Chapter 2. Chain Structure and Configuration

Polymer chains have three basic properties: 1.The molecular weight and molecular distribution. 2.The conformation of the chains in space. 3.The configuration of the chain. Coil chain conformation

2.1.1 Head-to-head and head-to-tail configurations 2.1 Examples of configurations and conformations 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 Chemical methods of determining microstructure

2.3 Stereochemistry of repeating units 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 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 1,2 1,4 3,4 addition polymerization Synthesis of diene type polymers 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 Block copolymer Semi-IPN IPN Cross-linked

Nanoscale ‘microphase’ segregation:  N > (  N) ODT with (  N) ODT = f(f) Melt state

‘Solution’ state: Swollen micelles and dissolved single-chains Blends?

Crystalline state

Block Copolymer (microphase separation) volume fraction < ~ 0.35> 0.35

Transition between mesomorphic phases

Block Copolymer phase diagram disorder

Representative phase diagram of diblock copolymers (Khandpur et al., Macromolecules 1995, 28, 8796)

3-D TEM micrographs for PS PLLA 307 (  PLLA = 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 t g-g+ Arrhenius type: Exp(-E act /kT)

2.9 Analysis of polymers during mechanical strain Far from the neck region In the neck region

2.10 Photophysics of polymers A + h  = A* A* + B = A + B* A* + A = (AA)* Excimmer formation (AA)* = 2A + h  E quench

Experimental Studies Microstructure of polystyrene

Infrared