Polymer Synthesis CHEM 421 Odian Book Chapter 5-2.

Polymer SynthesisCHEM 421

• Odian Book

Chapter 5-2

Polymer SynthesisCHEM 421

Cationic Polymerization

Polymer SynthesisCHEM 421

Cationic Polymers

CH2 C

CH3

CH3

CH2 C

CH3

CH3

CH2 C CHCH3

CH2

Commercial and Technological SignificanceChemical Name Trade Name Formula

• Polyisobutylen Vistanex, Oppanol

• Isobutylene-isoprene copolymer and chlorinated copolymer

Butyl Rubberand Chlorobutyl

•Polyoxymethylene Trioxane-epoxide copolymer

~98% ~2%

~2%

DelrinCelcon

CH2 O

CH2 O C C OR

Polymer SynthesisCHEM 421

Cationic Polymers

CH2 CH2 CH2 OCH2

CH2 C CH2

CH2Cl

CH2Cl

O

Commercial and Technological SignificanceChemical Name Trade Name Formula

•Polyepichlorohydrin

•Poly(THF) or Poly(tetramethylene oxide)

•Polybischloromethyl Oxetane

Hydrin Rubber

Lycra or Spandex

Penton

CH2 CH O

CH2Cl

Polymer SynthesisCHEM 421

Cationic Polymerizations

C

R

R'

X

CH3O CH3

R = electron releasing group

R, R’= Poly(isobutylene)CH3

CH3

C2H5R

H

H

H

H

H

Polymer SynthesisCHEM 421

Cationic Polymerization

OO

CH2Cl

O

…Also cyclics

Hydrin RubberPoly(oxymethylene) Delrin

O O

O

Polymer SynthesisCHEM 421

Cationic Polymerization

HX

RX

or

H

R

Xor

HCl AlCl3

1) Priming

2) Initiation Step

H AlCl4

R H2C C R CH2 C

Polymer SynthesisCHEM 421

Cationic Polymerization

R CH2 C H2C C R CH2 C CH2 C

C H2C C

3) Propagation

4) CM

CH

C H3C C

Polymer SynthesisCHEM 421

Initiators

H2C CHA H CH2 C A

CH3 S OH

O

O

A) Bronsted Acids

ionic

covalent

A can not be too nucleophilic

HCl is not very good

Methanesulfonic acid

C ACH3

Polymer SynthesisCHEM 421

Initiators

BF3 H2O

RCl SnCl4

RCl AlCl2R

B) 1)Lewis AcidsSnCl4, AlCl3, TiCl4, BF3

R3Al, R2AlCl, RAlCl2

2) Co initiatorHOBF3 H

R SnCl5

R AlCl3R

Polymer SynthesisCHEM 421

Auto Ionization

Bone dry

AlBr32 AlBr4 AlHBr2

BF3 H2C C

Polymer SynthesisCHEM 421

Chain Transfer

More Important in Cationic than in Anionic

1) To MonomerCH2 CH HSO4 CH2 CH

CH CH CH3 CH HSO4

Polymer SynthesisCHEM 421

Chain Transfer

2) Ring Alkylation on Solvent

CH2 CH HSO4

CH2 CHH

CH3 CH HSO4

CH2 CH

Polymer SynthesisCHEM 421

Chain Transfer

CH2 CH HSO4CH2 CH

3) Ring Alkylation on Polymer

Polymer SynthesisCHEM 421

Chain Transfer

CH2 CH CH2 C

H

HSO4

4) Hydride Abstraction from Polymer

CH2 CH2 C HSO4

Polymer SynthesisCHEM 421

Poly(isobutylene)

Low MW (Mn<50,000 g/mol)Liquids adhesives caulking sealants motor oils - important

Tpzn= 0 to – 40 oC w/AlCl3

Polymer SynthesisCHEM 421

Poly(isobutylene)

High MW (Mn= 50,000-5,000,000)Elastomeric

Tpzn= –100 oC w/ AlCl3

w/ 1-5 % isoprene (to vulcanize)

Methylchloride as solvent

SlurryCH2 C CH2

CH3

CH3

C

CH3

CH CH2

Polymer SynthesisCHEM 421

Butyl Rubber Advantages

• Lower Temp Capability

– -50 oC NO TM

– -70 oC = TG

• More Resistant to Ozone

• Very Low Gas Permeability

inner tire tubes

Polymer SynthesisCHEM 421

Temperature Dependence

_ Xn

1/T

Polymer SynthesisCHEM 421

Temperature Dependence

As T Termination and CT

Break

change in mode of CT

[ions] vs [ion pairs]

Polymer SynthesisCHEM 421

CH2 CH2 C

CH3

CH3

A

Complications

H2C CH

CH

CH3

CH3

RH2C CH

CH

CH3

CH3

A

3-methyl-1-butene

As T , % isomerization

Polymer SynthesisCHEM 421

Complications

H2C CH

CH

CH3

CH3

3-methyl-1-butene

Temp %isomerization-130 oC 100 %-100 oC 70 %

CH2 CH

CH

CH3

CH3

CH2 CH2 C

CH3

CH3

Polymer SynthesisCHEM 421

Isomerization

H2C CH

CH

CH3

CH3

CH2

Polymer SynthesisCHEM 421

Cationic Living Polymerization

CH

OEt

H2CH3C CHI

OEt

HI/I2

-30 OCn-hexane

H3C CHI

OEt

I2 H3C CH

OEt

I3

H3C CH

OEt