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Introduction
Polymers: a giant molecule, made up of many repeat units covalently joined together
Common characteristics: long, string-like molecules
Living polymers: long-chain objects whose subunits are joined by physical bonds, e.g., actin filaments
Variety of Polymeric Materials
Polymer chemistry Stereochemistry Architecture Homopolymers and Copolymers Physical state
Polymer chemistry (conti.)
The main chain can have different side groups: polymethyl methacrylate(聚甲基丙烯酸甲酯)
Polymer chemistry (conti.)
The polymer can be multiply connected, forming a ladder structure, e.g., poly(dioctyl fluorene)
Polymer chemistry (conti.)
The main chain can contain no carbon atoms at all, e.g., PDMS (silicone oil)
Stereochemistry
If a polymer has more than one type of chemical group attached to each main chain (carbon) atom, then different arrangement of the groups in 3D are possible: isotactic, syndiotactic, and atactic.
Architecture
Linear vs. Branched polymers Linear polymers can be characterized by N, the
number of repeated units: degree of polymerization
N is proportional to the relative molecular mass M
Degree of polymerization is not a constant for a group of polymers – a distribution
PDI: polydispersity index ≡ (weight average)/(number average)
PDI=Mw/Mn
Number average: Weight average: Standard error:
i
ii
NMN
ii
ii
i
ii
MNMN
wMw 2
2
222
nwn
i
ii
ii
ii
MMM
N
MN
MN
MN
Branched Polymer
The polymers may be branched The branched points introduce quenched
disorder, and hinder the formation of crystals
A lot of branch points – a network
Copolymers
The building units are all the same – homopolymers
Different building units – copolymers Phase separation and microphase separat
ion DNA and proteins are copolymers