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

Abstract

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 pK a 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.

Evidence of gel effect and living free radicals in particles: Soap‐free emulsion polymerization of styrene by using 2,2'‐azobis(isobutyronitrile)

“…58 A proper description of a microdroplet is a tiny region where the quantity of monomer is dominant relative to the solvent, rather solely a microsphere of pure monomer. For example, in the precipitation/dispersion polymerization, [59][60][61][62][63][64][65][66] the microdroplets form due to the changes of thermodynamic properties, thus the lyophilic monomer molecules cannot completely phase separated from the solvent. Based on forced diffusion, microdroplet nucleation and microdroplet transportation are the natural consequences.…”