Science and Technology ofPolymers (2nd cycle)

Polymers Reactions andPolymers Production (3rd cycle)

Ana C. Marques

MEQ, MQ, DEQuim, DQuim

2nd semester

2017/2018, IST-UL

Lecture 1

Lectures 1 to 6

Fundamentals of Macromolecular Chemistry:

✓ Definitions, nomenclature, polymer classifications.

✓ Macromolecular structure and characterization.

✓ Polymer solutions.

✓ Average molecular weight and molecular weight distributions: definitions and methods of determination.

Block 1

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INTRODUCTION

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Statistical data

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(annual sales volume net)

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Fundamentals of Macromolecular Chemistry

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Polymers Poly “many” mers “parts” (greek)

• A polymer is a long-chain molecule composed of a large number of repeating units (monomer residues) ofidentical structure. n = number of repeating units in a polymer chain = degree of polymerization (DP) MW(Polymer) =DP×MW(Repeating Unit)

• Polymers: macromolecules of relative molecular weight of at least 1000 or a DP of at least 100

Structure of polyethylene (PE) (crystalline region)

Secondary bondings(Van der Waals)

Example: Polystyrene (PS)

Repeating unit (RU): styrene, C8H8

Thermal and mechanical properties depend on n:• DP or n > 1000Mw (styrene) = 104 average Mw of PS = 104000 brittle solidthat does not soften until it is heated to ca. 100ºC• DP or n=7 viscous liquid at RT

Note: when n<10 oligomers (oligo = “some”)

According to IUPAC, polymersare named bypoly(monomer)

• The repeating units are covalently bonded to each other.

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Polymers Poly “many” mers “parts” (greek)

Some polymers are derived from the mutual reaction of two or more monomers that are chemically similar but not identical.

The RU consists of two structural units, residues of both monomers employed

Example: Nylon 6,6

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Questions

What is the degree of polymerization of a sample of polyethylene which has a molar mass of 100000 g/mol? (R: 3570 mers/mol)

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Typical properties of polymers (Appendix):

- Insulators- Amorphous or semi-crystalline- Low density- Varied strength and ductility- Tend to degrade or melt at higher temperatures (e.g. T>200ºC)- Corrosion resistant- Tend to be flammable

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History

1. Natural polymers– Natural rubber (isoprene)

– Polysaccharides (cellulose, cotton, starch)

– Proteins (wool, silk)

2. Synthetic polymers (commodities)– PE, PP, PS, PVC, PET

3. Engineering Polymers– PMMA, PC, PU, POM, PPO, …

4. Functional polymers

5. Biopolymers

Naturally Occurring Polymers

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Milestones in polymer industry

Bakelite(phenol-formaldehyde resin)

the 1st fully synthetic polymer

Celluloid

Polymers were thought to beaggregates of small moleculeslinked by secondary forces (Van der Waals)

Staudinger (1918-1920) proposed that in manymacromolecules the repeatingunits were covalently bonded(high molecular weight molecules)

Notion of Mw and itsdetermination by viscometry

Carothers (1931):1st polycondensationreactions (polyesters, polyamides) leading to highMw polymers

Prior to the early 1920's, chemists doubted the existence of molecules having molecular weights greater than a few thousand...

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from “Introduction to Physical Polymer Science, 4th Ed., L.H. Sperling, John Wiley & Sons, Inc., 2006”

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Milestones in polymer industry

Development of high performance engineering plastics that could compete with more traditional materials, such as metals in automotive and aerospaceapplications

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Polymers classification by:

• Natural or synthetic

• Polymerization mechanism (condensation, addition)

• Polymer structure:

• Chemical structure:

- Homopolymers or copolymers;

- Characteristic interunit linkage: polyolefins, unsaturated polyolefins, vinyl resins, acrylic

resins, styrenic resins, polyesters, polyamides, polycarbonates, polyurethanes, polyureas, …

• Chain topology: linear, branched, cross-linked, ladder…

• Stereoregularity: syndiotatic, isotatic, atatic

• Thermoplastics, thermosets, elastomers, fibers

• Inorganic backbone or organic backbone

• Amorphous or crystalline

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• Thermosets

Types of polymers• Commodities: HDPE, LDPE/LLDPE, PP, PVC, PS, PET• Engineering: PA, PC, PMMA, POM, PU,…• Speciality: Kevlar, Kapton, PEEK, …

• Natural (cellulosic – cotton, wool, silk…)• Synthetic (cellulosic and non-cellulosic – Polyester (PET); Polyamides (PA 6,6);

Acrylic (PAN), Polyolefinic (PP)…)

