PRIMER
Fundamental concepts + languageNomenclatureChemical bonding, chemical interactions, entanglementsMolecular weightThermal transitions
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WHAT IS A POLYMER?
Berzelius (1883) – Poly (many) + mer (unit)Polystyrene polymerized in 1938; polyethylene glycol made in 1860sEarly polymer products were based on cellulose- gun cotton = nitrated cellulose
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A polymer is…
• Long chain molecule, often based on organic chemical building blocks (monomers)
• Long molecules (Mw ~100,000 Da) have solid-like properties
• The chain may be amorphous (no regular structure), crystalline (a regular repeating structure), crosslinked,…
• Dendrimers and oligomers have different properties
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HOW DO YOU BUILD A MOLECULE?
Chemical structureChain morphology – constitution, configuration, conformationDegree of polymerization = number of repeating unitsBuilding block sources – hydrocarbons, renewable materials
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Building blocks
• 5% of petroleum goes into polymers
• Sustainable use is possible
• Energy recovery is possible if solid polymers are combusted
Type C H O
gas NG 3 1 0
liquid Crude 6 1 0
solid Coal 14 1 0
Renew-able
cellulose 6 1 5.3
Hemi-cellulose
6 1 8
lignin 6.8 1 3
protein
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‘Building’ methods
Chain (addition)• Example – polyethylene
(PE) from ethylene• Small number of reacting
chains at any one time, which can grow into long molecules prior to termination
• Long reaction times needed to achieve high conversions
Step (condensation)• Example – poly(ethylene
terephthalate) (PET) from terephthalic acid and ethylene glycol
• Endgroups react to build the chain; long reaction times needed to achieve high polymer
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Multiple building blocks
• Copolymers, terpolymers, …• Using multiple building blocks leads to
polymers with intermediate properties or unique properties compared to the homopolymers
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Chain configurations
• Linear – repeating units are aligned sequentially
• Branched – large segments ‘branch’ off the main chain/carbon backbone
• Crosslinked/network – chemical crosslinks between chains add mechanical strength
• EXAMPLES?
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Multiphase systems
• Composites– Structural– Random– Other– Nanocomposites
• Blends– Dispersed lamellae, cylinders, spheres
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HOW DO WE CLASSIFY POLYMERS?
Structure – chemical, configurationsolid performance (mechanical + thermal properties)other
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Mechanical + Thermal
• Thermoplastic – solidified by cooling and reheated by melting
• Thermosets – retain their structure when reheated after polymerization (usually crosslinked)
• Elastomers – rubbers, deform readily with applied force
• Thermoplastic elastomers• other
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WHAT IS IN A COMMERCIAL PRODUCT?
Very few commercial products are ‘pure’MWD – molecular weight distributionadditives
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Polymeric materials
• Compete well on a strength/weight basis• Easy to form into 3D shapes• Creep under load is usually poor; this behavior
is usually corrected by adding fillers or fibers• Low corrosion in the environment compared
to metals• Generally good solvent resistance
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Thermoplastics
• Commodities: 75% of the polymer volume used is with 4 polymer families, polyethylene, polystyrene, polypropylene and poly(vinyl chloride) [low cost]
• Intermediate: higher heat deflection temperatures
• Engineering plastics: can be used in boiling water
• Advanced thermoplastics: extreme properties
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Thermosets
• High moduli, high flex strengths, high heat deflection temperatures
• Shape is retained during thermal cycling• Often made with step/condensation
polymerization systems• Crosslinking is usually used
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HOW DO WE MAKE A PART?
