Self-Catalyzed Hydrolysis of Nitrile-Containing RAFT Chain-Transfer Agent and Its Impact upon Polymerization Control of Methacrylic Monomers

Self-catalyzed hydrolysis upon storage of the common RAFT chain-transfer agent (CTA) 4-cyano-4-[(thiothiopropyl)sulfanyl] pentanoic acid (CTPPA) is confirmed, where the nitrile group is transformed into an amide by catalysis from the adjacent carboxylic acid moiety. The amide-CTA (APP) is found to poorly control molecular weight evolution during polymerization of two methacrylates, methyl methacrylate (MMA) and N,N-(dimethylamino)ethyl methacrylate (DMAEMA), likely due to poor reinitiation speed in the pre-equilibrium. However, when attached to a macromolecule, the impact of this amide moiety becomes insignificant and chain extension proceeds as expected with CTPPA. In light of CTPPA and similarly hydrolyzable CTAs being extensively employed for aqueous polymerizations of methacrylates, these findings highlight the importance of CTA purity when performing RAFT polymerizations.


Experimental Section
Materials and Methods Table S1.Overview Polymerizations

Supporting Data
Figure S1: NMR characterization of CTPPA. Figure S2: NMR characterization of APP. Figure S3: FTIR of CTPPA and APP. Figure S4: Degradation of CTPPA to APP upon storage.
The red oil (5.94 g, 1 eq, 19.68 mmol) was dissolved in 50 ml ethyl acetate.6.62 g ACVA (1.2 eq, 23.62 mmol) was added and the mixture was degassed by Argon bubbling, and then refluxed at 95 o C overnight under inert atmosphere.The solvent was removed and the crude was purified by silica gel column chromatography with eluent heptane:ethyl acetate (1:2).49 % yield of red-orange oil.

Chain extension of PDMAEMA
A macroCTA was synthesized with CTPPA or APP according to the protocol above, and reacted for 19 hours (conversion ~90 %).The polymer was precipitated in cold heptane, decanted and dried under reduced pressure to a brittle solid.

Characterization
NMR spectra were recorded using a Bruker Advance 400 spectrometer equipped with a 5 mm broadband multinuclear (PABBO) probe at 25 o C. Data analysis was preformed using MestReNova software. 1H-NMR was used to calculate monomer conversion by comparing intensity of the alkene signals of the monomers (5.5 -6 ppm) to methyl signals from the polymer (0.8-1.2 ppm).
FTIR spectra were recorded with a Perkin-Elmer Spectrum 2000 FTIR equipped with a MKII Golden Gate, single reflection ATR crystal with a MKII heated diamond 45 o ATR top plate (from Specac Ltd, London, UK).
Size exclusion chromatography (SEC) was performed on a TOSOH EcoSEC HLC-8320GPC system equipped with EcoSEC RI detector and three columns PSS PFG 5 μm; Microguard, 100 Å, and 300 Å; MW resolving range: 100-300 000 g mol−1) from PSS GmbH, using DMF as solvent with 0.01 M LiBr as the mobile phase at 50 °C with a flow rate of 0.2 mL min−1.PMMA standards between 700 -2 000 000 g mol -1 were used for the calibration.

Figure S5 :
Conversion kinetics of polymerizations of MMA in THF.

Figure S6 :
Elugrams showing chain growth in polymerizations of MMA in THF.FigureS7: Conversion kinetics of polymerizations of DMAEMA in dioxane.

Figure S8 :
Elugrams showing chain growth in polymerizations of DMAEMA in dioxane.

Figure S9 :
Elugrams showing chain growth in polymerizations of DMAEMA in dioxane.
[M]/[CTA] = 100, [CTA]/[I] = 10, [M] = 2.5 mol L -1 .The vial was closed, cooled to 0 o C, degassed with Argon, and then warmed to room temperature 30 min.Reactions were performed in 70 o C oil bath.Kinetic aliquots were taken during the course of the reaction for NMR (100 ul sample in 600 ul CDCl 3 ) and SEC (100 ul sample in 1 ml eluent).Polymers used for chain extension were precipitated once in cold heptane.

Figure S3 :
Figure S3: FTIR of CTPPA (upper) and APP (lower).In APP spectrum we clearly see the disappearance of the nitrile signal, and appearance of amide peaks at 3500-3300 and distinct double signal 1635-1575 cm -1 .