The controlled ring-opening polymerization of racemic allyl-beta-butyrolactone (rac-BLallyl) in toluene or in bulk, catalyzed by the discrete beta-diiminate zinc amido [(BDI/(Pr))Zn(N (SiMe3)(2))] (1) or {amino-methoxy-bis(phenolate))yttrium amido [(ONOOtBu)Y(N(SiHMe2)(2))(THF)] (2) complexes, in association with an alcohol, gave poly(beta-hydroxyalkanoate)s (PHAs) with allylic side chains. These PHAsallyl exhibit either a slightly isotactic-enriched (P-m = 0.61) or highly syndiotactic-enriched (P-r = 0.82) backbone structure, respectively, with high molar mass ((M) over bar (n) up to 21,100 g mol(-1)) and narrow molar mass distribution values (1.05 < <(M)over bar>(w)/(M) over bar (n) < 1.28), as evidenced by detailed C-13 NMR and size exclusion chromatography analyses. Postpolymerization rhodium-catalyzed hydroboration of the resulting PHAsallyl with pinacolborane quantitatively afforded the corresponding PHAsboron. Introduction of boron into the pendant chains did not alter neither the structure of the polymer backbone nor the macromolecular features (<(M)over bar>(n), (M) over bar (w)/(M) over bar (n), and stereoregularity). However, differential scanning calorimetry analyses revealed a significant increase of the glass transition temperature on modifying the allyl for the boron function in these PHAs. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 907-917, 2011