An efficient process for the Cu(0)-mediated synthesis and subsequent chain extension of poly(methyl acrylate) macroinitiator

Abstract

A process combining a continuous tubular and a semi-batch reactor is established as an efficient method for the synthesis of block copolymers.

Toward an Efficient Process for the Cu(0)‐Mediated Synthesis and Chain Extension of Poly(methyl acrylate) Macroinitiator Using PMDETA as Ligand

“…Only 23% conversion was reached after 3 h reaction at room temperature with 30 wt% PGME as solvent using an initial MA:MBP:PMDETA molar ratio of 10:1:0.05 (Expt B‐RT‐P‐MBP), whereas conversions were greater than 80% for similar reaction conditions using Me 6 TREN. [ 9 ] In addition, MW analysis indicated that only a small fraction of the MBP in the system successfully initiated chain growth. The addition of ASC increased the conversion to over 90% but resulted in loss of controlled chain growth, while the addition of water as cosolvent promoted reaction rate and improved initiation efficiency, but not to the extent required for the tubular process.…”

“…The addition of ASC increased the conversion to over 90% but resulted in loss of controlled chain growth, while the addition of water as cosolvent promoted reaction rate and improved initiation efficiency, but not to the extent required for the tubular process. While reaction temperature did not provide an improvement in rate or control when Me 6 TREN was used as ligand, [ 9 ] increasing the reaction temperature to 60 °C led to almost complete reaction of the MA (98% conversion) in the batch trials, while simultaneously lowering dispersity ( Ð ) to 2.37 (Table 1, Expt B‐60‐P‐MBP). However, the average chain length of 26 was much higher than the target value of 10, indicating that initiation efficiency with MBP remained low.…”

“…[ 2–8 ] We have recently demonstrated that low molecular weight (MW) macroinitiator chains with number‐average molecular weight ( M n ) of less than 1000 g mol –1 and dispersity ( Ð ) of ≈1.20 can be synthesized by feeding methyl acrylate (MA) with 30 wt% 1‐methoxy‐2‐propanol (PGME) as solvent through a copper tube that serves both as reactor vessel and the source of the Cu(0) mediator/activator; conversions of ≈70% were achieved with a residence time of 32 min. [ 9 ] Both the reactor feed and reactor body are at room temperature, although the temperature of the reaction mixture increases slightly with the exothermic reaction. Tris[2‐(dimethylamino)ethyl]amine (Me 6 TREN) was used as the ligand, fed at a level of 1 mol% relative to the amount of methyl‐2‐bromopropionate (MBP) initiator, with the MA:MBP molar ratio kept at 10:1.…”

“…The same study demonstrated that the low MW macroinitiator solution produced in the tubular setup could be stored and chain extended in a semibatch reactor, without further purification, using either MA or other acrylates. [ 9 ] Conversions of >90% and very clean chain extensions ( Ð of 1.1–1.2) were achieved, with reaction rates sufficiently high under room temperature operation such that “starved‐feed” operation could be maintained during the 3 h feed period; i.e., the polymer production rate is controlled by the rate at which monomer is fed to the reactor, the method commonly used to produce polymer resins for coatings applications. [ 10,11 ] These results were obtained without the addition of supplemental copper during chain extension through the judicious use of additional ligand as well as ascorbic acid (ASC) as reducing agent, [ 12,13 ] thus lowering copper concentration in the polymer product to levels below 100 ppm.…”

“…Use of the tubular reactor to produce low MW macroinitiator ensures that solution viscosity remains low to minimize pressure drop and eliminate plugging concerns, with PGME selected as a common industrial solvent that provides similar reaction rates as those achieved with DMSO. [ 9 ] As well as matching current practice in the coatings industry, employing a semibatch system for chain extension offers flexibility in monomer sequencing to precisely control block copolymer structure. The overall process uses only 0.04 mol of Me 6 TREN per polymer chain (i.e., 0.04 mol% relative to monomer content for a target chain length of 100), well below the levels of ligand commonly used in Cu(0)‐mediated studies.…”