Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Polymer Chemistry > Part 1 L4-6 > Flashcards

Part 1 L4-6 Flashcards

1
Q

Initiators for cationic polymerization

A

(a) Classical protonic acids or acid surfaces–HCI, H2SO4,HCIO4;
(b) Lewis acids or Friedel-Crafts catalysts– BF3, AICI3 , TiCI4 ,SnCI4; + ionization agent (protogen or cationogen)
(c) Carbenium ion salts.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a protogen?

A

Protogen: proton donor such as water, hydrogen halide, alcohol, and carboxylic acid, etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a cationogen?

A

Cationogen: carbocation donor such as an alkyl halide (e.g., t-butyl chloride and triphenylmethyl chloride), ester, ether, or anhydride, etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Give an example of termination with the counter ion in cationic polymerization

A

S10 L4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does a polar solvent do to cationic polymerization?

A

Polar solvents which favour ion-pair separation (e.g. dichloromethane) and large counter-ions (e.g. SbCl6
-), which associate less strongly with cations, give rise to
higher values of kp.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does a large Counter ion do in cationic polymerization?

A

larger and less tightly bound anions give a higher rate of reaction. Small and tightly bound = no space for monomer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Cationic Ring Opening Polymerization. Draw mechanism with reaction with R+ A-

A

Slide 17 L4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Mechanism for living cationic polymerization

A

Slide 20 L4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Initiators in anionic polymerization

A

A variety of basic (nucleophilic) initiators have been used:
Covalent or ionic metal amides such as NaNH2 and LiN(C2H5)2, alkoxides, hydroxides, cyanides, phosphines, amines, and organometallic compounds such as n-C4H9Li and PhMgBr. Initiation involves the addition to monomer of a nucleophile (base), either a neutral (B:) or negative (B:-) species.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Termination of anionic polymerization to form either carboxylic acid, alcohol or alkene

A

Reaction with CO2, ethylene oxide (followed by H+) and alcohol respectively.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Termination of anionic polymerization to form either acid chloride or star polymer

A

Reaction with COCl2 or SiCl4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Anionic polymerization: Effects of solvent

A
  1. The reactivity of ion pairs is greatly enhanced by the use of a more polar solvent which increases the ion-pair separation.
  2. When the solvation is absent or weak, the rate coefficient for ion-pair propagation increase as the size of the counter-ion increases (i.e. K+ > Na+ > Li+) due to the consequent increase in the separation of the ions. However, in polar solvating solvents, the opposite trend often is observed because the smaller counter-ions are
    more strongly solvated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the formula for average degree of polymerization final

A

Xn(final) = [M]0/ [I]0 = amount of monomer consumed/number of chains

[I]0 is the number of initiators

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Monomer conversion formula

A

x = ([M0]-[M])/[M0]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Anionic Ring Opening mechanism (reaction with alkoxides)

A

Slide 32 L4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Main advantage with living anionic polymerization

A

PDI can be lower than in living radical polymerization

17
Q

Main disadvantages with living anionic polymerization

A
  1. Extremely clean conditions
  2. Limited number of solvents
  3. Limited number of functional groups (no OH, COOH)
  4. Limited number of functional monomers (in principle)
18
Q

How can you make a block copolymer using living anionic polymerization

A

Synthesis of block copolymers by sequential monomer addition

19
Q

What is the properties and structure of an isotatic polymer?

A

Can crystallize L5 S3

20
Q

What is the properties and structure of an syndiotatic polymer?

A

L5 S3

21
Q

What is the properties and structure of an atatic polymer?

A

Amorphous cannot crystalize L5 S3

22
Q

How can isotatic polymers be formed

A

Highly isotactic polymers can be prepared by ionic polymerization if there is strong coordination of the counter ion with the terminal units in the polymer chain and with the incoming molecule of monomer

Requirements
• Monomer with polar substituent groups (for strong coordination)
• Low temperature
• Non polar solvent
• Initiator which yields a small counter ion

For non polar monomers, the Isotactic polymers can be prepared by polymerizations involving coordination to transition metals

23
Q

What is the properties of cis/trans isoprene.

