聚偏氟乙烯/聚4-乙烯基吡啶Janus粒子的制备

Preparation of Poly(vinylidene fluoride)/Poly(4-vinyl pyridine) Janus Particles

用聚偏氟乙烯(PVDF)乳胶粒子作为种子,4-乙烯基吡啶(4VP)作为功能性单体,通过无皂种子乳液聚合的方法,制备了具有雪人形结构的不对称复合粒子,重点考察了氨水加入量对产物粒子形态的影响.采用动态光散射法测定了复合粒子的平均粒径及粒径分布,利用扫描电镜表征了复合粒子的微观形貌,通过红外光谱分析验证了复合粒子的化学组成,借助示差扫描量热仪研究了复合粒子中PVDF的结晶行为.在该体系中,引入适量的氨水对于控制体系的稳定性以及生成的复合粒子结构的均匀性起到了至关重要的作用,这是由于氨水的加入抑制了4-乙烯基吡啶在水相聚合时的成核和凝聚.最终获得了一端为PVDF半球,另一端为带有吡啶基团的P4VP雪人形粒子,其具备反应活性位点.

Snowman-like Janus particles of PVDF/P4 VP were prepared via a soap-free seeded emulsion polymerization using poly（vinylidene fluoride）（PVDF） latex particles as seeds and 4-vinyl pyridine（4 VP） as functional monomer. All seeded emulsion polymerization was carried out in a four-necked round-bottom flask of 100 mL capacity. First, dialyzed PVDF latex（4.0 g） with a solid content of 12.5 wt% was dispersed in deionized water（40.0 g）, and the dispersion was further ultrasonicated for 40 min to avoid any particle agglomeration. The flask was placed in a water bath preset at 30 oC and nitrogen-purged for 15 min to remove O_2 before additions of ammonia solution（1.0 g） and 4 VP（0.5 g）. Nitrogen-purge was maintained during the entire reaction process. The mixture was stirred at 250 r/min for 1 h to allow the monomers to swell the PVDF seed particles, followed by heating to 60 oC. Subsequently, 1.5 mg of K_2S_2O_8 were added to trigger the polymerization, and the reaction lasted for 4 h. The average particle diameter and particle size distribution（PDI） of the composite particles were determined by dynamic light scattering. The micromorphology of the composite particles was characterized by scanning electron microscopy. The chemical composition of the composite particles was confirmed by Fourier transform infrared spectroscopy. The confined crystallization of PVDF in the composite particles was studied by differential scanning calorimetry. In this study, the introduction of an appropriate amount of ammonia solution into the polymerization system played a vital role in maitaining the stability of the reaction system and the uniformity of the composite particles, possibly due to the prevention of P4 VP nucleation in the aqueous phase. One side of the compsite particles obtained was PVDF and the other side was P4 VP with pyridine groups, which could be used for further modification and assembly.