Chapter 2 chain structure and configuration
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Chapter 2. Chain Structure and Configuration. Polymer chains have three basic properties:. The molecular weight and molecular distribution. The conformation of the chains in space. The configuration of the chain. Coil chain conformation. 2.1 Examples of configurations and conformations.

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Chapter 2. Chain Structure and Configuration

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Chapter 2. Chain Structure and Configuration


Polymer chains have three basic properties:

  • The molecular weight and molecular distribution.

  • The conformation of the chains in space.

  • The configuration of the chain.

Coil chain conformation


2.1 Examples of configurations and conformations

2.1.1 Head-to-head and head-to-tail configurations

head-to-tail

head-to-head

Thermodynamically and spatially preferred structure is usually the head-to-tail configuration.

The H-to-H and H-to-T configurations cannot be interchanged without breaking primary chemical bonds.


2.1.2 Trans-Gauche Conformations

The trans-gauche conformations of polymer chain can be interchanged by simple rotation about the single bond linking the moieties.


2.2 Theory and instruments

2.1.2 Chemical methods of determining microstructure


2.3 Stereochemistry of repeating units

2.3.1 Chiral centers

*

Chemically identical but they rotated plane-polarized light in opposite directions.


2.3.2 Tacticity in polymers

Polymerization of monosubstituted ethylene

Pseudochiral center


isotactic

syndiotactic

atactic


Stereo-isomers


2.4 repeating unit isomericsm

2.4.1 Optical isomerism


2.4.2 Geometric isomerism

The cis-trans isomerism arises because rotation about double bond is impossible without disrupting the structure.


2.4.3 Substitutional isomerism

Synthesis of diene type polymers

1,2

1,4

3,4

addition polymerization

isoprene


2.4.4 Infrared and Raman spectroscopic characterization

C-H bending823 cm-1

C-O stretching1164 & 1231 cm-1

C=O stretching1506 cm-1

Skeletal ring vibration1776 cm-1


2.5 Common types of copolymers


Copolymers

Terpolymers


Polymer blend

Graft copolymer

IPN

Block copolymer

Semi-IPN

Cross-linked


Nanoscale ‘microphase’ segregation:

cN > (cN)ODT

with (cN)ODT = f(f)

Melt state


‘Solution’ state:

Swollen micelles and

dissolved single-chains

Blends?


Crystalline state


Block Copolymer (microphase separation)

volume fraction

< 0.20

0.20 ~ 0.35

> 0.35


Transition between mesomorphic phases


Block Copolymer phase diagram

disorder


Representative phase diagram of diblock copolymers(Khandpur et al., Macromolecules1995, 28, 8796)


3-D TEM micrographs for PS280-PLLA307 (fPLLA= 0.37) solution-cast samples sectioned along different planes. As shown, the xy plane is the basal plane normal to helical axes and the yz and zx planes are planes parallel to helical axes


‘Knitting’ pattern


2.8 Conformational states in polymers

Arrhenius type:

Exp(-Eact/kT)

g-

g+

t


2.9 Analysis of polymers during mechanical strain

Far from the neck region

In the neck region


2.10 Photophysics of polymers

quench

A + hu = A*

A* + B = A + B*

2.10.2 Excimmer formation

A* + A = (AA)*

(AA)* = 2A + huE


2.10.3 Experimental Studies

2.10.3.1 Microstructure of polystyrene


Infrared


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