The alcohol product contains two different types of hydroxyl groups. Why does the polymer-supported reaction with methanol convert only one of the hydroxyl groups to an ether group but not the other

The other may not be free.

Explanation:

In the polymer-supported reaction with methanol, the reaction will undergo at one hydroxyl group because others may not be free due to bonding with other molecules. The hydroxyl groups could be bonded with the polymer with the help of hydrogen bonding of molecules. The hydroxyl group has to be bonded to only the compatible molecules and free molecules.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.