The Controlled Free Radical Polymerization Manipulate With Dithioesters And Trithiocarbonates

Controlled, or "living" free radical polymerization is one of the most importantresearch area in polymer chemistry and polymer preparation, to both academic andpractical researchers in recent years. Four ways to manipulate the free radicalpolymerization have been investigated: Initiation-transfer-termination (Iniferter),nitroxide-mediated polymerization (NMP), atom transfer radical polymerization(ATRP) and reversible addition fragmentation chain transfer (RAFT) process.The RAFT process combines the advantages of both free radical polymerizationand living anionic polymerization. Since its discovery in 1998, it has been receivedmuch more attention and has become a powerful and versatile tool for synthesis ofwell-defined polymers and copolymers with controllable molecular weight, designedarchitectures and functionalized end groups. Although the RAFT has been greatlyimproved, there is still a lot of research need to be done. This research focused on therelationship between chemical structures of RAFT reagents and the controlling ofpolymerization. Dithioester and trithiocarbonate RAFT reagents were synthesizedby different methods, and were used for the polymerization of styrene ormethacrylates, by thermal, thermo-initiator and photo-initiation. The chain transferconstants of the trithiocarbonates were determined. The controlling properties of thetrithiocarbonates were studied and compared with the density functional theorycalculations. It was found that the prediction by calculations for RAFT agents wasquite agreed with the experimental results. The research and main results are outlined as following:(1) Chain transfer reagents, dithiobenzoates, 2-cyanoprop-2-yl dithiobenzoate(BDTB), 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB), and dithiobenzoateacid(PhCSSH) were synthesized by Grignard agent method. TrithiocarbonatesS,S'-bis (α,α′-dimethyl-α" -acetic acid) trithiocarbonate (TTC1),3-(2-carboxyethylsulfanylthiocarbonylsulfanyl) propionic acid (TTC3),2-(2-carboxyethylsulfanylthiocarbonylsulfanyl) propionic acid (TTC4) and2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (TTC5) weresynthesized by phase transfer method. Bis-(2-oxo-2-phenyl-ethyl) trithiocarbonate(TTC2) were synthesized with anion-exchange resin for the first time. The structuresof these compounds were characterized with FT-IR, ~1H-NMR spectra and meltpoint.(2) The controlled free radical polymerizations of styrene (St), methylmethacrylates (MMA) and butyl acrylate (BA), initiated by thermal andthermo-initiator, were investigated using these RAFT agents. It was found that thepolymerization usingBDTB, EPDTB, PhCSSH, TTC1, TTC2, TTC4 and TTC5as RAFT reagent exhibited the characteristics of "living" polymerization.Polymerization kinetics, and the structure of these polymers determined by GPC,FT-IR, ~1H-NMR spectra indicated that TTC1, TTC2, TTC4 and TTC5 are effectiveRAFT agents.(3) The controlled free radical polymerization of styrene (St) and butylacrylate (BA) by photoinitiation with the five trithiocarbonates as RAFT agents wereinvestigated. The four trithiocarbonates TTC1, TTC2, TTC4 and TTC5 are effectiveRAFT agents.(4) Block copolymerizations of St and BA were carried out with initiator andphoto-initiation. The triblock copolymers, PSt-PBA-PSt, with controlled molecularweight and polydispersity, were prepared using PSt-S-C(=S)-S-PSt as themacromolecular initiator.(5) The C-S bond dissociation energies (BDE), C-S bond length and atomicspin densities for radicals were calculated by density functional theory for the fivetrithiocarbonates RAFT reagents compounds. The effects of the five trithiocarbonates on the controlled polymerization were predicted with these data.The calculation results for RAFT agents were agreed with the experimental.(6) The effects of the structure of trithiocarbonates on the controlledpolymerization of styrene, butylacrylate, initiated by AIBN and photoinitiation wereevaluated. The chain transfer constants of TTC1,TTC2,TTC4 and TTC5 in freeradical polymerization of styrene at 70℃were determined using Mayo's method.The results exhibit that the structure of trithiocarbonatcis has influence on the controlability. The controlling ability for styrene RAFT polymerization is better when aconjugation group connected to the trithiocarbonate. In addition, the leaving group Rin the trithiocarbonate also affects the controlling. With secondary and tertiary alkylleaving groups the trithiocarbonates will exhibit better controlling on molecularweight and polydispersities in free radical polymerization.