Converting a thesis or dissertation into one or more journal articles is an acceptable practice. Most journals will not have any issues with this as long as you mention this in your cover letter and cite the source in your manuscript. However, the plagiarism checking software used by the journal will detect a high percentage of similar content if you directly copy paste from the dissertation. Some journals might have a problem with this. Therefore, it is advisable to paraphrase or rewrite the content. Additionally, a thesis and a journal article are two completely different sub-genres of academic writing. Each caters to a different audience and sets different expectations. Therefore, it is best to take the ideas and rewrite the content using the style and format of a journal submission.

  Recommended reading:

• The basics of converting your PhD thesis into journal articles
• Tips on rewriting your thesis as a journal article