Lecture 3

Question 1

What is the classification of polymers in the formative years of polymer science based upon?

Answer 1

it is based on a comparison of the molecular formula of a polymer with that of
the monomer(s) from which it was formed

Question 2

What is condensation polymerization and addition polymerization? (this will be repeated again below)

Answer 2

• Condensation polymerizations are those which yield polymers with repeat units having fewer atoms than are present in the monomers from which they are formed. This usually arises from chemical reactions which involve the elimination of a small
  molecule (e.g. H2O, HCl).
• Addition polymerizations are those which yield polymers with repeat units having identical molecular formulae to those of the monomers from which they are formed

Question 3

Why was the classification of polymers in the formative years deemed unsatisfactory and what was suggested instead?

Answer 3

Carothers’ method of classification was found to be unsatisfactory when it was recognized that certain condensation polymerizations have the characteristic features of typical addition polymerizations and that some addition polymerizations have features characteristic of typical condensation polymerizations. A better basis for classification is provided by considering the underlying polymerization mechanisms, of which there are two general types—step-growth polymerizations (discussed in this lecture) and chain-growth polymerizations (discussed in future lectures).

Question 4

What is the relation between the reactivity of functional groups and the molecular size?

Answer 4

Chemical reactions proceed as a consequence of collisions during encounters between mutually reactive functional groups. At each encounter, the functional groups collide repeatedly until they either diffuse apart or, far more rarely, react. Under normal circumstances, the reactivity of a functional group depends upon its collision frequency and not upon the collision frequency of the molecule to which it is attached. As molecular size increases, the rate of molecular diffusion decreases, leading to larger time intervals between encounters (i.e., fewer encounters per unit time). This effect is compensated by the greater duration of each encounter giving rise to a larger number of functional group collisions per encounter. Hence the reactivity of a functional group can be
expected to be approximately independent of molecular size.

Question 5

What is the principle of equal reactivity of functional groups?

Answer 5

Mathematical analysis of polymerizations is simplified greatly by assuming that the intrinsic reactivity of a functional group is independent of molecular size and unaffected by the reaction of other functional group(s) in the molecule of monomer from which it is derived. This principle of equal reactivity of functional groups was proposed by Flory who demonstrated its validity for functional groups in many-step polymerizations by examining the kinetics of model reactions. Similarly, analysis of the kinetics of chain polymerizations shows that it is reasonable to assume that the reactivity of the active species at the chain end is independent of the degree of polymerization.

Question 6

What is step-polymerization?

Answer 6

In polymer chemistry, step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long-chain polymers. They are based on simple linking reactions that are very well-known in the organic chemistry world.

Note that step polymerizations are used extensively for commercial production of polymers

Question 7

How are step-growth polymers grouped and what the types of step-growth polymers?

Answer 7

Most step polymerizations involve reactions which produce links that contain a heteroatom and so the polymers normally are grouped into generic classes according to the type of links created in
the polymerization. Some of the most common classes of polymers named according to the linking group in the chain backbone are shown in Table 3.1.

Question 8

What is the greatest challenge faced in linear step polymerization?

Answer 8

the greatest challenge is the need to take the reactions to extremely high conversions in order to produce chains of sufficient length to realize useful properties. This is very demanding and, as a consequence, most polymers produced by linear step polymerization have molar masses in the range 10−100 kg mol−1, but more often 15–30 kg mol−1, which is much lower than for polymers prepared by chain polymerizations (typically 50–10,000 kg mol−1).

Question 9

What is the difference between linear step-growth polymerization and other step-growth polymerization?

Answer 9

linear step polymerizations only involve reactions of difunctional monomers. If a trifunctional monomer were included, a reaction at each of the three functional groups would lead to the formation of a branched polymer and may ultimately result in the formation of a network

Question 10

What is polycondensation?

Answer 10

Step polymerizations that involve reactions in which small molecules are eliminated!

Question 11

What is the synthesis of polyesters?

Answer 11

Check notes

The reaction between carboxylic acid and alcohol groups is slow and the reactions have to be performed at moderate-to-high
temperatures (80–300 °C), usually in the presence of an acid catalyst. Carboxylic acid halides are much more reactive and their reaction with alcohol groups to produce polyesters proceeds at room temperature, so they often are used in simple laboratory syntheses of polyesters.

Reactions of the type shown in notes are referred to as RA2+RB2 step polymerizations where R is any divalent group and A and B represent the mutually-reactive functional groups.

Polyesters also can be prepared from single monomers which contain both types of functional group, i.e. ω-hydroxy carboxylic acids as shown in written notes (but not ω-hydroxy carboxylic acid halide monomers because they cannot be synthesized due to the high reactivity of carboxylic acid halide groups towards hydroxyl groups)

Question 12

What is the advantage of ARB polymerization compared with RA2 + RB2?

Answer 12

The use of ARB polymerization has the advantage that, provided they are pure, an exact stoichiometric equivalence
of the two functional groups is guaranteed. On the other hand, slight excesses of one monomer in an RA2+RB2 polymerization significantly reduce the attainable
degree of polymerization because the polymer chains become terminated with functional groups derived from the monomer present in excess (e.g. both end-groups are ultimately of type B if RB2
is in excess). Since these functional groups are unreactive towards each other, further growth of the chains is not possible

Question 13

What is the synthesis of polyamides?

Answer 13

Check written notes

Question 14

What are Aliphatic polyamides called?

Answer 14

they are called nylons!

Question 15

How are polyamides named?

Answer 15

Check written notes!

Question 16

What is the synthesis of polyethers?

Answer 16

Check written notes!

