Studies On Inorganic Rate-accelerating Additives Of Atom Transfer Radical Polymerization Of Styrene

Atom Transfer Radical Polymerization is one of the living free radical polymerization techniques. Advantages of the ATRP technique are numerous: catalytic amounts of transition metal complexs are used; many initiators are commercially available, including multifuctional and hybrid systems; a large range of monomers can be polymerized. This technique is driven by the desire to prepare advanced materials with new physical and mechanical properties combined with the realization that control of macromolecular architecture can lead to these property improvements. Nevertheless, relative high reaction temperature and slow rate of polymerization inhibits its prevailing application in industry. A definite need for the development of simple rate accelerating additives therefore exits. The main purpose of this paper is to explore a variety of inorganic rate-accelerating additives of ATRP of styrene.Firstly, ATRP of styrene was investigated in the presence of boric oxide (BO). BO was found to be effective to accelerate ATRP of styrene and conversions were improved to 78.5% in 6h at 85℃. An optimal molar ratio of BO/EBP for the polymerization of styrene was 4:1. First-order kinetics, increase of BO with respect to conversion, and the relatively narrow polydispersity demonstrated that polymerization of styrene in the presence of BO proceeded in a living fashion. The apparent rate constant of polymerization was improved by a factor of 1.82,1.54 and 1.5 at 65,75 and 85℃respectively. The preliminary mechanism for rate enhancement of BO was proposed basing on ~1HNMR method and uv-vis spectrum of mixtures of BO, ligand, and copper salts. The possible mechanism was that interreaction between BO, ligand, and copper salts weakened the coordination of copper salts and ligand resulting in facilitating the transfer process of bromine atom, then improving the rate of ATRP of styrene.Borax was another additive that had rate-accelerating effect on ATRP of styrene we have seen. The results showed that borax was able to enhance the polymerization. The optimum ratio of borax to initiator was 2:1. The conversion of styrene reached 69.1% in 6 hours at 85℃in the presence of borax, while that of typical ATRP of styrene in the similar condition was 56.9%. First-order kinetics, the molecular weight that increased linerly with conversion, and the value of PDI about 1.25 demonstrated that this system was a controlled/living free radical polymerization. The rate constants were improved with a multiple of 1.48, 1.60 and 1.64 at 65℃, 75℃and 85℃respectively. The possible mechanism of borax was similar with that of BO. The interreaction between borax, ligand, and catalyst weakened the coordination of catalyst and ligand resulting in facilitating the transfer process of bromine atom.Zinc hydroxide as a promoter was used in ATRP of styrene to promote the polymerization. Zinc hydroxide was found to enhance polymerization rate, and conversions was 68.3 at 85℃for 6 hours. Excellent controllability was obtained with the indication of first order kinetical curves, linear increased of Mn with conversion, and well-defined polymer with narrow distribution (PDI=1.26). The acceleration mechanism of Zinc hydroxide was hypothesized that the medium , resulted from the reaction between Zinc hydroxide and catalyse system(CuBr/PMDETA), interacted with Br, accelerating the exchang of Br. It is worthy of studying the detailed mechanism in the future.NMR study indicated that no influence occurred on structure of polystyrene when the three kinds of inorganic compounds were added as promoter. However, the fact that the real molar mass was less than the theoretical one could be assigned to some unknown bypass reaction making the suppression of molar mass.These inorganic promoters are beneficial to improve the slow polymerization rate of ATRP of styrene and promote its industrial application.In the last section, four inorganic additives, Zinc chloride, Sodium metaborate, Carbonic acid monosodium salt and Potassium fluoborate were researched as promoter for ATRP of styrene. The results showed that only Carbonic acid monosodium salt could promote the ATRP of styrene, and got a controlled molecular weight and narrow polydispersity polystyrene. And the optimum ratio of Carbonic acid monosodium salt, kinetical behavior and the enhancing mechanism need to be further studied.