Polymer Engineering

Classification of Polymers

• Natural Polymers

• Synthetic Polymers

• Deformable Materials

• Non-Deformable Materials

• Thermoplasts

• Duromers

• Elastomers

• Dispersions

• Varnishes and Paints

• Functional Polymers

Molecular Architecture

• Linear Homopolymer

• Branched Homopolymer

• Statistical Copolymer

• Block Copolymer

• Multi-block Copolymer

• Graft Copolymer

Examples

• High Density Polyethylene (HDPE)

• Low Density Polyethylene (LDPE)

• Styrene Acrylonitrile Copolymer (SAN)

• Styrene-Butadiene Block Copolymer (SB)

• Styrene-Butadiene-Styrene Block Copolymer (SBS)

• Styrene-Butadiene Graft Copolymer (B-g-S)

Non-Deformable Polymers - Examples

• Dispersions based on styrene/n-butylacrylate

• Acrylamide-sodiumacrylate

• Alkylacrylate-copolymers

• Superabsorber

• Polycarboxylate

• Polyethyleneimine

• Paper finishing

• Detergent additives

• Partially crosslinked Acrylamide-sodiumacrylate-alkylene-copolymer

Application

• Precipitants

• Paints

• Polymer

Functional Polymers

• Functional variety by changing the length of molecules…

Example:

• Polymers based on acrylic acid

  • Molar mass 5,000 g/mol: Dispergents

  • Molar mass 70,000 g/mol: Detergents

  • Molar mass 2 Mio. g/mol: Precipitants, Thickeners, Superabsorbers

  • Cross-linked

Functional Polymers - Copolymerization

• Polyacrylic acid

• Acrylic acid/Maleic acid Copolymer

• Polyvinylpyrrolidone

• Vinylpyrrolidone/Vinylacetate Copolymer

• CH_2=CH

• CH_2=CH

• COOH

• CH_2=CH

• CH_2=CH

• COOH

• COOH

• CH_2=CH

• CH_2=CH

• N=O

• CH_2=CH

• N=O

• CH_2=CH

• OOCCH_3

Classification of Thermoplastic Polymers

• High Temperature Thermoplasts

  • TCU: 150°C – 260°C

  • Examples: PAEK, LCP, PAI, PPS, PSU, PEI, PES

• Technical Polymers

  • TCU: 90°C - 140°C

  • Examples: PC, PBT, PET, PA, PPE-Blends, POM, SAN, ABS, PMMA

• Standard Polymers

  • TCU: < 90°C

  • Examples: PS, PVC, LDPE, HIPS, LLDPE, HDPE, PP

Thermoplastic Polymers - Examples

• Polyethylene (LDPE, HDPE, LLDPE): CH2-CH2

• Polypropylene (PP): CH2-CH(CH3)

• Polystyrene (PS): CH2-CH(C6H_5)

• Polyvinylchloride (PVC): CH_2-CH(Cl)

Thermoplastic Polymers - More Examples

• Polyamides (PA-X.Y, PA-X): Reactions of diamines and dicarboxylic acids forming amide links.

• Polyethyleneterephthalate (PET, X=2)

• Polybutyleneterephthalate (PBT, X=4)

• Polymethylmethacrylate (PMMA): C(CH3)(COOCH3)-CH_2

• Polyoxymethylene (POM): (CH2O)n

High Temperature Thermoplasts - Structures and Properties

• Polyethersulphone (PES): Continuous use temperature 190°C

  • [O-C6H4-SO2-C6H4]n

• Polysulphone (PSU): Continuous use temperature 160°C

  • [O-C6H4-SO2-C6H4-C(CH3)2-C6H4]n

• Polyetherimide (PEI): Continuous use temperature 180°C

  • Complex structure involving imide and ether linkages.

• Polyphenylenesulfide (PPS): Continuous use temperature 240°C

  • [C6H4-S]_n

High Temperature Thermoplasts - More Structures and Properties

• Polyphenylenesulphone (PPSU): Continuous use temperature 160°C

  • [C6H4-SO2-C6H4-O-C6H4]n

• Polyetheretherketone (PEEK): Continuous use temperature 250°C

  • [O-C6H4-O-C6H4-CO-C6H4]_n

• Polyetherketoneetherketoneketone (PEKEKK): Continuous use temperature 250°C

  • [O-C6H4-CO-C6H4-O-C6H4-CO-C6H4-CO-C6H4]_n

Examples for Duromers

• Unsaturated Polyester Resin (UP) - Use temperature: 120 – 150 °C

• Epoxy Resin (EP) - Use temperature: 80 – 180 °C

• Phenolic Resin (PF) - Use temperature: 110 – 150 °C

• Melamin-Formaldehyde Resin (MF) - Use temperature: 80 – 120 °C

• Vinylester Resin (VE) - Use temperature: 100 – 140 °C

Molecular Structure of a Polyurethane Elastomer

• Soft segment

• Stiff segment

Energy for Production

The energy required to produce different materials in kg oil equivalent per liter of material, from lowest to highest:

