1. Addition-Condensation system1.1 Addition polymerization (แบบการเติม) 1.2 Condensation polymerization (แบบควบแน่น)

2. Chain growth-Step Growth System

2.1 Chain growth polymerization (แบบลกูโซ)่2.2 Step growth polymerization (แบบขัน้)

Classification(3): polymerization methods

1.2 Condensation polymerization (แบบควบแน่น)

Part of the monomer molecule is kicked out when the monomer becomes part pf the polymer.

The part that gets kicked out is usually a small molecule like water (H2O), or HCl gas

1.1 Addition polymerization (แบบการเติม)

1. Addition-Condensation system

Monomer molecules become part of the polymer without kicking any molecules out.

2. Chain Growth-Step Growth System

monomers become part of the polymer one at a time.

2.1 Chain growth polymerization (แบบลกูโซ)่

2.2 Step growth polymerization (แบบขัน้)

monomer + monomer = dimerdimer + monomer = trimerdimer + dimer = tetramertrimer + dimer = pentamern-mer + m-mer = (n+m)mer

or

Two short chains can react to form longer chain

Chain-Growth (or addition) polymerization

nn

monomer polymer

C = C

H

H H

H

C C

H

H

H

Hn

When ethylene is polymerized to make polyethylene, the every atom of the ethylene

molecule becomes part of the polymer (none gained, none lost)

Ethylene Polyethylene

Example:

In General;Addition Polymerization = Chain Growth Polymerization - do not give off by product - monomers become part of the polymer one at a time• ประกอบด้วยขัน้ตอนต่างๆ 3 ขัน้ตอน และมกีารใชส้ารเคม ี

2 ชนิด 1. initiation ขัน้เริม่ต้นปฏิกิรยิา 1. monomer 2. Prapagation ขัน้ดำาเนินไปของปฏิกิรยิา 2. initiator 3. termination ขัน้สิน้สดุปฏิกิรยิา

Free radical Anionic -Cationic +

1.Monomer – Becomes repeating units in polymer

chains– Monomer need to have at least

1double bond 2. Initiator

- add into monomer to activate joining of monomers into long polymer chains

Functions of the 2 basic chemicals

There are 3 types of chain growth

polymerizations:

• Free radical polymerization (Free radical

initiator I)

• Anionic polymerization (Anionic initiator I-)

• Cationic polymerisation (Cationic initiator I+)

(names depend on type of initiator)

Free radical polymerizationInitiator• peroxide (ROOR, HOOH)• Azo compound (-N=N-) easily decompose into

2 free radicals when exposed to heat

H3C – C

CH3

CN

N N+ + C - CH3

CH3

CN

C – O – O - C

O O+

O

C – O O - C

O

O

C – O

O

CO

+

H3C – C – N = N – C - CH3

CH3 CH3

CN CN

1. Initiation step

Free radical จะกระตุ้นใหพ้นัธะคู่ในโมโนเมอรแ์ตกออก แล้วเกิดพันธะใหม่ขึ้น

C = C

H

H H

H

C C

H

H

H

H

2. Propagation Step

Free radical ท่ีปลายจะไปกระตุ้น monomer ตัวท่ีอยูใ่กล้คียงใหพ้นัธะคู่แตกออก Monomer ตัวท่ีเหลือจะเข้าต่อท่ีปลายในลักษณะเดียวกันไปเรื่อยๆ

C C

H

H

H

H

C = C

H

H H

H

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

Hn

ขัน้การสิน้สดุของปฏิกิรยิา ม ี3 แบบ :1. Coupling: Mx + My Mx+y

2. Disproportionation: Mx + My Mx + My-1

3. Chain transfer agent:

3. ขัน้สิน้สดุปฏิกิรยิา (Termination step)

-C = CH H

C

H

H

+Cl – C – Cl

Cl

Cl

C – Cl

H

H

+ Cl – C

Cl

ClInitiate another chain

Anionic polymerization (I-)Initiator CH3 – CH2 – CH2 – CH2 - Li

butyl lithium

CH3 – CH2 – CH2 – C + Li+CH3 – CH2 – CH2 – CH2 - Li

H

H

-

1.ขัน้เริม่ต้นปฏิกิรยิา (Initiation step I-)

CH3 – CH2 – CH2 – C Li+

H

H

-C = C

H

H H

H

CH3 – CH2 – CH2 – CH2 - C Li+

H

H

-

2. ขัน้ดำาเนินไปของปฏิกิรยิา (Propagation Step II.)

