Introduction to Macromolecules CHM5080 (CUHK) – CHEM588 (HKUST) – CHEM6108 (HKU)

2006/2007 Macromolecules

Introduction to MacromoleculesIntroduction to MacromoleculesCHM5080 (CUHK) – CHEM588 (HKUST) – CHEM6108 (HKU)CHM5080 (CUHK) – CHEM588 (HKUST) – CHEM6108 (HKU)

Lecturers: Chi WU (CUHK) [email protected] Ben Zhong TANG (HKUST) [email protected] Wai Kin CHAN (HKU) [email protected]

Time/date: CUHK: L1 & L2 Science Centre Feb 10 & March 3 10:00-12:30 HKUST: Rm 2405 (Academic Building) March 17 & 3114:00-17:30 HKU: P3, Chong Yuet Ming Physics Building April 14 & 28

Final Exam: CUHK/HKUST/HKU May 12, 10:00-12:30 (Saturday)

Textbooks:

“Introduction to Macromolecular Science”By Petr Munk, 1989, John Wiley & Sons, QD381.M85

“Introduction to Polymers”, 2nd editionBy R. J. Young and P. A. Lovell, 1991, Chapman & Hall, QD381.Y68

TA: Ms Shi Feng, Room 226C, 2609-6266, [email protected]


OutlinesCUHK 1. Concept of macromolecules 2. Structures of macromolecules 3. Characterization of macromolecules

HKUST 4. Classification of polymerization reactions 5. Step (or condensation) polymerization 6. Chain (or addition) polymerization 7. Copolymerization

HKU 8. Ionic polymerization 9. Coordination polymerization10. Controlled radical polymerization11. Synthesis of polymers with special properties


Natural Macromolecules

Proteins, DNA, RNA Polysaccharides

(cellulose: plants & animals)

Synthetic Macromolecules

Polystyrene, polyethylene Poly(vinyl chloride)

Polyesters, polyurethane, ...

Small molecules Oligomers (M > 104 g/mol) Macromolecules

The difference between small molecules and macromolecules

* Homogeneous* No swelling in dissolution* Purification methods* Low viscosity* Simple structures

* Inhomogeneous (size & mass)

* Swelling in dissolution* Precipitation, GPC, …* High viscosity* Complicate structures.

The Basics of Macromolecules


Structures of macromolecules

* Primary structures Composition: number & types of atoms

Configuration: how they are connectedHomopolymer & heteropolymers:block, seqential, graft, random, ...

* Secondary structures

linear, branching, star, grafting, ladder, ...

Comformation: folding, helix, sheet, ...

* Tertiary structures Special arrangements of larger segments(helix & sheet) to form a complicate structure

* Quaternary structures Spatial multi-chain aggregates, intra- andinter-chain interaction, e.g., triplethelix and enzyme


Pri

mar

y st

ruct

ure

s * Backbone contains only carbon atoms

- Polymeric hydrocarbons: Polyethylene Polypropylene isotactic, syndiotactic & atactic

Polybutadiene 1,2 addition and 1,4 addition (cis & trans)

Polyisoprene -(CH2C(CH3)=CHCH2)n- natural rubber

Polystyrene

Low (H.P.) and high (L.P.) density PE

The most representative polymer

- Halogen-containing: Poly(vinyl chloride)Polytetrafluoroethylene

-(CH2CCl)n- common polymerTeflon, The king of plastic

Polytrifluorochloroethylene Tough and inert

- With polar side groups: Poly(methyl methacrylate) Organic glass

Poly(hydroxyethyl methacrylate) Gel contains 35% water

Polyacrylamide Typical water soluble polymer

Polyacrylic acid Washing power, useful polymers

Poly(vinyl alcohol), Poly(vinyl pyrrolidone), ….

- Polymers with heteroatoms in the backbone:

Polyether - PEO; Polyesters -(O-(CH2)a-CO)n-, PCL; Polycarbonates -(O-R-O-CO)n-;

Polyamides -(NH-(CH2)a-CO)n-; Polyurethanes -(NH-R1-NH-CO-O-R2-O)n-; Polyureas; ...


