The dimethylaluminum compounds {3-tBu-2-(O)C6H3CHN−R}AlMe2 [R = C6H5 (1); 2,6-iPr2C6H3 (2); C6F5 (3)] were used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone, l-lactide, and d,l-lactide. Compound 3, in combination with 1 equiv of methanol, exhibited a living behavior in the ROP of the cyclic esters. Such a feature allowed the preparation of poly(d,l-lactide-block-ε-caprolactone) and poly(l-lactide-block-ε-caprolactone) copolymers. Random copolymers of ε-caprolactone and l-lactide and of ε-caprolactone and d,l-lactide were also synthesized by compound 3. NMR and DSC characterization confirmed a highly random structure of these copolymers, even in the absence of transesterification reactions. All the materials, characterized by GPC, showed high molecular weight and narrow molecular weight distributions.

Copolymerization of ethylene and styrene in the presence of the catalytic system η5-C5Me5Ti(CH2Ph)3−B(C6F5)3 has been investigated. Independently from the feed composition, basically alternating ethylene−styrene copolymers are obtained, together with some polyethylene and syndiotactic polystyrene, from which the former can be separated by solvent extraction. NMR analysis of suitably 13C-enriched end groups shows that the regiospecificity of styrene insertion in the initiation step is largely secondary. A tentative explanation for the preferentially alternating comonomer incorporation is proposed.

The history of resorbable polymers containing glycolide, lactide, ε-caprolactone and trimethylene carbonate, with a special emphasis being placed on the time frame of the 1960s–1990s is described. Reviewing the history is valuable when looking into the future perspectives regarding how and where these monomers should be used. This story includes scientific evaluations indicating that these polymers are safe to use in medical devices, while the design of the medical device is not considered in this report. In particular, we present the data regarding the tissue response to implanted polymers, as well as the toxicity and pharmacokinetics of their degradation products. In the translation of these polymers from “the bench to the bedside,” various challenges have been faced by surgeons, medical doctors, biologists, material engineers and polymer chemists. This Perspective highlights the visionary role played by the pioneers, addressing the problems that occurred on a case by case basis in translational medicine.

The monomethylaluminum complexes 1 and 2, bearing pyrrolylpyridylamido as dianionic [−NNN–] tridentate ligands with general formula [NNN]AlMe, were synthesized and tested as initiators in the ring-opening polymerization (ROP) of ε-caprolactone, l-lactide, and d,l-lactide. In the presence of 1 equiv of alcohol, compounds 1 and 2 were highly active initiators in the ROP of ε-CL (TOF up to 4000 molCL molAl –1 h–1), and they showed moderate activity in the ROP of lactides (TOF up to 1.7 molLA molAl –1 h–1). The polymerization processes proceeded with a living mechanism; moreover, the obtained PLAs resulted isotactic-enriched with P m values up to 76%. More interestingly, this class of catalysts promoted the random copolymerization of ε-caprolactone and lactides. In particular, compound 1 allowed excellently controlled random copolymerization of ε-caprolactone and d,l-lactide as indicated by both the values of the reactivity ratios of the two monomers (r LA = 1.17; r CL = 1.36) and the average lengths of the caproyl and lactidyl sequences (L CL = 2.0; L LA = 2.5).

One constrain in the use of micellar carriers as drug delivery systems (DDSs) is their low stability in aqueous solution. In this study "tree-shaped" copolymers of general formula mPEG-(PLA)n (n = 1, 2 or 4; mPEG = poly(ethylene glycol) monomethylether 2K or 5K Da; PLA = atactic or isotactic poly(lactide)) were synthesized to evaluate the architecture and chemical composition effect on the micelles formation and stability. Copolymers with mPEG/PLA ratio of about 1:1 wt/wt were obtained using a "core-first" synthetic route. Dynamic Light Scattering (DLS), Field Emission Scanning Electron Microscopy (FESEM), and Zeta Potential measurements showed that mPEG2K-(PD,LLA)2 copolymer, characterized by mPEG chain of 2000 Da and two blocks of atactic PLA, was able to form monodisperse and stable micelles. To analyze the interaction among micelles and tumor cells, FITC conjugated mPEG-(PLA)n were synthesized. The derived micelles were tested on two, histological different, tumor cell lines: HEK293t and HeLa cells. Fluorescence Activated Cells Sorter (FACS) analysis showed that the FITC conjugated mPEG2K-(PD,LLA)2 copolymer stain tumor cells with high efficiency. Our data demonstrate that both PEG size and PLA structure control the biological interaction between the micelles and biological systems. Moreover, using confocal microscopy analysis, the staining of tumor cells obtained after incubation with mPEG2K-(PD,LLA)2 was shown to be localized inside the tumor cells. Indeed, the mPEG2K-(PD,LLA)2 paclitaxel-loaded micelles mediate a potent antitumor cytotoxicity effect.