CH3 – CH2 – CH2 – CH2 - C Li+

H

H

- + C = C

H

H H

H

CH3 – CH2 – CH2 – CH2 - C – C – C Li+

H

H

-

H H

H H

C C

H

H

H

Hn

-

Living anionic polymerization

Living polystyrene

butadiene

Living styrene-butadiene block copolymer

Here A stands for the initiator fragment end groups. Sometimes it’s a butyl group from butyl lithium, sometimes it isn’t.

- A – A – A – A – A – A – A – A – B – B – B – B – B – B – B - B

Block copolymer

Cationic polymerisation (I+)

+ +

+ +

1.ขัน้เริม่ต้นปฏิกิรยิา (Initiation step I+)

+ +

-

Initiator: AlCl3/H2O

AlCl3/H2O

2. ขัน้ดำาเนินไปของปฏิกิรยิา (Propagation Step)

n

Step-Growth (Condensation) Polymerization

In General;Condensation Polymerization = Step Growth Polymerization - give off by product - monomers become part of the polymer one at a time or two short chain react to form longer chain

H + H2O

acid alcohol ester

เอสเทอรร์ฟิเิคชนั (esterification)

monomer ท่ีใชต้้องมหีมูฟ่งัก์ชนัอยา่งน้อย 2 หมู่

diacid dial

polyester

PET

+n H2O

The first thing the two monomers will react to form a dimer.

Terapheyl chloride Ethylene glycol

ester dimer

2-mer + 2-mer = 4-mer

+ HCl

monomer + monomer = 2-mer2-mer + monomer = 3-mer2-mer + 2-mer = 4-mer3-mer + dimer = 5-mern-mer + m-mer = (n+m)mer

Nylon 6,6

This Cl atom and this H atom don’t end up in the polymer, they split off to form HCl gas.

+ N-CH2-CH2-CH2-CH2-CH2-CH2-N

H

HH

HCl-C-CH2-CH2-CH2-CH2-C-Cl

O O

nylon 6,6

adipoyl chloride hexamethylene diamine

HCl+ C-CH2-CH2-CH2-CH2-C-

O O

N-CH2-CH2-CH2-CH2-CH2-CH2-NHH

n

In a condensation polymerization, some atoms of the monomer don’t end up in the polymer.

HCl+ C-CH2-CH2-CH2-CH2-C-

O O

N-CH2-CH2-CH2-CH2-CH2-CH2-NHH

n

When nylon 6,6 is made from adipoyl chloride and hexamethylene diamine, the chlorine atoms from the adipoyl chloride, each along with one of the amine hydrogen atoms, are expelled in the form of HCl gas.

+ N-CH2-CH2-CH2-CH2-CH2-CH2-N

H

HH

HCl-C-CH2-CH2-CH2-CH2-C-Cl

O O

One example is the polymerization which produces polyurethane.There are also addition polymerization which are step growth polymerizations.

Isocyanate groups

a diisocyanate a diol

Not only monomers react, but also dimers, trimer, and so on. This makes it a step growth polymerization.Also, because no small molecule by-products are produced, it is an addition polymerization.

