evaluation, characterization, & analysis of polymers - youngstown

Chemistry 5861 - Polymer Chemistry 1

Evaluation, Characterization, & Analysis of Polymers (Chapter 5 in Stevens)1

I Introduction

A) Requisite Information

1)

a)

b)

c)

d)

2)

a)

b)

c)

d)

e)

3)

a)

Molecular Weights

Distributions

i)

i)

ii)

iii)

i)

Single or Multiple Curves

MW Averages

Polydispersity Index

Molecular Weight Determination Methods in Section 2

Chemical Composition

Repeating Units

Side Chains

Crosslinking Groups

End Groups

Additives

identity

concentration

localization

Stereochemistry & Configuration

Are structures independent of MW and place in chain

random

1 The graphics in these notes indicated by “Figure/Table/Equation/Etc., x.x in Stevens” are taken from our lecture text: “Polymer Chemistry: An Introduction - 3rd Edition” Malcolm P. Stevens (Oxford University Press, New York,

©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry


ii)

iii)

iv)

i)

ii)

i)

ii)

iii)

some type of alternation

blocks

grafts

b)

c)

II

Stereoregular or Random Side Chains

tacticity

head/tail structures

Linear or Branched

branching topology

amount of branching

branch lengths

Chemical Methods of Analysis

A) Examples

1)

2)

a)

b)

c)

d)

e)

f)

Mostly of historical interest now

Head/Tail Structure of Vinyl Polymers

Poly(vinyl alcohol)

Oxidation by HIO4 or Pb(OAc)4

Head-Head links have 1,2-diols

These are cleaved by these strong oxidizing agents (eventually to terminal

carboxylic acids)

⇒ reduced average MW

⇒ reduced viscosity

1999).



g)

3)

a)

b)

4)

III

This experiment run in our Physical Chemistry Lab

Double Bond Location in Polydienes

Ozonolysis

i)

ii)

i)

ii)

Hydrolysis or polyesters, polyamides, etc.

1st O3, 2nd H2O

cleaves olefin links to ⇒ aldehyde and/or ketone groups

Polyisoprene

⇒ H(O)C-CH2-CH2-C(CH3)O as organic product

was how polyisoprene structure determined

Spectroscopic Methods of Analysis

Main Spectroscopic Methods A)

1)

B)

Table 5.1 in Stevens

Infrared Spectroscopy

1)

a)

2)

3)

Need change in dipole moment

i.e., asymmetric vibration modes

FT-IR Databases

Analysis by comparison to Model

Compounds

a) Figure 5.1 in Stevens



4) Spectral subtraction to observe minor species

a)

b)

5)

a)

b)

c)

C)

Figure 5.2 in Stevens

e.g., spectrum of crystalline

regions

Polymer Blends

To look for new interactions

From Polyblend spectrum

subtract that for the two homopolymers

the difference spectrum is that for any new chemical or physical interactions

Raman Spectroscopy

1)

a)

b)

2)

a)

b)

Need change in polarizability

i.e., symmetric vibration modes

∴ especially sensitive to vibrations with little or no change of dipole moments

i) e.g.,

C-C vibrations

cis-trans isomerism

sulfur crosslinks in rubber

Problems/Limitations:

Instruments relatively expensive

Raman method harder to apply to colored materials



D) NMR Spectroscopy

1)

2)

a)

Backbone & Side chain Structure

Tacticity Analysis in Solution

Isotactic PMMA

i)

i)

ii)

i)


b) Polypropylene


identification via model compounds

3)

a)

Solid State NMR

CP-MAS

Narrows the broad lines

characteristic of solid state NMR



ii)

iii)

iv)


Cross Polarization

E)

transfer of polarization from 1H

⇒ faster 13C relaxation

Magic Angle Spinning

Magic Angle - 54.7°

thousands of tens of thousands of Hz spin rate

Electron Spin Resonance, ESR, Spectroscopy

1)

2)

a)

b)

Requires Free Radical in Sample

Excellent for mechanistic studies

synthesis

degradation

3)

a)

F)


usually plotted in derivative mode

Other Methods

1)

2)

3)

UV-Visible Spectroscopy

Fluorescence

etc.



IV X-ray, Electron, and Neutron Scattering

Principles of Diffraction A)

1)

2)

a)

b)

c)

d)

3)

a)

b)

B)

1)

2)

C)

1)

2)


WAXS

Wide Angle X-Ray Scattering

i) coherent

increased crystallinity ⇒ sharper rings

orientation of crystallites ⇒ arcs & then spots

single crystal studies

SAXS

Small Angle X-Ray Scattering

incoherent

Electron Diffraction

need conducting polymer (or coated polymer)

TEM, Transmission Electron Microscopy

Neutron Diffraction

especially sensitive to proton positions

require a “cold” neutron source!



V Characterization & Analysis of Polymer Surfaces

A) Surface Analysis

1) Table 5.2 in Stevens

Attenuated Total Reflectance Spectroscopy, ATR B)

1) Figure 5.8 in Stevens

C) Electron Spectroscopy for Chemical Analysis, ESCA

1) ESCA



a)

b)

c)

d)

e)

also called XPS

i)

i)

i)

X-ray Photoelectron Spectroscopy

uses soft X-rays to detach electrons from surfaces

Binding Energy of Electron = hν - Emitted electron energy

valence electrons

⇒ chemical information

core electron

⇒ localized elemental analysis

f)

D)


Secondary-Ion Mass Spectrometry, SIMS, and Ion-Scattering Spectroscopy, ISS

1)

2)


Identification of Surface

Species



Atomic Force Microscopy E)

1)

2)

3)

VI


in physical contact with surface

surface does not need to be

conducting

Thermal Analysis

Differential Scanning Calorimetry, DSC, & Differential Thermal Analysis, DTA A)

1)

2)

a)

b)

c)

3)

a)

b)

4)

a)

b)

c)

DTA is older technique now generally replaced by DSC

Sample heated and heat flow watched

typically in an inert atmosphere

typically wrt. to a reference sample

0.5 to 10 mg samples sizes typical

DTA

sample and reference heated by same source

∴ measure difference in temperature

DSC

sample and reference heated separately

different currents applied to keep same temperature

differences in applied current reflect differences in thermal properties

5) Figure 5.15, 5.16, 5.17, & 5.18 in Stevens



B) Thermomechanical Analysis, TMA, Dynamic Mechanical Analysis, DMA

1)

2)

C)

A probe is in contact with the sample

Detects phase transitions by change in modulus or volume

Thermogravimetric Analysis, TGA



1)

a)

b)

c)

d)

e)

Measures weight changes on heating

depolymerization

oxidation

desolvation

additive loss

etc.

2)

3)

a)


Often hyphenated technique

TGA-MS

i) Figure 5.20 in Stevens

b)

c)

d)

VII

TGA-FTIR

TGA-MS-FTIR

etc.

Measurement of Mechanical Properties

Instron Mechanical Tester A)

1) Figure 5.22 and 5.23 in Stevens




VIII

Evaluation of Chemical Resistance

A) Evaluation

1)

2)

IX

Predictable from chemical reasoning when wetting, pores, etc., taken into account

tested by immersion

Evaluation of Electrical Properties

A) Resistivity

1) Inverse of Conductivity

2) Figure 5.24 in Stevens

evaluation, characterization, & analysis of polymers - youngstown

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