[PPT] - properties by Nitroxide Mediated Polymerization (NMP) in homogeneous PowerPoint Presentation

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1 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

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2 Methusalem Advisory Board meeting, Ghent, 17 June 2011

NMP: principle and objective

active species dormant species

Nitroxide mediated polymerization (NMP) principle: 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

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Bulk NMP: system & kinetic model

initiator (alkoxyamine) monomer

Bulk NMP of styrene initiated by SG1-phenylethyl at 396 K Classical synthesis approach:

initial molar ratio of monomer to initiator 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

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Side reactions

Diels Alder reaction: Monomer assisted homolysis: Formation of 1,2- diphenylcyclobutane: Ene reaction: DIMER

THERMAL INITIATION

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5 Methusalem Advisory Board meeting, Ghent, 17 June 2011

Side reactions

Chain transfer to monomer: Chain transfer to dimer: Transfer from nitroxide to dimer: Transfer from nitroxide to monomer:

(CHAIN) TRANSFER REACTIONS

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Classical synthesis approach: results

TCL(-) TCL(-)

Experimental data from Lutz et al., Macromol. Rapid Commun., 2001, 189

TCL(-)

OBTAINED average chain length = 557 end group functionality = 0.57

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Classical synthesis approach: results (2)

NUMBER CLD MASS CLD

Chain transfer to dimer mainly responsible for loss of control over average chain length, PDIpol and polymer end-group functionality TCL=960

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Classical synthesis approach: results (3)

OBTAINED average chain length (-) CONVERSION = 0.85

TCL= 1000

Non-classical synthesis (fed-batch) approach ?

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Case I: predetermined amount of M added (1)

15 % improvement OBTAINED average CL polymer end group functionality PDIpol 794 0.39 1.65 800 0.54 1.46

nstyrene= 8.74 10-2 mol

TCL 2000

initial TCL = 500 nstyrene= 8.74 10-2 mol

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10 Methusalem Advisory Board meeting, Ghent, 17 June 2011

Case I: predetermined amount of M added (2)

REACTION PROBABILITY FOR MACRORADICALS (RPi

bulk)

Ri +M

PROPAGATION CHAIN TRANSFER TO MONOMER CHAIN TRANSFER TO DIMER DEACTIVATION TERMINATION BY RECOMBINATION WITH MACRORADICAL

+X +M +D

TERMINATION BY RECOMBINATION WITH INITIATOR RADICAL

+Rj +R0

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Case I: predetermined amount of M added (3)

PROPAGATION CHAIN TRF TO DIMER TERMINATION (RECOMB) DEACTIVATION

REPEATED TEMPORARY SUPPRESSION OF CHAIN TRF TO DIMER

REACTION PROBABILITY FOR MACRORADICALS (RPi

bulk)

RPi

bulk,propagation (-)

RPi

bulk,chain TRF to D (-)

RPi

bulk,termination by recomb(-)

RPi

bulk,deactivation(-)

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Case I: predetermined amount of M added (4)

IMPROVEMENT OBTAINED average chain length (-)

MULTIPLE ADDITION of predetermined amount

CONVERSION = 0.85

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13 Methusalem Advisory Board meeting, Ghent, 17 June 2011

Case II: criterion based amount of M added (1)

OBTAINED average CL polymer end group functionality PDIpol 1042 0.19 1.90 1594 0.62 1.37 >43 % improvement

initial TCL = 100

TCL 5000

after each addition: [styrene]/[alkoxyamine] = 100

no classical equivalent

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Case II: criterion based amount of M added (2)

PROPAGATION CHAIN TRF TO DIMER TERMINATION (RECOMB) DEACTIVATION

EFFECTIVE SUPPRESSION OF CHAIN TRF TO DIMER AND TERMINATION

REACTION PROBABILITY FOR MACRORADICALS (RPi

bulk)

RPi

bulk,propagation (-)

RPi

bulk,chain TRF to D (-)

RPi

bulk,termination by recomb(-)

RPi

bulk,deactivation(-)

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Case II: criterion based amount of M added (3)

IMPROVEMENT OBTAINED average chain length (-)

MULTIPLE ADDITION of criterion based amount MULTIPLE ADDITION of predetermined amount

CONVERSION = 0.85

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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…

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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

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‘Ideal’ miniemulsion: concept

emulsifier initiator (alkoxyamine) EMULSIFICATION BEFORE POLYMERIZATION ASSUMPTIONS:

oil-soluble initiator
uniform monomer droplet size
homogeneous initiator concentration

monomer water monomer droplets

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‘Ideal’ miniemulsion: concept

BEFORE POLYMERIZATION ASSUMPTIONS:

oil-soluble initiator
uniform monomer droplet size
homogeneous initiator concentration

POLYMERIZATION ASSUMPTIONS:

polymerization only in oil phase
no mass transfer to aqueous phase
constant particle size

monomer droplets

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‘Ideal’ miniemulsion: modeling approaches for NMP

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

In literature: mainly TEMPO/styrene

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)

