Tin ii 2 ethylhexanoate

Dry toluene, dry dichloromethane (DCM), α-bromoisobutyryl bromide (BIBB), copper(ii)bromide, N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMTDA) and tin(ii) 2-ethylhexanoate were purchased from Alfa Aesar. Styrene, ethyl-α-bromoisobutyrate (EBIB), triethylamine (TEA) dimethylformamide (DMF) and aminopropyltrimethoxysilane (APTMS) were obtained from Sigma Aldrich. N-Aminoethyl-aza-2,2-dimethyl-4-methylsilacyclopentane (thereafter referred to as cycloazasilane) and 2,2-dimethoxy-1-thia-2-silacyclopentane (thereafter referred to as cyclothiasilane) were purchased from Gelest. The fluorescent dyes ATTO 647 NHS and ATTO 655 maleimide were obtained from ATTO-TEC GmbH, Germany. Dibenzocyclooctyne-(polyethyleneglycol-12)-N-hydroxysuccinimidyl ester (NHS-PEG12-DBCO) was purchased from Click Chemistry Tools, USA. Azido-HaloTag-Ligand (click-HTL) was synthesized as described previously.^{31 (link)} The IUPAC name of click-HTL is 3-(4-azidophenyl)-N-(2-(2-(6-chlorohexyloxy)ethoxy)ethyl)propanamide. HaloTag-fused monomeric enhanced GFP protein (HaloTag-mEGFP) and poly(l-lysine)-graft-poly(ethylene glycol) terminated with methoxy groups (PLL-PEG-OMe) were prepared according protocols described previously.^{32,33 (link)} Chemicals for preparing HEPES buffered saline (HBS), such as 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and NaCl were purchased from Sigma Aldrich.

l-Lactide, a product of PURAC was kindly supplied by Thyssen-Uhde (Berlin, Germany) and recrystallized from toluene (99.89% extra dry, ACROS Chemicals, Geel, Belgium). Ethyl l-lactate was purchased from Sigma-Aldrich (Taufkirchen, Germany) and used as received, tin(ii) 2-ethylhexanoate (>96% purity) was purchased from Alfa Aesar (Karlsruhe, Germany) and used as received. DSTL,^{24 (link)} BuSnBuCa,^{25 (link)} BuSnBiph^{26 (link)} and SnBiph^{27 (link)} were synthesized as described in previous publications dealing with syntheses of cyclic poly(l-lactide)s by means of these catalysts. Those publications also contain the experimental evidence for the cyclic topology of the resulting polylactides.