the only possibility is a crystallinity increase

for mechanical properties:

increase of youngs modlus, yield stress, decrease of yield strain and strain at break

lots of references dealing with that

regards

thanx,

but i think when a polymer material heated above Tg in relaxed form lost its strength

when measuring on room temperature after cooling down, then what will happen?

thanx

There are some data on this in our paper from 2002: http://www.tandfonline.com/doi/abs/10.1081/MB-120013068#.VZ5Ao2Aw-M8