Chemistry 367L/392N

Macromolecular ChemistryMacromolecular Chemistry

Lecture 6 Lecture 6

∑∑=

Ni

MiNiMn

∑∑

∑∑ ==

NiMi

NiMi

Wi

WiMiMw

2

MM

PIn

w=

Chemistry 367L/392N

Molecular Weight Molecular Weight Distribution in Polymeric Distribution in Polymeric

MaterialsMaterials

Molecular weight

Polymer%

Chemistry 367L/392N

Radical Chain Growth PolymerizationRadical Chain Growth Polymerization

� Among the initiators used for radical chain-growth polymerization are diacyl peroxides, which decompose as shown on mild heating

∆O

O

O

O

Dibenzoyl peroxide

O

O

2 + 2 CO2

A phenyl radical

A benzoyloxy radical

2

Chemistry 367L/392N

InitiationInitiation

CHH2C CH2 CH

Chemistry 367L/392N

PropagationPropagation

CHH2CCH2 CH CH2 CHH2C CH

Chemistry 367L/392N

TerminationTermination

Ph*

RR

n2

Ph*

RR

n

R R

n Ph*

Ph*

RR

n2

R

n PhH3C

DisproportionationDisproportionation

CouplingCoupling

+

Chemistry 367L/392N

Radical GenerationRadical Generation

�� ThermolysisThermolysisR N N R' R N N R'•

R'R N2+ + •• +

Thermal decomposition of Thermal decomposition of azoazo--compoundscompounds

NN

NC

CNN

N

CN

CN

2,22,2’’--azobis(2azobis(2--methylpropanenitrile)methylpropanenitrile) 1,11,1’’--azobis(1azobis(1--cyclohexanenitrile)cyclohexanenitrile)(AIBN)(AIBN)

Chemistry 367L/392N

R O O R' R O R' O +

Thermal decomposition of peroxidesThermal decomposition of peroxides

OO

O

OO

O OS

OO

SO

O

O

O

O

Na+

Na+

BenzoylperoxideBenzoylperoxide (BPO)(BPO) didi--terttert--butylperoxidebutylperoxide sodium sodium persulfatepersulfate

Thermolysis of peroxides Thermolysis of peroxides --OO--OO--

Chemistry 367L/392N

Photolysis

O

OR

R' C

O

C O

R

R'

hνννν +

Photolysis of Photolysis of benzoinbenzoin (R=R(R=R’’=H).=H).

Chemistry 367L/392N

RedoxRedox InitiatorsInitiators

OO

H Fe2+

O Fe3+

OH_

+ + +

RedoxRedox decomposition of decomposition of cumylcumyl hydroperoxidehydroperoxide

RedoxRedox decomposition of decomposition of persulfatepersulfate

O3SO

OS3O

-- Fe(II) SO4

--SO4

*- Fe(III)+ + +

Chemistry 367L/392N

Self initiation of monomerSelf initiation of monomer

H+

Diels-Alderdimerization

molecular-assistedhomolysis

Chemistry 367L/392N

= 0.693/k= 0.693/kdd

For efficient polymerization rate For efficient polymerization rate -- need sufficient radicals.need sufficient radicals.

Too few Too few -- slow, poor conversion with tslow, poor conversion with tToo many Too many -- exothermic, low mol. wtexothermic, low mol. wt

AIBNAIBN 6464 10 hrs10 hrs8282 1 hr1 hr100100 6 6 minsmins120120 1 min1 min

Optimum = 75Optimum = 75--9090ooCC ----> Reaction Time ~ 2> Reaction Time ~ 2--3 (t3 (t1/21/2 ))