DNA

The living organisms (1-10 x 107)

Natural macromolecules: DNA, RNA, Proteins, Polysaccharides …

fundamentally similar inside

infinitely different outside

Heredity(1-10 x 1013 cells)

four nucleotides

Psugar

base Adenine ThymineGuanine Cytosinepurines pyrimidines

Replication DNA

RNA

Transcription

sugar

H

sugar

OH

Thymine UracilDNA / RNA

Proteins

Translation

catalytic function H2N-C-COOHH

R

3 basic ones2 acidic ones5 polar ones

10 non-polar ones

GenomesDNA chains

GenesSegments

regulatory sequences

exon (~1.5%) intron (~25%)

~30%

Procaryotes + eucaryotes


Physical formsPhysical forms

Powders

Solutions

Hydrogels

Hydrocolloids

Fibres

Films

VariablesVariables

Monosaccharide substituents

Glycosidic linkages

Molecular size profile

Substitution patterns

Cross-linking

Polysaccharides: Physical Forms and Variables


HO

CH2OH

OH

O

OOHO

OH

CH2OH

O

n4)--D-Glcp-(14)--D-Glcp-(1

Principal constituent of plant cell walls.Wood & Cotton are the major industrial sources

Cellulose


Major industrial sources of starch are wheat, maize (yellow maize & waxy maize starches), potato, rice, tapioca and sago. The ratio of amylose to amylopectin is characteristic of botanical origin.

O

HOOH

CH2OH

O

OO

HOOH

CH2OH

OO

HOOH

CH2OH

O

4)--D-Glcp-(14)--D-Glcp-(1

amylose O

HOOH

CH2OH

O

OO

HOOH

CH2

OO

HOOH

CH2OH

O

O

HOOH

CH2OH

O

O

amylopectin

Starch ( Amylose & Amylopectin )



* Primary structures Composition: number & typs of atoms



linear, branching, star, grafting, laddle, ...

Conformation: folding, helix, sheet, ...

* Tertiary structures Special arrangements of larger segmentsto form a complicate structure, e.g., helix



Structure of a protein chain: Primary: Secondary and Tertiary Structures


Sec

onda

ry s

tru

ctu

res

- C

onfo

rmat

ion

*. Helical structure - Proteins, amylose and nucleic acids

Energy vs Entropy Random coil vs Ordered conformation

It requires two hydrogen bonds in the formation of the helix (not proline).

It contains 3.6 amino acid residues per turn; subsequent residues are rotated 100owith a pitch of 5.4 A; and the translation is 1.5 A per residue.

*. Chain folding of some regulated heteropolymer chains

O rd ere d co il

R an d o m co il

C o lla p sedco re -sh e ll

n an o p artic le

h ea t h ea t

Stickers moverandomly like a

“gas”Stickers move in

a more correlated fashion like a

“liquid” Stickers arerestricted

like a“solid”


Sec

o nda

r y s

t ru

c tu

r es

T < ~32 oC

PNIPAM-g-PEO

Tincreases

dcreases

A single polymer chaincore-shell nanostructure

Chi Wu, Xingping Qiu, Physical Review Letters, 79, 620 (1998); Macromolecules, 30, 7921

Applications

One of the envisionedapplications is the smarttemperature-sensitivedrug delivery device. 0 10 20 30 40 50

1.2

1.4

1.6

1.8

t / min

0

20

40

60

I 1/I 3

T / oC

80pyrene: an imitated drug

Protein denaturation Heat denatured & chemical denatured


Tertiary structures - Arrangement of larger segments

Secondary structure - helix

Heat

Chemical

Enzymatic Catalysis Specific & fast

Particular spatial arrangement

Energy - adenosine triphosphate (ATP)

Chymotrypsin - a “hydrophobic pocket - aromatic amino acids

Trypsin - an ionized carboxyl - interacted with the basic groups


A zig-zag chain A thread chain A random coil

Let us start with a polymer chain in one dimensional space.It has N segments and each segment has a length of b.

ob-b

A random walk

After N steps and if n steps are positive, R = bn + (-b)(N-n) = b(2n-N)2/Nn

NIf

The chance (probability) to find n positive steps is a binomial distribution because Pn is related to (p + q)N when p = q = 1/2. !)(!

!

nNn

NP

N

n

2

1

The mean value of n can be calculated as

22

2

1

1

1

2

1

2

1 1

100

NN

nNn

NN

nNn

nNnPn N

N

n

NNN

n

NN

nn

!)(!)(

!)(

!)(!

!

NN

n

nNn qpnNn

Nqp )(

!)(!

