Polyglycolic acid, PGA, is a polymer that we know rather well how to control the structure of (even though there are currently only limited applications). So in the lab we have created two types of PGA for testing, a linear chain PGA and a branched chain PGA. Assume comparable molecular weight.
If cooled from a melt at the same rate, of these two, which has a larger molar volume?
linear structure
branched structure
If cooled at the same rate, which will have a higher glass transition temperature, Tg?
linear structure
branched structure
In the melt, which would you expect to be less viscous?
Linear, because it has a lower molar volume.
Branched, because it has a lower molar volume.
Linear, because it has a smaller excess free volume. Branched, because it has a smaller excess free volume. Linear, because the branches can become more entangled than the linear chain.
Branched, because of the greater amount of electrostatic interactions in the linear chain.
Branched, because the pendant groups are less restricted sterically
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