Okay, welcome to this course on introduction to polymer science and I am Dibakar Dhara

from Department of Chemistry, IIT Kharagpur.

Today we will discuss about the importance of polymer science and I will just give brief

historical background of polymer science.

Now first question of course you will ask that why you need to get introduced to polymer

science.

Now if you think and go back about the ages of mankind, you will see that human civilization

marked by several ages and which are all based on the materials which are mostly used.

For example, we have Stone Age, Bronze Age, Iron Age, and now we have polymer materials

age.

Of course, probably going forward we will have age of elements, which includes silicon,

uranium, lithium and so on.

But currently we are, we basically are in the age of polymers.

Lord Alexander Todd, who is who was the President of Royal Society of London, and Nobel laureate

in chemistry in 1957 once said that, I am inclined to think that the development of

polymerization is perhaps the biggest thing that chemistry has done where it has the biggest

effect on everyday life.

Now you now know that the polymers are one of the most important materials in our everyday

life.

And as a student of science and technology, you must have basic understanding or introductory

understanding about polymers to even talk about.

No matter which industry you are working for or which discipline is your research area,

the basic understanding or introductory understanding of polymers is actually very much essential

for getting success in your regular activities.

Now why there is this age of polymers?

The polymers are the materials of choice as of now and one of the biggest success stories

in new materials development has been polymers over the last century.

And polymers are actually increasingly replacing and has also replaced conventional materials

like wood, metals, stone or ceramics in several applications.

And especially when you think about any new material applications at present polymers

are now, very often the choice of material.

And as a result, polymers are everywhere.

If you think about plastics, rubber, paints, surface coatings, resins, additives, and several

specialty applications, you will find that polymers are everywhere.

And just to show some photographs of the areas in of polymer use, you will find if you get

up in the morning and you start brushing your teeth, you will use a polymeric material.

And then get ready for going to your classes or colleges you will wear dresses, clothes,

shoes, and these are all made of polymers basically.

And you will take a vehicle whether it is cycle or a scooter or a car, you will find

many of the components in those vehicles are made up of polymers.

And you can see from these photographs that, you know, very commonly used materials are

made up of polymers.

Not necessarily the most common materials which you use.

For example, in several medical applications you will find that plenty of applications

products are made of polymers, which includes some of the applications where the polymers

are not visible from outside.

For example, a disposable or a biodegradable suture which you are using for, you are tying,

stitching during operations, artificial heart valve, contact lenses, display devices.

And there are so many other applications where polymers are hidden inside the device.

So basically, you can either see the polymers in applications or they can be also invisible.

So you know, most of us are convinced that polymers are everywhere and we need to study

or we need to understand the behavior of polymers and as a result we basically need to get ourselves

introduced to polymers sciences.

Why are polymers so popular?

When you think about any material applications, you will think that the materials should have

high strength.

That means, it should be able to bear large amount of load.

It should be resilient, which means it should give comfort, soft feeling and preferably

you can have materials which you will be able to see through, or in other words that the

material should have transparency.

And of course, if anybody wants to have all these properties at lower cost.

Now the conventional materials like metal, ceramics, glass, wood .none of these non-polymeric

materials can satisfy all these characteristics.

For example, if you consider glass, they are having very high strength and they can bear

high load.

But the problem is that it is actually brittle.

So you need to be very careful during use otherwise glass actually breaks and there

is a hazard involved in that.

You talk about metal, metals are very difficult to get in a transparent condition and also

for long use of metal in ambient conditions gives you corrosion.

We get problem.

And of course, these materials are much heavy material.

You know you want something, a material which would be light so that you can carry, carrying

is always easier and transport cost comes down.

So polymers give or satisfy all these properties plus it gives additional advantages which

I have listed in the next page.

So basically other beneficial properties of the polymers are that they are durable.

You know polymers are made of mainly carbon, compound containing carbon, hydrogen, organic

materials.

So carbon, hydrogen, oxygen.

So they are mostly the regular plastics or polymers which we use, they are, hydrophobic

in nature.

As a result they are resistant to hydrolysis and they are stable.

And also they are stable against electrochemical corrosion.

They are very light.

So if you consider the strength versus weight, the polymer gives you the maximum strength

versus weight ratio.

For a given weight of a material you can achieve high strength in polymers.

Polymers gives you design flexibility, because the melting temperature or processing temperature

of polymers are much lower.

So you can actually make products out of polymers at a low cost and spending much lower energy.

And because you can melt polymer and so you can actually design lot of polymeric products

as per your choice.

So basically it gives you design flexibility.

Polymers are generally thermal and electrical insulators.

So that gives you lot of advantages in use.

And because there are plenty of options in polymers there you can actually have many

choices in polymer material.

Additionally, it gives you feedstock flexibility in it.

Most polymers nowadays are used or made from petroleum fractions, but it can be also made

from natural gases and coal.

And some polymers are can also be made from agricultural and forest products and biomass

as an alternative resources.

But mostly polymers are made from synthesized from petroleum products.

So that means, polymers are actually part of petrochemical industry.

So basically when you talk about polymer industries, we talk about petrochemical industries like

in West Bengal we have Haldia Petrochemicals which produces polymers.

You have Reliance Petrochemicals, which also produces polymers.

And there are other petrochemical companies which actually produce polymers.

So what is the origin of good properties of polymers?

For that we just briefly know what are polymers.

I have not discussed what are polymer.

But just briefly if we look what are polymers you know polymers are large molecules or in

short we call macromolecules which consists of many repeating structural units.

So pictorially we can show that just to give you example, that you have small repeating

units which are shown here and they actually get linked with each other to produce a polymeric

large molecular weight.

And polymers are mostly made of organic compounds that gives you the lightweight and other beneficial

properties.

And if you compare small molecule and a polymer molecule, the reason for polymer, you know

good properties of polymer comes from that the fact that if you compare small molecules

to a bowl of rice, say we have now, rice are made of small molecules.

So basically you can put a spoon and easily take out a spoon of rice, boiled rice and

eat it.

That is possible because the molecules or the rice are very small.

So they do not entangle with each other.

As a result, you can easily separate them.

And those individual molecules, in this case rice they behave independently.

They do not you know, basically they do not interfere with the movement of other molecules.

Now when you compare polymeric molecules because they are large, because they are large, you

basically find that they are entanglement.

Like if you have a bowl of noodles, then if you put your spoon and if you want to take

it out you cannot take a single chain of noodles from the sample or from the bowl.

Because of large length, they are entangled with each other.

So basically they are completely entangled and as a result, the molecules cannot move

independently.

Now this gives basically the advantageous properties or strength of the polymers, the

toughness of the polymers because the polymer chains as they are entangled, so if you apply

some forces, they can basically easily dissipate those forces and give you high strength and

toughness and so on.

We will come back on these topics more going forward.

So basically the high molecular weight helps in providing superior properties like high

tensile strength, impact resistant, toughness, melt viscosity, and so on.

So we will now look at the brief history of science of polymers.

And as we already know that polymers are nothing but macromolecules.

They are basically used, the terms, two terms polymers and macromolecules are often used

synonymously.

So we will talk about brief history of science of polymers.

We can also talk about the science of macromolecules.

So polymer science is unlike the normal, other topics or other areas of physics and chemistry,

where first there is a strong theoretical basis based on which basically the subsequent

research and industrialization happens.

Polymer science is the other way around.

Initially polymer science was born in great industrial laboratories of the world, you

know.

Before a basic understanding about polymers, polymer related industries were up and running.

And polymers existed in natural form for a long time till the life began.

For example, in our body we have DNA macromolecules like DNA, RNA, proteins and polysaccharides,

which plays crucial role in plants and animal life.

And you know from ancient times these naturally occurring polymers were exploited by man for

making several items like they were used for clothings, decoration, shelters, tools, and

also for printing materials and etc.

So the origin of today s polymer industry happened in 19th century when important discoveries

were made, related to modification of some of these natural polymers.

So basically, the first research on polymers happened in 19th century when people or scientists

actually tried to modify, took these natural polymers and modified them for making or improving

their properties.

Some of the examples of those research is shown here.

And for example, if you talk about Goodyear; Goodyear, who actually found that heating

natural rubber, rubber with sulfur actually increases the elasticity of the natural rubber

and also tackiness which is very beneficial for use of natural rubber.

Later, you know Hancock and Goodyear himself they found that if you use large amount of

sulfur and heat with natural rubber you can actually make very hard rubber which are called

vulcanite.

And later Hancock was actually granted a patent in England and then Goodyear s, Charles Goodyear

s brother Nelson Goodyear was actually granted a patent in US at 1851 for this compound vulcanite.

There was also cellulose nitrate, was basically or nitrocellulose, sometimes they call was

basically used for several applications like celluloid and celluloid photographic films

and so on.

So before 1907, actually there lot of research happened for modification of these natural

polymers but 1907 is when the first, when the first fully synthetic polymers were invented

by Leo H. Baekeland by reaction of phenol with formaldehyde and the product was called

Bakelite.

And it went to commercial production in 1910.

So Bakelite was the first fully synthetic polymers invented by Leo H. Baekeland from

the reaction of phenol and formaldehyde.

So he was granted US patent in 1909, following which in 1910 this product was commercialized.

He basically was trying to invent a material, polymeric material which was substitute for

shellac, which was then solely supplied from India to the world.

And in the process he made first man-made polymeric material, which basically started

the age of plastics or polymers which we talked about in the beginning.

The material was heat resistant and insulating and he actually founded a company called Bakelite

Corporation in 1910 to manufacture this product.

Now till now, during these inventions and also modification of these natural polymers,

there was not, practically there was no understanding about the nature of the polymers.

In most cases, it was thought that these polymer molecules are associated colloids or basically

they are associated aggregates of small molecules like micelles which are formed from soap molecules.

So there was no idea existed that polymers were actually made up of large macromolecules

which are joined, which are basically having a repeating units are having joined by covalent

bonding.

So from there, this concept of macromolecules came and so, as I said the polymer industry

was running well without proper understanding of the nature of polymers.

And for over a century scientists believed that the polymers consisted of physically

associated aggregates of small molecules like micelles or surfactants.

Only in 1920 Hermann Staudinger, was a professor of organic chemistry at ETH Zurich, first

conceived that the polymers are made of very large molecules containing large sequence

of simple chemical units linked together by covalent bond.

Covalent bond is the word you must notice.

So this is the first time somebody actually conceived that polymers are actually large

molecule which were made of by linking of repeating units by covalent bonds.

That is the reason this Hermann Staudinger is considered as father of macromolecular

chemistry.

So he propounded the revolutionary concept that macromolecules can be formed by linking

of a large number of small molecules by means of covalent bonds.

And was, he could not basically experimentally prove, or basically there was no, at that

time there was no experimental evidence to prove that indeed this is the case.

So basically from his intuition and imagination he proposed and he published a paper titled

Uber Polymerization in the journal it is mentioned here in 1920.

So that is the year, which has considered the basically the start or beginning of macromolecules

as a science.

And so this year 2020 is the 100 year of macromolecular chemistry and that is the reason this year

has been celebrated by many chemical societies and chemists across globe as 100 years of

macromolecular chemistry.

However, it was not easy for him to convince the scientific community.

The contemporaries were very reluctant to admit the existence of extremely large compounds

with molecular weight exceeding 5000.

As I mentioned earlier, they actually believed that these polymers are nothing but micelle

type aggregates like as observed for soap molecules.

And which basically accounts for these you know, unusual properties of these polymeric

materials like high viscosity and so on.

Moreover, some scientists were convinced that the size of a macromolecule or molecule could

not, could never exceed the size of the unit cell as measured by X- ray crystallography.

But Staudinger did not give up.

He actually tried and convinced the rest of the scientific community and so, to do that

he actually performed additional experiments.

And so basically, he uses the traditional classical organic chemistry experiments to

support the existence of high molecular polymers.

His experiments on hydrogenation of natural rubber did not show any dissimilar properties

than normal hydrogenated, normal unsaturated rubber.

And during late 1920s, Staudinger provided additional evidences based on viscometry to

confirm that the molecular weights remain unchanged during chemical modification of

polymers.

Despite these impressive experiments, Staudinger continued to encounter very strong opposition

from eminent scientists of that period.

And some of the noted among them, some of the notable were Emil Fischer and Wieland

and both were Nobel Prize winners.

So you can imagine that somebody, a young scientist who is proposing something from

an imagination and intuition, which has been opposed by the Nobel laureates, then he must

be some genius to basically to fight for his, you know convincing others to prove his conception

that the polymers are indeed made up of large macromolecules.

But end of 1920s and during 1930s Staudinger s macromolecular concept found increasing

acceptance by other chemists.

And that was especially due to the work by Herman Mark and Wallace H. Carothers and finally

in 1953, Staudinger was awarded Nobel Prize for his discovery or his work on macromolecular

chemistry.

We need to talk about other pillars of macromolecular chemistry.

The Herman F. Mark was actually a crystallographer, who basically helped Staudinger to convince

that, that the molecules can have molecular weight more than 5000 or it can be larger

than unit cell.

So basically, he was one of the pillars which who basically helped Staudinger to convince

the scientific community that polymers are indeed large molecules.

William H. Carothers who basically confirmed the existence of molecules of extremely high

molecular weight and he led and developed the first totally synthetic fiber for use

in consumer products, which are basically used for consumer products.

He first invented linear polymers from condensation polymers and used it for making polyamides.

And later Paul J. Flory who actually developed fundamental understanding both theoretical

and experimental in the physical chemistry of macromolecules.

So basically Staudinger along with these three other scientists Herman F. Mark, Wallace H.

Carothers and Paul J. Flory should be considered as the pillars of macromolecular chemistry.

Now following these understanding, there was plenty of activities among scientists for

developing new polymers.

And there were large scale polymer production happening during this 1950s to 70s and which

continued till 1990s.

So basically in this timeframe, the polymers were discovered

which was facilitated by the cheap or availability of petrochemicals.

So in now, when we move forward to the new millennium and beyond 2020 basically polymer

sciences are now looking for newer applications or more specialized applications for polymers.

So basically in 2020 onwards, we have the second

century of polymer sciences.

So basically I will, I will stop with this now.

So in the next lecture, what I will do I will talk more about the polymer as a whole, give

you the bird eye picture of polymer as a product and then talk about what is the problem of

polymers and what are the present research needs for polymer science.