Free Radical Polymerizations

1
Free Radical Polymerizations
2

• Reading assignments
• Chapter 3-3, 3-4, 3-5, 3-8 (Odian)

3
Free Radical Solution Polymerizations

• Initiation
• Propagation
• Termination

d R / dt 2 kd I
2 f kd I
- d R / dt ki R M
rp kp M M
- d P / dt 2 kt P2
4
Free Radical Solution Polymerizations

• Overall rate expression
• Assumptions?
• Steady State Approximation (Ri Rt)

Rp kp M M
2 f kd I 2 kt M2
M (kd f I / kt)1/2
Rp kp M (kd f I / kt)1/2
5
Free Radical Solution Polymerizations

• Overall rate expression
• Rate is first order in monomer
• Rate is ½ order in initiator
• To increase Rp

Rp kp M (kd f I / kt)1/2
6
Determination of Orders of Reaction
T 75 C, P 4000 psig, ?CO2 0.74 g/ml
Rp (VF2IN-VF2OUT)/?
DEPDCIN 3 mM
Rp (mol/L x sec)
Rp/VF2out (1/ sec)
I
Iout 0.5 (mol/L)
VF2out (mol/L)
7
Experimental Ways of Determining Rp

• 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

8
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
9
Dilatometer
10
Free Radical Solution Polymerizations

• Overall rate expression
• Rate is first order in monomer
• Rate is ½ order in initiator
• Qualitative picture?

Rp kp M (kd f I / kt)1/2
11
Free Radical Solution Polymerizations

• Kinetic Chain Length (?)
• Average number of monomer units polymerized per
  chain initiated

12
Free Radical Solution Polymerizations

• Kinetic Chain Length (?)
• To increase molecular weight
• To increase Rate of Polymerization

?
13
Kinetic Chain Length (?) vsDegree of
Polymerization (DP)

• Termination by combination
• Termination by disproportionation

14
(No Transcript)
15
Classes of Free Radical Initiators
16
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
• Integrateor
• Half life?

- dI / dt kd I
I I0 e-kdt
17
(No Transcript)
18
Factors which Influence Initiator Choice

• Temperature of polymerization
• Solubility of the initiator
• End group control or functionalization

19
Factors which Influence Initiator Choice

• End group control or functionalization

20
Pulsed-laser Polymerization in Homogeneous Phase
Determination of kp
21
Pulsed-laser Polymerization in Homogeneous Phase
Determination of kp
22
Evaluation of kp
23
Kinetic Chain Length Profile in a PLP Experiment
24
Lii kp M td
25
Lii kp M td