PolymerizationFormulationFabrication
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Formulation
• Additives are used to modify properties and/or lower costs
• Additives: heat stabilizer, light stabilizer, lubricant, colorant, flame retardant, foaming agent, plasticizer
• Reinforcement: particulate minerals, glass spheres, activated carbon, fibers
• Blends, alloys, laminates
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Additives can change:
• Processing properties• Performance properties• Composites: polymers with fiber fillers• Packaging: multiple layers often used
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Formulation operations
• Thermoplastics: melting or solvent processing• Thermosets: additive addition to monomers
or to prepregs
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Fabrication
• Varies by industry sector– Adhesive– Coating– Elastomer– Plastic– fiber
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Overview of the polymer industry
Industry General product requirements
adhesive Strong surface forces; epoxy, superglue
coatings Film-forming; LDPE with good impact
composites Structural materials; epoxy + fibers
elastomers Large deformation and recovery; rubber in tire and seals
fibers High strength/area; polyacrylonitrile
foams Light weight, low thermal conductivity; polyurethane
plastics Stable deformation under static load; HDPE, PP, PVC
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Commodity plastics
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Polymer Major uses
LDPE Packaging film, wire and cable insulation, toys, flexible bottles, housewares, coatings
HDPE Bottles, drums, pipe, conduit, sheet, film, wire and cable insulation
PP Automobile and appliance parts, rope, cordage, webbing, carpeting, film
PVC Construction, rigid pipe, flooring, wire and cable insulation, film, sheet
PS Foam and film packaging, foam insulation, appliances, housewares, toys
Film blowing
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High strength films are achieved by orienting the crystallites. The film is biaxially oriented; the wind-up rolls stretch the film in the machine direction and the expansion of the film radially provides a hoop stress force.
Wire coating
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Wire coating speeds can be high, and process start-up is challenging. Metal wires may need sizing, or wetting agents in the polymer melt for good adhesion.
Calendaring
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Thin and thick section calendaring is used to make wide sheets (8-12 ft).
Bottle blowing
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The parison is inflated, developing biaxially orientation similar to that of blown film. The sides of the mold provide cooling, quickly ‘freezing’ in the orientation developed during the blowing process. When this process is used to make soda bottles of PET, the orientation is critical to achieving low carbon dioxide permeation rates (and long bottle shelf life).
Thermoset applications
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Polymer Major uses
Phenol-formaldehyde resins (PF)
Electrical equipment, automobile parts, utensil handles, plywood adhesives, particleboard binder
Urea-formaldehyde resins (UF)
Similar to the above; textile coatings and sizings
Unsaturated polyester (UP)
Construction, vehicle parts, boat hulls, marine accessories, corrosion-resistant ducts, pipes and tanks, business equipment
Epoxy (EP) Protective coatings, adhesives, electrical parts, industrial flooring, highway paving materials, composites
Melamine-formaldehyde resins (MF)
Similar to UF resins; decorative panels, counter and table tops, dinnerware
Elastomers
• The polymers used for elastomers usually have very low heat deflection and melt temperatures
• Solids with good mechanical properties are made by crosslinking polymer chains together
• The “molecular weight” of elastomer parts is the size of the object
• Vulcanization of rubber uses sulfur to provide crosslinks between the C=C bonds of natural rubber.
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Fibers
• Fibers are based on highly crystalline polymers that can be oriented axially to have great strength. Orientation (cold drawing) develops crystal structure in the solid.
• Most natural fibers from biomass are based on cellulose; spider silk has different compositions and is based on a set of copolymers
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Elastomer polymersPolymer family description
Styrene-butadiene Copolymers with a range of constitutions; SBR – styrene-butadiene rubber
Polybutadiene Cis-1,4-polymer
Ethylene-propylene EPD – ethylene-propylene-diene monomer; the small amounts of diene provide unsaturation
Polychloroprene Poly(2-chloro-1,3-butadiene); this polar elastomer has excellent resistance to non-polar organic solvents (gasoline, diesel)
Polyisoprene Poly(cis-1,4-isoprene); synthetic natural rubber
Nitrile rubber Copolymer of acrylonitrile and butadiene
Butyl rubber Copolymer of isobutylene and isoprene
Silicon rubber Rubber based on polysiloxanes
Urethane rubber Elastomer with polyethers linked via urethane groups
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Synthetic fibersFiber type description
Cellulosic
acetate rayon Cellulose acetate
viscose rayon regenerated cellulose
Non-cellulosic
Polyester Mostly poly(ethylene terephthalate)
Nylon Nylon 6,6; nylon 6, nylon 10; other aliphatic, aromatic polyamides
Olefin Polypropylene; copolymers of vinyl chloride + acrylonitrile, vinyl acetate, vinylidene chloride
Acrylic > 80% acrylonitrile; modacrylic = acrylonitrile + vinyl chloride or vinylidene chloride
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Coatings
• Coatings. Major area for expansion; solar cells, windows, … Supplier base is highly fragmented.
