Polymer Types, Performance, and Properties

• Plastics offer versatility, lightweight, cost-effectiveness, and corrosion resistance
• They also allow design freedom with insulating properties
• Plastics have flammability, high-temperature performance limitations, and tolerance control issues

Polymer Classification

• Thermoplastics feature entangled chains(long molecules) without cross-links and reversible entanglements
• They show weak intermolecular interaction between chains from Van der Waals, dipolar, and hydrogen bonds, resulting in low stiffness
• Elastomers have some cross-links with reversible entanglements
• Thermosets have permanent cross-linked 3D networks

Polymer Performance

• Bulk polymers offers moderate durability at a low cost
• Engineering polymers, at a medium cost, provides a higher modulus and operating temperatures
• Specialty polymers are high-performance, high-temperature materials but at elevated costs

Determining Properties

• Polymerization type, chain length, regularity, and chain conformation affects polymer properties

Polymerization Mechanisms

• Addition Polymerization involves a double C=C bond opening, which allows multiple monomers to bond
• Condensation Polymerization causes monomers with reactive groups to release small molecules like water, forming polymers such as polyamides

Chain Configuration

• Saturated carbon-carbon bonds in the main chain allows more flexibility
• Unsaturated carbon-carbon bonds (double or triple) reduces flexibility due to fewer attached hydrogen atoms
• The presence of other atoms in the main chain (benzene) or side groups affects flexibility

Glassy Polymers

• Primary bonds within polymers are strong covalent bonds
• Secondary bonds between polymer chains include Van der Waals and hydrogen bonds

Temperature Stability

• A polymer's temperature resistance depends on the backbone atoms and the bonds composing them
• Polyethylene has everyday usage such as in packaging
• Polyimides can withstand extreme conditions such as aerospace applications

Chain Length

• Longer chains causes more entanglements, creating stronger materials with increased wear resistance
• Chain length dictates a material state, as short chains result in fluids and long chains make solids

Molecular Weight

• Number Average Molecular Weight (Mn) means all chains contributes equally
• Weight Average Molecular Weight (Mw) shows heavier chains having more impact
• Z-Average Molecular Weight (Mz) emphasizes the longest chains
• Polymers are polydisperse if they have different weights
• Number-Average Molecular Weight (Mn) determines strength, as very short chains do not entangle
• Weight-Average Molecular Weight (Mw) determines melt viscosity, which rises if there's an increase in entanglements
• Z-Average Molecular Weight (Mz) determines melt elasticity, and the highest molecular weight fraction ensures elasticity
• Degree of Polymerization (P) indicates the average number of monomers in a chain and directly correlates with mechanical properties and chain length

Degree of Dispersity

• Dispersity (D) gauges chain length distribution, otherwise known as molecular weight
• Monodisperse polymers, which have chains that share the same molecular weight and length (D = 1), are stronger and more uniform

Polydisperse Mixtures

• This is a Weight Average of the mixtures
• The weight fraction of each grade is represented by wk
• The Weight-average molecular weight of each grade is is represented by Mw,k
• It is used to calculate properties of polymer blends

Grades

• These are Number Averages of the mixture
• Branching disrupts regularity, branches are present
• Low-Density PE has irregularly branched chains
• High-Density PE has linear chains with great strength and density
• Linear Low-Density PE and Medium-Density PE features short, regulary placed branches

Chain Regularity

• Regular arrangement (isotactic, syndiotactic) of side groups affect material properties
• With Copolymerization, copolymers can develop when two or more types of monomers participate in polymerization
• Types of Copolymerization include Random, Alternating, and Block copolymerization

Chain Conformation

• Chains are flexible but constrained by entropic concerns, rotation hindrances, and valence angles
• Characteristic Chain Stiffness (C∞) measures chain rigidity, for example, PS is stiffer than PE
• The Endpoint Distance for Random Walk (ro) formula is (ro^2)=nlb^2C inf

Equation

• the ro= Root of (x^2+y^2)

Variables

• n represents number of chain segments, b0 represents the segment length, and C ∞ represents chain steric hindrance/bond angles

Significance

• It predicts the spatial dimensions of a polymer chain in 3D space
• Average Endpoint Distance should consider the Valence Angle
• Adjusts for restrictive geometry from the bond
• This is key for refining polymer predictions in more realistic conditions
• Calculation of Endpoint Distance (ro) incorporates molecular weight, chain stiffness, and segment length to determine the average chain conformation
• Polydisperse Blends occur as polymer grades mixes or changes to molecular weights average and its dispersity increase

