Saoud, Fozi (2010-03)
Living chains prepared by RAFT polymerization and NMP reactions using Z-carboxylate and Z-phosphate RAFT agents, and X-phosphate NMP initiators, were efficiently attached to the surface of magnetic nanoparticles (MNPs) and used for the separation of dead chains formed in these polymerization reactions prior to the attachment of the RAFT agents and NMP initiators to the surface of MNPs. All the living chains that attach selectively to the surface of MNPs contained RAFT or NMP functionalities, had a low polydispersity index (PDI), and could be reactivated to form new polymer extensions or block copolymers with no detectable deviation from 100% efficiency. RAFT chains prepared by RAFT polymerization using the Z-carboxylate RAFT agent and an excess of free radical initiator were also attached to the surface of MNPs and separated in the presence of an external magnetic field. Separated RAFT-functional chains contained no dead chains formed by combination or disproportionation reactions, but a substantial amount of cross-terminated by-product with a low UV absorbance at 320 nm.
The cross-termination of the intermediate radical formed in the RAFT polymerization reactions was also investigated in the monomer-excluded free radical reaction model of polystyryl benzyl-(4-carboxyl dithiobenzoate) and polystyryl ethyl-2-bromoisobutyrate. The Z-carboxylate 3- and 4-arm star polymers (formed by cross-termination reactions) were then efficiently attached to the surface of MNPs and separated from the remainder of the polymer solution. They were separated from MNPs and characterized by 1H and 13C-NMR spectroscopy, and MALDI-ToF-MS.
Living chains prepared by a RAFT miniemulsion polymerization reaction using Z-carboxylate RAFT agent were attached to the surface of MNPs and used for the separation of all dead chains and uncontrolled high molecular weight polymer of secondary particle formations occur during a miniemulsion polymerization reaction prior to the attachment. Separated dead chains had high PDI values and contained a significant fraction of uncontrolled high molecular weight polymer that lacked RAFT functionality.
Initiator-derived chains formed in RAFT polymerization reactions of styrene (St) and methyl methacrylate (MMA) using phosphate free radical (PFR) initiator were selectively attached to the surface of MNPs and separated from R-group-derived polymer chains in the presence of an external magnetic field. All separated initiator-derived chains contained large fractions of dead chains with weak UV absorbance, and which lacked RAFT functionality, and small fractions of RAFT polymer chains. The separated initiator-derived chains had higher PDI values than the as-prepared polymer in the polymerization of St, but lower PDI values than the as-prepared polymer in the polymerization of MMA.
RAFT agents attached to the surface of MNPs by the Z group were used as mediating agents for the synthesis of polymers grafted to the surface of MNPs. The polymers grafted to the surface of MNPs were separated from the solution of the free polymer by applying an external magnetic field. The amounts of the polymers grafted to the surface of MNPs greatly increased as the number of RAFT agents attached to the surface of MNPs decreased. When ethyl acetate was used as solvent, it reached 65% by weight and 50% by number of chains. Separated polymers grafted to the surface of MNPs had high PDI values and contained RAFT functionality.
Investigations into the kinetics of the RAFT-mediated polymerization reaction on the surface of MNPs revealed that the polymerization reaction mediated using a RAFT agent attached by its Z group to the surface of MNPs had a faster polymerization rate than that mediated using a free Z group RAFT agent. The molecular weight of the grafted polymer increased linearly with conversion, and the reaction rate was pseudo-first-order.
Lewende polimeerkettings, berei deur middel van RAFT-beheerde polimerisasie en NMP reaksies waarin Z-karboksilaat en Z-fosfaat RAFT-verbindings en 'n X-fosfaat NMP afsetter gebruik is, is geheg aan die oppervlaktes van magnetisenanopartikels (MNPs), en gebruik vir die skeiding van dooie kettings wat tydens die RAFT en NMP reaksies gevorm is. Alle lewende kettings wat aan die oppervlakte van die MNPs geheg is, is geskei van die oorblywende polimeeroplossing deur die aanwending van ‗n eksterne magnetise veld. Alle kettings wat selektief aan die oppervlaktes van die MNPs gekoppel is met RAFT of NMP funksionaliteit, het ‗n laë poliverspreidingswaarde (PDI) gehad en kon heraktiveer word om ‗n nuwe polimeerverlengings of blokkopolimere te vorm met geen merkbare afwyking van 100% doeltreffendheid nie. RAFT-kettings wat gedurende RAFT-polimerisasie met 'n Z-karboksilaat RAFT-agent en oormaat vrye-radikaalafsetter berei is, is ook geheg aan die oppervlaktes van MNPs en geskei in die teenwoordigheid van 'n eksterne magnetiese veld. Die geskeide RAFT-funksionele kettings het geen dooie kettings bevat nie (gevorm deur kombinasie reaksies), maar 'n aansienlike hoeveelheid ongekontroleerde hoë molekulêremassa polimeer (met lae UV absorpsie by 320 nm).
