A thesis is an examination document and a unit of work which must be produced in order to be awarded a degree. If you intend to publish elements of your thesis, it is recommended that you check how potential publishers will view its public availability. In a few cases, they may view it as prior publication and reject submissions on that basis. This is rarely the case for journal publishers, so there is rarely a need to restrict access to your thesis because you intend to publish articles from it.
On the other hand, some monograph publishers, particularly in Humanities and Social Sciences may view public availability of your thesis online as prior publication. For this reason, where you are planning on publishing a monograph from your thesis, you are permitted to request an embargo for up to 12 months, with the option to extend once you have secured a publishing contract and can demonstrate that the publisher in question requires a further restriction. We would always recommend you discuss availability of your thesis with your publisher and try to minimise any embargo as your thesis is a key way that other researchers will engage with your work, leading to it being recognised, cited and improving your own reputation in your field.