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The glass transition temperature ( T g ) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect , i.e., the Fox-Flory relationship between T g and the average molecular weight between crosslinking points ( M c ), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)- l -polyisobutylene (PMMA- l -PIB) conetworks was prepared and investigated. Two T g s were found for the conetworks by DSC. Fox-Flory type dependence between T g and M c of the PMMA component ( T g = T g,∞ - K/M c ) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5-20 nm, but the correlation between T g and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors ( scissors effect ), and the T g of PMMA depend exclusively on the M c in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.