28.02.2013 Views

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

5 SPECIAL APPLICATIONS OF SEC FOR RUBBERS<br />

SEC is used for the characterization <strong>of</strong> the molecular weight parameters <strong>of</strong><br />

rubbers; however, there is an inverse SEC consideration in which the<br />

determination <strong>of</strong> the porous structure <strong>of</strong> the column packings (if the packings<br />

are vulcanized rubber) might be elucidated by examining the retention<br />

data for polymers having known molecular weights. This technique is called<br />

inverse SEC. This seems to be a natural extension <strong>of</strong> inverse gas<br />

chromatography (68).<br />

In 1984, Haidar <strong>and</strong> others (39) reported their inverse SEC results for the<br />

elucidation <strong>of</strong> structural differences in networks prepared by chemical <strong>and</strong><br />

photochemical reactions <strong>of</strong> EPDM. They used conventional GPC for their<br />

inverse SEC, except for the columns, in which fine powders <strong>of</strong> crosslinked<br />

EPDM were packed. Polystyrenes <strong>of</strong> various molecular weights were used as<br />

the probe.<br />

Their elution data for st<strong>and</strong>ard polystyrenes from EPDM packed columns<br />

showed clearly the differences presented between two vulcanizing methods: one<br />

was photo-crosslinked <strong>and</strong> the other was peroxide-cured EPDM. From this study<br />

they concluded that the Mc, the molecular weight between crosslinking junctions,<br />

was different for the two samples.<br />

In1985,Capillon<strong>and</strong>others(69)gavethecriticismthattheinverseSECgives<br />

erroneousresultswhenusedingelsthatswelltoomuch,suchasvulcanizedrubbers.<br />

Subsequently,very little work has been done using inverse SEC for the<br />

characterization <strong>of</strong> the network structure <strong>of</strong> rubbers.<br />

6 CONCLUSION<br />

Rubbers based on dienes can easily be analyzed for their molecular<br />

characterization by SEC; however, special rubbers, such as polyorganophosphazenes,<br />

show some difficulty because <strong>of</strong> their imperfect dissolution in SEC<br />

solvents. Fluoro-rubbers are hard to dissolve in solvents. The application <strong>of</strong> SEC<br />

to such rubbers is not covered in the literature cited in Table 5.<br />

Recent application trends <strong>of</strong> SEC to rubbers are multidetector systems<br />

to obtain much more information on the molecular characteristics in a<br />

single SEC run. A properly arranged SEC system gives almost a complete<br />

molecular characterization <strong>of</strong> rubbers if the rubbers are dissolved in SEC<br />

solvents.<br />

For the appendix we could not find a role for SEC in the quality control <strong>of</strong><br />

rubber production processes despite its technological importance. Furthermore,<br />

we expect that much work on the correlation between SEC analysis <strong>and</strong><br />

mechanical properties <strong>of</strong> rubbers is in development.<br />

© 2004 by Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!