Kinetic Monte Carlo (Tobita)
intrinsic kinetic model
focus on the effect of particle size on overall polymerization rate

Our approach: SG1/styrene

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‘Ideal’ miniemulsion: modeling

droplets with i macroradicals, r initiator radicals, j nitroxide radicals

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‘Ideal’ miniemulsion NMP: modeling

Generalized Smith-Ewart equations = NA vp ka,app τ0 (Ni-1,r

j-1 - Ni,r j)

dNi,r

j

dt + NA

1 vp
1 <kda,app ,0> ( (i+1)(j+1)Ni+1,r

j+1 – (i)(j)Ni,r j)

+ NA

1 vp
1 <kda0,app ,0>((r+1)(j+1)Ni+1,r

j+1 – (r)(j)Ni,r j)

+ NA vp kthi,app [M][D](Ni,r-2

j – Ni,r j)

+ NA

1 vp
1 <ktc,app ,0> ((i+2)(i+1)Ni+2,r

j – (i)(i-1)Ni,r j)

+ NA

1 vp
1 ktc00/2 ((r+2)(r+1)Ni,r+2

j – (r)(r-1)Ni,r j)

+ NA

1 vp
1 <ktc0,app ,0>((i+1)(r+1)Ni+1,r+1

j – (i)(r)Ni,r j)

+ <ktrM,app ,0>[M]((i+1)Ni+1,r-1

j – (i)Ni,r j)

+ <ktrD,app ,0>[D]((i+1)Ni+1,r-1

j – (i)Ni,r j)

+ kp0 [M]((r+1)Ni-1,r+1

j – (r)Ni,r j)

+ ktrXD[D]((j+1)Ni,r-1

j+1 – (j)Ni,r j)

droplets with i macroradicals, r initiator radicals, j nitroxide radicals i-1 r j-1 i+1 r j+1 i r-1 j-1 i r+1 j+1

+ NA vp ka0,app [R0X] (Ni,r-1

j-1 - Ni,r j)

i+1 r j+1 i-1 r j-1 i r+1 j+1 i r-1 j-1 i r-2 j i r+2 j i+2 r j i-2 r j i r+2 j i r-2 j i+1 r+1 j i-1 r-1 j i+1 r-1 j i-1 r+1 j i-1 r+1 j i+1 r-1 j i r-1 j+1 i r+1 j-1

number of droplets with i, r, j

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23 Methusalem Advisory Board meeting, Ghent, 17 June 2011

‘Ideal’ miniemulsion NMP: modeling

Generalized Smith-Ewart equations

droplets with i macroradicals, r initiator radicals, j nitroxide radicals

“Bulk” concentrations and conversion: continuity equations Average properties: modified moment equations

e.g. total concentration dormant macrospecies

dτ0 dt = <kda,app,0> (NAvp)2 i,j,r (i) (j) Ni,r

j

<ka,app,0> τ0 Ni,r

j

i,j,r

Avogadro constant droplet volume total number of droplets DEACTIVATION ACTIVATION

Viscosity effects included

Number of droplets with (i,r,j)

Analogous as for normal bulk NMP: Bentein et al. Macromol. Theory Simul. 2011, 20, 238

Ni,r

j

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Polymerization rate regions (dp)

TCL = 300

Miniemulsion NMP of styrene initiated by SG1-PhEt at 396 K

region I region II

acceleration retardation

region III bulk

MAXIMUM acceleration (conversion) conversion

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Control over chain length & livingness (dp)

TCL = 300 Full line = miniemulsion Dotted line = bulk always better worse higher MAX MAX MAX

MAXIMUM in region II

bulk bulk bulk

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Reaction probabilities

TERMINATION BY RECOMBINATION WITH MACRORADICAL

REACTION PROBABILITY FOR MACRORADICALS & INITIATOR RADICALS

Ri +M

PROPAGATION CHAIN TRANSFER TO MONOMER CHAIN TRANSFER TO DIMER DEACTIVATION TERMINATION BY RECOMBINATION WITH MACRORADICAL

+X +M +D

TERMINATION BY RECOMBINATION WITH INITIATOR RADICAL

+Rj +R0 R0 +M

PROPAGATION CHAIN TRANSFER TO MONOMER CHAIN TRANSFER TO DIMER DEACTIVATION

+X +M +D

TERMINATION BY RECOMBINATION WITH INITIATOR RADICAL

+Rj +R0

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Region I: retardation (reaction probabilities)

TCL = 300 region I dp = 15 nm fast decrease [R0X] with conversion lower PDI initiator radicals (exception): macroradicals: segregation of radicals and similar overall importance of chain transfer to dimer: higher livingness confined space effect: lower polymerization rate and positive effect on control over chain length and end-group functionality

