Study On Emulsifier-free Emulsion Polymerization With Reversible Addition-Fragmentation Chain Transfer (RAFT) Process

In this thesis, reversible addition-fragmentation chain transfer(RAFT) agent benzyl dithiobenzoate (BDB) was synthesized and the structure of the aim product was analyzed by IR spectrum as well as 1H-NMR. The preparation route and purification process for BDB were also studied in detail. The aim product BDB was purified by a column chromatography packed with silica, using petroleum ether as an eluant.The bulk copolymerization of styrene and acrylic acid was carried out in the presence of RAFT agent BDB for the preparation of oligomers having function of self-emulsification. The result shows that the polymerization with RAFT agent is a first order reaction to monomer. The molecular weight of co-polymer prepared with BDB shows linear relationship with the conversion of monomer, which is characteristics of a living radical polymerization. When the amount of AA in the total monomer of bulk system is 15%, and the monomer conversion in copolymerization is between 40% and 65%, the oligomers mixed with styrene monomer can be self-emulsified easily and the emulsifier-free emulsion system formed is very stable.Preparation route for the emulsifier-free emulsion system was studied. It order to keep the emulsifier-free emulsion system stable, triethylamine was needed to neutralize carboxylic acid at a degree of 80%~100%. It will be an availability to emulsify oligomers when acetone is used. The emulsifier-free emulsion polymerization rate is fast and the system is stable, when the polymerization is carried out at 75℃. For all polymerizations, the number-average molecular weight of polymers increases linearly with the increase of conversion, which is consistent with the behavior of a living reaction system. Compared with theoretical calculations, the number-average molecular weight of polymers shows a higher value. The molecular weight distribution becomes broader with increasing conversion of monomer. With the increase of the ratio of BDB to AIBN and the concentration of BDB, the reaction rate decreases, the molecular weight for polymer with similar monomer conversion during the emulsion polymerization becomes smaller, and the molecular weight distribution will also be narrower. The diameter of the latex ranges from 250nm to 300nm and the index of diameter distribution is 1.335.