Dodecafluoroheptyl methacrylate (DFMA)

n-butyl acrylate (BA) and methyl methacrylate (MMA) were copolymerized for preparation of fluorinated latexes through miniemulsion copolymerization without any costabilizer.In this reaction system

extremely hydrophobic DFMA was used as a chemical reagent which made the monomer droplets unimodal distribution.But after a while

the monomer droplets coalescenced together and made the monomer droplet size changing from about 130 nm to 400 nm.The oligomers of poly(dodecafluoroheptyl methacrylate)

containing a lot of —CF2— and —CF3 segments with low surface energy

were generated quickly and it was proved from 1H-NMR spectrum which showed DFMA has a high composition in the earlier copolymer.The oligomers not only with extremely hydrophobic but also oleophobic natural capacity would take the same effect of conventional costabilizer on the miniemulsion polymerization to increase the surface of monomer droplets and decrease the monomer droplets size.The monomer droplet or particle size distribution of the semifinished and the final products was determined using LS-230 Coulter particle size analyzer.As the process of polymerization was going on

the smaller monomer droplets or particles would detach from the larger ones.Simultaneously

the particles did not maintain unimodal distribution after the beginning of polymerization.However

as the process of polymerization was going on

the particle size distribution would return to the unimodal distribution again.Between the processes of polymerization

the particle sizes changed from about 400 nm to 80 nm.On the base of fundamental theory of miniemulsion polymerization

the particle sizes of the latexes with the convensional costabilizer would not change too much.So

the reason is the oligomers

first generated at the process of polymerization

contain a lot of —CF2— and —CF3 segments with low surface energy to make the smaller particles existence stably.There is no differences about the particle size distributions between the final products initiated by potassium persulfate (KPS

water-soluble initiator) and 2

2′-azobisisobutyronitrile (AIBN

oil-soluble initiator).There were too much differences between the two kinds of initiator

the final products of this polymerization would exhibit bimodal distributions

if some crosslinking agents were added into the systems to reduce the activities of oligomer chains.One of the peaks was at about 80 nm

equaling to that one without any crosslinking agent

the other one was at about 400 nm

equaling to that one before polymerization.With the same contents of crosslinking agents

the effect on particle size distribution of the final products was much more initiated by AIBN.Because the polymerization was taken place in the center of the particles initiated by AIBN to generate the oligomers

the crosslinking agents would reduce the movement activity of the oligomer and make the oligomers shift to the surfaces of the particle more difficult.However

the effect on particle size distribution of the final products was less initiated by KPS.Because the polymerization initiated by KPS was taken place at the inside surface of the particle

as well as the generated oligomers

the movement of the oligomer was not necessary.On the base of the experimental results

the mechanism of miniemulsion polymerization with in situ formed costabilizer was presented.