เอกสารประกอบจาก ดร.ธนาวดี ล้ีจากภัย MTEC

Conclusion• Chain growth polymerization: generally =

addition polymerization : monomer become part of the polymer one at

a time.– Polymer chain grows rapidly to a long size as soon as

the initiation step starts.– High molecular weight polymer is formed immediately.– monomer concentration decreases as the number of

high polymer molecules increase– the reaction mixture contains-monomer, high-

molecular weight polymer, growing chain

• Step growth polymerization: generally = condensation polymerization

: Two short chains can react to form longer chain.– monomer disappears much faster– molecular weight increase through out the

course of the reaction– high molecular weight polymer is not

obtained until the end of the reaction

Conclusion

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

Classification(4): Architecture of ChainEach structures respond to solvents differently.• Linear and Branched Polymers – can be soluble in suitable solvents

Linear polymers Branched polymers

HDPELDPE

LLDPE

• Crosslink polymers –Heavily crosslinked not soluble and not swell

ex. Ebonite bowling ball – no swelling

–Lightly crosslinked not soluble but swell in solvent

Classification(5): Number of repeating unit present in the polymer chains

• homopolymer (PE, PP, PS, PVC, PMMA, PC, PET),

• copolymer (SBR, NBR),

• terpolymer (ABS)

Different types of copolymers

—xoxoxoxoxoxoxo—Alternating copolymer

—xxoooxoxooxxxox—Random copolymer

—xxxxxooooooxxxx—Block copolymer

—xxxxxxxxxxxxxxxxxxxxxxxxx— o o o o o o o o o o o o o o Graft copolymer Graft copolymer

โคโพลิเมอรท่ี์มคีารบ์อนเป็นโครงสรา้งหลัก

(Ref: A. Kumar and R.K. Gupta, McGraw-Hill 1998)

(Ref: A. Kumar and R.K. Gupta, McGraw-Hill 1998)

Classification(6): orientation of polymer chains(Morphology)

• Amorphous

• Semi-crystalline

Polymer

Thermoplastic Elastomer Thermoset

Semi-Crystalline Amorphous

( lightly cross linked) (heavily cross linked )Network

Cross linked polymers

Linear/branched polymers(no cross linked)

T

% crystallinity~70%

Tg

Tm

Viscous melt

Hard&StrongBrittle

rubbery

Leathery ductile

Influence of molecular weight on properties of polymers

( Ref: A. Kumar and R.K. Gupta, McGraw-Hill 1998)

Chapter 4:

Orientations and Crystallinity of Polymers

Orientation of Polymer Chains

1. Connection of chain (Configurational features) - Geometric details of how each repeat unit adds to the growing chain

- Occur during polymerization process (cannot change by rotation)

2. Rotation and twisting of chain (Conformation)- rotation of backbone or side group

Factors affecting Crystallinity of Polymers

Factors that affect properties of polymers1. Architectural features2. MW and MWD3. Configurational features4. Stereoregularity (conformation)

1. Architectural features:- Branching- Cross linking- Nature of copolymer

2. Molecular weight (MW), Molecular Weight Distribution (MWD):

Polymers with long chain and narrow molecular

weigth distribution more crystallinity

High MW

Low MWDEasily crystallized

3. Configurations: Geometric details of how each repeat unit adds to the growing chain affect properties of polymers

- Head to Head

- Head to Tail (normal arrangement)

- Tail to Tail

“Head to tail”

“Head to Head”/“Tail to Tail”

Configuration: cannot be changed by rotation of the backbone.

4. Stereoregularity—rotation around the backbone

• Rotation of Cn-Cn+1 bond• Gauche positive (g+)• Trans (t) [lowest potential energy—most probable]• Gauche negative (g-)

• Cis-Tran Isomer for C=C

Trans conformation: all backbones lie in the same plane-planar zigzag plane

- Rotation of side group- isotactic- syndiotactic- atactic (Ref: A. Kumar and R.K. Gupta, McGraw-Hill 1998)

(rotation of backbone or side groups)- Rotation of backbone

•Gauche positive (g+)•Trans (t) •Gauche negative (g-)

potential energy of each conformation

Trans conformation

(Ref: A. Kumar and R.K. Gupta, McGraw-Hill 1998)

Rotation of Cn-Cn+1 bond

Cis-Trans Isomer(Rotation of Cn=Cn+1 bond)

Poly (cis-1,4-isoprene) Poly (trans-1,4-isoprene)

Rotation of side groups (Stereoisomerism)Ex. Repeat unit.

