Are University Professors considered "Public Personalities" (defamation)

They might be "public," or quasi-public, depending on how big the school is and how well known and how outspoken the professor is.

Defamation doesn't mean unfavorable, it means provably false. There are plenty of statements that are unfavorable but truthful and not defamatory.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

A professor may be a limited purpose public figure depending on the facts. If the professor is a public figure, he or she would have to prove actual malice to prevail on a defamation claim. Actual malice means that the publication of the defamatory statement was made with knowlegde of its falsity or with reckless disregard to its truth.