dic.yahoo.co.jp、weblio.jp、and other dictionaries, state that the parts of speech for「たくさん」are noun and 形容動詞。imho, usage cases where たくさん is used as 形容詞 is uncommon. I have seen たくさん take the な particle in sentences such as "写真{しゃしん}がたくさんな記事{きじ}" . But, I have never seen たくさん take the に particle.
I recently heard the sentence:
"人がたくさん参加{さんか}した。"
That sounds ok to me but looks weird. I cannot help but wonder if something grammatically needs to be between "たくさん" and "参加". Surely, there must be a 助詞{じょし}, Perhaps, can you write:
人がたくさん に 参加した
To function as a full-fledged 形容動詞、たくさん must be able to take the 「に」助詞. I've never said "...たくさんに...". I would like to add this to my vocabulary. examples please?
In the thread titled たくさん:形容動詞 Tonky seems to say that "...たくさんに..." never happens. In the lengthy thread titled usage of たくさん vs. 多い no one creates a sentence that has the "...たくさんに..." construct.
If たくさん can take な, but not a に、then it would be questionable whether it is really a 形容動詞, right?