• Duromers

• Low density polyethylene

• Polypropylene

• High density polyethylene

• Polyvinylchloride

• Polystyrene

• Steel

• Copper

• Aluminum

From Crude Oil to Polymers

• Naptha is cracked and separated to produce:

  • C2 (Ethylene) -

    • PE

    • C2H4Cl_2 -

      • PVC (via C2H3Cl )

  • C3 (Propylene) -

    • PP

  • C6 (Benzene) -

    • Ethylbenzene (C8H{10}) -

      • Styrene -

        • PS

Types of Polymerization Reactions

• Chain-growth polymerization

  • Radical chain polymerization

  • Cationic chain polymerization

  • Anionic chain polymerization

  • Coordinative chain polymerization

• Step-growth polymerization

  • Polycondensation

  • Polyaddition

Structure of Bifunctional Monomers

• O=C=N-R-N=C=O + HO-R'-OH -> [-R-N-C-O-R'-O-C-N-]_n (Polyaddition)

• Monomers suitable for polymerization need to be at least bifunctional

Functionality of Monomers

• MONOMER Monofunctional group or Monofunctional group

• MONOMER Bifunctional group

Polycondensation of PA6.6

• H2N-(CH2)6-NH2 + HOOC-(CH2)4-COOH -> [-NH-(CH2)6-NH-CO-(CH2)4-CO-]n + nH2O

• Loss of water during polymerization.

Radical Polymerization under High Pressure (LDPE)

• Starting reaction: ROOR -> 2RO with "relic" R typically H in case of H2O2

• Chain Growth: RO + H2C=CH2 -> RO-H2C-CH2 followed by RO-(CH2-CH2)n + H2C=CH2 -> RO-(CH2-CH2){n+1}

• Termination:

  • Disproportionation: RO-(CH2-CH2)n-CH2-CH2 + RO-(CH2)n-CH2-CH2 -> RO-(CH2-CH2)n-CH=CH2 + RO-(CH2-CH2)n-CH2-CH3

  • Recombination: RO-(CH2-CH2)n + RO-(CH2-CH2)n -> RO-(CH2-CH2)_{2n}-OR

Overview of Polymerization Methods

• Radicalic chain polymerization:

  • Low density polyethylene (LDPE)

  • Polymethylmethacrylate

  • Polystyrene

  • Polyacrylicacid, -acidester, -amide, -nitrile

  • Polyvinylchloride

  • PTFE and Polyvinylidenefluoride

• Anionic chain polymerization:

  • Polybutadiene

  • Polyformaldehyde

  • Polyisoprene

  • Poly-ε-caprolactam

  • Polymethylcyanoacrylate

  • Technically most important method for manufacturing block-copolymers: Styrene-Butadiene Polyetherester, with hard and soft blocks

• Cationic chain polymerization (technically less important):

  • Polyisobutylene

  • Polyalkylvinylether

  • Polyformaldehyde

• Polyinsertion:

  • High density polyethylene (HDPE, ZN)

  • Isotactic polypropylene (PP, ZN, Metallocene)

  • Linear low density polyethylene (LLDPE, ZN, Metallocene)

  • Ethylene-Propylene-Terpolymer (EPDM, ZN, Metallocene)

  • (ZN: Ziegler-Natta-Catalyst, Metallocene: Metallocene-Catalyst)

High Pressure Polymerization of Low Density Polyethylene

• Autoclave reactor or Tube reactor, Compressor, Precompressor

• Low pressure separator, High pressure separator

• High pressure circuit, Low pressure circuit

• Extruder : resulting in Pellets

• Temperature: 200 – 300°C

• Pressure: 2000 – 3000 bar

• Reactants

Processing Scheme for Linear Low Density Polyethylene

• Hydrogen, Comonomer, Ethylene

• Fluidized bed reactor

• Catalyst

• Compressor, Cooler, Polymer

• Temperature: 85 – 100°C

• Pressure: 20 – 40 bar

• Residence times of hours

• Reactor volumes of several 100 m³

Summary of Intro to Polymer Materials

• Polymer materials are ubiquitous.

• The world-wide consumption of polymer materials is significantly higher than that of steel if related to volume.

