o-Ps lifetime and intensity of PMMA/ladderlike PPSQ in-situ blend sversus percentage of PPSQ showed that some interactions involved between PMMA and PPSQ. Positron annihilation lifetime spectra of PMMA/PPSQ blends at three different compositions (PMMA/PPSQ
95/5
90/10
80/20) over 20—150℃ were studied. Two structural transitions were observable. β transition temperatue ( T β) of PMMA/PPSQ (95/5) was the highest among three blend samples due to good miscibility and strong interactions.The similarity of T g for samples M5 (PMMA/PPSQ 95/5) and M20 (PMMA/PPSQ 80/20) indicated that phase-separation occurred (PPSQ>5%). Characteristics of free-volume voids in the blends were also analyzed. Size and fraction of free-volume voids in PMMA/PPSQ (90/10) were the largest among three blend samples