Lect 3 Microstructure Ch 2 Pt2.2014

8/12/2019 Lect 3 Microstructure Ch 2 Pt2.2014

1/26

Chain Microstructure

Linear chains,branching

Cross - linking and network formationSequence isomerism

Stereoisomerism in vinyl polymers

Diene polymers (structural isomerism)

Copolymers and blends

TOPICS COVERED :


2/26

Philosophical ApproachThere is a direct connection betweenstructure and properties.

Consider crystallinity in polymers.

RANDOM COIL

Like cooked spaghetti

CRYSTALLINE

Like "uncooked spaghetti


3/26

Effect ofCrystallinity on the Properties

Crystallinity affects

Strength

StiffnessToughnessBarrier PropertiesSolubility

TransparencyThermal PropertiesEtc


4/26


5/26

Whats covered, whats next . . .

Linear chains, branching Networks Cross-linking Sequence isomers

Stereo-isomers, tacticity Structural isomers

Copolymers, terpolymers

Degree of polymerization Molecular weights Number average and weight average MWs MW distributions


6/26

Copolymers and Terpolymers

Copolymers- two different polymers in thechain.

Mer variations composition (relativeamounts), structure (distribution) andarchitecture.

These variations affect the properties of thecopolymer.

Terpolymer three monomers, same mer

considerations, more complicated.


7/26

Copolymers

Graft

-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-

A-A-A-A

-A-A-A-A-

A-A-A-A-A-A-A-A-A-A-

A-A-A-A-A-A-

-A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-B-A-A-A-A-A-A-

Block

-A-B-B-B-A-A-B-A-B-A-A-A-B-A-B-B-A-B-B-A-A-A-B-

Random

-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-

Alternating


8/26

Copolymers: Adjusting Properties

How would you design a polymer to adjustthe following . . . . . . Disrupt the packing order? Improve the compatibility with water?

How would the properties of a copolymerchange with mer Composition?

Structure? a


9/26

MW directly impacts the properties

of the polymer

Molecular Weight

Mol. Wt.

Melt ViscosityTensile Strength

Mol. Wt.


10/26

Gases

Liquids

IncreasingMolecular Weight

16304458

114

450

420030

CH4

CH3CH2CH3

CH3CH3

CH3CH2CH2CH3

CH3(CH2)6CH3

CH3(CH2)30CH3

CH3(CH2)30000CH3

--------------------------------

------------------------

-----------------------------------------

---------------

---------------

---------------

----------

Semi-solid

Solids

Incr. MW

Molecular Weight


11/26

Molecular Weight of Polymers

Degree of Polymerization (DP) Number of mers in the polymer

MWpolymer/ MWmonomer

Polymers MWs

are averages (weight, number)

have distributions breadth or skewness (polydispersity)


12/26

Molecular Weight DistributionsSynthetic polymers have adistribution of chain lengths.

The distributions can have-different widths.-several distributions.

So, there will be a-distribution of chain MWs,-an average MW, and-a width to the MW

distributions.


13/26

Defining an Average

200 monomers form 10 chains.The average chain length is 20


14/26

Molecular WeightNumber Average and Weight Average

200/20 provides thenumber average MW.

Mn =NxMx

Nx


15/26

110 ,000] 4 1]4 1

~ 2,000

Number Average Molecular Weight (Mn)

Mn

NxMx

Nx

Number average favors

the number of chains.

4 Mosquitos(weighing 1 lb ea.)

10,000 lb Elephant


16/26

Weight Average Molecular Weight (Mw)

MwW

xM

x

Wx

10, 000 10, 000] 41]10, 000 4

~ 10, 000

Weight average favorsthe wt of the chains.

4 Mosquitos(weighing 1 lb ea.)

10,000 lb Elephant


17/26

5 chains DP 100

5 chains DP 150

5 chains DP 200

Consider a sample with

5 (moles) chains of length 100(DP of 100 mers/chain)

5 (moles) chains of length 150 5 (moles) chains of length 200.

Ave. DP. = 150 (Mn).

If the MW of each mer were 100,the Mn= 15,000. (DP x M)

Mn

NxMx

Nx

Number Average Molecular Weight


18/26

510, 000] 515, 000] 520, 000]5 5 5

50 ,000 75 ,000 100 ,000

15

15,000

What about weight average MW?

Heres how the equation works;

Number Average Molecular Weight

Mn

NxMx

Nx


19/26

Weight Average Molecular Weight

Wx NxMx

Definition of weight average;The total wt of species x is theMW of each chain of type, x ,multiplied by the number of

chains of this type.

5 chains, each of wt. 10,000,means that wxis 50,000.

Substituting into the topequation gives a differentform of the equation for

weight average;

Mw WxMx

Wx

NxMx2

NxMx

Mw WxMx

Wx


20/26

510 ,000 2 515 , 0002 520 , 0002510 ,000 515 , 000 520, 000

16 ,111

Mn

Polydispersity =Mw

1

NxMx2

NxMx

MwW

xM

x

Wx

Weight Average Molecular Weight

Polydispersity (PD) = Mw/ Mn

Always greater than 1.


21/26

Molecular Weight of PolymersWhat Average ?

Number Average Molecular Weight Weight Average Molecular Weight

Go from Mn to Mw average by multiplying each of the terms inside thesummations by Mx.Higher order averages are constructed in the same way.For example, the z-average,

The ratios of these averages relates to the moments of the distributionand reveal the breadth and skewdness

Mn

NxMx

Nx

Mz

NxMx3

NxMx2

Mw

NxMx

Nx

2

Mx


22/26

Mole (Number) and WeightDistributions

A narrowMW distributionplotted according to number(left) and weight(below).

20000010000000

200000

400000

600000

800000

1000000

1200000

Molecular Weight

Weig

ht

Mw = 104,500_

20000010000000

2

4

6

8

10

12

Molecular Weight

Moles

Mn = 100,000

_


23/26

Molecular Weight Distributions

30020010000.00

0.01

0.02

0.03

0.04

0.05

0.06

Weight Fraction

Number Fraction

Degree of Polymerization

Faoohn

30000020000010000000

2

4

6

8

10

12

Moles

Molecular Weight

Mw@1 1 8 , 2 0 0

Mn@1 0 8 , 5 0 0


24/26

MW Distributions

Unimodal, bimodal, trimodal

Strongly affect properties

Produced in synthesis; Subsequent blending

Minor population

Lower MW

Higher MW


25/26

Moles, Numbers, Fractions, Etc. inCalculations of Averages

Deg. polymerization (x) and MW MWp = (x)(MWmer) [MW of mer]

Chain count: Number = moles x NA

MN = (ni)(MWi)/(ni) can be written as

NA(molesi)(MWi)/NA(molesi)

Weight ratio = weight fraction ratio

(wi)(MWi)/(wi) can be written as

((w1/wi)(MWi)/(wi/wi) =((1/wi)/(1/wi)) ( (wi)(MWi)/(wi))


26/26

Average Degree of Polymerization (Xn)

Deg. polymerization (x) and MW

MWi = (xi)(MWmer) [MW of mer]

MN= (XN) (MWmer)

MN = (ni)(MWi)/(ni)

(XN)(MWmer) = (ni)(xi)(MWmer)/(ni)

(XN) = (ni)(Xi)/(ni)

Documents

Lect 3 Microstructure Ch 2 Pt2.2014