!

0

<R> = 0

4

1

11

1

2

1

2

1

1 10

2

0

22 )(

!)(!)(

!

!)(!)(

!)(

!)(!

!

NN

nNn

N

nNn

Nn

nNn

NnPnn

N

n

N

n

NN

n

NN

nn

42 N

n

2

0

222 )]2([ NbPNnbRRRN

nn

Step motion: Rn = b or -b nmmn bRR 2 2

1

2

11

2 NbRRRRN

nn

N

mm

N

nn

22 NbR bNRRRMS2

1

2

12


!)(!

!

nNn

N

2

1P

N

n

?

,

nP

NWhen


In a good solvent, a chain is in the random coil state.

Radius of gyrationHydrodynamic Radius (Rh)

51.h

g

R

R2

1212

0

2

12 bNR

N

iiRMS

/

rR

End-to-EndDistant

R = rN - ro

2

1

6

NbRg


Let us imagine an increase in monomer size from 0.1 nm to 1 cm.

N ~ 102-1010 in poor solvent

R = bN cm m

Polymer size: Polymer size depends on solvent quality

N ~ 102-1010 in theta solvent

R = bN ~ 10 cm -1 km

N ~ 102-1010 in good solvent

R = bN~ 16 cm – 40 km R = bN ~ 100 cm - 105 km

N ~ 102-1010; A rigid chain

Earth

Moon


Thin rod: Rg2 = L2/12

Thin disk: Rg2 = (1/2)R2

N

ii

N

ii

N

ii

N

ii

N

ii

i

g

m

m

m

m

m

mR

1

1

2Gi

1

1

2GjGi

1

2j

N

1ii

2

)rr(

2

)]rr()rr[(

2

)rr(

For an idea chain jibjiij 222 rrR

)(

)()()(

16

2

2

1

2

21

2

1 1

2

1

1

2

2

N

NNb

N

iib

N

jib

m

jibmR

N

i

N

i

N

jN

ii

N

ii

g

bNRRRMS21212 //

66

,2/12/1

2

12 bNN

bRRNAs gg

4526 .g

RSM

R

R

Short rangeConfiguration

1) IR: vibration and rotation; 2) NMR: chemical shift;3) chemical analysis, GC, UV and MS; and ….

Long rangeConformation

1) viscometry: ~ Vh or Rh; 2) laser light scattering: Rg and Rh; 3) fluorescence: NRET; 4) x-ray and neutron scattering & diffraction; 5) relaxation: mechanical, electrial, optical, ...

Experimental Methods









* Quaternary structures Spatial multi-chain aggregates, intra- andinter-chain interaction, e.g., triplethelix & enzyme


Small molecules Conventional colloidsassembly Physical methods

Chemical methods

Macromolecules Polymeric colloids (supramolecules)assembly

P o l y ( p h e n y l v i n y l s u l f o x id e ) ( P V S O ) P o ly a c e ty le n e (PA )P o ly (p -m e th y l s ty re n e )

n P h S O H


Qu

ater

nar

y st

ruc t

ure

s

Rc

RR

More Chains

Assembled

Self-assembly of rod-coil diblockcopolymers in dilute solution


DNA

--OOCOOC

NHNH22

PPPP

Lipid Lipid bilayerbilayer

CytosolCytosolSingle-pass Single-pass multi-pass multi-pass

Non-cytosolNon-cytosol

Cell Membrane Proteins


Molar mass distributons Mn , Mw , Mz, M

Absolute methods The end-group, colligative properties MS, light scattering, ultracentrifuge.

Relative methods viscosity, chromatography, FFFelectrophoresis, flow birefrigence

fn(M); fw(M); fz(M)

M

f M Mf Mw n( ) ( ) f Mf M M f Mz w n ( ) ( )2

The n-average molar mass

MMf M dM

f M dMn

no

no

( )

( )M

M N

Nn

ii

i

ii

1

1

The w-average molar mass MM f M dM

Mf M dM

Mf M dM

f M dMw

no

no

wo

wo

2 ( )

( )

( )

( )M

M W

W

M N

M Nw

ii

i

ii

ii

i

i ii

1

1

2

1

1

The z-average molar mass MM f M dM

Mf M dM

M f M dM

M f M dMz

wo

wo

no

no

2 3

2

( )

( )

( )

( )M

M W

M W

M N

M Nz

ii

i

i ii

ii

i

i ii

2

1

1

3

1

2

1

fM

Mf Mw

nn ( )

Schulz-Zimm Distribution

f Mb

zM ew

zz bM( )

( )

1

1

Poisson Distribution

f MM

w ( ) ( ) exp[( )

]/ 2

21 2

2

Logarithmic normal distribution

f M Az

nM

PwM

( ) exp[ ( ( )] 1

iii nMW 2iiiii nMnWZ

?n

w

M

M


Review MacromoleculesNatural: DNA, protein, Polysaccharides ...