• Paints. Major area for expansion; vehicles,… Materials supplier base is clustered; painting systems base is clustered; user base is fragmented
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Foams
• Major area: insulation for housing, sound control,…
• Materials: polystyrene, polyurethanes, …
• Reaction injection molding example
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Composites
• Thermosets and thermoplastics• Sheet molding compounds• Filament winding
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HOW DO WE NAME POLYMERS?
Polymer nomenclature is widely varied.Trademarks and common names may be industry-sector specific.Nomenclature: Polymer Handbook. Chapter 1.
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Source-based names• Source-based name when the polymer is derived
from a single (original or hypothetical) monomer; or random co-/ter-polymers– Poly(vinyl alcohola)– Poly(styrene-co-butadiene)– Polyformaldehyde (not polyoxymethylene)b
– Poly(ethylene oxide) (not poly(ethylene glycol)b
a – when the name is long, parentheses are used to separate the name from ‘poly’
b - actually the second name is quite common
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Structure-based names
• Structure-based name when the constitutional repeating unit (CRU) has several components
• The CRU is independent of the monomers and polymerization methods– Poly(hexamethylene adipamide)– Poly(ethylene terephthalate)
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copolymersType Connective Example
unspecified -co- Poly(A-co-B)
statistical -stat- Poly(A-stat-B)
random -ran- Poly(A-ran-B)
alternating -alt- Poly(A-alt-B)
periodic -per- Poly(A-per-B-per-C)
block -block- (-b-) Poly(A-b-B) or Poly A-block-poly B
graft -graft- (-g-) Poly(A-g-B) or Poly A-graft-poly B
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Source-based name Structure-based name Trade name, abbreviation
polyethylene polymethylene PE, LDPE, HDPE, LLDPE
polypropylene Poly(propylene) PP
polyisobutylene Poly(1,1-dmethylethylene) PIB
polystyrene Poly(1-phenylethylene) Styron, Styrofoam
Poly(vinyl chloride) Poly(1-chloroethylene) PVC
Poly(vinylidene chloride) Poly(1,1-dichlorethylene) Saran
polytetrafluoroethylene Poly(difluoromethylene) Teflon
Poly(vinyl acetate) Poly(1-acetoxyethylene) PVAC
Poly(vinyl alcohol) Poly(1-hydroxyethylene) PVAL
Poly(methyl methacrylate) Poly(1-methoxycarbonyl-1-methylethylene)
PMMA; Lucite, Plexiglass
polyacrylonitrile Poly(1-cyanoethylene) PAN; Orlon, Acrilan fibers
polybutadiene Poly(1-butenylene) BR rubber
polyisoprene Poly(1-methyl-1-butenylene) NR rubber
polychloroprene Poly(1-chloro-butenylene) Neoprene04/19/23 Chapter 1. Primer/introduction 45
Polymers with other backbones
Source-based name Structure-based name Trade name, abbreviation
polyformaldehyde Poly(oxymethylene) POM
Poly(ethylene oxide) Poly(oxyethylene) PEO
Poly(ethylene glycol adipate) Poly(oxyethylene oxyadipoyl) Polyester 2,6
Poly(ethylene terephthalate) Poly(oxyethylene oxy-terephthaloyl) PET; Dacron
Poly(hexamethylene adipamide)
Poly(iminoadipoyl imino-hexamethylene)
Nylon 6,6
Poly(-caprolactam) Poly(imino[1-oxohexamethylene]) Nylon 6
polyglycine Poly(imino[1-oxoethylene]) Nylon 2
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WHY ARE LONG CHAIN MOLECULES SOLIDS?
Bonding along the backbone is not extraordinary.With long chains, secondary valence forces, integrated over the entire chain, provide considerable ‘bonding’ forces.Chain entanglements provide physical linkages.