• Chemically cross-linked (isoprene, butadiene, isobutylene,…)• Physicaly cross-linked / thermoplastic elastomers (ABS, SAN, SBS, …)

• Phenolics (phenol-formaldehyde)• Amino-based (urea-formaldehyde, melamine-formaldehyde,…)• Unsaturated poliesters• Epoxides• Polyurethanes

• Silicones, polysilanes• Polyphosphazenes• Polygermanes, polystannanes

one of the monomers must be trifunctional or greater. Insoluble;

rigid, breakable, higher termal and mechanical resistance

56% 15%

85%

• Thermoplastics

• Elastomers

• Fibers

• Inorganic polymers

90%

90%

11%

18%

50%70%

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• Polysaccharides (cellulose, starch / amylopectin, chitin / chitosan, ...)• Lignin • Proteins (wool, silk, ...)• Phosphoric acid polyesters (nucleic acids, ...)• Aliphatic polyesters (poly-b-D-hydroxy-butyrate, suberin, ...)• Polyprenes (natural rubber (polyisoprene-cis), ...)

• Adhesives and sealants

• Paints and coatings

• Biological polymers

• Solvent-lesso Non-reactive: hot-melt; Reactive: photoresists

• Solvent-basedo Non-reactive: lacquers, inks (latex/emulsions)o Reactive: varnishes, inks (pigments, solvents)

Hot melts (thermoplastics); Contact (termoplastics + …); Structural (thermosets)

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The ultimate mechanical properties of any polymer result from a balance of:

• Molecular weight or molecular weight distribution

• Chemical structure

The structure and molecular weight condition the intermolecular forces:

• Hydrogen bonds

• Van der Waals forces permanent dipole - permanent dipole (Keesom forces)

permanent dipole - induced dipole (Debye forces)

instantaneous dipole - Induced dipole (London forces)

• Ion-dipole forces

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Kevlar®:Absence of aliphatic

units in the mainchain: high

thermooxidativestability; highly

crystalline material, forming a stronger

fiber than that of steelon an equal weight

basis

Number of carbon atoms in the chain matters…

Comparison of paraffinwax and polyethylene

structure and morphology:

PE chains are long enough to connectindividual stems together within a lamellar crystallite by chain folding

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Polymers structure

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Polymers structure

PrimaryRelates to the chemical structure (atomic composition) of the monomers.

Results from the covalent bonds between RUs:

✓ Homopolymers/Copolymers

✓ Chain topology: linear, cyclo-linear, branched, cross-linked (macromolecular networks), …

✓ Natural Macromolecules

SecondaryRelates to the size (Mw) and shape (conformation andconfiguration) of an isolated single macromolecule(single polymer chain).

Results from the spatial arrangement of the main chainsegments, dictated by stereochemistry (most stableconformation) or H bonding.

TertiaryAggregation of polymer chains

Results from 3D structure of the chain dictated byintramolecular forces and H bonds between distantsegments of the chain

QuaternaryResults from the interaction between different chains

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Homopolymers• Only one type of RU

It should be noted that some polymers, such as nylon 6,6 and PET have RUscomposed of more than one structuralunit these are still consideredhomopolymers!

Copolymers• Composed of two or more RUs.

• Called terpolymer if there are 3 RUs.

• Different sequences depending on themonomers reactivity:

Random (statistical)

Alternating (regular)

Block (regular)

Graft (regular)

CH2 NHNH

C

O

CH2 C .

O.

6

4

nylon 6,6(polyamide 6,6)

Ex. of ABA-triblock: PS-block-polybutadiene-block-PS (SBS)

by polymerizing a monomer in the presenceof a fully formed polymer of other monomer(e.g. elastomeric SBR, and high impactpolymers: high-impact PS and ABS)

Chemical structure

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Some common homopolymers and their typical applications

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Some common homopolymers and their typical applications

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Some common homopolymers and their typical applications

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Questions

A copolymer consists of 35 wt% acrylonitrile and 65 wt% styrene. Determine the mole fraction of the two components of this copolymer. (R: 0.51 and 0.49)

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Skeletal structure (chain topology)

• Linear: chain with two ends

(the sequence of linkages between bifunctional monomers is necessarily linear)

• Branched: side chains of significant length bonded to the main chain

(reaction between polyfunctional molecules)

• Network polymers: 3D structure in which each chain is connected to all others by a sequence ofjunction points and other chains; characterized by their cross-linking density (number of junctionpoints per unit volume):

• Loose networks: low cross-linking density (e.g. vulcanization (i.e. sulphur cross-linking) of natural rubber) flexibleelastomer (elementary chain, i.e. portion of chain in between 2 branching points, is more than 5 monomeric units)