[I] kk = = kkmaxmaxe e --E/E/kTkT

[Time]

dtdtIIdd ]][[

−−==kkddI I →→ 2 R2 R·· kkdd

kt

d

2ln2/1 =

Chemistry 367L/392N

Decomposition of Thermal InitiatorDecomposition of Thermal Initiator

OO N

NCN

CNO

OO

O

O

O

di-tert-butylperoxide AIBN di-tert-butylperoxalatef = 0.65 f = 0.75 f=0.95

[ ] [ ]Ikfdt

Rdd

2•

Ri

==

Efficiency factor ( Efficiency factor ( ff ):):

k dI → 2 R·

Chemistry 367L/392N

Temperature of 1 hr Temperature of 1 hr tt1/21/2

Chemistry 367L/392N

-- dd[[MM··]]RRii== dtdt

== 2 2 kktt [[MM··]]22 Where Where kktt = = kktctc+ + kktdtd

RRpp= = dtdt--d[[MM]]

= = kkpp[[MM][][ MM··]]

[[MM··]]==

Kinetics of free radical polymerizationKinetics of free radical polymerization�������� SSteady state assumption:teady state assumption:

What is the Propagation rate ( What is the Propagation rate ( RpRp ))

22]][[22]][[22 ⋅⋅== MMkkIIfkfk ttddtt

dd

kk

IIfkfk ]][[

RRpp= = dtdt--dd[[MM]]

= = kkpp[[MM]]tt

dd

kkIIfkfk ]][[

SoSo……

RiRi = = RtRt

Chemistry 367L/392N

Average kinetic chain lengthAverage kinetic chain length (( ӮӮ ))

DisproportionationDisproportionation: :

Combination : Combination :

Kinetics of free radical polymerizationKinetics of free radical polymerization

ӮӮRR

RR

RR

RR

tt

pp

ii

pp ==

ӮӮ]][[((

]][[22

]][[22

]][[

]][[22]]][][[[

22 IIkkfkfk

MMkk

MMkk

MMkk

MMkk

MMMMKK

ddtt

pp

tt

pp

ttpp ==⋅⋅

==⋅⋅

⋅⋅==

DP =DP = 22ӮӮ

DP =DP = ӮӮ

Chemistry 367L/392N

Arthur K. Doolittle AwardArthur K. Doolittle Award

The Arthur K. Doolittle Award, established by the Union The Arthur K. Doolittle Award, established by the Union Carbide Corporation, is given to the authors of an outstanding Carbide Corporation, is given to the authors of an outstanding paper presented before the PMSE Division at each national paper presented before the PMSE Division at each national meeting of the ACS. A prize in the amount of $1,000.00 is meeting of the ACS. A prize in the amount of $1,000.00 is financed with the gift of royalties from A. K. Doolittle's book,financed with the gift of royalties from A. K. Doolittle's book,Technology of Solvents and PlasticizersTechnology of Solvents and Plasticizers. All papers are . All papers are evaluated on the basis of content, with emphasis on evaluated on the basis of content, with emphasis on originality and development of new concepts, and on the originality and development of new concepts, and on the quality of presentation. Recipients are selected by an quality of presentation. Recipients are selected by an anonymous panel of judges appointed by the Chairman of the anonymous panel of judges appointed by the Chairman of the Doolittle Award Committee. Doolittle Award Committee.

Chemistry 367L/392N

TEMPO Controlled PolymerizationTEMPO Controlled Polymerization1993 M. K. Georges, R. P. N. 1993 M. K. Georges, R. P. N. VereginVeregin, P. M. , P. M. KazmaierKazmaierand G. K. and G. K. HamerHamer(Xerox (Xerox Corporation), "Narrow Molecular Weight Resin by Free Radical ProCorporation), "Narrow Molecular Weight Resin by Free Radical Process."cess."

I

+ O N

IO N

Monomer

Polymer + O NPolymer O N

DP =[monomer]

[Initiator]

(2,2,6,6-tetramethylpiperidinyl-1-oxy)TEMPO

Chemistry 367L/392N

Controlled Free Radical Controlled Free Radical PolymerizationPolymerization

Chemistry 367L/392N

Control of polymer ArchitectureControl of polymer Architecture

O

O

O

N

+

O

OCH3

AIBN

OO

OTEMPO

OOCH3

OOCH3

OOCH3

OO

OTEMPO

Chemistry 367L/392N

OO

OTEMPO

OOCH3

OOCH3

OOCH3

OO

OTEMPO

OO

OOCH3

OOCH3

OOCH3

OO

Ph

Ph

Ph

Ph