Andrzej Duda

Summary: The electrospinning technique based on single and multi‐jet systems was applied for poly(L‐lactide) (PLA) nano‐ and microfibers as well as fibrous mats manufacture; the latter with dimensions suitable for the tensile tests. The PLA's employed were prepared by the controlled ring‐opening polymerization of the L,L‐lactide (LA) monomer. The resulting fibers thickness was correlated with molecular weights of PLA's and viscosities of spinning solutions. The scanning electron microscopic, thermal, and tensile characteristics of the polymeric materials and fibrous mats were also examined.

L,L‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared. magnified image

Recent advances in the controlled ring‐opening polymerization of aliphatic cyclic esters are briefly reviewed. Particular attention is paid to the high molecular weight linear, branched, and star‐shaped poly(lactide)s and poly(ε‐caprolactone) synthesis. It is concluded that despite the plethora of initiating and/or catalytic systems applied for this purpose the best results so far were achieved with Al‐ and Sn(II) derivatives. Analytical methods employed for aliphatic polyesters of various architectures characterization, including SEC‐MALLS, LC‐CC, and fluorescence spectroscopy, are also discussed.

Linear telechelic, α,ω‐ditelechelic, and star‐shaped tri‐, tetra‐, penta‐, and hexa‐arm poly(L‐lactide)s (PLAs) fitted at every arm with pyrene end group have been prepared. Internal dynamics and mobility of the PLA chains in tetrahydrofuran solution at 25 °C, with regard to the number of PLA arms in one macromolecule and the individual arm average degree of polymerization, was followed by fluorescence spectroscopy. Analysis of both static and time‐resolved spectra of the star‐shaped polymers revealed dynamic segmental motion resulting in end‐to‐end cyclization, accompanied by an excimer formation. Probability and rate of the latter reaction increased with increasing number of arms and with decreasing their polymerization degree. Moreover, time‐resolved measurements revealed that for macromolecules containing few arms (2 or 3) the pyrene moieties are located in the interior of the star‐shaped PLAs, whereas in the instance of the higher number of arms (4–6) they are located at the periphery of the star‐shaped PLAs. Thus, increasing the number of arms leads to their stretching away from the center of the star‐shaped PLA macromolecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4586–4599, 2005

Recent advances in the controlled ring‐opening polymerization (ROP) of cyclic aliphatic esters are reviewed with a particular attention to thermodynamics and kinetics of the polymerization of industrially important monomers, namely: lactide (LA), 1,4‐dioxan‐2‐one (DX), and ϵ‐caprolactone (CL). For comparison, polymerization of β‐lactones is discussed. Progress in stereocontrolled polymerization of monomers bearing centers of chirality [LA and β‐butyrolactone (BL)] is also briefly reviewed.

Coupling atom transfer radical polymerization (ATRP) and coordination‐insertion ring‐opening polymerization (ROP) provided a controlled two‐step access to polymethacrylate‐graft‐polyaliphatic ester graft copolymers. In the first step, copolymerization of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) was carried out at 80 °C at high MMA concentration by using ethyl 2‐bromoisobutyrate and [NiBr₂(PPh₃)₂] as initiator and catalyst, respectively. Kinetic and molar masses measurements, as well as ¹H NMR spectra analysis of the resulting poly(MMA‐co‐HEMA)s highlighted the controlled character of the radical copolymerization, while the determination of the reactivity ratios attested preferential incorporation of HEMA. The second step consisted of the ROP of ε‐caprolactone or L,L‐dilactide, in THF at 80 °C, promoted by tin octoate (Sn(Oct)₂) and coinitiated by poly(MMA‐co‐HEMA)s obtained in the first step. Once again, kinetic, molar mass, and ¹H NMR data demonstrated that the copolymerization was under control and started on the hydroxyl functions available on the poly(MMA‐co‐HEMA) multifunctional macroinitiator. Comparison of the SEC traces for the poly(MMA‐co‐HEMA) macroinitiator P2 (line only), the polymethacrylate‐g‐PLA copolymer C2 (line marked by ○), and the polymethacrylate‐g‐PLA C3 (line marked by ▵). magnified image Comparison of the SEC traces for the poly(MMA‐co‐HEMA) macroinitiator P2 (line only), the polymethacrylate‐g‐PLA copolymer C2 (line marked by ○), and the polymethacrylate‐g‐PLA C3 (line marked by ▵).