chapter 2. principles of polymerization - hsbr1. · pdf filehydrolysis polyvinyl ... with...

CHEM 4364 – © Dr. Houston Brown - 2016

Chapter 2.Principles of Polymerization

CHEM 4364 – © Dr. Houston Brown - 2016

PolymerizationIn order to form a polymer, a monomer must have a functionality of two or greater. (Think about it…)

CHEM 4364 – © Dr. Houston Brown - 2016

Polymerization Reactions• Condensation Polymerization• Repeat unit has fewer atoms than the monomer from which they are formed.

• Usually from the elimination of a molecule like HCl or H2O.

• Note that the reverse reaction may NOT always involve the gain of the same molecule (i.e. a polymer opening).

• Addition Polymerization• Repeat unit has an identical formula to the monomer from which it was formed.

• Usually easy to “unzip” and find the monomer.

• These two methods of classification can be improved upon!

CHEM 4364 – © Dr. Houston Brown - 2016

CHEM 4364 – © Dr. Houston Brown - 2016

Polymerization Reactions• Step-growth polymerization. (Step polymerization)• 2 pieces come together.

• Degree of polymerization increases steadily throughout the reaction.

• Functional groups become links between repeating units. The degree of reaction must be high!

• Think about it… If one in 100 fails, you are stopped at a chain length of 100.

• Chain-growth polymerization. (Chain polymerization)• 1 monomer at a time

• High degree of reaction even at low rates of conversion.

• The chemistry must be clean! The presence of side reactions, multiple products will kill the polymer.

• Note that the previous slide had all examples of linear polymerizations, and all a functionality of two.

CHEM 4364 – © Dr. Houston Brown - 2016

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CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group Reactivity and Molecular SizeChemical reactions proceed between mutually-reactive functional groups.

Each encounter results in diffusion apart, or more rarely, reaction.

Reaction is usually dependent on frequency of the functional group, not the molecule to which it is attached. As molecular size increases, the rate of molecular diffusion decreases, leading to larger gaps of time between potential to react.

Each reaction for a large molecule becomes longer, and hence, more productive.

This leads to the reactivity of a functional group being independent of molecular size. (To a good approximation…)

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group Reactivity and Molecular SizeMathematical analysis of polymerizations is simplified greatly by this assumption.

This principle of equal reactivity of functional groups was proposed by Flory.◦ Flory proceeded to demonstrate the validity for functional groups in many step polymerizations by

examining the kinetics of model reactions.

◦ Analysis of the kinetics of chain polymerizations shows that it is reasonable to assume that the reactivity of the active species at the chain end is independent of the degree of polymerization.

CHEM 4364 – © Dr. Houston Brown - 2016

Polymer ModificationIn the next few chapters, we will look at polymer synthesis.

However, let’s assume we already have a polymer. Can a polymer be modified?

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionHydrolysis

◦ Polyvinyl acetate to polyvinyl alcohol

◦ Treatment with sodium hydroxide (with by-products of acetic acid and sodium acetate

◦ Treatment of with sulfuric acid in methanol (with by-product of methanol

◦ Degree of hydrolysis up to 90% possible

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionHydrolysis

◦ Polyacrylamide to polyacrylic acid

◦ Treatment with sodium hydroxide (with by-products of acetic acid and sodium acetate)

◦ Degree of hydrolysis up to 50% possible

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionChlorination and chlorosulfonation of polyethylene

◦ Treatment with UV light and chlorine (by-product of HCl)

◦ Treatment of chlorine gas bubbled in a solution (or suspension) with chlorobenzene and temperature of 130 C.◦ treatment yields a chlorine every 3 to 4 units

◦ polymer has decreased flammability over untreated polyethylene

◦ polymer is blended with PVC to improve impact strength

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionChlorination and chlorosulfonation of polyethylene

◦ Treatment of polyethylene with chlorine and sulfur dioxide.◦ Gases are bubbled in a solution (or suspension) with

tetrachloroethylene and free radical initiator (like AIBN)

◦ Treatments yields a chlorosulfonyl group every 40 to 45 units

◦ chlorosulfonylpolyethylene is crosslinked with treatment of lead(IV) oxide or magnesium oxide

◦ DuPont tradename is Hypalon (also known as CSM rubber)