Ref.: L.H. Sperling, John Wiley & Sons, Inc. (1992)

Requirement for crystallinity– Need ordered regular chain structure (syndiotactic+isotactic)– The 2nd forces holding chains > disorder effect of thermal

energy

“Anything that reduces the regularity of backbone reduces the crystallinity.”

• Ex. PE, PP are crystalline polymers copolymer of PP/PE is amorphous

“There is no complete crystalline polymers”% crystallinity – show fraction of crystal structure inside polymers

1. The Fringed Micelle Model

2. Folded-Chain model

Models for Crystal Formation

3. Folded-Chain model

Tie molecules

Crystal Growth

Ref.: L.H. Sperling, John Wiley & Sons, Inc. (1992)

Ref.: L.H. Sperling, John Wiley & Sons, Inc. (1992)

Steps of Spherulite Formation

Spherulite (cont.)

Ref: R.J. Young and P.A. Lovell, Chapman&Hall 1991

Spherulites

Spherulites grow radiallyfrom a point of nucleationuntil other spherulites are encountered.

XRD patterns of Amorphous and Semi-crystalline Polymers

Ref: R.J. Young and P.A. Lovell, Chapman&Hall 1991

Size: size of spherulites can be controlled by the number of nuclei present. (normally dia. ~ 0.01 mm)

No. Nucleation site Size of spherulites

How to enhance transparency and reduce brittleness?Add nucleating agents

Quench polymers (increases nucleation sites)

or

Spherulite (cont.)

Effect of Crystallinity on Mechanical Properties

• more crystallites

– Ex: (density) > >

branching < < % crystalline > >

• Degree of crystallinity: สมการ amorphous + crystalline

• Branching: more branching less crystallinitya

ccc

aa

cc )w1(www1

HDPE LLDPE LDPE

Tacticity crystallinity optical properties

Atactic -->mostlyAmorphous polymers transparent

Isotactic mostly crystalline polymers

Syndiotactic

/refractive index of phase amorphous = phase crystalline transparent

Ex1: Foam ex. Foamed PS เป็นสขีาวทึบเพราะแสงผ่านเฟส PS และgas bubblesEx2: high-impact PS เป็น PS ท่ีมอีนุภาค polybutadiene rubber ขนาด 1-10 m.

กระจายอยูใ่น amorphous PS

Size of crystallites < wavelength of visible light transparent

Low degree of crystallinity fairly transparent

Effect of crystallinity on optical properties

Basic concept: เมื่อขนาดของอีกเฟสหนึ่งมขีนาดใหญ่กวา่

light passes btw. two phases ความยาวคล่ืนของแสงเกิดการหกัเหทึบแสง

w/ different refractive indices เมื่อขนาดของอีกเฟสหนึ่งมี

ขนาดเล็กกวา่ ความยาวคล่ืนของ

แสงไมเ่กิดการหกัเหโปรง่แสง

LightPasses through

Light scatters.

Liquid Crystalline Polymers

• Molecules that show a degree of order in the liq. Phase– If liq. Phase is solution lyotropic LCP– If liq. Phase is melt thermotropic LCP

• is self reinforced composite

• Ex. (lyotropic) Kevlar เป็น aromatic polyamid (“aramid”) with repeating unit

pull into fibers in the solution of H2SO4

use for bullet-proof vests (เสื้อเกราะกันกระสนุ)

Ex. (thermotropic LCP)

Note: liq. Crystalline polymers have highly aromatic backbone inhibit rotationstiff, rigid extended chain

Xydar

Vectra

Extended chain crystal

• When pulled polymer will align in the flow direction crystallize (extended chain crystal)

(the more you pull, the stronger it becomes)

Stretching Curve and Crystal Orientation

Crystal Orientation with Stretching

XRD ring with Stretching