Synthetic: different polymers ...

Difference between small and macro-moleculesHigh-order structures

Polydispersity, solubility, ...

The statistic nature of chain conformations

R = <R2>1/2 = N2b

Rg = <Rg2>1/2 = N2b/6

Rh ~ Rhard with the same D

Different distributions of molar mass : Number- MN , weight- MW and Z- MZ ...

Different scaling relationships between the size and mass of linear flexible coiled chains

5

3

3

1 withM~Rg

5

4

2

1 withM~


Experimental Methods

For polymer chains,molar mass distribution, conformation chain size distribution are important because “M and R” are directly related to properties and performance.

Absolute methods

which does not require atleast two or more narrowlydistributed standards withknown molar masses

for low molar mass chains :

end-group; vapor pressure osmometry; NMR;colligative properties; and MALDI-TOF-MS

for high molar mass chains :

membrane osmometry; ultracentrifugation; and static laser light scattering,

Relative methods which requires calibration

fractionation; translational diffusion; viscocity; chromatographic methods;dynamic laser light scattering; and …


Macromolecules In solution

In bulk (solid)

thermodynamicshydrodynamicsamorphouscrystallinegels - hydrogels

In solution:In solution: dissolution process G G n Gmix ii

N

i

1

o

G

nii

*The Flory-Huggins Theory Simple & Effective: ~1940’s developed on the basis of a “pseudo lattice” model.

G H T Smix mix mix 2)( pspsmix VH

m

i ip V

F

The Hildebrand’s solubility equation

Condition : no volume change in the mixing

= e1/2 and e is the cohesive energydensity, i.e., the vaporization energy of unit volume liquid under zero pressure.

F is the attractionforce per molar

chemical groups.

G = H - TS when T = constant


The end-group analysis Mn < 10,000 g/mol

e.g., Nylon-6 H2N(CH2)5CO-(-NH(CH2)5CO-)n-NH(CH2)5COOH

We can titrate the number of ends H2N- and -COOHFor a monodisperse sample : M = W/n ; For a polydispersed sample, W = niMi ; n = ni , and Mn = W/n

Colligative properties The boiling or freezing point change

limC

b or f

v or f n

T

C

RT

H M

0

2 1

why Mn ?

Membrane osmometry

solution solvent

popo+ /C = RT/Mfor small molecules

/C = RT/Mn

for macromolecules C

RTM

A C A Cn

( )1

2 32

MALDI-TOF-MS and NMRThere will be special courses to cover them.Here we only ontline their basic principles.


RTPVornRTPVornT

PVR m

TkPvTkN

VP BB

A

m

R = kBNA

v

TkP B

particle one

VWhen one particle agitated by the

thermal energy (kBT) undergoes

a Brownian motion. It produces

a pressure (in solution, it is often

called osmotic pressure).


The diameter decreases

D

rb = Rg

rb ~ D

D

D > Rg

D < Rg

The concept of “blob” in polymer science


Nv

TkBosmotic

N

2NV

TkBosmotic

N’

V V

2'B'osmotic V

TkN

'osmoticosmotic

'NN

N”

V

'" NNN

"osmoticosmotic 'osmotic

"osmotic


Laser Light ScatteringLaser Light Scattering


Laser light scattering (LLS)

E = Eosin(2vt - )Es = k (d2P/dt2)

= E = 4’P = p +

H = ocE i = <EsHs> = oc<Es2>

ir

c Er

Io

o oo

o 16 164 2

4 22

4 2

4 2

' '

( )i ~

-4 i ~ r --2

i ~ ‘2 ~ V 2

For N particles

I = Ni

Rayleigh ratio : Rvv(q) = Ir2/Io = KCM Kn

dndC

N

o

AV o

4 2 2 2

4

( )Rvv(q) = KCMw

For a large particle :

i

j

Rqr

qro

i j

ijj

N

i

N

16 4

42

sin( ), KC

R q M P qA C

vv w( ) ( )

12 2

qn

o

4

2

sin p q

R q q

R qq Rvv

vvg( )

( )

( )

0

11

32 2

KC

R q Mq R A C

vv wg Z( )

( ) 1

11

322 2

2

why <Rg2>Z ? The z-average ?