A

Trans
1 4 polyisoprene is able to crystallize due to its regular structure —- hard, rigid materials
Cis
1 4 polyisoprene has a less symmetrical structure that does not allow easy crystallization under normal conditions amorphous rubbery material

24
Q

Draw the Ziegler

Natta coordination polymerization Mechanism

A

Propagation: mechanistic overview there are certain mechanistic features which now are widely accepted on
the basis of experimental evidence
1. Monomer initially is coordinated at vacant d orbitals of transition metal atoms at the catalyst surface
2. The orientation of a coordinated molecule of monomer is determined by its steric and electronic interactions with the ligands around the transition metal atom One particular orientation is of lowest energy
3. The propagation step is completed by insertion of the coordinated molecule of monomer into a metal carbon bond
4. The orientation of the molecule of monomer as it inserts into a metal carbon bond determines the configuration of the asymmetric carbon atom in the newly formed terminal repeat unit
5 Isotactic polymer is formed when the preferred orientation for coordination of monomer is of much lower energy than other possible orientations each successive molecule of monomer then adopts the
same preferred orientation as it undergoes coordination and then insertion
6 The mechanism of monomer insertion always leads to the formation of linear polymer chains, irrespective of the detailed stereochemistry.

25
Q

What is a Metallocenes

A

L5 S27

26
Q

What is the mechanism for Mechanism of polymerization with Zirconocene: Mao Catalysts

A

L5 S30

27
Q

Study the catalyst for used in the lecture S15-36 in L5

A

Come on!

28
Q

What are the 4 principal strategies for synthesizing of block copolymers?

A

1.
Linking polymer chains together through mutually reactive end groups If the polymer chains are α,ω functionalized such reactions are akin to step polymerizations where the monomers are end functionalized prepolymers
2.
Polymerization of different monomers in sequence In the simplest case, this involves using the living polymer formed from one monomer as the initiator for polymerization of a second monomer
3.
Polymerization of one monomer followed by conversion of the active end group to a form that initiates a different type of polymerization to which the second monomer added is susceptible
4.
Use of reactive end groups on a polymer chain to initiate formation of another polymer by chain polymerization.

The best control of block copolymer architecture and block length is achieved using ‘ polymerizations to produce each of the individual
blocks

29
Q

Draw mechanism for Synthesis of Block Copolymers by Living Anionic Polymerization

A

L6 S5

30
Q

Synthesis of Block Copolymers by Reversible-Deactivation (Living) Radical Polymerization.
Draw mechanism for Living Radical Polymerization: Nitroxide-Mediated Polymerization (NMP)

A

L6S9

31
Q

Synthesis of Block Copolymers by Reversible-Deactivation (Living) Radical Polymerization.
Draw mechanism for
B: Atom Transfer Radical Polymerization (ATRP)

A

L6S10

32
Q

Draw the mechanism for Synthesis of Block Copolymers by Active Center Transformation

A

L6S14,15 (two methods)
Methods involving transformation from one type of living polymerization to another were developed for use in preparing block copolymers when the second monomer to be polymerized is not susceptible to the type of chain
polymerization used to form the first block

33
Q

Come w. examples for 1.3 Synthesis of Block Copolymers by Coupling of Polymer Chains

A

Eg CuAAC

34
Q

What are the tree methods for preparing graft copolymers?

A

1 Activation of groups on a backbone polymer to initiate polymerization of a second monomer, thus forming branches of a different polymer.
2 Copolymerization of the principal backbone forming monomer(s) with a macromonomer (a prepolymer with terminal polymerizable group).
3 Linking end functionalized chains of one polymer to a backbone polymer that has reactive side groups.

35
Q

How does crosslinking occour?

What is the purpose?

A

Crosslinking reactions during polymerization (both step growth polymerization and chain growth polymerization) can occur in systems with monomers with a functionality of more than two.

Eg Natural rubber.

Purpose: Introducing chemical resistance, elastomeric properties, solvent resistance, preparation of microgels

Polymer Chemistry (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions