Chemistry 367L/392N

Macromolecular ChemistryMacromolecular Chemistry

Berzelius Staudinger Carothers

Chemistry 367L/392N

� The raw scores that you earn on the exams will be converted to Standard T-scores. Using T-scores removes bias in favor of the tests with the highest standard deviation. It represents the fairest way I know of to “grade on a curve”. This statistical approach is used in grading nearly all national exams such as the MCAT, SAT, GRE, etc. Each exam will be returned with a raw score and a T-score so that you will know exactly where you stand after each exam. The average of your T-scores will be used to determine the course grade according to the following table:

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Grading Question Grading Question

Chemistry 367L/392N

Some early MilestonesSome early Milestones

� 1833 Berzelius coins term polymer� 1880-1900 Man made fibers by modification of

natural material cellulose acetate, nitrocellulose, etc

� 1900-1930 “Colloid Controversy”� 1910 Bakelite� 1920 Staudinger macromolecules� 1930- 1937 the Carothers period Neoprene,

nylon,etc.

Chemistry 367L/392N

Natural PolymersNatural Polymers� Natural polymeric materials have been used

throughout history for clothing, decoration, shelter, tools, weapons, and writing materials

� Examples of natural polymers:– Cellulose (wood, cotton)

– Hair (wool)

– Silk

– Rubber

– Horn

� Modified natural polymers– Nitrocellulose (lacquer, smokeless powder)

– Rayon, etc

Chemistry 367L/392N

CelluloseCelluloseCelluloseCelluloseCelluloseCelluloseCelluloseCellulose

Cellulose is the most widely distributed plant skeletal polysaccharide. It constitutes over half of the cell wall material of wood. Cotton is almost pure cellulose.

Cellulose is a linear polysaccharide of D-glucose units joined byβ-1,4-glycosidic bonds.

Chemistry 367L/392N

• The average MW of cellulose in 400,000 g/mol, corresponding to about 2200 D-glucose units per molecule.

• Cellulose molecules act a lot like stiff rods and align themselves side by side into well-organized water-insoluble fibers. The -OH groups form numerous intermolecular hydrogen bonds adding strength to the network.

• This arrangement leads to high mechanical strength and water insolubility, hence the strength and utility of wood and cotton fiber.

CelluloseCelluloseCelluloseCelluloseCelluloseCelluloseCelluloseCellulose

Chemistry 367L/392N

RayonRayonRayon is made by first treating cellulose with carbon disulfide in base solution.

Cellulose-OH+ CS2NaOH

cellulose xanthate

Then the solution of cellulose xanthate is passed through a smallOrifice or slit into an acidic solution.

Cellulose-OH+ H+Cellulose-O-C-S-Na+=

S

Cellulose-O-C-S-Na+=

S

Chemistry 367L/392N

RayonRayon

Chemistry 367L/392N

ShellacShellac

Bug Bug “do do”

Lots of bug “do do”

Chemistry 367L/392N

ShellacShellac� natural polymer secreted by a

southeast Asian lac beetle � Excellent quality of moulding detail

leads to:� Early 78 rpm records

– 25% "shellac“, cotton filler, powdered slate, and a small amount of wax

Chemistry 367L/392N

MeyerBaekeland

The History of Novolac

C.H. Meyer and/or L.H. Baekeland Discovered Novolac ca. 1900 ???

OH

CH3

Chemistry 367L/392N

BakeliteBakeliteBaekeland’s Phenol-formaldehyde

resins, which he called Bakelite.

Chemistry 367L/392N

Natural RubberNatural Rubber

Chemistry 367L/392N

TThe Mayan Ball Game: he Mayan Ball Game: life or death with a littlelife or death with a littlerubber ballrubber ball ……

�� The Ball Court was used for The Ball Court was used for symbolic religious games. symbolic religious games.

�� It is formed of two parallel It is formed of two parallel walls. walls.

Chemistry 367L/392N

What are Polymers??What are Polymers??

Jöns Jacob Berzelius(1779-1848)

Coined the term "polymer" in 1833 to describe organic compounds that share identical empirical formulas but differ in overall molecular weight …a kind of “isomer”.. acetylene cyclobutadiene, benzene and styrene, for example.

This concept lasted until Carothers.

Chemistry 367L/392N

The Association PeopleThe Association People

Thomas Graham

1805-1869

Graham thought that cellulose and other colloids consisted of large numbers of structurally simple molecules held together by "association." ….also called “partial valency” ??!!