◦ An elastomeric material, used as a synthetic rubber

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionChloromethylation of polystyrene

◦ 1. Friedel-Crafts reaction with chlorodimethylether and AlCl3

◦ 2. High conversion rates are possible to yield polyvinylbenzylchloride

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionFurther modifications are useful

◦ amination with a tertiary amine yields an anion exchange polymer

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionSulfonation with sulfuric acid yields an cation exchange polymer

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionLithiopolystyrene derivatives

◦ Butyllithium with tetramethylethylene diamine (TMEDA) yields lithiated polystyrene (para position favored over ortho position)

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionReaction with carbon dioxide to yield benzoic acid derivative that is used as a less water-soluble flocculent

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionReaction with orthorhombic sulfur and lithium aluminum hydride to yield thiophenolderivative that can be crosslinked via the creation of disulfide bonds

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionReaction with benzophenone to yield a derivative with a light stabilizer as part of the polymer structure.

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionPolyvinylamine from polyacrylamide

◦ Treatment with bromine and hydroxide to form isocyanate, then treatment with water to form amine (by-product of carbon dioxide).

◦ The treatment is a Hoffmann degradation.

◦ Polyvinylamine has anti-bacterial properties

◦ Polyvinylamine is used to impregnate paper for packaging.

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionPolyvinylbromide (head-to-head)

◦ Bromination of 1,4-polybutadiene

◦ Bromination adds flame retardation to polymer

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionEpoxidation of rubber

◦ Treatment of polyisoprene with H2O2 in EtOHand HOAc

◦ Epoxidation increases oil resistance and decreases gas permeability of rubber.

CHEM 4364 – © Dr. Houston Brown - 2016

Functional Group SubstitutionConversion of polyvinylchloride to polyvinylcyclopentadienyl

◦ Treatment with dimethylaluminumcyclopentadienyl

◦ Polyvinylcyclopentadienyl is ready to crosslink via a Diels-Alder reaction

◦ Crosslinking is reversible; thus, the thermoset material has the potential to be recycled.

CHEM 4364 – © Dr. Houston Brown - 2016

Skeletal UnsaturationPolyvinylacetate to polyacetylene

◦ Pyrolysis of polyvinylacetate (or polyvinyl alcohol) ( ~600 C) yields trans-polyacetylene

◦ Polyacetylene is a conductive polymer (when doped with I2)

CHEM 4364 – © Dr. Houston Brown - 2016

Skeletal UnsaturationPolyvinylchloride to polyacetylene

◦ (pyrolysis at 130 – 400 C)

CHEM 4364 – © Dr. Houston Brown - 2016

Cyclization and Ladder FormationPolyacrylonitrile

◦ Pyrolysis at T = 300 C yields a imino ladder polymer.

◦ Further pyrolysis at T = 1000 C rearranges double bond

◦ Final stage of pyrolysis at T = 2800 C yields graphene (linear graphite)

CHEM 4364 – © Dr. Houston Brown - 2016

Cyclization and Ladder FormationPolymethylvinylketone

◦ Base catalyst causes cyclization

◦ Polymer not a true ladder polymer, only three or four cycles are grouped together leaving functional groups (ketone, methyl) between cycle groups.

CHEM 4364 – © Dr. Houston Brown - 2016

Cyclization and Ladder FormationPVC to polymethylene cyclopropane

◦ Cyclization of polyvinyl chloride may occur with heat and a powdered zinc catalyst.

◦ Cyclization is incomplete.

CHEM 4364 – © Dr. Houston Brown - 2016

Cyclization and Ladder FormationPVA to cyclic acetal

◦ Reaction of polyvinyl alcohol with a ketone and an acid catalyst yields the reaction of a cyclic acetal in the polymer chain.

◦ Cyclization can be up to 90%.

◦ Polyvinyl butyral is used as a laminate in safety glass.

CHEM 4364 – © Dr. Houston Brown - 2016

Cyclization and Ladder FormationEpoxidation of polyisoprene

◦ Reacting polyisoprene with hydrogen peroxide and acetic acid yields the epoxidation of natural rubber.

◦ Epoxidized NR has increase oil resistance and decreased gas permeability.

CHEM 4364 – © Dr. Houston Brown - 2016

Still to cover…Cross linking

Grafting

Surface reaction