| A consistent mechanism of heterophase polymerization--Nucleation and Transfer Theory of Nano(Micro)Monomer Droplet(hereinafter referred to as"Nano(Micro)Monomer Droplet Theory")has been postulated by Henmei Ni et al.,covering all the chemical approaches of particle formation such as emulsion polymerization,mini-/microemulsion polymerization,precipitation/dispersion polymerization,etc.The rationality of this theory has been widely demonstrated over the past two decades,but the role of surfactants in the mechanism has not been fully explained.Based on the previous research results of our laboratory and the research results of hydrophobic interaction,water dynamics and micelle structure,in this paper,the protonicity theory of surface entropy charge of a hydrated cage is first proposed,and introduced the hydrophobic interaction and the structure of the hydration layer into the formation mechanism of the polymer Nano(Micro)particles.The theory describes the process of dissolution and precipitation of hydrophobic molecules in water.The dissolution process of hydrophobic molecules is the process in which water molecules interact with each other on their surface to form a hydration cage by hydrogen bonds.The ordered structure of the hydration cage inevitably leads to the relative excess of negative charge on its surface-entropy charge,thus producing affinity for protons.The dynamic nature of entropy charge determines that the number of protons on the surface of the cage varies with the concentration of hydrophobic molecules with non-linear statistical properties.The protons bind to the hydration layer and break the hydrogen bond interactions in the hydration cage.If the number of protons reaches a certain level,the hydration cage is destroyed and the hydrophobic molecules are extruded from the hydrogen bond network of water,resulting in phase separation.Therefore,a large number of protons is beneficial to the phase separation of monomer and water and the stability of polymer microspheres,but not to the stability of monomer mini-droplets.This theory reorients the role of surfactant in heterogeneous polymerization process and solves the world problem that polyvinyl alcohol dissolves in water and polyformaldehyde insoluble in water.In order to verify this theory,the p H of n-hexane and styrene aqueous solutions were determined in this paper.The results showed that the p H was all higher than that of water,which confirmed that hydrophobic molecules trapped free H~+.The results also overturn the long-held hypothesis that hydroxide ions adsorbed on the surfaces of oil droplets and bubbles in water are negatively charged.As an application of the theory in heterogeneous polymerization,this paper used azodiisobutyronitrile(AIBN)and potassium persulfate(KPS)as initiators to conduct soap-free emulsion polymerization of styrene at different p H values.The results show that protons play a key role in the formation of polystyrene(PSt)particles/microspheres.For example,under p H2.0(HAc),p H4.0(HCl)and p H2.0(HCl)conditions,PSt microspheres were not prepared using initiator AIBN.Using initiator KPS,however,microspheres can be obtained regardless of p H.AIBN is insoluble in water,so these results indicate that the short chain PSt with sulfate anion which is polymerized by KPS in water traps protons and plays an important role in the stability of monomer droplets.When the AIBN was used and the p H was 6.8,30%of the short chain PSt with average molecular weight(M_n)of 300-1500 were found in the particles.However,at p H8.0 and p H10.0,these small molecular weight PSt particles disappeared,but PSt with conversion of 17.2%and 32.5%were found in the aqueous phase,respectively.These results indicate that,as expected by the Nano(Micro)monomer droplet theory,the low molecular weight PSt particles are produced by the polymerization of the last remaining monomer.These PSt particles have low molecular weight due to the high concentration of AIBN,which are soluble in water under alkaline conditions and therefore do not appear in the GPC particle molecular weight determination.It fully demonstrates the effect of proton concentration on the solubility of PSt.When using KPS,20%and 30%(conversion)of PSt were dissolved in the aqueous phase at p H2.0(HCl)and p H10.0(NaOH),respectively.However,at p H4.0-8.0,the water-soluble PSt was very small,which indicated the amphoteric properties of PSt.Under the extremely acidic condition of p H2.0(HCl),the benzene ring in the low molecular weight PSt generated in the aqueous phase was protonated and dissolved,while under the extremely alkaline condition of p H10.0(NaOH),the oligomer became soluble because the dissociation of water was severely inhibited.In addition,when AIBN is used,the GPC curve presents a unique flat-roof peak,that is,the weight fraction of each molecular weight is equal,or the higher the molecular weight is,the equal ratio of the number of molecules decreases.For example,the number of molecules with a molecular weight of 10,000 is half that of 5,000.The results confirm the rationality of Nano(Micro)monomer droplet theory.Due to the disturbance of monomer phase/water boundary layer,nano(micro)monomer droplets are generated.The distribution of AIBN in the styrene monomer phase interface layer is less,so the concentration of AIBN in the initial droplets is low,and the generated PSt has a large molecular weight and a small amount.With the consumption of monomers,the concentration of AIBN in the monomer phase increases,and the concentration of AIBN distributed to the interface layer increases.Therefore,when the droplet binds to the particle,part of the monomer in the droplet diffuses into the particle,making the free radical chain in the particle continue to grow,and the remaining monomer is evenly divided by multiple free radicals.The flat-proof peaks in the GPC curve also indicate that the free radicals in the particles are always living.Similar to water,hydrogen bond network also exists in alcohols,so the entropy charge theory can be further applied to alcohols in this paper.However,because there is only one proton in the alcohol molecule,the linear or ring structure can be formed only through hydrogen bond,and the cage structure cannot be formed,combined with the metal ions,the alcohol interaction of the hydrophobic molecules presents a very complicated situation.In the third chapter,the precipitation polymerization of styrene in EG(ethylene glycol),Me OH(methanol),Et OH(ethanol)and IPA(isopropanol),with AIBN as initiator,under the influence of different acids and bases was also studied.The results show that the p Ka of alcohol has a significant effect on the formation of microspheres.Microspheres were successfully prepared in EG and Me OH systems but could not be prepared in Et OH and IPA systems.In addition,MAA,HAc,NaOH and KOH were used to regulate the proton concentration in Et OH and IPA systems.The results showed that PSt microspheres were successfully obtained by adding HAc,NaOH and KOH into Et OH and IPA systems.Meanwhile,the effects of NaOH/KOH on the molecular weight and particle size of PSt microspheres were also investigated.Microspheres diameter of 0.93?m and 1.11?m were prepared by 15wt%St and0.1154 mol/L NaOH in Et OH and IPA systems,respectively,while no microspheres were prepared by KOH under the same conditions. |
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