Chemistry 367L/392N

Hermann Staudinger Hermann Staudinger

18811881--19651965

The statement of a German chemist after a debate with Staudinger in 1926: ‘We are shocked like zoologists would be if they were told somewhere in Africa an elephant was found who was 1600 feet long and 300 feet high’. Staudinger received the Nobel Prize in chemistry in 1953.

Chemistry 367L/392N

ColligativeColligative PropertiesProperties

�� ColligativeColligative properties of solutions are properties of solutions are properties that depend upon the properties that depend upon the concentration of solute molecules or ions, concentration of solute molecules or ions, but not upon the identity of the solute. but not upon the identity of the solute. ColligativeColligative properties include freezing point properties include freezing point depression, boiling point elevation, vapor depression, boiling point elevation, vapor pressure lowering, and osmotic pressure. pressure lowering, and osmotic pressure.

Chemistry 367L/392N

OsmometryOsmometry

Semipermeable membrane: stops polymers, passes solvent.

h

Define a pressure Π = ρ g h

Chemistry 367L/392N

The gas law in reviewThe gas law in reviewPV =NRT or PV/nRT = 1

PV/nRT

P (atm)

1.0 (Ideal)

( N2 )

( Real )

PV/nRT = 1 + BP + CP2 + DP3…..etc

Virial fudge factors

Chemistry 367L/392N

ρ g h = ΠSo…. Π V / n R T = 1 or P = (n/V) R T

n / V = m (Molar concentration)

So…. Π = m R T this is the van’t Hoff Relationship

For molal m = n / V = c / M

Where M = mass of solute per unit volume of solvent

So…. Π / c = R T / M

and we can cheat…. Π / c = R T /M + Bc + Cc2 + …..

Applying to “ideal solutions”

Chemistry 367L/392N

Π / c

MMRT

C

Reduced osmotic pressure (Reduced osmotic pressure (ππ/c) /c) vsvs concentration (c)concentration (c)

Slope = B

Chemistry 367L/392N

MorphologyMorphology� Many polymers tend to crystallize as they precipitate

or are cooled from a melt

� But, they are very large molecules, often with complicated and irregular shapes, which inhibits crystallization and tends to prevent efficient packing into exactly ordered structures

� As a result, polymers in the solid state tend to be composed of ordered crystalline domainsand disordered amorphous domains

Chemistry 367L/392N

Polymer MorphologyPolymer Morphology

Crystalline and semi crystalline Amorphous

Chemistry 367L/392N

MorphologyMorphology� Polymers with regular, compact structures and

strong intermolecular forces, such as hydrogen bonds have high degrees of crystallinity. – as crystallinity increases, the polymer becomes more

opaque due to scattering of light by the crystalline regions…for example, teflon -(CF2CF2)-“looks” white

� Melt transition temperature, Tm: the temperature at which crystalline regions melt– as the degree of crystallinity increases, Tm increases

Chemistry 367L/392N

Polymer CrystalsPolymer Crystals

Chemistry 367L/392N

CrystallinityCrystallinity

proportion of crystalline / amorphous strong influence on properties

PE carrier bag - amorphous, toughened pipe 95% crystalline

amorphous

crystalline

Chemistry 367L/392N

MorphologyMorphology� Example:poly(ethylene terephthalate),

abbreviated PET can be made with crystalline domains ranging from 0% to 55% depending on how it is processed. It can have the properties of drink bottles or Dacron fiber.

OO

OO

nPoly(ethylene terephthalate)

Chemistry 367L/392N

MorphologyMorphology

� Amorphous PET is formed by cooling the melt quickly– plastic beverage bottles are PET with a low degree of

crystallinity

� By cooling slowly, more molecular diffusion occurs, chains become more ordered and crystalline domains form– PET with a high degree of crystallinity can be drawn into

textile fibers and tire cords (dacron)

Chemistry 367L/392N

MorphologyMorphology� Amorphous polymers are referred to as glassy

polymers– they lack crystalline domains that scatter light and are

transparent….Poly(methyl methacrylate)– they are weaker polymers and generally more flexibility– on heating, amorphous polymers are transformed from

a hard glass to a soft, flexible, rubbery state

� Glass transition temperature, Tg: the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid (ca. 100 degrees for polystyrene)

Chemistry 367L/392N

Differential Scanning CalorimetryDifferential Scanning Calorimetry

Chemistry 367L/392N

A DSC PlotA DSC Plot