PKG825 Exam 1 - Polymerization

What is an addition reaction?

polymers are made from monomers with ring structures or double bond by a chain reaction. No molecules are lost during polymerization. polymer constitutional unit is the same as the monomeric unit

What is a condensation reaction?

Polymers are made from monomer with two reactive functional groups by a step-wise reaction (small byproduct molecule is produced at each reaction step). Usually water or CO2 molecules are lost. Polymer constitutional unit is different from the monomer

What are some examples of step growth polymers (condensation)? 

polyesters (PET), polyamides (nylons), polycarbonates

What are some examples of chain growth polymers (addition)? 

PVC, PMMA

What are the three steps of free-radical polymerization steps?

initiation, propagation, termination

How does termination happen?

termination of the radical centers occurs by bimolecular reaction between two radicals (by coupling (combination), disproportionation, chain transfer)

what is disproportionation?

a proton (H) is transferred and a double bond is formed

what is a chain transfer reaction? 

chain transfers arises when hydrogen or some other atom X is transferred from a molecule in the system to the polymer radical 

why are metallocene catalysts unique?

• can produce a much higher MW PE than PE made by the Ziegler-Natta recipe

• it is also good for making polymers of very specific tacicity

What are properties of PET?

transparent, good O2 and Co2 barrier, low viscosity, low melt strength

What are some results of low melt strength?

necking of melt, sagging of melt

What is the purpose of PET copolymers

to improve the melt strength

How does PETG improve PET properties?

The presence of the additional ring structure imparts additional rigidity, the irregularity introduced by the comonomer prevents crystallization, so it is clear amorphous polymer, and has good melt strength

What are properties of nylons?

linear polymers that contain the amide group, thermoplastics, contain nitrogen, good gas barriers, excellent thermal stability, low temp flexibility, and good barrier to odor

what does nylon 6,7 mean

there are 6 carbons in the amide, 7 carbons in the acid

what is nylon 6

has only one kind of carbon chain made by ring opening polymerization

What chemical property is affected by copolymerization

reactivity (makes it possible to cross link) - useful for making thermosets, rubbers, and coatings

how are physical properties modified?

through random copoylmerization

What are some limitations of the fox equation? 

does not take into account intermolecular interactions 

how does adding copolymer affect crystallinity?

crystallinity decreases

What are properties of ordered copolymers?

single characteristic Tg between the Tgs of homopolymer A and B, a different crystal lattice than either of the homopolymers, and a Tm between the homopolymers

What is the purpose of Ziegler-Natta polymerization?

it allows one to make polymers of specific tacticity

What are limitations of Ziegler natta polymerization?

It does not work for polymers such as PVC and acrylate

What are examples of polymers that can be produced by Ziegler-Natta rxn?

PE, PP

Are nylons thermoplastic or thermoset?

thermoplastic