Polymers Test 1

Polystyrene

"Polystyrene" is atactic polystyrene with optical clarity Syndiotactic polystyrene has great engineering applications of polymer Crystallinity is what gives sPS its good mechanical stability at high temperares

Free Radical Chain Growth

1. Addition takes about 1ms per monomer; So, high molar mass polymer is terminal immediately 2.Steady decrease in monomer, what is present throughout the reaction. Reactions can be done in bulk, where the monomer is the solven 3. Active center/reactive site is critical; not just propagation but chain transfer recombination disproportionation 4. long reaction times != long polymers 5. Raising Temperature != longer polymers

Unsaturated Polymer

2 carbon atoms in "mer" unit are bonded with double bonds

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons. It has enormous impact on the secondary bonding forces that drive conformation

Thermosets

A special group of polymers that decompose rather than melt upon heating. They are normally quite brittle due to a relatively rigid, three-dimensional network structure (e.g. polyurethane). *involve a curving process to form a cross linked networks. These cannot be remelted or reformed.

Types of Step Growht Polymerization Reactions

Amide (nylon, kevlar, nomex) Ester Bond Urethane

Where do Chain Growth systems attack?

An alpha-olefin typically has the initiator attack on the beta position because there is greater stability in a secondary carbon

What makes polymerization non-living?

Anything terminates a chain Xn=v_propigation/v_termination v_propigation is the rate of propigation v_temination is the rate of termination KNH2 can be used to terminate chains. The generally, the chain transfer compound takes the active site to and put it on the solvent (like KNH2).

Why do we neglect end groups?

Because they are smaller than other errors in characterization

Polymer Stereochemistry

Bend/backgone configuration with R groups PE is zig-zag in crystalline state alpha-olefins are helical in solid state isotactic polypropylene is the simplest polyolefin to discuss syndiotactic Polystyrene

What are the key building blocks for most polymers

C, H, N, O

Saturated polymer

Carbon atoms in "mer" unit is bonded to 4 other atoms

Thermal polymerization

Chain growth system A purely thermal polymerization is one in which monomer is converted to polymer by thermal energy alone. ... In most cases of self-initiated polymerization, the identity of the initiating radicals and the mechanisms by which they are formed remain obscure. The occurrence of true thermal polymerization can be difficult to establish since trace impurities in the monomers or reaction vessel often prove to be the actual initiators. In most cases of self-initiated polymerization, the identity of the initiating radicals and the mechanisms by which they are formed remain obscure.

Electron donating groups

Groups that push (donate) electron density towards another functional group through sigma or pi bonds. favor cationic polymerization Ex is vinyl ethers

Drying Oils

Highly Unsaturated oils which can cross link and form protective coatings

Heterogeneous chain growth systems

Highly active multiphase. The initator can be unknown

Schotter-Boumann Reaction

Is an interfacial reaction, react sumultaneously and form HCL and nylon Removing membrane allows for reaction to continue at interface From Adipic acid and Hexamethylene diamine

Free Radical Polymerization

Is the dominate polymerization process industrially To achieve long polymer chains, [dot] must be as low as useful, because we know that eventually all the radicals will recombine Addition of a unit is about 1ms

Polypropylene

Isotactic propylene everywhere in food prep/preservation/storage. Isotactic because it is crystalline with a low glass transition temp Atactic is rubbery or elastomeric

Stereoconfigurations

Isotactic-same side of backbone Syndiotactic-every other side of backbone (alternating) Atactic-random Crystalline polymers are isotactic and syndiotactic Amorphous polymers are Atactic Chain growth polyolefins can be all of them

Salt Dehydration

It locks the stoichiometry in place, applying heat removes water and drives products to polymer

Thermoplastics

Materials that can be repeatedly softened by heating and hardened by cooling. Examples include acrylic, pvc, and nylon. *rely on the thermo reversiblitiy for manufactureing and recycling

Mn equation with P

Mn=(Mo)/(1-p)=Mo*Nx

Step Growth equation for Mn

Mn=Summation(Nx*Mx)/Summation(Nx)

diamine

Molecule with two amine groups

diacid

Molecule with two carboxly groups

Copolymers

More than one monomer Linear Copolymers +Statistical (random) +Alternating +Block' +stereo-block +graft

