Polymer Chemistry - Lesson 10

Assuming a steady-state concentration of propagating radicals.
Consumption rate of monomers equals the propagation rate.
Copolymerization Equation derived from the terminal model to predict copolymer composition.

Expressed in terms of mole fractions.
Commonly used in the industry, relates to monomer concentration. The exact formula is not transcribed, but its purpose is highlighted.

Monomer A has a reactivity ratio ( $r_1$ ) of 0.68.
Monomer B has a reactivity ratio ( $r_2$ ) of 0.55.
Problem: Determine the composition of monomer A in copolymerization with equimolar quantities of A and B.

Coordination catalyst developed by Karl Ziegler and Guilio Natta.
Consists of a transition metal compound (e.g., titanium trichloride, $TiCl<em>3$ ) and an organometallic compound (e.g., triethylaluminum, $AlEt</em>3$ ) as a cocatalyst.
Widely used to polymerize α-olefin under mild conditions.
Produces polymers with higher linearity (e.g., HDPE) and narrower molecular weight distribution compared to free radical polymerization.
Example copolymer: Not explicitly mentioned, but implied α-olefin copolymers.

Example: polystyrene-block-poly(methyl methacrylate).
The reactivity of the living polymer chain is sensitive to the order of monomer addition.
Specific method for block copolymer formation not fully detailed in provided text.

Polystyrene-block-poly(methyl methacrylate) will not form if methyl methacrylate monomers are polymerized first.
Reason: At the end of polymerization, there is no carbocation, where its chain end is no longer active.

Initiators not required.
Chain growth occurs throughout the matrix.
Characteristic of monomers with more than one functional group per molecule.
Reaction steps are similar and repeated throughout the process.
Allows near monodispersity as the overall composition of the copolymer will usually close to the composition of the monomer mixture.

By adding monomers with a deliberate sequence, alternating copolymers are possible.
More achievable to produce block copolymers.
Homopolymers like polyether and polyurethane can be linked via step-growth mechanisms.
This method is called the two-prepolymer method.

Two types of prepolymers are synthesized first.
Prepolymer: a di-telechelic polymer, which is a bifunctional linear polymer having reactive groups at two chain ends (α- and ω-chain ends).
Serves as a starting material for further polymerization.
Example: Hydroxyl-terminated polyether reacted with isocyanate-terminated polyurethane produces polyether-block-polyurethane.
Also known as segmented polyurethane.

Synthesis of polyether-block-polyurethane uses the two-prepolymer method.
Di-telechelic polymers are bifunctional linear polymers having reactive groups at two chain ends.
Adjusting the ratio of the two telechelic polymers allows production of a wide range of polyurethanes.

Graft copolymers can be formed via a few methods, including the “grafting from” technique.
“Grafting from” technique involves polymerizing monomers in the presence of a previously formed polymer through the initiation of growth through active sites.
The frequency of the transfer will decide the number of branches within the graft copolymer.

Synthesis of poly(vinyl acetate)-graft-polyethylene via “grafting from” technique.
1. Poly(vinyl acetate) is previously formed.
2. Poly(vinyl acetate) is initiated via chain transfer.
3. Ethylene monomers are added.
Grafting usually happens at carbons adjacent to double bonds in polydienes or on carbons adjacent to carbonyl groups.

Desired resin properties to overcome warpage:
- Dimensional stability
- Rigidity
- Toughness
- Chemical resistance
- Glossy surface appearance
Question: What polymer resin could solve the warpage issue, and how is it formed?

ABS (Acrylonitrile Butadiene Styrene) polymer is suggested.
Polybutadiene exists as a soft, rubbery segment embedded in a hard, glassy matrix of poly(styrene-co-acrylonitrile).
Comprises of acrylonitrile, 1,3-butadiene, and styrene monomers.

Copolymerization of acrylonitrile and styrene monomers occurs while grafting onto the polybutadiene backbone as branches.

Formed via emulsion process.
Polybutadiene is polymerized in the first emulsion process.
The second emulsion process involves the copolymerization of styrene and acrylonitrile.
Butadiene is polymerized first in aqueous emulsion using radical initiators and emulsifiers.
Polybutadiene is present in latex form.
Adding salt helps achieve controlled coagulation, separating the solid resin from the aqueous solution.