Methusalem Advisory Board meeting, Ghent, 17 June 2011 Model-based optimization of polystyrene properties by Nitroxide Mediated Polymerization (NMP) in homogeneous and dispersed media Lien Bentein 1
Methusalem Advisory Board meeting, Ghent, 17 June 2011 NMP: principle and objective Nitroxide mediated polymerization (NMP) principle: dormant species active species Objective of NMP: synthesis of well-defined polymers, i.e., polymers having a high end-group functionality and a low polydispersity index, in homogeneous and heterogeneous media Synthesis challenge: controlled polymer properties for average chain lengths higher than ~500 2
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Bulk NMP: system & kinetic model Bulk NMP of styrene initiated by SG1-phenylethyl at 396 K monomer Classical synthesis approach: initial molar ratio of monomer to initiator initiator (alkoxyamine) equal to targeted chain length at complete conversion TARGETED chain length (TCL) = [styrene] 0 /[SG1-phenylethyl] 0 Kinetic model: main reactions (activation, deactivation, propagation, termination) side reactions (thermal initiation, (chain) transfer reactions) diffusional limitations accounted for (mainly important on termination & deactivation) Bentein et al. Macromol. Theory Simul. 2011 , 20, 238 3
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Side reactions THERMAL INITIATION DIMER Diels Alder reaction: Monomer assisted homolysis: Formation of 1,2- diphenylcyclobutane: Ene reaction: 4
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Side reactions (CHAIN) TRANSFER REACTIONS Chain transfer to monomer: Chain transfer to dimer: Transfer from nitroxide to monomer: Transfer from nitroxide to dimer: 5
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Classical synthesis approach: results OBTAINED average chain length = 557 TCL(-) TCL(-) end group functionality = 0.57 Experimental data from Lutz et al., Macromol. Rapid Commun. , 2001 , 189 TCL(-) 6
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Classical synthesis approach: results (2) TCL=960 MASS CLD NUMBER CLD Chain transfer to dimer mainly responsible for loss of control over average chain length, PDI pol and polymer end-group functionality 7
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Classical synthesis approach: results (3) CONVERSION = 0.85 TCL= 1000 OBTAINED average chain length (-) Non-classical synthesis (fed-batch) approach ? 8
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case I: predetermined amount of M added (1) n styrene = 8.74 10 -2 mol 15 % TCL 2000 improvement initial TCL = 500 n styrene = 8.74 10 -2 mol PDI pol OBTAINED polymer end group average CL functionality 794 0.39 1.65 800 0.54 1.46 9
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case I: predetermined amount of M added (2) REACTION PROBABILITY FOR MACRORADICALS (RP i bulk ) +X +M PROPAGATION DEACTIVATION +R j +M TERMINATION BY RECOMBINATION R i CHAIN TRANSFER TO MONOMER WITH MACRORADICAL +D +R 0 CHAIN TRANSFER TO DIMER TERMINATION BY RECOMBINATION WITH INITIATOR RADICAL 10
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case I: predetermined amount of M added (3) REACTION PROBABILITY FOR MACRORADICALS (RP i bulk ) PROPAGATION CHAIN TRF TO DIMER bulk,chain TRF to D (-) bulk,propagation (-) REPEATED TEMPORARY SUPPRESSION OF CHAIN TRF TO DIMER RP i RP i bulk,termination by recomb (-) TERMINATION (RECOMB) DEACTIVATION bulk,deactivation (-) RP i RP i 11
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case I: predetermined amount of M added (4) IMPROVEMENT CONVERSION = 0.85 MULTIPLE ADDITION of predetermined amount OBTAINED average chain length (-) 12
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case II: criterion based amount of M added (1) no classical equivalent TCL 5000 > 43 % improve- ment initial TCL = 100 PDI pol OBTAINED polymer end group average CL functionality after each addition: [styrene]/[alkoxyamine] = 1042 0.19 1.90 100 1594 0.62 1.37 13
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case II: criterion based amount of M added (2) REACTION PROBABILITY FOR MACRORADICALS (RP i bulk ) PROPAGATION CHAIN TRF TO DIMER bulk,chain TRF to D (-) bulk,propagation (-) EFFECTIVE SUPPRESSION OF CHAIN TRF TO DIMER AND TERMINATION RP i RP i bulk,termination by recomb (-) TERMINATION (RECOMB) DEACTIVATION bulk,deactivation (-) RP i RP i 14
