活性自由基英文文献总结_精品文档.pptx

1、Free Radical PolymerizationRadical PolymerizationHigh tolerance of growing radical species toward many functional groupsCopolymerizations between various monomers are quite straightforward and high molecular weight polymers are formed earlyRadical polymerization can be carried out in a wide range of

2、 temperatures and conditionsArchitectural controlIonic Polymerizationcombine the advantagesControlled Radical PolymerizationF.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021Free Radical PolymerizationControlled Radical Polymerization(i)The rate of initiation is faster than that o

3、f propagation,so that all chains form and grow simultaneously.(ii)The concentration of active radicals is low in order to slow down termination reactions.(iii)The concentration of propagating chains is high so only a small fraction of them are terminated.(iv)The polymerization system remains suffici

4、ently homogeneous,so that the active centers are readily available.requirementsF.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021Organometallic mediated radical polymerization,is based on the fast and reversible homolytic cleavage of a metal-carbon bond in the metal complex.Depend

5、ing on the type of monomer used,the specific metal/ligand combination and the initiation strategy,OMRP can occur through either RDC or DT or both mechanisms.Chain-breaking reactions such as CCT may also competitively take place.F.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021Tra

6、nsition metal complexes that have been reported to polymerize olefins via a RDC mechanism include Ti,Mo,Os,Co,and Rh compounds.reversible deactivation by coupling(RDC)mechanismF.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021Catalytic chain transfer(CCT),when its rate is sufficie

7、ntly high,the molecular weight distribution of the resulting oligomers can be described by a ShultzFlory statistics(Mw/Mn 2).Efficient CCT has been reported with certain Mo,Fe,and especially Co complexes.F.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021Catalytic chain transfer(CC

8、T)processDegenerative transfer(DT)processF.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021The method is known as degenerative transfer(DT)radical polymerization.The exchange process usually takes place through a short-lived intermediate that in some cases can be considered a tran

9、sition state.Since the CoC bond cleavage of Organo-cobalt(III)complexes can be achieved under mild conditions,organocobalt complexes have been used as sources of carbon-centered radicals for organic synthesis and in polymer chemistry.A.Debuigne et al./Progress in Polymer Science 34(2009)211239Additi

10、on of(TMP)CoII reduces the rate of polymerization,and the poly-merization process can be effectively stopped and restarted repetitively by cycling the reaction temperature between 5 and 60.A linear increase in Mn with MA conversion along with relatively small PMA polydispersities(Mw/Mn=1.1-1.2)indic

11、ates that a preponderance of the polymer chains are growing in a manner characteristic of a living polymerization process.(TMP)Co-CH2C-(CH3)3 1(TMP)Co-MA 2Reaction of 2 with MA at 60 in benzene results in formation of PMA with relatively small polydispersity(1.1-1.3)and linear increase in Mn(1 X 104

12、 to 1.7 X 105)with MA conversion(5-80%,DP=125-2000).In spite of the processes that can limit polymer growth,observation of linear increases in Mn with conversion,formation of block copolymers,and relatively small polydisper-sities clearly demonstrate that 1 and 2 initiate an effective living radical

13、 polymerization of acrylates.Bradford B.Wayland/J.Am.Chem.SOC.1994,116,7943-7944In 2004,the Wayland research group showed that,in the presence of a radical source such as AIBN or V-70,the polymerization of MA could be mediated by catalytic amounts of(TMP)Co.At 60C and in benzene,after a short induct

14、ion period,PMA of molecular weight up to 120,000 and polydispersity as low as 1.06 were produced.Low polydispersity poly(MA-b-BA)copolymers were also efficiently synthesized.Mechanism(i)the induction corresponds to the time required to produce sufficient radicals to convert all of the Co(II)species

15、into Co(III)R,which controls the polymerization via a slow RDC mechanism.(ii)The continued influx of radicals from V-70 changes the process to a faster DT-based polymerization in which both ln(M0/M)vs.time and Mn vs.conversion increase linearly.(iii)After the influx of new radicals from V-70 has end

16、ed,the polymer-ization reaction reverts to the slower RDC pathway.F.di Lena,K.Matyjaszewski/Progress in Polymer Science 35(2010)9591021The accuracy of theoretical calculations in terms of molecular structure,energetics and physical properties has made enormous progress in the last couple of decades.The application of computational tools,especially Density Functional Theory(DFT)methods,in view of their relatively good performance at comparatively low computational cost,is becoming routine in a va