Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50 - 300 K are carried out to study positronium formation in 40 keV B<^>+-ion implanted polymethylmethacrylate (B:PMMA) with two ion doses of <$E 3,13~cdot~10 sup 15> and <$E 3,75~cdot~10 sup 16> ions/cm<^>2. The investigated samples show the varioustemperature trends of ortho-positronium lifetime <$E tau sup 3> and intensity <$E I sub 3> in PMMA before and after ion implantation. Two transitions in the vicinity of ~ 150 and ~ 250 K, ascribed to <$Egamma> and <$Ebeta> transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (<$E M sub w>) which known from literature. It is found that B<^>+-ion implantation leads to decreasing <$E M sub w> in PMMA at lower iondose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution).

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