Part III.3: Transition in Polymers

- Level of Movement in the Amorphous Part of Polymer Chains

- Factors that influence Tg and Tm

- Transition at Tg and Tm

- The metastable amorphous state

- Changes in Tg and Tm of Copolymers

- Changes in Tg and Tm of Crosslinked Polymers

- Instrument for Thermal Analysis

OUTLINE

AE 449 TEPE: Cattaleeya Pattamaprom

Level of Movement in the Amorphous

Part of Polymer ChainsStep 1: -vibration of atoms at equilibrium

-movement of 1-2 carbon atoms

-happen below Tg of polymers

Step 2: -movement of 5-6 carbon atoms

or movement of side groups

-happen at around Tg

Step 3: -movement of 40-50 carbon atoms

-polymers become soft and rubbery

-happen above Tg

Step 4: -movement of the whole polymer chain

- polymers flow as in viscous melt

Factor that influences Tg

1. The free volume of the polymer (vf) vf = v – vs

vol. of solidly packed molecules free volume bulk specific vol. (ปริ�มาตริจำ�าเพาะของช่�องว่�าง)

vf more room to move around Tg

2. The attractive forces between molecules

difficult to move around

Tg

Factors that influence Tg

3. Steric hindrance more difficult Tg to move around

4. The stiffness of chain difficult to coil up and fold Tg

5. The chain length

Tg Tg

length

(con’t)

(bulky groups)

Factors that influence Tm

Melting Point (Tm) or so called “Crystalline melting

point”

Thermodynamics of melting

Gm = Hm - T Sm

energy needed to overcome crystalline bonding

at eqn Gm 0 Tm = Hm

Sm

- short chain S

- long chain S or stiff chain

Factors that influence Tm

Ex

O O O [ -O-C-N-(CH2)n-]X [-C-N--(CH2)n-]x [-N-C-N--(CH2)n-]x

H H H H

polyurethane polyamides polyureas

Tm < Tm < Tm

- Polyurethane: contains the -o- swivel high Sm most flexible low Tm

- Three polymers have comparable magnitude of hydrogen bonding

- Polyurea: with extra N-Hextra hydrogen bonding extra Hm high Tm

Example: Rank Tm of different polymers

(Ref.: S.L. Rosen, John Wiley&Sons 1993)

Transition at Tg

(Ref.: S.L. Rosen, John Wiley&Sons 1993)

Transition at Tm

(Ref.: S.L. Rosen, John Wiley&Sons 1993)

Low cp

High cp

Schematic of DSC curve

Example PET is cooled rapidly from (state 1) 3000C to

(state 2) room temp. Get perfectly transparent and rigid polymer

Then heat up to (state 3) 1000C and maintain at 1000C then cool down to (state 5) room temp. get rigid, translucent polymer

Question : 1. Sketch general specific volume (v) curve

2. Show DSC curve

1

5

42

3

Tg = 690 C

Tm = 2670 C

V (CC/g)

Temp.

Specific volume (v) curve

DSC curve

General Observation about Tg and Tm

• Polymers with symetric repeat unit

Tg/Tm ~ 1/2 (absolute temp)

n

Ex. Polyethylene Poly vinylidine chloride

Ex. Polypropylene Polychlorotrifluoride

• Polymers with asymetric repeat unit

Tg/Tm ~ 2/3 (absolute temp)

The metastable amorphous state

• metastable amorphous state :

–Occur when decreasing temperature of polymer melts quickly

–Produce transparent polymers

รู�ปที่�� 1 Amorphous polymer structure

The metastable amorphous state

• An example of metastable amorphous application

in polymer industries

– PET (soda bottles)

PET Bottle Resin – Before and After Annealing

PET After annealing(Cold Crystallization)

Pressed PET Bottle Resin

Effect of Heating Rate on Temperature of Cold

Crystallization in PETHeating RateAfter QuenchCooling

Tg

melt

Crystallization [kinetic event]

Volume changes of the metastable

amorphous state

•Study the changes in temperature and specific volume of crystallizable polymer

Ex. PET –Tm = 267 °C และ Tg = 69 °C –Molten PET at initial temp of 300 °C (state 1)

The metastable amorphous state

V (CC/g)

1

4

3

Tg = 690 C

Tm = 2670 C

Temp.

5

2

Fig. 8.5 Specific volume – temperature relation for

crystallizable polymer

State 2 = metastable amorphous, State 5 = semi-crystalline

(Ref.: S.L. Rosen, John Wiley&Sons 1993)

Changes in Tg and Tm of Copolymers

apparent Tg reduce / cannot

crystallize

less mobility hinder alignment

Effect of crosslinklightly crosslinked : same as before

heavily crosslinked : crosslink

Changes in Tg and Tm of Crosslinked Polymers

Summary crosslinking in polymers : leads to

(I) higher Tg (II) obstruct and reduce crystallization

Instrument for Thermal Analysis

• Two popular instruments in measuring

temperature response of polymers

- Differential Scanning Calorimeter (DSC)

- Thermogravimetric Analysis System (TGA)

DSC: Differential Scanning

Calorimeter

• This technique can analyze characteristic temperatures and heat flow from thermal transition of material with respect to temperature or time.

Differential Scanning Calorimeter

Heat flow vs. temp.Heat flow vs. time

DSC: Differential Scanning

Calorimeter

• DSC used to analyze :

– Temp and heat that makes polymers or ceramics

melt, crystalize or change phases

– Crytallinity of polymers

– Glass transition temperature (Tg) of polymers

– Heat capacity of materials

Main Parts of DSC

DSC: Differential Scanning

Calorimeter

DSC: Differential Scanning

Calorimeter

DSC Thermogram

DSC: Differential Scanning

Calorimeter

Endo

Exo

TGA: Thermogravimetric Analysis

• Use for analyzing

weight changes of

material when exposed

to heat by using

sensitive balances

(thermobalance)

รู�ปที่�� 3 แสดงเคริ��องThermogravimetric

Analysis

TGA: Thermogravimetric Analysis

• TGA can be used to analyze :      

– Additives in plastic products

– Water or solvent in paints coatings adhesives

or ceramics

– Compositons of rubber products ex. Rubber

content, organic fillers, and inorganic fillers

TGA: Thermogravimetric Analysis

Main Parts of TGA

TGA: Thermogravimetric Analysis

TGA Thermogram

HW Chapter 8. Phase transition and Thermal properties of polymer

• Sketch scanning calorimeter traces upon heating from room

temperature for each of the following situations labelling

temperatures and exothermic/endothermic directions on each.

1. A 50/50 glassy crystalline polymer, Tg = 50 oC, Tm = 120 oC

2. A blend of two incompatible crystalline polymers with Tm’s of

90 oC and 160 oC

3. A 50/50 blend of two compatible glassy polymers with individual

Tg’s of 110 oC and 200 oC

4. A crystallizeable polymer which has been quenched from above

it’s Tm rapidly enough so that crystalline does not occur upon

cooling. (Tg = 100 oC, Tm = 250 oC)

5. Polyvinyl chloride plasticized 20% with dioctyl phthalate (DOP)?

(Tg of pure PVC = 85 oC)