Answer to Question 1
The melamine monomer has three amine groups attached to the ring, with each amine group containing a nitrogen and two hydrogens. Each of these nitrogens is capable of being a crosslinking site. Therefore, the hardness in melamine plastics comes from the very high crosslink density that is possible because of the multiple crosslink sites.
Answer to Question 2
Resole and novolac resins are both types of phenolics. The resole resins are linear polymers that are cured simply by heating, while the novolacs must have a hardener added to them and then heated to cure. The resoles are, therefore, one-stage polymers, meaning that only one step is needed to complete the crosslinking, whereas the novolacs are two-stage polymers.
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