Encoder

Photomultiplier tube

Preamplifier/Discriminator

Stepping motor

Monitor diode

Focus Lens

Diode Laser Pumped Nd:YAG Laser532nm Wavelength

400 祄 pin-hole

Cell housing and index matching vat

Position-sensitive Detector

Cuvette

PhotonCounter

Static, Classic LLS(time average intensity)

Dynamic, Modern LLS(digital time correlator)

Polymer : 5x103 - 107 g/molParticles : 2 - 2000 nm

Dilute solution / suspension C = 10-3 - 10-6 g/ml

Rotating Arm

Spectra-Physics Helium Neon Laser632.8 nm Wavelength

Laser Light Scattering Spectrometer incorporated with differential refractometer

Laser

Laser


Static LLS Angular and Concentration dependence of <I>

CAqR

MqR

KC g

WVV2

22

2)3

1(1

)(

4

222 )/(4

oAN

dCdnnK

)2/sin(4

o

nq

)()()(o

r

o

r

S

roVVVV n

n

II

II

II

qRqR

A plot ofKC

R qvs C A

VVq"[

( )] " 0 2

A plot ofKC

R qvs q R

VVC g"[

( )] " 0

2 2

The extroplation ofKC

R qM

VVC q W[

( )] ., 0 0

<Rg2>

z1/2

A2

1/Mw

1 < < 2


Dynamic laser light scattering

* Intensity fluctuation :

I

slow

* Doppler frequency shift :

~ 1015 Hz ; Hz It is rather difficult to detect .

* Time correlation function:

deGg

)()0(0)E(E

)(0)E(E)(

0*

*

)1(

c1

20

2 )(

2)(

S

deSEE i

)()()0( *

deEES i

)()0(

2

1)( *

+

-

fast

]|),q(|1[)0,q(

),q()0,q(),q(

2)1(2

|)2(

gI

IIG

The Siegert relation

Dynamic LLS

It

The fast the movements, the fast the fluctuation


A typical time correlation function of the chains in solution

0.0 20.0 40.0 60.0 80.0 100.00.00

0.20

0.40

0.60

0.80[g

(2)(t

,q)-

A]/

A

t / ms

0.00

4.00

8.00

12.00

-2

10-1

10

G(

)

/ ms -1

)1)(1( 222 qRfCkDq gd

Dq

Cq

00

2


temperature

size

Physical Review Letters 83, 4105 (1999)

The transition on surfacePhysical Review Letters

86, 822 (2001)

JACS, 123, 1376 The transition in mixed solvents

Physical Review Letters79, 4092 (1998)

Physical Review Letters77, 3053 (1996)

The folding of a single homopolymer chain

Macromolecules, 28, 5225 (1995);

28, 5388 (1995); 28, 8381 (1995);

29, 4998 (1996); 30, 0204 (1997);

30, 7921 (1997); 31, 2972 (1998).

No additional knotting

The molten globular state


The collapsing of a single homopolymer chain

2.00 4.00 6.00 8.000.50

1.00

1.50

2.00

0

35.9 oC, Globule, R

g = 17.9 nm, R

g/R

h = 0.72

30.1 oC, Coil

Rg = 127 nm

Rg/R

h = 1.5

(Chi Wu) Figure1

[KC

/Rv

v(q

)] /

10-7

(m

ol/

g)

q2 / 10

10 cm

-2

Mw-1

101 1020.00

0.40

0.80

1.2035.9 oC 30.1 oC

f(Rh)

Rh / nm


Ultra-fast infrared laser heating pulse induced conformation change

= 1.54 mWidth ~ 20 ns


0 1 2 3 4

0.00

0.01

0.02

0 1 210-2

10-1

100

1-f

t / ms

I F(t

)-I F

(0)

(a.u

.)

t / ms

Kinetics of the coil-to-globule transition of single polymer chains


0 1 2 3 40.00

0.25

0.50

0 1 2 3 40.0

0.2

0.4

[Is(t

)-I s(0

)]/I

s(0)

(%)

t / ms

I scat

teri

ng (

a.u.

