polymer powerpoint

8/10/2019 polymer powerpoint

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POLYMER

STRUCTURE

AND PROPERTIES

Alsua, Melissa Joy D.

Realoza, Janshara B.

Sison, Felicia Chloe L.


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POLYMER

poly = many mer = repeating units

substance consisting of large molecules that are

made of many small, repeating units called monomers,

or mers.

C C C C C C

HHHHHH

HHHHHH

Polyethylene (PE)

ClCl Cl

C C C C C C

HHH

HHHHHH

Poly(vinyl chloride) (PVC)

HH

HHH H

Polypropylene (PP)

C C C C C C

CH3

HH

CH3CH3H


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- most polymers are hydrocarbons

Saturated hydrocarbons

Each carbon singly bonded to four other atoms and no newatoms may be joined without the removal of others that are

already bonded.

Example:

Ethane, C2H6 Methane, CH4

Propane, C3H8Butane, C4H10

Pentane, C5H12 Hexane, C6H14

COMPOSITION


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Unsaturated Hydrocarbons

Molecules that have double and triple covalent bonds.

each carbon atom is not bonded to the maximum(four) other atoms

somewhat unstable can form new bonds

Double bondfound in ethylene or ethene - C2H4

Triple bondfound in acetylene or ethyne - C2H2

4

C C

H

H

H

H

C C HH


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Isomerism

two compounds with same chemical formula can have

quite different structures

for example: C8H18

normal-octane

2,4-dimethylhexane

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C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=

H3C CH

CH3

CH2 CH

CH2

CH3

CH3

H3C CH2 CH3( )6


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Polymers are substances that consist of very large

molecules called macromolecules that are made up of many

repeating subunits.

The molecular subunits that are used to synthesize

polymers are called monomers and the reactions by which

monomers are joined together are called polymerizations.

Many polymerizations can be initiated by radicals.

Polymer Molecules


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When all the repeating units along a chain are of the same

type, the resulting polymer is called a homopolymer.

Chains may be composed of two or more different repeat

units, in what are termed copolymers.

monomers have an active bond that may react to form twocovalent bonds with other monomers forming a two-

dimensional chain-like molecular structure is termed

bifunctional.


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In general the functionalityis the number of bonds that a

given monomer can form.

example, monomers such as phenolformaldehyde are

trifunctional; they have three active bonds from which a

three dimensional molecular network structure results.


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Molecular Structures

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B ranched Cross-Linked NetworkLinear

econdary

bonding


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Linear polymers

are those in which the repeat units are joined

together end to end in single chains.

These long chains are flexible and may be thought of

as a mass of spaghetti

For linear polymers, there may be extensive van der

Waals and hydrogen bonding between the chains.

Some of the common polymers that form with linearstructures are polyethylene, poly(vinyl chloride),

polystyrene, poly(methyl ethacrylate), nylon, and the

fluorocarbons.


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The branches considered to be part of the main-

chain molecule may result from side reactions that

occur during the synthesis of the polymer. The chain

packing efficiency is reduced with the formation of side

branches, which results in a lowering of the polymer

density.

Those polymers that form linear structures may also

be branched. For example, high density polyethylene(HDPE) is primarily a linear polymer, while low density

polyethylene (LDPE) contains short chain branches.

Branched polymers


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Cross-linked

adjacent linear chains are joined one to another atvarious positions by covalent bonds.

The process of cross-linking is achieved either

during synthesis or by a non-reversible chemical

reaction.

Often, this cross-linking is accomplished by additive

atoms or molecules that are covalently bonded to

the chains.

Many of the rubber elastic materials are cross-

linked; in rubbers, this is called vulcanization


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Multifunctional monomers forming three or

more active covalent bonds, make three-

dimensional networks

Actually, a polymer that is highly cross-linked

may also be classified as a network polymer.

These materials have distinctive mechanical

and thermal properties; the epoxies,

polyurethanes, and phenol-formaldehydebelong to this group.

Network polymers


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MOLECUL R WEIGHT

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Molecular weight, M: Mass of a mole of chains.

Low M

high M

Not all chains in a polymer are of the same lengthi.e., there is a distribution of molecular weights


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xi = numberfraction of chains

in size range i

iin MxM

wi = weight

fraction of chains

in size range i

Mi = mean (middle)

molecular weight ofsize range i

Number-average molecular weight

iiw MwM

Weight-average molecular weight


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Degree of Polymerization, DP

DP= average number of repeat units per chain

m

MDP

n

16

:followsascalculatedisthiscopolymersfor

unitrepeatofweightmolecularaveragewhere m

mol. wt of repeat

unit i

Chain

fraction

iimfm


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Molecular Configurations

Configurationsused in reference to arrangements of

units along the axis of the chain, or positions that are

not alterable except by the breaking and then reforming

of primary bondsStereoisomerismdenotes the situation in which atoms

are linked together in the same order (head-to-tail) but

differ in their spatial arrangement


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C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

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Types of stereoisomers

Isotactic configuration - all Rgroups on same side of chain

Syndiotactic configuration -Rgroups alternate sides

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

Atactic configuration -Rgroups randomly positioned

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC


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Geometrical isomerism

- Possible within repeat units having a doublebonds between chain carbon atoms.

Two kinds of geometrical isomers :

C C

HCH3

CH2 CH2

C C

CH3

CH2

CH2

H

cis

cis-isoprene

(natural rubber)

H atom and CH3

groupon

same side of chain

trans

trans-isoprene

(gutta percha)

H atom and CH3

group on

opposite sides of chain


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Copolymers

- two or more monomerspolymerized together

TYPES:

randomA and B randomlypositioned along chain

alternating

A and B

alternate in polymer chain

blocklarge blocks of A unitsalternate with large blocks ofB units

graftchains of B unitsgrafted onto A backbone

A B 20

random

block

graft

alternating


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Polymer Crystallinity

Crystallinity is indication of amount of crystalline region inpolymer with respect to amorphous content

X-ray scattering and electron microscopy have shown thatthe crystallites are made up of lamellae which,in turn, arebuilt-up of folded polymer chains


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i) Chain lengthii) Chain branching

iii) Interchain bonding

Crystallinity occurs when linear polymer chains are

structurally oriented in a uniform three dimensionalmatrix. Three factors that influence the degree of

crystallinity are:


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Ordered atomic

arrangements involving

molecular chains

Crystal structures in terms

of unit cells

Example shown

polyethylene unit cell

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Arrangement ofmolecular chains in a

unit cell ofpolyethylene


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Crystalline regions

thin platelets with chain folds at faces

Chain foldedstructure

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10 nm


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Polymers rarely 100% crystalline

Difficult for all regions of all chains to

become aligned

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Degree of crystallinity

expressed as % crystallinity.-- Some physical properties

depend on % crystallinity.

-- Heat treating causes

crystalline regions to grow

and % crystallinity toincrease.

crystallineregion

amorphousregion


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Polymer Single Crystals

Electron micrographmultilayered single crystals

(chain-folded layers) of polyethylene

Single crystalsonly for slow and carefully controlled

growth rates

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Semicrystalline Polymers

Some semicrystallinepolymers form

spherulitestructures

Alternating chain-folded

crystallites andamorphous regions

Spherulite structure for

relatively rapid growth

rates

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Spherulite

surface


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PhotomicrographSpherulites in Polyethylene

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Cross-polarized light used

-- a maltese crossappears in each spherulite


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Source : Material Science and

Engineering 7e Callister

THANK YOU!!!

polymer powerpoint

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