RESUMO
A one-pass continuous flow strategy to form block copolymer nanoaggregates directly from monomers is presented. A key development towards such a sophisticated continuous flow setup is a significant improvement in continuous flow dialysis. Often impurities or solvent residues from polymerizations must be removed before block extensions or nanoaggregate formation can be carried out, typically disrupting the workflow. Hence, inline purification systems are required for fully continuous operation and eventual high throughput operation. An inline dialysis purification system is developed and exemplified for amphiphilic block copolymer synthesis from thermal and photoiniferter reversible addition fragmentation chain transfer (RAFT) polymerization. The inline dialysis system is found to be significantly faster than conventional batch dialysis and the kinetics are found to be very predictable with a diffusion velocity coefficient of 4.1 × 10-4 s-1. This is at least 4-5 times faster than conventional dialysis. Moreover, the newly developed setup uses only 57 mL of solvent for purification per gram of polymer, again reducing the required amount by almost an order of magnitude compared to conventional methods. Methyl methacrylate (MMA) or butyl acrylate (BA) was polymerized in a traditional flow reactor as the first block via RAFT polymerization, followed by a 'dialysis loop', which contains a custom-built inline dialysis device. Clearance of residual monomers is monitored via in-line NMR. The purified reaction mixture can then be chain extended in a second reactor stage to obtain block copolymers using poly(ethylene glycol) methyl ether acrylate (PEGMEA) as the second monomer. In the last step, nano-objects are created, again from flow processes. The process is highly tuneable, showing for the chosen model system a variation in nanoaggregate size from 34 nm to 188 nm.
RESUMO
Diffusion-ordered NMR spectroscopy (DOSY) allows for accurate molecular weight calibration and determination that can be corrected for solvent influences. Polystyrene and poly(ethylene glycol) standards have been used to calibrate DOSY diffusion data for a variety of solvents, showing a high correlation of data when the bulk viscosity of the solvent is accounted for following the Stokes-Einstein equation. In this way, a type of universal calibration is introduced that allows for determinations of average molecular weight that are at least as accurate as those of traditional size-exclusion chromatography (SEC), if not better. Further, we demonstrate that DOSY calibrations can be used between laboratories, hence removing the need for individual calibration of setups as currently done.
RESUMO
The increasing demand for renewable materials in the world has resulted in sustained efforts to utilize biomass in a better way. Lignin, a natural and abundant polymer in plants, has provided an ongoing challenge for many researchers seeking ways to better utilize this abundant resource. Here, we report a very efficient lignin depolymerization strategy with the assistant of microwave radiation. Copper sulphate (CuSO4) and hydrogen peroxide (H2O2) were used to generate hydroxyl radicals to depolymerize lignin under the irradiation of microwaves. Three different types of lignin, organosolv lignin, kraft lignin, and alkali lignin, were all successfully depolymerized using microwave irradiation at a temperature of 110 °C for 7 min. The use of 1H/13C two-dimensional nuclear magnetic resonance spectroscopy enabled the confirmation of structural changes, comparing before and after depolymerization. Liquid chromatography-mass spectrometry was used to characterize the products. Both monomers and oligomers were detected after depolymerization.
