Modification of Solid Polymer SurfaceSurface reactivitySolvent compatibilityFunctionalization of Surfaces with Polymers“Grafting From” Approaches “Grafting To” Examples (Handout)First Attempts at Living Free Radical Polymerization Original Free Radical MechanismNitroxide Stable Free RadicalStable Free Radical Mechanism10.569 Synthesis of Polymers Prof. Paula Hammond Lecture 31: “Living” Free Radical Approaches: Stable Free Radical Polymerization, Atom Transfer Radical Polymerization Modification of Solid Polymer Surface e.g. the of PMMA slab C OCH3O the of PS surface Surface reactivity • must have access to functional groups • interfacial energy may impact presentation of functional groups to surface • surfaces are dynamic → small rearrangement can occur • also have to consider surface impurities that might prevent or occlude access to functional groups ⇒ issues around solvent choice and surface properties Solvent compatibility Need to have reaction solvent that wets surface but does not dissolve the solid ⇒ By altering solvents, get differing degrees of penetration into surface (varying from hundreds of nm to Å’s) ⇒ Solvent impacts % yield and kinetics ⇒ availability of surface groups and solubility of reagent Remember surfaces are heterogeneous Have morphology (e.g. crystallinity) Have potential for plasticization w/solvent Functionalization of Surfaces with Polymers “Grafting From” Approaches 1. Surface irradiation w/high energy + monomer MMMmonomer insolventhν••••MMM••••••MMMmonomer insolventhν••••MMM•••••••••••• Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.2. Covalent attachment of initiating species 10.569, Synthesis of Polymers, Fall 2006 Lecture 31 Prof. Paula Hammond Page 2 of 5 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date. OHOHOH+OHOHOH+Cl C CH2CH2NNCCNCH2CClO OCCNCH2 OC (CH2)2NNCCN(CH2)2CClO OCCN + M+ Mheat+ monomerheat+ monomerOC (CH2)2OCCN “Grafting To” X+Y X YX+Y X Y Anionic/Cationic CH2CHEtO COEtO CO Step Growth OHCl CO+ e.g. polyester Issues for grafting to Lower yields Steric constraints to full coverageExamples (Handout) Free Radical - Accounts for ∼50% of all mass production of polymers - Emulsion - Suspension - Bulk solution Most robust method of chain growth Insensitivity to solvent Insensitivity to impurities (NH3, H2O) Insensitivity to atmospheric conditions Open to widest variety of chain growth monomers - vinyl halogens ClFFFF - vinyl esters 10.569, Synthesis of Polymers, Fall 2006 Lecture 31 Prof. Paula Hammond Page 3 of 5 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date. limited in ionic polymerization easy in free radical polymerization - acrylates HOCRHORO protic NOT vinyl ethers OR First Attempts at Living Free Radical Polymerization (Otsa et al, 1982) initiator Ini fer ters: transfer Plays all three roles termination C2H5N C S S C NSSC2H5C2H5C2H5Dissociation R2IIH+nMinit.I-MnI"termination"I-Mn-IreversibleI-MnMMIIMn+1+IH+IMn+1-IIMn+IMnew chaintransfer Get increased molecular weight over time, but road PDI. 1985 = Solomon et al. Introduced first nitroxide free radical systems. → act as “adducts” but not initiators N O+AIBNH3CCCH3CNN N CCH3CNCH3CH2-ONreversible bond 10.569, Synthesis of Polymers, Fall 2006 Lecture 31 Prof. Paula Hammond Page 4 of 5 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.Original Free Radical Mechanism I RRMM+RInitiationR[M]rMRM + rMPropagation2R[M]rMTerminationCombinationDisproportionation Nitroxide Stable Free Radical 10.569, Synthesis of Polymers, Fall 2006 Lecture 31 Prof. Paula Hammond Page 5 of 5 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date. “TEMPO” NONOR RRMust not actas initiatorin polymerization! Stable Free Radical Mechanism RadRInitiatorFragmentRadRFewTerminationEventsSmall amountof free radicalONR'R''RadRONR'R''Adduct breaksand thenrecombinesFor "living"system,need forwardrate >