学

Kinetics of Dispersion Polymerization of Acrylamide in Ethanol/Water Media

以聚乙烯吡咯烷酮(PVP)为稳定剂,亚硫酸氢钠和过硫酸铵为引发剂(I),丙烯酰胺(AM)为单体,在体积分数为90%的乙醇水溶液中,采用分散聚合方法合成了聚丙烯酰胺(PAM)双水相乳液。考察了聚合反应温度、引发剂质量分数、单体质量分数、PVP质量分数对分散聚合转化率、聚合速率、聚合物分子量和乳液稳定性等性质的影响。结果表明,AM质量分数从10%提高至25%时,初始聚合速率、最终转化率及聚合物相对分子质量增大,其中初始聚合速率增大约20倍。但单体质量分数不可过高,否则会因体系粘度过大而形成凝胶。PVP质量分数增大,初始聚合速率及最终转化率变小,但PVP质量分数过大和过小均不利于双水相乳液的稳定。随着温度的升高,聚合速率显著增加,而聚合物相对分子质量从20℃时的5.08×105降至70℃时的0.39×105。引发剂的质量分数从0.05%增加至0.15%时,单体AM转化率增大,而聚合物PAM的相对分子质量则从4.31×105降至3.73×105。当引发剂质量分数为0.05%时,反应存在20～25 min的诱导期,导致最大聚合速率推后60 min左右出现。AM、引发剂和稳定剂的质量分数分别为15%、0.05%和6%时,在30℃下反应6 h所得乳液的粒径范围为10～75μm,平均粒径为21.94μm。粒径较大且分布较宽,乳液稳定性较差。转化率50%时分散聚合速率与各组分质量浓度的关系为:rp=kρ0I.33ρ0A.M84ρP-V2P.56,聚合反应表观活化能为40.95 kJ/mol。

Double water-phase polyacylamide（PAM） emulsion has been synthesized by dispersion polymerization of acrylamide（AM） in ethanol/water（90% volume fraction of ethanol） media with poly（vinyl pyrrolidone）（PVP） as the stabilizer,sodium bisulfite and ammonium persulfate as the initiator（I）.Influences of polymerization temperature,mass fraction of initiator,AM and stabilizer on monomer conversion,reaction rate,polymer relative molecular mass and emulsion stability have been investigated.The results showed that as the AM mass fraction increased from 10% to 25%,the initial polymerization rate,final conversion of AM,and polymer relative molecular mass also increased.Among them,the initial polymerization rate was increased by 20 times.However,the use of too high monomer mass fraction could cause gelation because of high viscosity and fast reaction rate.With increasing the stabilizer PVP mass fraction,the initial reaction rate and the final conversion of AM decreased,and it was unsuitable for the double water-phase emulsion stability when the mass fraction of PVP was either too high or too low.Increase of the polymerization temperature resulted in a significant increase of reaction rate and decrease of polymer relative molecular mass from 5.08×105 at 20 ℃ to 0.39×105 at 70 ℃.The monomer conversion increased and polymer relative molecular mass decreased from 4.31×105 to 3.73×105 as the initiator mass fraction was increased from 0.05% to 0.15%.The induction period appeared within about 20~25 min and the maximum rate was postponed until 60 min as the initiator mass fraction was 0.05%.A double water-phase PAM emulsion with the particle size distribution of 10~75 μm and average particle size of 21.94 μm was synthesized at 30 ℃ in 6 h when mass fraction of AM,initiator and PVP was 15%,0.05% and 6%,respectively.The emulsion had poor stability because of its broad particle size distribution and large particle size.The relationship of polymerization rate at AM conversion 50% with the mass concentrations of the initiator,AM and stabilizer is as follows：rp=kρ0.33Iρ0.84AMρ-2.56PVP.The apparent activation energy of the dispersion polymerization is 40.95 kJ/mol.