• Cross-linked: high cross-linking density rigid plastic

Depends on the functionality of themonomers (mono, bi or multifunctional)

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LinearE.g.: extra pair of electrons in the double bond of styrene 2 bonds styrene is bifunctional PS has linear structure

Two condensable groups in hexamethylenediamine (-NH2) and adipic acid (-COOH) makes each of these monomersbifunctional nylon 6,6 has linear structure

Carbon chain linear polymers: HDPE, PP, PIB, PS, polybutadiene, polyisoprenePolymers containing halogen substituents: PVC, PTFE, polychloroprenePolymers with polar side groups: PMMA, poly-HEMA, polymethylacrylate, poly acrylic acid, polymethacrylic acid, poly sodium acrylate, poly cyano ethyl acrylate, poly acrylonitrile, polyvinylacetate, poly vinylbutyrate, polyvinylalcohol, poly vinylpyrrolidone, poly vinylcarbazole

Inorganic chain polymers: polymeric sulphur (…-S-S-S-S-…), polysilanes (…-Si-Si-Si-…), poly siloxanesor silicones (…-Si-O-Si-O-Si…), polyphosphazenes, …

Heteroatoms chain polymers: Polyethers (poly oxymethylene - POM, poly ethylene oxide – PEO); Polyesters (poly ethylene terephtalate – PET); polyanhydride; polyamides (poly caprolactam), nylon 6,6, Kevlar,..); PC, PU, PUs, poly isocyanates, … Polymers containing sulphur in the main chain: poly sulfone, …

Tm (linear PE) is 20C higher thanTm (branched PE)

the presence of polar pendant groups can considerably reduce room temperature

solubility.

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LinearExamples of some important Addition polymers (chain reaction polymerization) derived from ETHYLENE

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Linear

Examples of some functional groupsand their characteristic interunitlinkage in polymers:

Stepwise structures (polycondensation reactions) and nomenclature

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Cyclo-linearPolymers with alternating cyclic-linear fragments: poly phenylene oxide, poly vinylacetal, poly vinyl butyral, …

Polymers with bonded rings: poly p-phenilene, poly imides, poly phenylsilsesquioxane, poly imidazo-pyrrolone, cyclization of polyacrylonitrile…

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The transformation of this viscous liquid into a hard, cross-linked 3D molecular network involves the reaction of the prepolymer withreagents such as amines or Lewis acids CURING reaction.

1st) attack of an epoxide group by the primary amine:

2nd) the combination of the resulting secondary amine with a secondary epoxy group to form a branch point:

Cross-linked

E.g. EPOXIES exist at ordinary temperatures as low-molecular weight viscous liquids or PREPOLYMERS, such as DGEBA:

Unlike linear and branched polymers, cross-linked polymers do not melt upon heating and will not dissolve, though they willswell considerably in compatible solvents.

Examples: phenol-formaldehyde, unsaturated polyesters, polyurethanes, epoxys,…

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The presence of these branch points ultimately leads to a cross-linked infusible and insoluble polymer with structures such as:

Cross-linked

The stoichiometry in this reaction requires 1 epoxy group per 1 active hydrogen (amine hydrogen), whichmeans that components should be mixed in the proportion 1:1 (equivalent weigths), i.e. EEW/AHEW.

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Loose networks

C C

CH3

CH2 CH2 CH2

C C

CH3 H

CH2 CH2

C C

HCH3

. CH2 CH2

C C

CH3 H

CH2 CH2

C C

CH3

CH2 .

H H

borracha natural

C C

CH3

CH2 CH2

H

Example: Natural rubber (poly isoprene)

Vulcanization (light cross-linking)(>5 RUs between 2 branching points)

Heating the elastomer withsulfur and an accelerator, or with peroxides, nitro,

quinones or azo compounds, depending on

the polymer

Lightly cross-linked (vulcanization) long-range movement of the polymer molecules is restrained at the same time that highlocal segmental mobility is allowed large deformations under stress, but rapid and complete recovery of such deformation

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Questions

How much sulfur must be added to 100 g of polyisoprene rubber to cross-link 5% of the monomer units? Assume that all the sulfur is used and that only one sulfur atom is involved in each cross-link (S1). (R: 2.4 g sulfur)

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Ladder polymersLadder polymers, double-chain or double-strand polymers: two parallel linear strands of molecules with a regular sequence of crosslinks.

Two bonds must be broken at a cleavage site in order to disrupt the overall integrity of the molecule higher thermal and mechanical stability than linear polymers

Ex: poly(imidazopyrrolone)

Aromatic dianhydride(Pyromellitic dianhydride)

Ortho-aromatic tetramine (1,2,4,5-tetraaminobenzene)

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