The glass transition temperatures Tg, sub-glass transition temperatures sub-tg, melting points Tm, and apparent melting enthalpies δHf have been measured for poly-N-(n-octadecyl)maleimede (PMI-18) fractions having number-average molecular weights between 1.25×103 and 1.9×105 by using differential scanning calorimetry. The results showed a dependence of the galss transition temperature on molecular weight similar to that observed for conventional linear polymers. The variation of Tg of PMI-18 fractions with molecular weight cannot be conveniently represented by any of the usual equations. On the other hand, the variation of Tg with molecular weight can be described very precisely by means of the Ellis equation, which leads to a value of Tg(∞)=387.6 K. An analysis of the present data on Tg, in conjuntion with a similar treatment due to Cowie, has shown that a plot of Tg against log X n (where X n is the number average bacbone bond number of main chain segments, namely, number of backbone carbon atoms or backbone carbon-carbon bonds) may be delimited into three well-differentiated regions. The boundary conditions, however, do not agree with the limits given by Cowie for typical linear polymers. However, the nalysis of the data as a function of the number of free bonds = virtual bonds = degree of polymerization also shows three well-differentiated regions. Their boundary condi6tions now agree with those given by Cowie for some other polymers. This alternative treatment suggests the importance of the backbone chain complexity effect on the glass transition temperature as well as its molecular weight dependence. The sub-Tg = Tg transition, due to the local motion of the n-alkyl side chains, seems to be independent of molecular weight. The lack of a dependence of both the melting point temperature Tm and the apparent melting enthalpy δHf on molecular weight confirms that this motion is an internal one within the n-alkyl side chain of PMI-18 but without any interaction with the main chain. Fractions with molecular weights lower than 5.4×103 (DP n = 15.5), however, show the characteristic dependence of Tm on molecular weight of low molecular weight susbstances. Peer reviewed