聚甲基丙烯酸甲酯/聚(异戊二烯-co-苯乙烯)核壳纳米乳液的合成与直接氢化方法的研究

利用可控微乳液法合成粒径19~200 nm,且呈球状分布均匀的聚甲基丙烯酸甲酯/聚(异戊二烯-co-苯乙烯)(PMMA/PIS)核壳纳米粒子,通过水合肼产生原位氢的技术,对合成的PMMA/PIS乳液体系进行直接常压氢化,对影响氢化度的因素、聚合物氢化前后结构、热性能进行了研究.结果显示,聚合物粒径、水合肼及双氧水用量等都是影响聚合物的氢化度的因素.研究发现,氢化以PMMA为核,PIS为壳的核壳结构乳液可以显著提高PIS氢化程度,减少氢化过程中凝胶产生.利用FTIR、~1H-NMR、Na_2S_2O_3滴定法测定了乳液的氢化度.结果表明,当聚合物粒径小于200 nm时,乳液氢化度可达到95%以上,且无凝胶现象产生.GPC结果证明了反应是氢化而非凝胶过程.利用TEM、DLS测试了氢化后乳液的核壳结构和粒径.实验结果显示,PMMA/HPIS为核壳纳米结构.TGA结果显示,当氢化度为98%时,聚合物耐热性提高41°C.

Synthesis and Hydrogenation of Poly(methylmethacrylate)/Poly(isoprene-co-styrene) Core-shell Nanoparticles

The core-shell nanoparticles of poly(methyl methacrylate)/poly(isoprene-co-styrene) (PMMA/PIS) were prepared using a two-stage semi-batch microemulsion polymerization,i.e.,PMMA spherical seeds were synthesized in the first stage and the PIS shells around the seeds were formed in the second stage.The polymer particles with their diameter of 19-200 nm with a narrow distribution were achieved.It was found that there existed an optimal sodium dodecyl sulfate (SDS) amount,potassium persulfate (KPS) amount and an agitate speed,which were,for example,1.0 wt％ of SDS amount,0.10 wt％ of KPS amount and 200 r/min of agitation speed,in order to control the particle sizes of PMMA/PIS core-shell nanoparticles.After the second polymerization stage,a direct hydrogenation process was applied to saturate the residual carbon-carbon double bonds of PIS in the PMMA/PIS nanoparticles synthesized and the hydrogenation was realized by diimide reduction in presence of hydrazine and hydrogen peroxide using boric acid as a promoter without any organic solvent and precious metal catalysts.The effects of particle size,ratios of hydrazine hydrate,and hydrogen peroxide on the hydrogenation degree were investigated in detail.The hydrogenation degree of PMMA/PIS was determined using FTIR,1H-NMR and titration of Na2S2O3.Hydrogenation degree of more than 95％ was achieved and no cross-linking was detected,when the particle size of the latex was less than 200 nm,the molar ratio of hydrogen peroxide to hydrazine was 1.8∶1,the molar ratio of hydrazine to C=C double bonds was 2∶1,the reaction temperature was 50 ℃,and the reaction time was 6 h.Detailed characterizations of the microstructure,the molecular weight and heat resistance of PMMA/PIS and hydrogenated PMMA/PIS were conducted by TEM,GPC and TGA.The TEM results indicated that PMMA/PIS nanoparticles were well structured core-shell nanoparticles,in which PMMA was the core and PIS was the shell as designed.GPC results confirmed the hydrogenation of PMMA/PIS overwhelmed the crosslinking process during hydrogenation operation.The decomposition temperature of the hydrogenated PMMA/PIS was 382 ℃ while that of the parent PMMA/PIS was 341 ℃,which indicated that the heat resistance of the hydrogenated PMMA/PIS was significantly improved.