)

t / ms

Time dependent scattering intensity after the laser heating pulse


Nucleation and initial growthof pearls

Merging and coarseningof pearls

Nucleation and initial growthof pearls

Merging and coarseningof pearls


Size exclusion chromatorgraphy

V = V0 + Vifor small M : Ve = V0 + Vi

for large M : Ve = V0

In general : Ve = V0 + Vi

Ve = A + B log (M) Ve = A’ + B’ log ([]M)standards A’ and B’

In practice , one can obtain Ve and calculate []M . If knowing [], one can find M.

Detectors * differential refractometer ; * viscometer ; * UV ; and * small angle light scattering from Ve to M

Field flow fractionation (FFF)Field

wflow

C(x) = C0 exp(-x/l) where l = D/u = kT/f

If d << l < 400 nm, it will be a normal FFF - Smaller ones come out first.If d >> l > 2 m, it will be a steric FFF - Larger ones come out first.

f

TkD

fuF

B


Viscoelastic Properties of Bulk Polymers

Small molecules (liquid) Crystals and glass

Macromolecules (melts) Crystalline and amorphous

Temperature glassy melts viscoelastic

Several conceptsStress : F/A = Strain : L/L =

GG : the shear modulus Rigidity

J = 1/G (Compliance)

EE : the Young’s modulus Elasticity

E = 2G (1 + )

= -(d/d)/(L/L)

The tensile strength : The elongation at break

Viscosity ()

Shear stress F

L L

F

L

L

Normal stress

dt

d


The Maxwell Model The stress relaxation T = constant

Elastic

Viscous

viselT

011

dt

d

Gdtdtdt

d viselT )exp(0 t

where

G

elGvisd/dt) since

)cos()sin()cos(0 tG

CBt

G

BCt

)sin()1(

)cos()1(

)(2222

22

0 ttt

For a dynamic experiment

G’() G’’()

GG )("

lim0

0

Storage modulus Loss modulus

0 0

G

CBand

G

BC

1

)('

)("tan

G

G

)sin()cos(assuming&)sin(If 0 tCtBtT


The Voigt Model The creep experiment T = constant

viselT

dt

dGT

)exp(1)(

t

Gt T

where

G

)sin()()cos()()cos(0 tBGCtCGBt CGB 0

BGC 0

)sin()1(

)cos()1(

1)(

22220 ttt

For a dynamic experiment

G’() G’’()

GG )("

lim0

0

Storage modulus Loss modulus

)('

)("tan

G

G

elGvisd/dt) since

Ela

stic

Vis

cous

)sin()cos(assuming&)cos(If 0 tCtBtT


Example Polycarbonate withtwo molar masses.

The time domain can be divided into four regions, I, II, III and IV.

I : t << 10 -1 s & G ~ 1010 dynes/cm2

The glassy state : hard, stiff, brittleThe backbone chain cannot movebecause t is too short or T is too low.

II : 1 < t < 10 2 s & 108 < G < 1010

The glass-to-rubber transition andthe polymer becomes leathery

III : 102 < t < 10 6 s & G ~ 108

The rubbery plateau : tough, elasticThe chains are entangled, but theirsegments start to move at a relatively long t or a relatively higher T.

IV : t > 10 6 s & G < ~106

The viscous state : viscous liquid,no elasticity, no shape and flowingThe chains can move & entanglementsare overcome at a long t or a higher T.

The backbone chain has t or T to jostle into a more relaxed conformation.


logG

log t

log t1 log t3 log t2 log t4

log a1

log a2

logG

log t

log t1 log t2

log t2 - log a1

log t3 - log a1

log t3 - log a2

log t4 - log a2

The Time-Temperature Equivalency

G(t’, T’) = G(t’’, T’’) G(t2 , T1) = G(t1 , T2)

G(t3 , T1) = G(t2 , T2)G(t4 , T1) = G(t2 , T3)

log t1 + log a = log t2

…

The Williams-Landel-Ferry (WLF) equation

)(

)(

2

1

o

o

TTC

TTCaog

t1 = t2 / a

If Tg is taken as T0 ,

11

2

C

TT

C

C

aog

TT gg

The “universal” values of C1 and C2

C1 = 17.4

C2 = 51.6 T

VSP

Tg, true

Tg,2

Tg,1

a

e

bc

The glass transition temperature (Tg)


