Polymers Prelim 1

light work

Macromolecule/Polymer

molecules containing long sequences of (molecular) repeating units covalently linked together.

Monomer

A single unit that can repeat

Different chain structures?

Homopolymer?

Derived from one species of monomer. However, the repeat unit may contain one or more species of monomer unit. Example: nylon 6 6

Copolymer Types?

Made of 2 or more types of repeat units.

Block: Large chunks of A, then large chunks of B: AAAAAABBBBBBBBBAAAA

Random: Completely random which monomers are where AABABBABABBAABAB

Alternating: 2 units repeating back and forth: ABABABA

Graft: Chains of B split off of A. Lowk godrick the grafted but he’s A and arms are B

Statistical: Distribution of repeat units follows known statistical law/distribution ABAABA

Classes of Polymers?

Polymers can be:

• Thermoplastics: Linear/Branched, melt with heat

  • Crystalline: @T_m, order → disorder

  • Amorphous: @T_g, glassy(hard) → rubbery(soft)

• Thermosets: Rigid, lots of crosslinking.

• Elastomers: crosslinked, can stretch and return quick to og state

Molar Mass with Polymerization? simple

x: DOP, number monomers. X0: monomer molar mass

X_i mole fraction?

W_i weight fraction?

M_n number average Molar Mass?

Also, M_n = x_n (avg chain length) * M_o (mean molar mass)

Molar mass averages for polymers vs oligomers?

Weight and Z average Molar mass?

Polydispersity PDI?

PDI usually from 1.5-2. It’s the distribution in the sizes of chains. If all chains are the same length, PDI=1. Plotted Mi vs Wi, it looks like a distribution chart.

PDI = M_w/M_n

Viscosity, T_g, processability, Solubility as a function of M_n?

Functionality?

Number of chain links.

Linear polymers can only have functionality 2.

Branched or network polymers need 3+

Condensation Polymerization

n(H-A-H)+n(HO-B-OH) react to make H[A-B]nOH+H20(2n-1), meaning a byproduct is water. (might also be step growth?)

Examples: Polyester, PET, Polysiloxane, polyamides. More aromatic groups (benzene rings) make it perform better @ higher temps, etc…

Addition Polymerization

Like condensation, but R1 on A and R2 on B combine within the polymer instead of being ejected as water.

Step-Growth Polymerization

Monomer makes dimer that makes… quadmers? They just keep combining and adding on without any ejections or structure changes.

Chain Growth Polymerization

like step-growth, but only one adds onto the end of a chain every time.

Linear step polymerization

subset of step growth polymerization

needs functionality f=2

Chain links usually have heteroatoms: CO, NH, etc…

Require high conversion reactions: Xn = 1/(1-p) where p is conversion%.

molar mass 10-100kg/mol

Principle of Equal Reactivity

The reactivity of a functional group is independent of the length of the chain its on and doesn’t react with anything having to do with the other functional groups.

Carothers Theory

If I know how many monomers reacted, can I predict the avg chain length?

Xn = N0/N (# molecules before over # molecules after)

For linear, BALANCED step polymerization: Xn = 1/(1-p) where p=(#fct’l groups reacted/initial)

When unbalanced (A=/B), Xn=(1+r)/(1+r-2rp)

Carothers theory and purity?

first one means that the purer the reaction the longer the average chain length when NA=NB. bottom plot means that as NA and NB separate in either direction the avg chain length goes down

Probability of a monomer x long at y time existing?

p is extent of reaction, x monomer units, time t. P^(x-1): each monomer has p prob to react, and all of them have to link except the last one: x-1. the last one has to be unlinked: 1-p.

If you want the # of monomoers that length, multiply this probability by N0: total # monomers, and another 1-p since the other side has to be unlinked too.