Methylenelactide: vinyl polymerization and spatial reactivity effects

The first detailed study on free-radical polymerization, copolymerization and controlled radical polymerization of the cyclic push–pull-type monomer methylenelactide in comparison to the non-cyclic monomer α-acetoxyacrylate is described. The experimental results revealed that methylenelactide undergoes a self-initiated polymerization. The copolymerization parameters of methylenelactide and styrene as well as methyl methacrylate were determined. To predict the copolymerization behavior with other classes of monomers, Q and e values were calculated. Further, reversible addition fragmentation chain transfer (RAFT)-controlled homopolymerization of methylenelactide and copolymerization with N,N-dimethylacrylamide was performed at 70 °C in 1,4-dioxane using AIBN as initiator and 2-(((ethylthio)carbonothioyl)thio)-2-methylpropanoic acid as a transfer agent.

dioxane and diethyl ether before use was columned over basic alumina to remove peroxides and water. Triethylamine was stirred in potassium hydroxide for 48 h and then distilled and used immediately. 1 H NMR spectra were recorded using a Bruker Avance III 600 spectrometer at 600 MHz or on a Bruker Avance III 300 spectrometer at 300 MHz. The deuterated solvents were used as internal standards. 1 H NMR measurements for determination of monomer conversion were measured on a Bruker Avance III 300 spectrometer at 300 MHz. Withdrawn samples of 50 μL S3 monomer solution at the beginning and at certain points of time and at the end of the polymerization were terminated in liquid nitrogen and diluted with 0.7 mL of DMSO-d 6 including a constant amount of benzene-d 6  High-performance liquid chromatography (HPLC) measurements were carried out with a

Characterization methods
BioTek Kontron Instruments construction, type System 525. Detection was performed with a Dioden Array detector at λ = 220, 230 and 270 nm. A CC 250/4 Nucleodur 100-5 C18 ec (Macherey-Nagel, length 250 mm, diameter 4 mm, particle size 5 μm) was used as reverse phase column. A mixture of acetonitrile/water (60/40) was used as eluent with a flow rate of 0.5 mL/min under isocratic conditions. Removal of polymer particles from monomeric molecules was achieved by centrifuge and filtration of the sample and in addition after injection in the HPLC by an upstream LiChroCART®4-4 pre-column. (Merck KGaA). The calibration lines are listed in Figure S13.
Infrared spectra (IR) were measured on a Nicolett 6700 Fourier transform equipped with a diamond single bounce attenuated total reflectance accessory at room temperature.
Theoretical calculations were performed with the density functional theory (DFT) by using the software Spartan`16 with the method B3LYP and the basis set 6-31G.
Dynamic differential scanning calorimetry (differential scanning calorimetry, DSC) was performed on a DSC 822e equipped with the samples Sampler TSO801RO of the company S4 Mettler Toledo. The heating and cooling rates were 10 K/min in the first cycle and 15 K/min in the following (a total of four cycles).
Size exclusion chromatography (SEC) measurements were performed using a ViscotekGPCmax VE2001 system. The System has a column set compromising one MZ-Gel-SDplus, 100 Å pore size and 10 µm particle size, 50 × 8.0 mm [Length × ID]pre-column and two MZ-Gel SDplus linear, 10 µm particle size, 300 × 8.0 mm [Length × ID]columns. The columns were constantly heated to a temperature of 60 °C. N,N-Dimethylformamide (0.05 M LiBr) was used as eluent at a flow rate of 1 mL min −1 . For detection a Viscotek VE 3500 RI detector was used. The system was calibrated with polystyrene standards of a molecular range from 1280 g mol −1 to 1373000 g mol −1 .
UV-vis spectroscopic measurements were carried out using a dual-trace spectrometer  Table 1) was dissolved with 1 mL of withdrawn monomer solution in an inert atmosphere and afterward backfilled to the two-necked flask. After an additional S5 degassed time of 10 min the flask was set in an oil bath at 70 °C which was controlled over an internal thermometer. At 1.5 min the polymerization was terminated by adding hydroquinone monomethylether and cooling with liquid nitrogen. The polymer solution was allowed to warm-up to room temperature and pouring into 40 mL of methanol. The precipitated polymer was centrifuged, methanol was decanted off and the polymer was dried at 60 °C in vacuum (8•10 −2 mbar).

DPPH kinetics
In a microwave tube equipped with a stirring bar, MLA (0.515 g, 3.62 mmol) was added and dissolved in 2 mL of a freshly prepared stock solution of DPPH in 1,4-dioxane (c DPPH = 0.28 mM). The mixture was degassed by five freeze-pump-thaw cycles before the tube was backfilled with argon. Under inert conditions the complete solution was inverted into the cuvette by a syringe. The cuvette was placed in the UV-vis spectrometer which was preheated to 70 °C. The disappearance of the absorption at 525 nm of DPPH at 70 °C was followed. In case of the copolymerization of MLA with N,N-dimethylacrylamide (DMA) the polymer solution was diluted in 1 mL of acetone and poured in 50 mL of diethyl ether, filtered, and dried in vacuum (8 × 10 −2 mbar) at 60 °C. This purification procedure was repeated once.

Determination of the copolymerization parameter
The residual monomer content of six different polymerization mixtures (refer to Table S5, S7) was determined by high-performance liquid chromatography (HPLC), respectively. The conversion was kept below 27%.
The implementation is described by the example of run 18-1 (Table S3) The Q-e-equation:      (Table 4). Figure S22: 1 H NMR spectra of poly(N,N-dimethylacrylamide-co-methylenelactide) of run 12 to run 17 (Table 4) with zoomed CH signals of the MLA unit.    Table 5) employing EMP. On the left the first kinetic and on the right the repetition.