The Glass Trenasition Temperature (Tg)Tg > Troom Plastic materials

Tg < Troom Rubbery materials

Glassy RubberyG decreases 3-4 ordersThe factors affect Tg

1. The flexibility of the chain backbone Tg PE : -80 oC; PP : -20 oC; PMA : 3 oC

2. The size of the side groups Tg (Two exceptions: symmetric or too long)

3. The interaction between chains Tg

The methods to change Tg

1. The addition of small molecules with a high boiling point .

2. The copolymerization of A and B so that Tg,A < Tg < Tg,B or Tg > or < Tg,A and Tg,B

3. The chain length Tg

4. The crosslinking of the chains. 5. The mixing of different polymers.

How to change a plastic material to a rubbery one?


The Kinetics of Crystallization

The Avrami equation )exp(1 mKtis the crystallized fraction and can be determined by any property,such as volume, diffraction intensity, …. M depends on geometry, crystallization rate, & nucleation mode so that m is in the range 0.5-4.

0 1Pa

P Pc

P = Pa + (Pc - Pa)0

0

VV

VVt

e.g.,

In practice, plot “ ln [ ln [1/(1-)] ] versus ln t “

The glassy polymers

Non-equilibrium

The specific volume depends on how fast a sample was cooled down and how long it remains at a particular temperature.

V = V0 + VfreeV0 : the core and vibration & Vfree : the translation Vfree ~ 2.5%V

The elastic networks PTL

STF

,

)32

(2

2

vkS B

)1

(2

0

L

TvkF B

)1

(2

V

Tvk

A

F B

L

dL

V

Tvkd B

)

2(

2 )

2(

2

CM

RTE

CM

RTE

3

CM

RTG


The Crystalline Polymers f

fm S

HT

STHG

Folding chains and Spherulites G is continuous at Tm , but not S or V.

G = H - ST; H = U + PV; U = Q - PdV;

Q = TdS dG = VdP - SdT S

T

G

P

dTT

GdP

P

GdG

PT

VP

G

T

T

G

eT

?

?T

V or S

eT

In general, there are three regions:T < Tg ; Tg < T < Tm ; and T > Tm

In reality, the process of “Crystal < > Melts” is a kinetic process. For example,Tm decreases with Tcry; Tm is higher than Tcry, the crytal size decreases as thecooling rate increases; and Tm < Te (infinite size), ….

Tg is related to the cooling rate, but not Tm.

Glassy stateAmorphous - it can be viewed as a supercooled liquid

Crystalline (0-100%) - it can be viewed as “crosslinking points”


Morphology of crystalline polymers

The chain folding: 10-20 nm thicknessSpherulites in a concentrated solution.

Mechanical properties of crystalline polymers

0.5 < Tg/Tm < 0.8 Below Tg => Glassy and above Tm => Melts

Drawn in fibers

If Tg < T < Tm, the crystalline regions act as crosslinking points, so that the materials will be hard and tough. Such a structure can also be achieved by copolymering some hard segments into flexible chain backbone.


Multicomponent and multiphase materials

Plasticization of polymers

Addint small molecules to decrease Tg .

Blending of different polymers

To obtain different Tg and toughness.

Heterophase polymers

Block and other structure copolymers

2221 VnVn

G

V

GG mixmixV

mix

222,122

21

1

1 lnln B

VVRTGV

mix

1

2,12,1 V

RTB

where


SEM micrograph of pH-sensitive copolymer P(DEAM-co-MAA) hydrogels obtained at different pH values.

MD2 MD3 MD4

MD5 MD6 MD7pH = 7.0

MD2 MD3 MD4

MD5 MD6 MD7pH = 9.5

A polymer gel is a three-dimensional network swollen by a large amount of solvent. It has some properties between solutions and solids.


mixing

Protein network microgels25 oC 37 oC

swelling state shrinking state


Have a good term and Please do not forget chain conformations, different sizes, and so on

Introduction to Macromolecules CHM5080 (CUHK) – CHEM588 (HKUST) – CHEM6108 (HKU)

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Transcript of Introduction to Macromolecules CHM5080 (CUHK) – CHEM588 (HKUST) – CHEM6108 (HKU)