macromolecular chemistrywillson.cm.utexas.edu/teaching/chem367l392n/files/lecture...chemistry...
Post on 04-Feb-2021
0 Views
Preview:
TRANSCRIPT
-
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
top related