Methyl substituted Seven-Membered ring carbonates (7CCs), namely. 4-methyl- and 5-methyl-1,3-dioxepan-2-one (alpha-Me7CC and beta-Me7CC), have been synthesized in high yields (up to 70%) upon cyclization of the corresponding alpha omega-diols issued from green renewable acids. ("Immortal") ring-opening polymerization of these monomers has been carried out using various catalysts combined with an alcohol acting, as a co-initiator and a chain transfer agent. The Lewis acid Al(OTf)(3), the organometallic complexes [(BDIipr)Zn(N(SiMe3)(2))] ((BDIipr) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)-imino)-2-pen tenel and [(ONOOiBu)Y(N(SiHMe2)(2))(THF)] (ONOOiBu = amino-alkoxy-bis(phenolate)) or the organic 4-N,N-dimethylaminopyridine (DMAP), 1.5.7-trinzabicyclo-[4.4.0]dec-5-ene (TBD) or 2-terf-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphospho rine (BEMP) successfully afforded the corresponding poly(alpha- and beta-Me7CC)s with quite good control and activities. The dissymmetry or the monomers raises the question of catalyst selectivity in the ring-opening of the 7CCs. Detailed microstructural analyses of the poly(7CC)s using H-1 and C-13 NM R and MA LDI-ToF-MS techniques revealed (1) the higher regioselectivity - with preferential ring-opening at the most hindered oxygen-acyl O-C(O)O bond, that is, closest to the alpha-Me substituent of the zinc-based system followed by the yttrium, as compared to the lack of selectivity of the aluminum one, in the ring-opening polymerization (ROP) of alpha-Me7CC; (2) the absence of reeioselectivity in the ROP of beta-Me7CC, whichever the catalyst system used, most likely as a result of the OC(O)O further remote substitution site; (3) the expected a-hydroxy,w-alkoxyester chain ends. Differential scanninecalorimetry (DSC) analyses of these polymers underlined the influence of the position of the methyl substituent on the glass transition temperature. Noteworthy, this study represents the llist synthesis of the beta-Me7CC monomer and of the resulting polyearbonates.