Glass Transistion

• It showcases a change over from a hard, brittle glassy state to a more soft, gummy one
• Tg (Glass Transition Temperature) is the temperature in which glass transistions
• Melting occurs in semi-crystalline materials vs glass transistion occurring in amorphous ones
• Melting happens quickly vs glass transistion which occurs more gradually
• Tg is always lower than Tm

Amorphous Melting States

• Glassy states are chains that are frozen, modulus determined by interaction forces
• Rubber states are chains in segmental rotational movement, moving with the load, the material keeping its shape through entanglement
• Liquid states have mobility allows for chains to slip past one another

Specific Volume

• Also known as (V), declines as temperature decreases.
• Below Tg, glass has lower expansion rate
• Above Tg, glass has higher thermic expansion
• At Tg, main chain segments gain movement
• At Tf (flow temperature), the chains more past each other to allow flow

Relaxation

• A time-dependent molecular movement due to external forces or temperature changes.
• Relaxation time (τ) increases significantly as Tg is approached

Factors Affecting Tg

• Increase steric hinderance, increase chain stiffness
• Rigid bonds in main chain increase chain stiffness
• High molecular weight Mn is high
• Increased links (more bonds), the Tg is higher

Intramolecular Actions

• Primary bonding with covalent chains
• Seconday bonding is the process of mixing Van der Waals, dipole attraction, and hydrogen between chains, as well as the intermolecular forces
• Oxygen can cause dipole movement, higher crosslinks
• Stronger Hyrdogen bridges equals more crosslinks

Intermolecular Factors

• Van der Waals are weak attractions
• Dipole interactions enhance Tgs
• Polymers with more are stronger due to attractions which restrict its movements
• PVC is one of the strongest
• Secondary glass transistion occur below the primary Tg
• The Modulus decreases less dramatically when secondary Tgs happen vs primary Tgs

Occurrences

• Restricted Mobility in regions where movment is limited

Cooling

• the secondary Tg becomes clear once the polymer is chilled and global motion is reduced

Examples

• Polymethy (MMA) exibit motion because of its bulky chains
• Compatibile mixtures act like singular materials
• Incompatible mixtures: Show many tg values for each polymer

Glass Transition Applications

• Use polymer to find flexibility
• Food Indsustries: Tg is needed for the process of freezing

Polymer Transitions

• Tg showcases the change from glass to rubber(flexibility up)
• Tm showcases the change from crystal to liquid solid
• Amporphous polymes retains strenght while under Tg
• Semi crystals exhibit Tg

Cyrstallization

• The crystal will be cooler if coming from Tem
• Spherulites make lamllae(fold chains)
• With chain regularity, you want a strong bond between carbons
• Non regular( random placement will stay amorphosu

Chain Branching Impact

• Low Density has strong crystalline
• High dense reduces crystrallinity
• Copolymers need random copolymer to hinder crytalizaition

Conditions for Crystallization

• Need a balance between chains time and temp
• Slower cooling supports good structures but fast will leave bad strcutures
• All temp form under tim

Cooling Rate Influence

• Rapid Cooling is mostly amorphous
• slow cooling takes time
• higher chain molecular limit chain folding

Morphology Traits

• Stress with polymers will encourage chain with cooling

Characterization

• Calioritmerty use it for absorption
• X ray review strcutre

Flow and Temp

• Flow temp is where amourphous goes to viscous liquid state
• polymes need alot more energy not to destrangle
• cross linked poylmes dont have flow

Definiton

• Vicosoty its how hard its to destructure material
• Polymere exibit high vicisoty
• Shear thin use that trait to rate materal
• Chains destrangle and move in shear postion

Impact With weight

• Vusocity goes up with size of chains
• Critical entaglement weigh means it doesnt get very thick
• Higher size of the chain leads to even more tangle

Melt vs polymer

• Dide swells expnasion form materals
• Weisberge effect it climbs up
• Kaye effects rebounds

Characterizing Viscosity

• Academics is more measure vs industry
• Funnels are used in industry
• Low melt means high visocity
• High Melt mean low
• Limitations only tell value

Extrustsion

• Polyme goes into into dies for continues products
• Stress is more influenctial
• Fractures leads to surface issues'

Molding

• Steps platisize, cooling put back pressure
• limit the pressure to not flood, high heat spots, or have defects

Viscoelascity

• Combo of flex with memories
• Stress can show strain curves
• Limit liner strain due to its small range
• Liner it the best
• Elastic materials like strest

Viscous

• Vicosut linear with energy loss
• elastic shows momery of deformaton

Elastic Behaviours

• Elastic materials follow a direct link
• Viscosities are not elastic, shows no time dependent bejavoiur

Tests

• Creep show stress and time
• Relaxation measure tress decay

Tensile Compressions

• Tension or compressions show shear

Relaxsation

• Relax show stress declines 3