Molecular Dynamics of Star-Shaped Poly(L-lactide)s in Tetrahydrofuran as Solvent Monitored by Fluorescence Spectroscopy MARTIN DANKO, 1 * JAN LIBISZOWSKI, 1 TADEUSZ BIELA, 1 MARIAN WOLSZCZAK, 2 ANDRZEJ DUDA 1 1 Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lodz, Poland 2 Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Received 9 February 2005; accepted 16 May 2005 DOI: 10.1002/POLA.20932 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Linear telechelic, a,x-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 8C, 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 poly- mers revealed dynamic segmental motion resulting in end-to-end cyclization, accom- panied 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. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4586–4599, 2005 Keywords: fluorescence spectroscopy; poly(L-lactide); pyrene probe; star-shaped polymers INTRODUCTION Polymers composed of macromolecules with a nonlinear topology (having branched, 1,2 hyper- branched, 3–6 star-shaped, 7–14 or dendrimeric 15–19 structures) reveal solid state, melt, or solution properties considerably different from their lin- ear counterparts having similar molar masses. Star-shaped polymers, bearing strictly defined number of linear arms and low polydispersity, are particularly useful as model systems in studies of the branched macromolecular struc- tures. Fluorescence spectroscopy appears to be a useful and convenient technique for examination of the branched macromolecular structures. Recently, a number of studies on application of this method for characterization of the well- defined linear, dendritic, and star-shaped poly- *Martin Danko: On leave from Polymer Institute, Centre of Excellence for Degradation of Biopolymers, Slovak Acad- emy of Sciences, Dubravska cesta 9, 842 36 Bratislava, Slo- vak Republic. Correspondence to: A. Duda (E-mail: anduda@bilbo.cbmm. lodz.pl) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 4586–4599 (2005) V V C 2005 Wiley Periodicals, Inc. 4586