Die kruis-beëindiging van die intermediêre radikaal wat gevorm is tydens die RAFT-proses is ondersoek in die monomeer-uitsluitende vrye-radikaalreaksiemodel van polistirielbensiel-4-karboksielditiobensoaat en polistirieletiel-2-bromoisobutiraat. Die Z-karboksilaat 3- en 4-arm sterpolimere (gevorm a.g.v. kruis-terminasiereaksies) is effektief geheg aan die oppervlaktes van MNPs en geskei van die res van die polimeeroplossing, en daarna gekarakteriseer met behulp van 1H en 13C KMR, en MALDI-ToF-MS.
Lewende kettings, berei m.b.v. RAFT miniemulsiepolimerisasies met 'n Z-karboksilaat RAFT-agent, is geheg aan die oppervlaktes van MNPs en gebruik vir die skeiding van alle dooie kettings en sekondêre partikels wat tydens die reaksie voor die aanhegting gevorm het. Die geskeide dooie kettings wat agtergebly het, het 'n wye PDI getoon en het 'n aansienlike hoeveelheid ongekontroleerde hoë molekulêremassa polimeer, met geen RAFT-funksionaliteit nie, bevat.
Afsetterafkomstigekettings wat gevorm is tydens die RAFT polimerisasiereaksies van stireen (St) en metielmetakrilaat (MMA) met 'n fosfaat-vrye vrye-radikaalafsetter is selektief geheg aan die oppervlaktes van MNPs en geskei van R-groep-afkomstige polimeerkettings in die teenwoordigheid van 'n eksterne magnetise veld. Alle geskeide afsetter-afkomstige kettings het 'n groot hoeveelheid dooie kettings gehad (met swak UV absorpsie) en met geen RAFT-funksionalilteit nie, en klein fraksies van RAFT-polimeerkettings. Die geskeide afsetter-afkomstige kettings het hoër PDI waardes gehad as die ('as-prepared') polimeer in die polimerisasie van St, maar laer PDI waardes as die ('as-prepared') polimeer in die polimerisasie van MMA.
RAFT-verbindings wat aan die oppervlaktes van die MNPs geheg is deur middel van die Z-groep is as bemiddellingsagente (Eng: mediating agents) gebruik vir die sintese van polimere wat geënt is aan die oppervlakte aan MNPs. Die polimere wat aan die oppervlakte van die MNPs geënt is is geskei van die res van die polimeeroplossing deur die aanwending van ‗n eksterne magnetise veld. Die hoeveelhede van die polimere wat aan die oppervlaktes van die MNPs geënt is het sterk toegeneem namate die aantal RAFT-agente wat aan die oppervlaktes van MNPs geheg is afgeneem het. Wanneer etielasetaat as oplosmiddel gebruik is, was die waardes 55% m.b.t. gewig en 45% m.b.t. die aantal kettings. Die geskeide polimere wat aan die oppervlaktes van MNPs geënt is het hoë PDI getoon en het RAFT-funksionaliteit bevat.
Die kinetika van die RAFT-beheerde polimerisasiereaksies van St, wat gebruik maak van ‗n RAFT-agent wat aan die oppervlakte van die MNPs geheg is deur middel van die Z-groep, is ook ondersoek. Die tempo van polimerisasie was vinniger in die geval waarin die RAFT-agent geheg is deur sy Z-groep aan die oppervlakte van die MNPs as die reaksie met 'n RAFT agent met 'n vrye Z-groep. Die molekulêremassas van die entpolimere het liniêr toegeneem met omsetting, en die reaksie was pseudo-eerste-orde.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/3998