Polydensity Index

Mw/Mn PDI>1 bc more than one chain

Mw equation with P

Mw=Mo*(1+P)/(1-P)

Equation for Mw

Mw=Summation(Mx*Wx)/Summation(Wx) or Mw=Summation(Mx^2*Nx)/Summation(Mx*Nx)

Polyisoprene

Natural rubber is all 1,4-cis configureation polyisoprene This is the cononical example of rubber and latex Rubber is equivalent to a solid with young's modulus of ~10^6Pa Hard Materials ~10^9Pa & higher

Nx

Number of chains for a given length

Extent of reaction

P=(No-N)/No

PDI with P

PDI=Mw/Mn=1+P

Aliphatic

Pertaining to any member of one of the two major groups of organic compounds, those having straight or branched chain structures.

Pgel equation

Pgel=2/fave*(1-1/Xn) If Xn->inf Pgel=2/fave

Poly-Mer

Poly is many Mer is units or peices

Thermodynamics of Chain Growth

Polymerization is exothermic C-C is 350kJ/mol C=C is 600kJ/mol Enthalypy change -30 to -150k/J/mol which free radical systems, this heat must be controlled since the initators are quite often thermally activated If the reaction starts to overheat we can get into positive feedback As polymerization speeds up, viscosity increases and heat transfer gets worse What can we do to cool the reaction?? +The polymerization can be conducted in water. Monomers for these systems are organic and hydrophilic typically +Suspension polymerization ++mm length scale ++make plastic beads directly +Emulsion polymerization ++micron length scale ++Surfactant stabilized, surace active agent, latex or latices

Alternating Copolymers

Polymerization of A and B monomers where A and B are alternated r=0

Statistical(random) Copolymers

Polymerization of A and B monomers where A or B have an equal chance of being the next mer. r=1

Molecular Masses

Polymers have a range of molecular masses, a distribution. A mass spec shows a bell curve as the distribution for step growth

Polyolefins

Polymers whose mers belong to the category of alkenes. These include polyethylene and polypropylene.

Px

Px=(1-p)*P^(x-1) Based on limiting reactant

alcohol

R-OH

Termination Mechanism for Radical Polyerization

Recombination- this favors bond formation that termination myst be kept low; Xn=2v_bar Disproportiation-proton transfer; still have two chains; Xn=v_bar

For PET Ester Interchange

Removing MeOH and adding Ethylene glycol helps to increase chaing length and the formation of polymers P=1 bc no more carboxylic acid

Laquers

Shellac is another example of hydroxy aliphatic resin that is bio-based from the lac bug, but bad wear resistance. Novalac was synthesized to replace these materials

How do chains grow in a step growth system?

Small dimers and trimers dominate the reaction in the early reaction times Soon all the monomers are essentially tied up in dimers and trimers; at this point, the rate of reaction stuff starts to build

How do we determine how many monomers are left at a given point?

Step Growth X=1 Nx=No*(1-p)^2*p^(x-1) Nx=No*(1-p)^2 ^2 bc our mer is composed of two monomers

Step Growth vs. Chain Growth

Step Growth is dynamic, equiibrium determined configuration Living Chain growth is static, kinetically determined configuration

What difference does trans or cis make?

Tglass for cis and trans polyisoprene is 200K

What are we looking to predict in a copolymer?

The amount of each monomer incorporated into the polymer chains. This is F1 and F2. We cannot tune the reactivity ratios, but we can tune the feeds, F1&F2 =>Azeotropic copolymerization has a constant F1 given f1

Pi Stacking

The attractive, noncovalent interactions between aromatic rings; important in base stacking in nucleic acids.