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Case II: criterion based amount of M added (3) IMPROVEMENT CONVERSION = 0.85 MULTIPLE MULTIPLE ADDITION of ADDITION of criterion based predetermined amount amount OBTAINED average chain length (-) 15
Methusalem Advisory Board meeting, Ghent, 17 June 2011 Fed-batch NMP of styrene Theoretically, polymer properties can be improved for average chain lengths higher than 500 by a fed-batch approach But will the approach really work in practice ? …the experiments are currently being performed in collaboration with the Polymer Chemistry Research Group… 16
Methusalem Advisory Board meeting, Ghent, 17 June 2011 CRP in dispersed systems; miniemulsion? General • industrially attractive: excellent heat transfer, ease of mixing and handling/transporting of the final product • water-borne systems: more environmentally friendly and economically interesting • for CRP : emphasis on (mini)emulsion due to the expectation of similar/better properties than in bulk (inherent compartmentalization of radical species ability to manipulate overall reaction rates and control over polymer properties by adapting the particle size) CRP in miniemulsion • alter particle size by amount of added surfactant • ideally polymerization reactions only inside the particles , in which controlling agent is present styrene : radicals from thermal initiation captured by controlling agent • encapsulation of additives (pigments) • copolymerization of highly water-insoluble monomers 17
Methusalem Advisory Board meeting, Ghent, 17 June 2011 ‘ Ideal ’ miniemulsion: concept monomer BEFORE POLYMERIZATION initiator (alkoxyamine) water EMULSIFICATION monomer emulsifier droplets ASSUMPTIONS: - oil-soluble initiator - uniform monomer droplet size - homogeneous initiator concentration 18
Methusalem Advisory Board meeting, Ghent, 17 June 2011 ‘ Ideal ’ miniemulsion: concept BEFORE POLYMERIZATION POLYMERIZATION monomer droplets ASSUMPTIONS: ASSUMPTIONS: - polymerization only in oil phase - oil-soluble initiator - no mass transfer to aqueous phase - uniform monomer droplet size - constant particle size - homogeneous initiator concentration 19
Methusalem Advisory Board meeting, Ghent, 17 June 2011 ‘ Ideal ’ miniemulsion: modeling approaches for NMP In literature: mainly TEMPO/styrene • Kinetic Monte Carlo (Tobita) • intrinsic kinetic model • focus on the effect of particle size on overall polymerization rate • Modified Smith-Ewart equations • intrinsic kinetic model • often limited to low conversion (Zetterlund: TEMPO/TIPNO) • no thermal initiation, no compartmentalization of nitroxide, termination by disproportionation (Charleux: SG1) Our approach: SG1/styrene • Generalized Smith-Ewart equations • detailed reaction network (thermal initiation through Mayo mechanism, chain transfer to monomer, to dimer and transfer from nitroxide to dimer) • distinction between initiator radicals and macroradicals • diffusional limitations included up to high conversion • effect of particle size on overall polymerization rate as well as polymer properties 20
Methusalem Advisory Board meeting, Ghent, 17 June 2011 ‘ Ideal ’ miniemulsion: modeling droplets with i macroradicals, r initiator radicals, j nitroxide radicals 21
Methusalem Advisory Board meeting, Ghent, 17 June 2011 ‘ Ideal ’ miniemulsion NMP: modeling droplets with i macroradicals, r initiator i+1 r j+1 i r+1 j+1 i-1 r j-1 i-1 r+1 j i+1 r-1 j i r+1 j-1 i r-1 j-1 i-1 r-1 j i r+2 j i r-2 j i-2 r j i+1 r j+1 i-1 r j-1 i r-1 j-1 i r+1 j+1 i+1 r+1 j i r-1 j+1 i-1 r+1 j i+1 r-1 j i+2 r j i r+2 j i r-2 j radicals, j nitroxide radicals Generalized Smith-Ewart equations j dN i,r j-1 - N i,r j-1 - N i,r j ) = N A v p k a,app τ 0 (N i-1,r j ) + N A v p k a0,app [R 0 X] (N i,r-1 dt -1 v p -1 <k da,app ,0> ( (i+1)(j+1)N i+1,r j+1 – (i)(j)N i,r j ) + N A number of droplets -1 v p -1 <k da0,app ,0>((r+1)(j+1)N i+1,r j+1 – (r)(j)N i,r j ) with i, r, j + N A j – N i,r j ) + N A v p k thi,app [M][D](N i,r-2 -1 v p -1 <k tc,app ,0> ((i+2)(i+1)N i+2,r j – (i)(i-1)N i,r j ) + N A -1 v p -1 k tc00 /2 ((r+2)(r+1)N i,r+2 j – (r)(r-1)N i,r j ) + N A -1 v p -1 <k tc0,app ,0>((i+1)(r+1)N i+1,r+1 j – (i)(r)N i,r j ) + N A j – (i)N i,r j ) + <k trM,app ,0>[M]((i+1)N i+1,r-1 j – (i)N i,r j ) + <k trD,app ,0>[D]((i+1)N i+1,r-1 j – (r)N i,r j+1 – (j)N i,r j ) + k p0 [M]((r+1)N i-1,r+1 + k trXD [D]((j+1)N i,r-1 j ) 22
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