10.569 Synthesis of Polymers Prof. Paula Hammond Lecture 31: Living Free adical Approaches: Stable Free adical Polymerization, Atom Transfer adical Polymerization odification of Solid Polymer Surface e.g. the of PA slab H 3 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 eed 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 emember 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 monomer in solvent hν itation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, T penourseware (http://ocw.mit.edu/index.html), assachusetts nstitute of Technology, Date.
2. ovalent attachment of initiating species H H H l H 2 H 2 H 2 H 2 l (H 2 ) 2 (H 2 ) 2 l heat monomer (H 2 ) 2 Grafting To X Y X Y Anionic/ationic H 2 H Et Et Step Growth H l e.g. polyester ssues for grafting to Lower yields Steric constraints to full coverage Prof. Paula Hammond Page 2 of 5 itation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, T penourseware (http://ocw.mit.edu/index.html), assachusetts nstitute of Technology, Date.
Examples (Handout) Free adical - Accounts for 50% of all mass production of polymers - Emulsion - Suspension - Bulk solution ost robust method of chain growth nsensitivity to solvent nsensitivity to impurities (H 3, H 2 ) nsensitivity to atmospheric conditions pen to widest variety of chain growth monomers - vinyl halogens F F l F F - vinyl esters H limited in ionic polymerization easy in free radical polymerization - acrylates H protic T vinyl ethers First Attempts at Living Free adical Polymerization (tsa et al, 1982) initiator ni fer ters: transfer Plays all three roles termination 2 H 5 S S 2 H 5 2 H 5 S S 2 H 5 Prof. Paula Hammond Page 3 of 5 itation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, T penourseware (http://ocw.mit.edu/index.html), assachusetts nstitute of Technology, Date.
Dissociation 2 H n init. -n "termination" -n- n1 n1 - -n H reversible new chain n transfer Get increased molecular weight over time, but road PD. 1985 = Solomon et al. ntroduced first nitroxide free radical systems. act as adducts but not initiators AB H 3 H 3 H 3 H 3 H 2 - reversible bond Prof. Paula Hammond Page 4 of 5 itation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, T penourseware (http://ocw.mit.edu/index.html), assachusetts nstitute of Technology, Date.
riginal Free adical echanism nitiation Propagation r [] r Termination 2[] r ombination Disproportionation itroxide Stable Free adical TEP ust not act as initiator in polymerization! Stable Free adical echanism ad nitiator Fragment Few Termination Events Small amount of free radical ad ' '' ad ' '' Adduct breaks and then recombines For "living" system, need forward rate > p ad ' '' ad ' '' Prof. Paula Hammond Page 5 of 5 itation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, T penourseware (http://ocw.mit.edu/index.html), assachusetts nstitute of Technology, Date.