It is very hard to say TPP will affect greatly relations between China and ASEAN countries. Nowadays there are two of the most important factors, territorial disputes and economic interdependence, affecting China-ASEAN relations. Neither of the two factors can be changed greatly by TPP.
For the ASEAN countries which have no territorial disputes but benefit from economic interdependece with China, their relations with China may be in the grade of ˝A+˝. For the ASEAN countries which have territorial disputes but also benefit from economic interdepence with China, their relations with China may be in the grade of ˝A˝. For the ASEAN countries which have territorial disputes but benefit little from economic interdepence with China, their relations with China may be in the grade of ˝A-˝.
All in all, for China-ASEAN relations in economic field, China-ASEAN FTA will be much more influential than TPP. Meanwhile, if TPP can be successful in the future, which means the United States and ASEAN countries can share an open and prosperous market, then ASEAN countries may be a economic bridge between China and the United States, two of the biggest economies in the world.