• Classification of polymers:

  • Natural and synthetic polymers

  • Deformable and non-deformable polymers

• Molecular architecture:

  • Linear and branched homopolymers

  • Statistical, block and graft copolymers

• Chemical structure of various thermoplastics and duromers

• Polymerization methods

• Production of low density polyethylenes as examples of polymerization processes

Molecular Mass of Polymers

• Mi = PiMg + 2M{EG} ≈ PiMg (if P_i is high)

  • M_i: Molar mass of macromolecule i

  • P_i: Degree of polymerization of macromolecule i

  • M_g: Molar mass of the monomer unit

  • M_{EG}: Molar mass of the endgroup

Molar Masses of Structural Units of Some Polymers

• PE: Mg = (2x12 + 4x1) g/mol = 28 g/mol (CH2-CH_2)

• PP: Mg = (3x12 + 6x1) g/mol = 42 g/mol (CH2-CH(CH_3)

• PVC: Mg = (2x12 + 3x1 + 1x35) g/mol = 62 g/mol (CH2-CH(Cl)

Discrete Molar Mass Distributions

• Number average: Mn = \frac{\sumi ni Mi}{\sumi ni} = \sumi Mi f(M_i)

• Weight average: Mw = \frac{\sumi ni Mi^2}{\sumi ni Mi} = \frac{\sumi mi Mi}{\sumi mi} = \sumi Mi h(M_i)

• Definitions of average molar masses

• Number distribution: f(Mi) = \frac{ni}{\sum n_i}

• Mass distribution: h(Mi) = \frac{mi}{\sum m_i}

• mi = Mi n_i

Continuous Molar Mass Distributions

• Number average: Mn = \int0^{\infty} M g(M) dM

• Weight average: Mw = \int0^{\infty} M w(M) dM

• Polydispersity factor: PD = \frac{Mw}{Mn} ≥ 1

• Relations between distribution functions

  • w(M) = \frac{M g(M)}{M_n}

  • \int_0^{\infty} w(M) dM = 1

  • \int0^{\infty} g(M) dM = \frac{1}{Mn}

Example for Different Distributions

• Coins from a moneybox

  • Nominal Value, Number ni, Mass Mi,
    mi=Mi n_i

  • Number average: \frac{\sum ni Mi}{\sum n_i}

  • Weight average: \frac{\sum Mi^2 ni}{\sum Mi ni}

Molar Mass Averages of Some Commercial Polymer Materials

Molecular Modification by Branching

• Low Density Polyethylene (LDPE) - Long-chain branches, High pressure polyethylene

• High Density Polyethylene (HDPE) - Very few short-chain branches, Low pressure polyethylene

• Linear Low Density Polyethylene (LLDPE) - Variable C1 to C6-branches, Low pressure polyethylene

Modification of Low Density Polyethylenes by Copolymerization

• Non-polar comonomers are used to create LLDPE.

• Butene: CH2=CH-CH2-CH_3

• Hexene: CH2=CH-CH2-CH2-CH2-CH_3

• Octene: CH2=CH-CH2-CH2-CH2-CH2-CH2-CH_3

Ethylene Copolymers with Polar Groups

• Ethylene / Vinylacetate (E/VA) - CH2=CH-OOCCH3

• Ethylene / Acrylic acid (E/AA) - CH_2=CH-COOH

• Ethylene / Butylacrylate (E/BA) - CH2=CH-COOC4H_9

• Ethylene / Butylacrylate / Acrylic acid (E/BA/AA)

Molecular Modification by Changing the Tacticity

• Isotactic polypropylene: All methyl groups on the same side

• Syndiotactic polypropylene: Methyl groups alternate sides

• Atactic polypropylene: Methyl groups are randomly oriented

Summary of Structure of Macromolecules

1. Mathematical definition of molar masses (discrete and continuous distributions)

   • Number average: Mn

   • Weight average: Mw

2. Molecular modification

   • Branching: LDPE, LLDPE, HDPE

   • Copolymerization

   • Tacticity

Methods for the Determination of Molar Masses

• Osmometry

• Light scattering

• Gel permeation chromatography (GPC)

• Viscometry

Membrane Osmometry

• Van‘t Hoff law: \Pi = \frac{R T c}{M}, \Delta h = \frac{\Pi}{\rho g}

  • \Pi: Osmotic pressure

  • g: Constant of gravity

  • \rho: Density

  • c: Concentration

  • M: Molar mass

  • R: Gas constant

  • T: Absolute temperature

  • \Delta h: Height difference due to osmotic pressure

Example for Osmometric Data

• Osmotic pressure as a function of concentration for a polystyrene in toluene

Information Derived from Osmometry

*\frac{\Pi}{RT} = \frac{1}{M_n} + Bc

• M_n : Number average molar mass

• B : Second virial coefficient

• With osmometry the number average molar mass Mn can be measured

The Θ-Solution

• A polymer solution for which B=0 is called a theta(Θ)-solution.

• To a Θ-solvent the undisturbed chain statistics can be applied.

Principles of Light Scattering

• Measuring principle and definition of scattering angle Θ

• Polymer solution, Primary beam, Rotating photocell (detector)

• Scattering intensity i(Θ) as a function of the scattering angle Θ

Equations for the Evaluation of Light Scattering Experiments

• i(\Theta,c) = i(0,c) \frac{V_0}{r^2} \frac{1 + cos^2 \Theta}{2}

  • i(\Theta,c): Intensity of light scattered at an angle Θ from a polymer solution of concentration c

  • i_0: Intensity of incident light

  • V_0: Sample volume

  • r: Distance between scattering volume and photo cell

Evaluation of Light Scattering Experiments (cont.)

• \frac{K c}{i(\Theta)} = \frac{1}{M_w P(\Theta)} + 2Bc

  • K = 4 \pi^2 n1^2 (dn/dc)^2 / (NL \lambda^4)

    • n_1: Refractive index of solvent

    • n: Refractive index of solution

    • dn/dc: Refractive index increment of solution

    • \lambda = \lambda0/n1: Wavelength of incident light in solution

    • \lambda_0: Wavelength of incident light

    • N_L: Avogadro’s number

  • P(\Theta) = 1 - \frac{16 \pi^2 h^2}{3 \lambda^2} sin^2(\Theta/2)

    • h: Radius of molecule

    • B: Second virial coefficient

• From light scattering experiments the mass average molar mass M_w, the average radius of the molecules h, and the second virial coefficient B can be determined.

Gel Permeation Chromatography (GPC)

• Schematic illustration of the GPC

• Mechanism of separation by molecule size in a gel

• Large molecules elute first, followed by smaller molecules

Definition of the Viscosity of a Liquid

• \tau = \eta \dot{\gamma}

  • \dot{\gamma} = \frac{dv_x}{d}

Term 1: Natural Polymers
Definition 1: Polymers derived from natural sources
Term 2: Synthetic Polymers
Definition 2: Polymers synthesized from chemical processes
Term 3: Deformable Materials
Definition 3: Polymers that can undergo significant deformation without breaking
Term 4: Non-Deformable Materials
Definition 4: Polymers that resist deformation
Term 5: Thermoplasts
Definition 5: Polymers that soften when heated and harden when cooled, allowing for reshaping
Term 6: Duromers
Definition 6: Polymers that undergo irreversible hardening when heated and cannot be reshaped
Term 7: Elastomers
Definition 7: Polymers with elastic properties, capable of returning to their original shape after deformation
Term 8: Dispersions
Definition 8: Mixtures in which one substance is dispersed throughout another
Term 9: Varnishes and Paints
Definition 9: Coatings consisting of a resin dissolved in a solvent, often with pigments
Term 10: Functional Polymers
Definition 10: Polymers designed for specific applications due to their unique chemical or physical properties
Term 11: Linear Homopolymer
Definition 11: A polymer composed of a single type of monomer, arranged in a linear chain
Term 12: Branched Homopolymer
Definition 12: A polymer composed of a single type of monomer with branches extending from the main chain
Term 13: Statistical Copolymer
Definition 13: A polymer composed of two or more different monomers, arranged randomly
Term 14: Block Copolymer
Definition 14: A polymer composed of long sequences (blocks) of different monomers
Term 15: Multi-block Copolymer
Definition 15: A copolymer containing multiple blocks of different monomer sequences
Term 16: Graft Copolymer
Definition 16: A polymer with chains of one type of monomer grafted onto a backbone of another type of monomer
Term 17: Chain-growth polymerization
Definition 17: Polymerization in which monomers add to the growing chain one at a time
Term 18: Step-growth polymerization
Definition 18: Polymerization by combining monomers through a series of individual reactions
Term 19: Polycondensation
Definition 19: A type of step-growth polymerization with the release of a small molecule like water.
Term 20: Polyaddition
Definition 20: A type of step-growth polymerization without the release of a small molecule
Term 21: Discrete Molar Mass Distributions
Definition 21: Distribution of molar masses described using number average
Term 22: Continuous Molar Mass Distributions
Definition 22: Distribution of molar masses described using integration
Term 23: R
Definition 23: The gas constant
Term 24: T
Definition 24: Absolute temperature
Term 25: \Delta h$$
Definition 25: Height difference due to osmotic pressure
Term 26: The Θ-Solution
Definition 26: A polymer solution for which B=0