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Chemical bonding in polymers• Most primary bonds along the
backbone are covalent• Secondary valence bonds
– Much smaller forces than the covalent bonds, but become significant when integrated over the entire chain
– Consider the forces acting on this macromolecule as it is ‘pulled’ through the tube surrounding its structure in three dimensional space
– As each chain segment moves, it must overcome the local interactions at the tube surface
– Longer chains will have more resistance to motion
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Secondary valence forces
• Secondary valence forces affect the glass transition, the melting temperature, crystallinity, melt flow,…
• They include: nonpolar dispersion, polar dipoles, polar induction, and hydrogen bonds
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Secondary bond Bond energy, kcal/mol
Range of action, Angstrom
Dispersion 0.1-5.0 3-5 (r-6)
Dipole-dipole 0.5-5.0 1-2 (r-3)
Dipole-induced dipole
0.05-0.5 1-2 (r-6)
Hydrogen bond 1.0-12 2-3 (r-2)
WHAT ARE TYPICAL CHAIN LENGTH DISTRIBUTIONS?
Few synthetic polymers are monodisperse, i.e., have one chain length.Many biological polymers do have specific molecular weights, e.g., proteins, DNA, …The molecular weight distribution has critical effects on polymer properties in the melt and solid states.
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Typical effects of molecular weight distributions
• Homopolymers with different molecular weight distributions may be insoluble in each other
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# carbon atoms State Use
1-4 Gas Gaseous fuel
5-11 Low viscosity liquid gasoline
9-16 Medium viscosity liquid
kerosene
16-25 High viscosity liquid Oil, grease
25-50 Crystalline solid Paraffin wax
1000-3000 Plastic solid (crystalline + amorphous)
polyethylene
Linear alkane properties
MWD - oligomer• Poly(-olefin); PAO6• Synthetic base oil –
vehicle use• Trimer, tetramer,
pentamer, hexamer, heptamer
• Based on 1-decene• Ionic polymerization• Differential distribution
by size exclusion chromatography
• PeakFit™ used for curve deconvolution
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Two polyethylenes• Weight frequency, differential
distributions• Number-average molecular
weights are the same• Weight-average molecular
weights are different• Narrow MWD – PD ~ 5.7• Broad MWD – PD ~ 15• Differences in flow, tensile and
appearance properties
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HOW DOES CHAIN LENGTH AFFECT PROCESSING?
In-class exercise
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HOW DOES CHAIN LENGTH AFFECT PERFORMANCE?
In-class exercise
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WHAT ARE IMPORTANT THERMAL TRANSITIONS?
Thermal properties are often key criteria used to select polymers for specific applications.Five regions of viscoelastic behavior (many polymers have all five): < glass transition, power law region, rubbery plateau, rubbery flow, fluid flowOther – crystalline solids, crosslinked elastomers
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Five regions of viscoelasticity• Use amorphous polymers below Tg• Use crystalline polymers below Tm• Crosslinked elastomers at G• Melt processing between B and C
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regions• Viscoelasticity: most polymers creep(slow flow) under long-term stress.
Creep may not be recoverable, i.e., the sample may not recoil to its original dimensions. Over short periods of time, polymers are elastic.
• Solid yield and fracture: elasticity for < 0.1%; PS is brittle and fails at low elongations. PE yields, and then undergoes cold drawing to > 300% elongation.
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POLYMER SCIENCE DIRECTIONS
Medical applications are a rich applications area for polymers.Local variations in surface roughness at the nanoscale can induce strains in cell membranes, leading to the growth of F-actin stress fibers that span the length of the cell.W.E. Thomas, D. E. Discher, V. P. Shastri, Mechanical regulation of cells by materials and tissues, MRS Bulletin, 35 (2010), 578-583.
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Cells feel their environment
• Tissues are hydrated natural polymers with controlled elasticity
• Most animals cells require adhesion to a solid to be viable
• Tissue elasticity (~ kPa’s) is important for regulating cell growth, maturation and differentiation. Brain – 0.2 < E < 1 kPa; fat – 2 < E < 4 kPa; muscle – 9 < E < 15 kPa; cartilage – 20 < E < 25; bone – 30 < E < 40 kPa
• Nanoroughness seems to affect a number of cell processes
• 3D scaffolding is important• Mechanotransduction: cells adhere to surfaces via
adhesive proteins attached to adaptor proteins, to the actomyosin cytoskeleton.
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