M A T E 4 5 3 / M S E 5 5 3

Physical and Mechanical Properties of Polymers

Guided Lecture Notes for Fall 2012

Prof. Michael Kessler Department of Materials Science and Engineering

Iowa State University

P H Y S I C A L A N D M E C H A N I C A L P R O P E R T I E S O F P O L Y M E R S

1

Step-Growth and Chain Growth Polymerization

elcome to Physical and Mechanical Properties of Polymers. These notes are intended to summarize some of the material that we’ll be covering this semester. Several sections are intentionally left blank for you to fill in during the lecture. The best approach will be to follow along during the lectures, filling in the empty sections, as well as writing additional

notes on blank paper to insert with these pages. You may want to obtain a three ring binder to hold the notes in one place as we progress through the semester. In addition to these formal notes, many classes will not have notes prepared, and you’ll need to prepare your own notes from scratch based on the lecture and discussion. Additional material from the text book and references will also be assigned that may not be covered in these notes.

Polymer Synthesis Polymers can be categorized by

• their _____________________________________________ and by their

• _________________________________________________.

Chemistry of Synthesis

1.

Mechanism of Chain Growth

1.

Section

1 W

I C O N K E Y

Valuable information

Interesting fact

Definition

2

2.

2.

Step-growth polymerization involves _________________________________

Chain-growth polymerization involves _________________________.

3

Step-growth Polymerization

Step-growth & Condensation Polymerization

• Condensation polymerizations (i.e., polycondensation reactions) are those which yield polymers with repeat units having ____________________ atoms than those present in the monomers from which they are formed.

• The coupling of reactive end groups from each monomer (i.e., formation of covalent linkage) results in the formation of _________________________ molecular weight product (H2O, HCl, NH3, etc).

Examples of Condensation Reactions (step growth)

I) diol + diacid (Polyester)

II) diamine + diacid (Polyamide)

III) self-condensation of an A-B monomer

4

Step-growth & Non-condensation Polymerization

No liberation of small molecules

I) diisocyanate + diol (Polyurethane)

II) Nylon 6 (from ring)

Examples of polymers formed by step-growth polymerization

•

•

•

•

•

•

5

Degree of Polymerization in Condensation Polymerization

, where is weight-average molecular weight of polymerww ww

o

MX x MM

= =

, where is molecular weight of monomer molecule

and is number-average molecular weight of polymer

nn n o

o

n

MX x MM

M

= =

6

Degree of Polymerization as a Function of Conversion p

Chain-growth Polymerization

Growth of the polymer involves the successive addition of monomers through an _____________________________________(radical in free radical polymerization, anion in anionic polymerization, and cation in cationic polymerization).

p11xn−

=

7

The polymerization of _________________________________________ monomers (e.g., monomers with carbon-carbon double bond) typically involves a chain reaction.

There are three major stages that control addition polymerization:

a) _____________________________;

b) _____________________________;

c) _____________________________.

*: denotes the active center

Four Chain Growth Polymerizations

1. ___________________________________

Free Radical, R• (unpaired electron)

2. ___________________________________

Carbocation Ion, R⊕

3. ___________________________________

Carbanion, R—

4. ____________________________________

Coordination Complex

8

• Rapid, preferential growth of initiated polymer chains; high DP attained at start of the reaction.

• Monomer is capable of reacting only with an active end group (or initiator), resulting in a steadily decreasing (but significant) concentration of monomer throughout the polymerization.

Free Radical Polymerization Kinetics

Step 1a. Initiation: _________________________

• Initiator can decompose and generate ________________________upon thermolysis (as shown in the above), or photolysis (UV radiation ~360 nm), or high-energy radiation (including electrons, gamma rays, x-rays, and slow neutrons)

Step 1b. Initiation: _________________________

9

Step 2. _________________________

Step 3. _________________________

• Combination: Involves the ________________ together of two growing chains to form a single polymer molecule:

• Disproportionation: A hydrogen atom can be ___________________ from one chain to the other.

10

Kinetic Rate Expression

11

Gel Effect

• Also known as the _________________________________________

• At higher conversion, the termination rate decreases due increase in viscosity which leads to a lower diffusion rate of growing chains. As a result, their lifetime increases.

• The diffusion of monomer is also decreasing, but to a much smaller extent. The rate of polymerization and molecular weight significantly increase in a nonlinear fashion.

12

Inhibition and Retardation

• Certain substances react with the free-radical sites to produce species which are incapable of re-initiating polymerization.

• If such reaction is highly efficient, the polymerization is ___________________and the substance is called _______________________ (see curve c).

• When the reaction yields species that ________________________ polymerization, the rate of polymerization is reduced and the substance is referred to as a __________________(see curve b)

Comparison and Example

13

Example. Lactic Acid and Acrylic Acid

a) Lactic Acid b) Acrylic Acid

Both can be polymerized, write the repeat unit for each.