Question 17

What is special about polymers with aromatic groups?

Answer 17

Polymers with aromatic groups (e.g. 1,4-phenylene units) in the chain backbone tend to have improved mechanical properties and greater resistance to degradation on exposure to heat or radiation, effects which arise from the stiffening effect and high stability of aromatic groups. Such polymers are most easily prepared by step polymerization and find use in engineering and high-performance applications. Some specific examples of important aromatic polymers prepared by polycondensation are shown in Table 3.2.

Question 18

What is the Synthesis of Conducting Polymers by Polycondensation?

Answer 18

Check the written notes

Question 19

Synthesis of Polysiloxanes by Polycondensation?

Answer 19

Note: Polysiloxanes (also known simply as siloxanes) are unusual in that they have a completely inorganic backbone of –Si–O– bonds, which gives them high thermal stability.

Check written notes

Question 20

In the synthesis of polysiloxanes, how can we ensure that complete hydrolysis occurs without the side polymerization reactions?

Answer 20

In order to control the degree of polymerization attained upon complete
hydrolysis, it is usual to include monofunctional chlorosilanes, e.g. chlorotrimethylsilane would lead to a polysiloxane with unreactive trimethylsilyl end groups.

The mentioned structures are shown in the written notes

Question 21

What is the most important polysiloxane and its uses?

Answer 21

The most important polysiloxane is poly(dimethyl siloxane) (PDMS) which is made from the monomer dichlorodimethylsilane (R1 = R2 = CH3). structure of PDMS is shown in written notes

A massive range of commercial grades of PDMS are available, many of which are copolymers prepared by including low levels of other dichlorosilanes as comonomers, e.g. dichlorodiphenylsilane (R1 = R2 = Ph), which provides repeat units that further enhance thermal stability, and dichloromethylvinylsilane (R1 = CH3; R2 = CH=CH2), which provides C=C bonds for use in subsequent crosslinking. Polycondensation is used to prepare low-moderate molar mass grades of PDMS, which are liquids or soft solids. High molar mass grades for use as elastomers tend to be produced by ring-opening polymerization of cyclic siloxanes

Question 22

What are polyadditions?

Answer 22

polyadditions are Step polymerizations in which the monomers react together without the elimination of other molecules. In contrast to polycondensation, there are relatively few important prepared by polyaddition, the most important being polyurethanes and epoxy resins

Question 23

What is the Synthesis of Linear Polyurethane?

Answer 23

Check written notes

Question 24

What do the properties of properties of polyurethane depend on?

Answer 24

The choice of diisocyanate and diol determines the properties of the polyurethane, which can range from being a rigid solid (if low molar mass diols are used) to a rubbery material (e.g. if poly(propylene oxide) diols with molar masses of about 2–8 kg mol−1 are used). Many commercial linear polyurethanes are segmented copolymers prepared using a mixture of short- and long-chain diols

Question 25

What is the Synthesis of Linear Polyureas?

Answer 25

Check written notes

proceeds at very high rates, such that intimate mixing of the monomers requires specialist high-speed mixing equipment. The diisocyanates used are the same as for preparation of polyurethanes. In addition to simple aliphatic amines and α,ω-diamino polyethers akin to the diols used in
polyurethane synthesis, aromatic diamines also are used. By reacting diisocyanates with diols and diamines, poly(urethane-co-urea)s are produced.

Question 26

What is the Diels–Alder reaction of dienes with dienophiles?

Answer 26

it is a 4+2 cycloaddition (example of polyaddition)

The reaction is shown in written notes

The reaction proceeds at temperatures of 25–150 °C and works best when R1 and R2 are electron-donating and R is electron withdrawing (or vice versa), but it is reversible and the retro reaction occurs at high temperatures.

Question 27

What are two further examples of Diels-Alder polyaddition? (not sure if important)

Answer 27

1. Bis(2-buta-1,3-dienyl)methylacetal undergoes RA2+RB2 polyaddition with 1,4-benzoquinone to give a soluble amorphous Diels–Alder polymer:

• Shown in digital notes

2. Reaction of 2-vinylbuta-1,3-diene with
   1,4-benzoquinone, which first produces a monomeric adduct that then undergoes ARB polyaddition at higher temperature:

• Shown in digital notes
• More complex
• The polymer is insoluble except at very low degrees of polymerization and the chain is completely rigid with a more crooked contour than indicated here because there are two possible orientations for the addition reaction; the structure shown arises from the alternation of the orientation. Polymers of this type are called ladder polymers, based on the ladder-like nature of their backbone, and have improved thermal stability because two main-chain bonds must break for chain scission to occur.

Note: Step polymerizations highlights
the importance of using clean reactions in which contributions from side reactions are completely absent or negligibly small

Question 28

extra

Answer 28

Diels–Alder polymerizations largely have remained curiosities, but the RA2+RB2 polyaddition of diamines with bismaleimides has been commercialized. A generic example is shown in the notes

• As shown above, using an excess of bismaleimide produces oligomers with maleimide end-groups, which are known generically as bismaleimide (BMI) resins. This is only one of many methods for synthesis of BMI resins and a very wide range of structurally different BMI resins are available commercially for use
  as matrixes in composites and as high-performance adhesives. The BMI resins are converted to crosslinked materials in situ during processing by a second-stage reaction, e.g. free-radical polymerization of the C=C bonds in the maleimide end-groups or further reaction with polyfunctional amines.

Question 29

Content left from lecture slides

Answer 29

I’m so sorry it is literally half the lecture i am going to murder the lecturer GLLL

If confused maybe notes in the red notebook on one of the last pages can help give more insight