Polymer Synthesis CHEM 421 Free Radical Polymerizations

Polymer Synthesis CHEM 421 Reading assignments: Chapter 3-3, 3-4, 3-5, 3-8 (Odian)

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Initiation Propagation Termination d [ R ] / dt = 2 k d [ I ] - d [ R ] / dt = k i [R] [M] r p = k p [M] [M] - d [ P ] / dt = 2 k t [P] 2 = 2 f k d [ I ]

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Overall rate expression –Assumptions? »Steady State Approximation (R i = R t ) R p = k p [M] ( k d f [ I ] / k t ) 1/2 2 f k d [I] = 2 k t [M] 2 R p = k p [M] [M] [M] = (k d f [I] / k t ) 1/2

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Overall rate expression –Rate is first order in monomer –Rate is ½ order in initiator To increase R p R p = k p [M] ( k d f [ I ] / k t ) 1/2

Polymer Synthesis CHEM 421 Determination of Orders of Reaction R p (mol/L x sec) R p /[VF 2 ] out (1/ sec) [I] out 0.5 (mol/L)[VF 2 ] out (mol/L) T =75  C, P= 4000 psig,  CO2 = 0.74 g/ml R p = ([VF 2 ] IN -[VF 2 ] OUT )/  I* [DEPDC] IN =3 mM  R p  k p [I out -I*] 0.5 [VF 2 ] out 1.0

Polymer Synthesis CHEM 421 Experimental Ways of Determining R p Separation and isolation of product –Precipitation –Chromatography Chemical analysis –Titration of un-reacted double bonds… Spectroscopic methods –UV/Vis, NMR, FTIR Refractive index changes Dilatometry Calorimetry

Polymer Synthesis CHEM 421 React-IR  t = 30 s, 32 scans reaction conditions: p = 5000 p.s.i., T = 35 °C, 73 mol-% PDD in feed phase separation  emulsion

Polymer Synthesis CHEM 421 Dilatometer

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Overall rate expression –Rate is first order in monomer –Rate is ½ order in initiator Qualitative picture…? R p = k p [M] ( k d f [ I ] / k t ) 1/2

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Kinetic Chain Length (٧) –Average number of monomer units polymerized per chain initiated R p R i R t ٧ = — = — k p [M] 2 k t [M] = ——— k p [M] 2 (k t k d f [I] ) 1/2 = ————— k p [M] [M] 2 k t [M] 2 ٧ = ————

Polymer Synthesis CHEM 421 Free Radical Solution Polymerizations Kinetic Chain Length (٧) –To increase molecular weight… –To increase Rate of Polymerization ٧ = k p [M] 2 (k t k d f [I] ) 1/2 = —————

Polymer Synthesis CHEM 421 Kinetic Chain Length (٧) vs Degree of Polymerization (DP) Termination by combination Termination by disproportionation DP = 2 ٧ DP = ٧

Polymer Synthesis CHEM 421

Polymer Synthesis CHEM 421 Classes of Free Radical Initiators

Polymer Synthesis CHEM 421 Initiator Decompositions Differences in the decomposition rates of various initiators can be expressed in terms of initiator half life The rate of initiator disappearance is: Integrate: or Half life? - d [ I ] / dt = k d [ I ] [ I ] = [ I ] 0 e -k d t log —— = k d t [I]0[I]0 [I][I] set: [I] = —— [I]0[I]0 2 t 1/2 = ——— 0.63 kdkd

Polymer Synthesis CHEM 421

Polymer Synthesis CHEM 421 Factors which Influence Initiator Choice Temperature of polymerization Solubility of the initiator End group control or functionalization

Polymer Synthesis CHEM 421 Factors which Influence Initiator Choice End group control or functionalization

Polymer Synthesis CHEM 421 Pulsed-laser Polymerization in Homogeneous Phase: Determination of k p

Polymer Synthesis CHEM 421 Pulsed-laser Polymerization in Homogeneous Phase: Determination of k p

Polymer Synthesis CHEM 421 Evaluation of k p

Polymer Synthesis CHEM 421 Kinetic Chain Length Profile in a PLP Experiment

Polymer Synthesis CHEM 421 L i =i k p [M] t d

Polymer Synthesis CHEM 421 L i =i k p [M] t d