Synthesis Of Novel RAFT Reagents Based On Carbazole And Application In RAFT Polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization was a novel method of living radical polymerization. In this thesis, three novel RAFT reagents based on the main material of carbazole, benzyl N-carbazolecarbodithioate (BCBD), 1-phenylethyl N-carbazolecarbodithioate (PCBD) and 2-cyanoprop-2-yl N-carbazolecarbodithioate (CYCBD) were synthesized and identified by 1H-NMR, IR, MS, MS2 and UV. These RAFT reagents are solids and can be purified by recrystallization. In the present of BCBD, PCBD and CYCBD respectively, RAFT polymerizations of styrene (St), methyl methacrylate (MMA) and N-isopropyl acrylamide (NIPAm) were studied. These RAFT reagents were synthesized as follow. Firstly, carbazole reacted with natrium and CS2 to form natrium N-carbazolecarbodithioate. Then natrium N-carbazolecarbodithioate was reacted with benzyl chlorine or cumyl bromine to obtain the compounds of BCBD or PCBD with the yield 75% or 70% respectively. CYCBD was synthesized by the reaction of natrium N-carbazolecarbodithioate, iodine and AIBN. The crude product of BCBD, PCBD or CYCBD was subjected to recrystallize three times in petroleum spirits to abtain the BCBD or the CYCBD with the purification above 95% as a yellow solid or the crude PCBD with the purification above 85% as a viscous liquid at room temperature respectively. Subsequently the recrystallized PCBD was chromatographed on silica eluted with 10% THF in petroleum spirits to provide the PCBD with the purification above 95%. The stabilities of BCBD, PCBD and CYCBD were studied by means of MS and RAFT polymerization of styrene, and the results showed that these RAFT agents can be preserved steadily at least 30 days at room temperature, or at least 90 days under the condition of 4℃. These new RAFT reagents were used in styrene RAFT polymerization. The results displayed that under the new RAFT reagents St polymerization can succeed with essential characteristics of living radical polymerization: the number-average molecular weight of polymer increased linearly with the conversion of styrene, the molecular weight distributions were narrow, the Mw/Mn (D) were below 1.2, sometimes even below 1.15. The effects of polymerization conditions, such as polymerization temperature, molar ratioes of the RAFT reagents to AIBN, the AIBN concentrations, and the feed mode of AIBN in the RAFT polymerization of St were also studied. The results demonstrated that the polymerization temperature and methods such as solution polymerization in toluene and batch polymerization had little effect on polydispersity in RAFT polymerization of styrene. Keeping the amount of other ingredients invariable, D was increased from 1.18 to 1.56 with the molar concentration of AIBN increasing from 0.5‰ to 10‰, and decreased from 1.56 to 1.18 with the ratio of the RAFT to AIBN decreasing from 1/3 to 10/1. PSt with narrower molecular weight distribution (D <1.15) can be obtained by the means of intermission feed of AIBN. RAFT polymerization of MMA and NIPA were also studied. The results displayed that these new RAFT reagents have good controlling ability for NIPAm polymerization with D in the range from 1.2 to 1.3, but less controlling ability for MMA RAFT polymerization with Mw/Mn in the range from 1.3 to 2.0, CYCBD being better.