Study On The Synthesis And Application Of Functional RAFT Agents

"Living"/Controlled free radical polymerization (LRP) combine many advantages of living polymerization and free radical polymerization. LRP technique can realize "living" properties at the same conditions as those of free radical polymerization. Using this technique, it is easy to synthesize polymers with pre-designed structures and controlled molecular weight with narrow molecular weight distribution. There are three main LRP techniques which have been developed in the past decades, e.g. stable free radical polymerization (SFRP), atom transfer radical polymerization (ATRP), and reversible addition- fragmentation chain transfer (RAFT) polymerization. Among them, RAFT polymerization has been proven to be the most versatile one due to its high degree of compatibility with a wide range of functional monomers and mild reaction conditions. Thus, many attentions have being paid on the RAFT polymerization in recent years. Much development has been made in this field since it was reported. However, some problems still existed in RAFT polymerization technique, such as retardation and especially the precise mechanism in early stage of RAFT polymerization. Furthermore, the technique of synthesizing end functional polymers with well defined structures, molecular weight and narrow molecular weight distribution through RAFT polymerization is still under developed. Thus, sufficient investigation on the effect of R and Z groups in the RAFT agent on the RAFT polymerization can present much powerful and ample theoretical proof. As for the problems above, the work in this thesis can be summarized as the following:A series of RAFT agents with different functional groups (biologic, fluorescence and ferrocene) in Z or R groups were synthesized using a simple one step reaction between carboxylic acid and alcohol in the presence of P4S10. Then a series of polymers with function groups in the chain end were prepared with controlled structures and molecular weights. (A) The anthracene or pyrene group had been introduced into polymer chain end. The polymer solution showed characteristic fluorescence emission of anthracene or pyrene ring respectively. It provided an efficient method to synthesize fluorescence labeled polymers. (B) The polymers chain-ended with peppers may be used as bio-materials. (C) The polymer chain-ended with ferrocene group exhibited electrochemistry activity similar as ferrocene. Furthermore, the introduction of ferrocene group into polymer chain improved the glass transition temperature (Tg);The fluorescence properties of the end functional polymers were studied in detail, which provided an effective synthetic way for luminescent polymers. (A) The fluorescence property of polystyrene (PS) obtained from RAFT polymerization of styrene using benzyl anthracene-9-carbodihioate (BAC) (anthracene structure in Z group) and anthracene-9-ylmethyl benzodithioate (AMB) (anthracene structure in R group) as chain transfer agents were characterized in CHCl₃ solution, respectively. The result showed that the fluorescence intensity of AMB-PS was much stronger than that of BAC-PS. (B) The fluorescence emission spectra of the pyrene ring end labeled PS before and after the amine hydrolysis were compared each other. The results showed that dithio ester moiety didn't show obvious effect on the fluorescence property of polymer solution. All of these results confirmed that the quenching effect of sulfur atom. The distance between sulfur atom and chromophore played an important role in the self-quenching effect. (C) The fluorescence of the (naphthalen-1-yl)methyl-2-naphthaledithioate (NMNDT), which was beared with naphthalene groups both in Z and R, and the polymer prepared using NMNDT as RAFT agent were investigated. The results showed the different fluorescence property with naphthalene due to the interaction, congruence of the molecules and formation of inter- or intramolecular exciplex.;A series of dithioesters with different aromatic rings such as naphthally, anthracyl and pyrene in R groups were synthesized. The polymerizations of MMA using these dithioesters as the RAFT agents were investigated. The result showed that the polymerization of MMA using anthracen-9-ylmethyl benzodithioate (AMB) as the RAFT agent could obtain polymer with well controlled molecular weight and narrow polydispersities. The RAFT polymerization of MMA using AMB as the RAFT agent was studied in details. The Ab initio calculation technique was used to explain such experimental results;The retardation effect in RAFT polymerization was investigated. (A) The RAFT polymerization using those chain transfer agent with thiophene in Z group, e.g. benzyl thiophene-2-carbodithioate (BTCT) and benzyl benzodithioate (BBT), showed obvious retardation. The reason was revealed by the Ab initio calculation method. The results showed that the radical mediate derived from BTCT (with thiophene as Z group) was more stable than that from BBT (with benzyl as Z group). (B) The RAFT polymerization rates of styrene were compared with each other using(naphthalen-1-yl)methyl-2-naphthaledithioate (NMNDT) and (naphthalen-1-yl)methyl benzodithioate (NMBDT) as the RAFT agents. The result showed that the polymerization rate was faster when using NMBDT as the RAFT agent than that of NMNDT. This may be due to the increased stability of radical mediate resulted from the reinforced conjugated effect in Z group of the RAFT agent. In the RAFT polymerization, the reaction rate was reduced which was attributed to the slow decomposed rate resulting from the fine stability of the radical mediate. As a result, it can be concluded that the radical mediate was too stable to decompose rapidly in RAFT polymerization, which induced the polymerization rate slower. Therefore, the stability of radical mediates in RAFT polymerization was not only an important factor to realize a living polymerization, but also played an important role in the retardation of the RAFT polymerization;The polymerizations of styrene were investigated using five carbodithioates beared naphthalene in Z or R group as the RAFT agents and AIBN as the initiator. The results demonstrated that they all showed good controllabilities except NMCBDT. The "living"/controlled controllabilities using NMBDT and NMNDT beared with naphthalyl in R group as the RAFT agent were better than that of NCATBE and NCANBE beared with benzyl in R group. However, the Z groups beared with naphthalyl or benzyl group have no apparent difference in controllabilities. In addition, the controllability of the polymerization of St was reduced greatly by the introduction of-CN group at the p-benzyl group in Z group of benzyl benzodithioate.