Lecture 02: Classification and Molecular Structure

Flashcards covering key vocabulary and concepts from the lecture.

Molecular Characteristics

Molecular characteristics include chemistry (repeat unit composition), size (molecular weight), and shape (chain twisting, entanglement, etc.).

Molecular Structure

Linear, branched, crosslinked, and network structures are all possible.

Linear Polymers

Polymers in which the repeat units are joined together end to end in single chains.

Branched Polymers

Polymers in which side-branch chains are connected to the main ones.

Crosslinked Polymers

Adjacent linear chains are joined one to another at various positions by covalent bonds.

Network Polymers

Multifunctional monomers forming three or more active covalent bonds make three dimensional networks.

Chain Flexibility

How easily the main chain of the polymer can move; branching increases the chain flexibility.

Linear structure properties

Typically flexible and have low density; often amorphous.

Branched polymers properties

Often have improved melt viscosity.

Crosslinked polymers properties

Rigid and have high melting points, insoluble and resistant to solvents.

Network polymers properties

Extremely hard, rigid, and brittle; have high melting points and are insoluble in most solvents.

Thermoplastics

Can be melted repeatedly.

Thermosets

Once shaped, cannot be melted.

Thermoplastics (TP)

Soften when heated and harden when cooled--processes that are totally reversible and may be repeated.

Thermosets (TS)

Become permanently hard during their formation and do not soften upon heating.

Temperature-activated curing

Curing is caused by heat supplied during part shaping

Catalyst-activated curing

curing caused by small amounts of catalyst added to polymer

Mixing-activated curing

mixing of two ingredients causes chemical reaction that cures polymer

Copolymer

Composed of two repeat units with different sequencing arrangements along the polymer chains.

Random Copolymer

Units are randomly dispersed along the chain

Alternating Copolymer

Repeat units alternate chain positions

Block Copolymer

Identical repeat units are clustered in blocks along the chain

Graft Copolymer

Homopolymer side branches of one type may be grafted to homopolymer main chains that are composed of a different repeat unit