For Chain Growth Systems

The monomer must be activated by destabilizing the Pi bond So we use an activated initiator The chain then grows until it runs out of monomer or terminates

Mw

The weignt average molecular mass is taken over a wight basis

For Block Copolymers what if A and B are different

Then the copolymer will form a microphase segregation and form a micelle

Polyurethanes

These are very relavant industrial polymers and appear in many forms like foams, glues, paints, coatings and are usually heavily cross linked Hard segments are formed by the typical linking group Soft segments are like the poly ethylene glycol

Vulcanization

Uses Sulfer to cross-link polyisoprene by using the double bond in polyisoprene. This makes it almost impossible to melt it

Kinetic chain Length

V_bar=([Mo]-[M])/[*] V_bar vs Xn V_bar is still growing

Xn equation when ratio is not equal to 1

Xn=(1+r)/(1+r-2rp)

Carothers Equation

Xn=No/N No is the initial number of molecules N is the number of molecules Xn=1/(1-p)

Concentration of M for chain polymers

[M]=[Mo]*e^-t/Tau

Free radicals

are electrostatically neutral and polymerization by free radicals is a default option. Free radicals are stable and cheap, but their reactions are horribly complex

Kevlar and Nomex

are elementally indistingishable from nylon, but are far more superior thermal properties Spider silk is the holy grail of polymer materials. They key issue is not composition (configuration), the conformation is the stumbling block -Conformation is secondary structure protein folding. -Not knowing how to fold it is the issue

Structure and Properties

are intimately related

aromatic

aromaticity is a property of cyclic (ring-shaped), planar (flat) structures with a ring of resonance bonds that gives increased stability compared to other geometric or connective arrangements with the same set of atoms

xn

average chain length

Bioderived polymers

cellulose and proteins

Rubbery materials are

entropic springs & exhibit this behavior only above Tglass. A Tglass the key to a good rubber

fave

fave=#functional groups/#ofmolecules If fave=2, then P->1, Xn->inf or loops If fave>2, then we get a gel through crosslinking

Kevlar is spun

in fuming sulfuric acid because that is the only system that will break up hydrogen bonding

Chain Growth is driven by

initiators which are the only place polymerication will occur, which is completely unlike step growth

monomer

is one molecule building block before it is incorporated into a chain

x

is the chain length

Living anionic polymerization

is the simplest and most difficult polymerization we will discuss Butyl Lithium is a standard initiator LAP has no formal termination mechanism, under ideal conditions, the chains will propagate immediately However, high steric hinderance from large monomers may inhibit the reaction from continuing Monomers need extreme purity Number of initiators equals the number of chains Only have "one" reaction which is polymerization/monomer addition @kp = 1/Tau

Polyethylene

is the simplist polyolefin ethylene => polyethylene Fully saturated C-C backbone with tetrahedral angles Polyethylene will crystalize in a zig-zag fashion -high density polyethylene is 80% crystalline -This is why you can't see through milk jugs -Cystals scatter light -Low density Polyethylne is transparent because crystals are lower concnetration -Unit cell has nothing to do with molecular weight of the polymer

Mo

mass repeated unit (mass of mer)

Step Growth reactions

most synthetic stepgrowth polymer are modeled by their reactive groups Stoichiometry is important for full chains

Mn

number average molecular mass

N

number of all chains N=sumation(Nx)

First sysnthetic polymers included

nylon which replaced silk Bakelite and phenol-formaldehyde resins were used as binders for wood dust composites

stoichiometric ratio

r=NoA/NoB`

Reactive Ratio

r=kself/kother

Kinetics of Ester intercahnge

ra=-k[COOH][OH] Cokt=1/(1-P)-1=Xn-1 where Xn is proportional to t

NoA and NoB

reactive groups present at t=0

Mer

repeating unit as found in the polymer or oligomer

Homogeneous chain growth systems

single phase, catalytic, one initiator for many monomers

Electron Withdrawing groups

strongly electronegative and pull electron density away from rest of the molecule, and stabilize negative charge. favor anionic polymerzation because a carboanion will be more stable with less electron density Ex is Acrylonitrile->polyacrylonitile

glass transition temperature

temperature where material goes from rubbery to solid

Hydrogen Bonding

the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule

Chain growth polymerization

these are systems with unsaturated monomers and destabilizing the double bonds creates the chains. Fluctation in electron density for the pi bond indicates its behavior Radicals would rather form a bond or double bond than be alive Carbocation and carboanions are not happy either

diol

two hydroxyl groups

diisocyanate

two isocyanates on a molecule