Covalent bonds between H and C. 
- unsaturated: there are double/triple bonds
- saturated: all single bonds
- isomers: same composition, different arrangement

Are hydrocarbons, but gigantic. 
- Thus, we have repeat units (also called monomer, kind of)
- homopolymer: all repeating units along chain of same type.
- copolymers: chains composed of two or more different repeat units
- have: size, shape, structure 
- size in mol weight (or DP)
- shape in terms of degree of chain twisting, coiling, bending
- structure (linear, branched, crosslinked) in addition to several isometric configs.

Obtained by dividing the chains into a series of size ranges and then determining the number fraction of chains within each size range:

Based on the weight fraction of molecules within the various size ranges:

A way of expressing average chain size of a polymer:
DP = M(n)/m
where M(n) is number-avg mol weight, m is repeat unit molecular weight

Rotational flexibility is dependent on repeat unit structure (for example, chain with double bond is rotationally rigid).  
- Introduction of a bulky or large side group of atoms restricts rotational movement.

Linear, branched, crosslinked, network. 

Can be of several types:
- random copolymer
- alternating (exactly alternating)
- block (sections of each)
- gaft (branches of the other)

Packing of molecular chains to produce an ordered atomic array. 
- polymers often times are semicrystalline. 
- metals are almost entirely always crystalline
- ceramics either totally crystalline or non-crystalline
- polymers can range 

where ps = density of specimen, pa = density of totally amorphous polymer, pc = density of perfectly crystalline polymer 

A - brittle polymer (fractures while deforming elastically)
B - plastic polymer (like metallic)
C - elastomers (very elastic, rubberlike)

- Modulus of elasticity, ductility in % elongation - same as metals
- yield point is maximum point right after elastic region
- TS = stress at fracture
VS temp - becomes softer and more ductile 

When necking occurs, chains become oriented, which leads to localized strengthening.

For intermediate temperatures, polymers exhibit viscoelasticity (rubbery solid that exhibits combined mechanical characteristics of both extremes - like a glass and liquid)

As time increases, relaxation modulus decreases.

Stress necessary to maintain certain level of strain (as a function of time) at a constant temperature:

As temperature increases, relaxation modulus decreases.   At intermediate temps, we see viscoelasticity.