Head-To-Dul Concentration

DISCUSSION It is clear from the very low fraction of “head-to-head” linkages that this reaction is far less energetically favorable than the “head-to-tail” reaction, which occurs normally. The head-to-tail arrangement is preferred energetically due to steric and resonance effects. When the radical attacks the fourth (double-bonded) carbon, the new radical that is produced is more stable, as it may participate in resonance with the neighboring oxygen. Conversely, when the radical attacks the first carbon, it cannot resonate, since the substituents are not directly attached to the carbon with the unpaired electron. The head-to-tail reaction is also more favorable since the fourth carbon has less steric interference from the surrounding substituents. When adding in the head-to-head orientation, the acetate group portions of the monomers (which act as substituents to the polymer chain) are placed right next to each other— in the head-to-tail orientation there is one carbon in-between. Literature values indicate that there should be no more than 1 to 2 % of head-to-head linkages in polyvinyl acetate5. This differs from our results obtained for polyvinyl alcohol (0.34%) by 70 to 80%. One source of error may be from incomplete hydrolysis with the periodic acid. Literature values indicate that the degree of hydrolysis is typically 86.5 to 89%4. …show more content…
The uncleaved polymer was more viscous because it had more intermolecular forces—both between polymer molecules, and between the polymer molecules and those of the apparatus. Its chains were also more likely to get physically tangled, both upon themselves and with other molecules. These effects increase with longer polymer chains, so the larger the chain (and overall mass), the more viscous the liquid