Structure of Polymers - Chapter 5 Flashcards Preview

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1

Molecules that are termed unsaturated?

Molecules that have double and triple covalent bonds. Each carbon atom is not bonded to the maximum other atoms.

2

Molecules that are termed saturated?

All bonds are single ones, and no new atoms may be joined without the removal of others that are already bonded.

3

What is isomerism?

Hydrocarbon compounds with the same composition may have different atomic arrangements.

4

Polymer molecules are often referred to as?

Macromolecules.

5

Monomer?

Refers to the small molecule from which a polymer is synthesized.

6

Homopolymer?

When all of the repeating units along a chain are of the same type.

7

Copolymers?

Chains composed of two or more different repeat units.

8

Number-average molecular weight Mn?

=sum[XiMi]

Xi = The fraction of the total number of chains within the corresponding size range.

Mi = represents the mean molecular weight of the size range.

9

Weight-average molecular weight Mw?

=sum[WiMi]

Wi = the weight fractions of molecules within the same size interval.

Mi = The mean molecular weight within a size range.

10

Degree of Polymerization DP?

DP= Mn/m

Mn= number-average molecular weight

m= repeat unit molecular weight

11

Linear polymers?

Linear polymers are those in which the repeat units are joined together end to end in single chains.

There may be extensive van der Waals and hydrogen bonding between the chains.

12

Branched Polymers?

Branched polymers are synthesized in which side-branch chains are connected to the main ones.

The chain packing efficiency is reduced with the formation of side branches, which results in a lowering of the polymer density,

13

Crosslinked Polymers?

In Crosslinked polymers, adjacent linear chains are joined one to another at various positions by covalent bonds. The process of crosslinking is achieved either during synthesis or by a nonreversible chemical reaction.

14

Network Polymers?

Mutlifunctional monmers forming three or more active covalent bond make three dimensional networks and are termed network polymers.

15

Stereoismerism?

Stereoisomerism denotes the situation in which atoms are linked together in the same order but differ in their spatial arrangement.

16

Difference between thermoplastics and thermosetting polymers?

Thermosetting polymers are network polymers. They become permanently hard during their formation and do not soften upon heating. Network polymers have covalent crosslinks between adjacent molecular chains. During heat treatments, these bonds anchor the chains together to resist the vibrational and rotational chain motions at high temperatures.

Theromplastics soften when heated (and eventually liquefy) and harden when colled- processes that are totally reversible and may be repeated. On a molecular level, as the temperature is raised, secondary bonding forces are diminished so that the relative movement of adjacent chains is facilitated when a stress is applied.

17

Random copolymer?

Two different units are randomly dispersed along the chain in what is termed a random copolymer.

18

Alternating copolymer?

When the two repeat units alternate chain positions.

19

Block copolymer?

When identical repeat units are clustered in blocks along the chain.

20

Degree if polymerization for a copolymer?

m is replaced with m- ,

m- = sum[FjMj]

Fj = mole fraction

Mj = weight of repeat unit j