Roles of Proton in the Formation of Microspheres: Precipitation Polymerization of Styrene in Alcohols by Using AIBN as Initiator

摘要

In this paper, the alcoholization of lyophobic monomer similar to the hydration was introduced into the mechanism of polystyrene microspheres formation in alcohols. Entropic charges emerged on the surface of alcoholization shell due to the order structure of alcohol molecules. Such an electricnegative atmosphere attracted protons and cations which finally destroyed the alcoholization shell to release the lyophobic monomer. It was considered as the decisive factor on the stability of monomer mini-droplets and the microspheres. Large number of protons favored the phase-separation of monomer-solvent and the stabilization of microspheres, but unfavored the stability of mini-droplets. The precipitation polymerization of styrene was carried out in alcohols of EG, MeOH, EtOH and IPA by using AIBN. It was observed that pKa of alcohol significantly impacted the microspheres formation. Microspheres were prepared in EG and MeOH, but not in EtOH and IPA. According to the proposition of entropic charges, MAA, HAc, NaOH and KOH were employed to adjust the concentration of protons in EtOH and IPA. Consequentially, the microspheres were obtained by adding HAc, NaOH and KOH in EtOH and IPA. Effects of NaOH/KOH on the molecular weight of PSt and the size of microspheres were also investigated in EtOH and IPA. Microspheres of 0.93 and 1.11 μm were prepared with 15 wt% St and 0.1154 mol/L NaOH in EtOH and IPA, respectively, but not obtained with KOH.