Star-shaped poly(L-lactide)s with variable numbers of hydroxyl groups at polyester arms chain-ends and directly attached to the star-shaped core - Controlled synthesis and characterization

Star-shaped poly(L-lactide)s (PLAs) bearing variable numbers of secondary hydroxyl groups at linear arms chain-ends and primary hydroxyl groups directly attached to dipentaerithritol core (DPE) ((HO)(6-x)DPE(PLA-OH)(x), where x = 1- 6) were prepared and then analyzed by means of size exclusion chromatography (SEC), 111 NMR spectroscopy, MALDI-TOF mass spectrometry, and eventually by Liquid Chromatography at Critical Conditions (LC-CC). First, starting from DPE(OH)(6) a series of polyols with various number of hydroxyl groups has been obtained ((BnO)(6-x)DPE(OH)(x), where Bn denotes benzyl moiety and x = 1 - 6). The living ring-opening polymerization of L-lactide (LA) with (BnO)(6-x)DPE(OH)(x)/tin(II) octoate mixtures as initiating and catalytic system led to star-shaped (BnO)(6-x)DPE(PLA-OH), polymers with molar masses (M,) controlled by LA and DPE concentrations ratio in the feed. Finally, deprotection (via hydrogenation) gave a series of (HO)(6-x)DPE(PLA-OH), PLA's. SEC (with Multiangle Laser Light Scattering Detector (MALLS)), NMR, and MALDI-TOF analyses confirmed the assumed structures and M-n's of the prepared (BnO)(6-x)DPE(PLA-OH)(x) and (HO)(6-x)DPE(PLA-OH)(x) PLA's. LC-CC measurements revealed that for (BnO)(6-x)DPE (PLA-OH)(x) series the elution volumes increase monotonically with the increasing number of -PLA-OH arms in one macromolecule and are independent on the given PLA molar mass because of the critical conditions. Contrary to the polymers having the protected core hydroxyl groups, the elution volume for (HO)(6-x)DPE(PLA-OH)(x) series decreases with the increasing number of -PLA-OH arms reaching a minimum value for 4-arm PLA and then slightly increases for 5- and 6-arm PLA. (c) 2005 Wiley Periodicals, Inc.