Bx51 microscope

Crystalline morphology of the HMW PLLA/PDLA racemate was observed
using an Olympus BX51 microscope equipped with a Linkam LTS420E hot
stage and a T95-HS controller. The sample was heated to various T_s between two glass slides and annealed for
2 min before recording images during cooling the sample to room temperature
at a rate of 5 K/min.

Polarization microscopy experiments were performed on an Olympus BX51 microscope equipped with a Linkam hot stage THMS600, temperature controller TP94 and liquid nitrogen controller LNP. Samples were held between two glass slides and had a thickness of several 10 up to 80 μm. After fast cooling from the melt to different crystallization temperatures T_c, a series of images was recorded during isothermal crystallization and the growth velocity of spherulites was determined from their time-dependent area. For every temperature, an average of over three different spherulites was performed.

All starting materials and solvents were obtained from commercial sources and used without purification. Nuclear magnetic resonance (NMR) spectra were measured on a Bruker Avance 400 spectrometer. Chemical shifts are given in ppm relative to tetramethylsilane (TMS) and the solvent residual peak was used as the internal standard. Microanalyses were performed with a Perkin-Elmer 2400 microanalyzer. Infrared (IR) spectra were recorded on a Nicolet Avatar FTIR spectrophotometer using KBr pellets. Mass spectra (MS) were obtained on a MICROFLEX Bruker spectrometer. Optical microscopy was studied using an Olympus BX51 microscope equipped with a Linkam THMS600 hot stage. Thermogravimetric analysis (TGA) was performed using a TA Instruments Q5000 apparatus at a heating rate of 10 °C min⁻¹ under a nitrogen atmosphere. Transition temperatures and melting enthalpies were obtained by differential scanning calorimetry (DSC) using a TA Instruments Q20 device at a rate of 10 °C min⁻¹. Optical absorption spectra were recorded with a UV4-200 UV-Vis spectrophotometer from ATI Unicam. Fluorescence spectra were recorded with a Perkin-Elmer LS50B system. Thin-film spectra were recorded by front-face detection.