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Region I: retardation (particle distribution)

region I dp = 15 nm

inactive particle: 0 macroradicals 0 initiator radicals 0 nitroxide radicals

very low: confirming lower polymerization rate TCL = 300

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Region I: retardation (particle distribution)

region I dp = 15 nm

inactive particle: 0 macroradicals 0 initiator radicals 0 nitroxide radicals

very low: confirming lower polymerization rate

active particle: 0 macroradicals 1 initiator radical 1 nitroxide radical

TCL = 300 1 nitroxide radical in very small volume → high concentration (Tobita: Single Molecule Concentration Effect)

active particle: 1 macroradical 0 initiator radicals 1 nitroxide radical

„living‟ characteristics: confirming good control

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Region II: acceleration (reaction probabilities)

TCL = 300 region II dp = 30 nm better overall suppression of termination and chain transfer to dimer reactions (compared to region I): higher livingness clearly propagation favored: higher polymerization rate, higher initial chain lengths very slow decrease [R0X] with conversion higher PDI

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Region II: acceleration (particle distribution)

TCL = 300 region II dp = 30 nm higher: in agreement with higher polymerization rate

0 macroradicals 0 initiator radicals 0 nitroxide radicals 0 macroradicals 0 initiator radicals 2 nitroxide radicals 0 macroradicals 0 initiator radicals 4 nitroxide radicals

inactive particles

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Region II: acceleration (particle distribution)

TCL = 300 region II dp = 30 nm

1 0 5

higher: in agreement with higher polymerization rate well-balanced amount of nitroxide radicals: good livingness

1 macroradical 0 initiator radicals 1 nitroxide radical 1 macroradical 0 initiator radicals 3 nitroxide radicals

active particles

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Transition region II to region III

TCL = 300 region II → III dp = 70 nm similar rates on average: indicative of transition convergence to “bulk” properties: diminished suppression of termination and chain transfer to dimer lower livingness faster decrease [R0X] with conversion lower PDI

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Transition region (2)

TCL = 300 region II → III dp = 70 nm

inactive particles: 0 macroradicals 0 initiator radicals

more nitroxide radicals: retardation → “bulk” high

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Transition region (2)

TCL = 300 region II → III dp = 70 nm

inactive particles: 0 macroradicals 0 initiator radicals

more nitroxide radicals: retardation → “bulk” high

active particles: 1 macroradical 0 initiator radicals

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Effect of diffusional limitations (dp)

TCL = 300 most pronounced at higher dp (bulk limit) Macroradicals Nitroxide radicals

r i j j r i p R

iN N n

, ,

1

r i j j r i p X

jN N n

, ,

1

Full line = with diff. lim. Dotted line = without diff. lim. region II dp = 30 nm region II → III dp = 70 nm region I dp = 15 nm

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Effect of diffusional limitations (dp)

TCL = 300 most pronounced at higher dp (bulk limit) Macroradicals Nitroxide radicals

r i j j r i p R

iN N n

, ,

1

r i j j r i p X

jN N n

, ,

1

Full line = with diff. lim. Dotted line = without diff. lim. main effect at high conversion region II dp = 30 nm region II → III dp = 70 nm region I dp = 15 nm

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Interplay TCL and dp for miniemulsion characteristics

TCL = 300 TCL = 800 TCL = 2000 higher TCL: more improvement at higher dp higher TCL: maximal acceleration at higher dp higher TCL: more effect at higher dp higher TCL: limited increase PDI conversion = 0.70

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Conclusions

bulk NMP of S (SG1-mediated; 396 K)

chain transfer to dimer reactions are important for high TCL
fed-batch approach theoretically proven to improve polymer properties

miniemulsion NMP of S (SG1-mediated; 396 K)

strong effect of droplet/particle size on polymerization rate and control
ver polymer properties:
polymer end-group functionality always higher than in bulk
maximal acceleration corresponding with maximal end-group

functionality

improvement of all properties compared to bulkonly for very small

particles

diffusional limitations are only important for high particle sizes at high

conversion

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Acknowledgements

1.

L. Bentein acknowledges financial support from a doctoral fellowship

from the Fund for Scientific Research Flanders (FWO). 2. This work was supported by the Interuniversity Attraction Poles Programme - Belgian State - Belgian Science Policy and the Long Term Structural Methusalem Funding by the Flemish Government. The research leading to these results has received funding from the European Community’s Sixth framework Programme (contract nr 011730).

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Glossary



CRP: controlled radical polymerization



Livingness: polymer end-group functionality



NMP: nitroxide mediated polymerization



Targeted chain length (TCL): the chain length that would be obtained by an ideal, controlled polymerization at 100% conversion, i.e., the initial ratio of monomer/initiator



Reaction probability of a molecule: the ratio of the rate of a particular reaction to the rates of all other possible reactions that the molecule can undergo



Segregation effect of radicals: physical segregation of radicals in particles, allowing the suppression of bimolecular termination



Confined space effect: smaller particle/smaller volume leads to increased concentrations and increased rates (in this case: of deactivation)



Single molecule concentration effect: one molecule present in such a small volume that its concentration is higher than the concentration of this species in the equivalent bulk system



Mn

pol: number average molar mass of the polymer

