Synthesis of Highly Branched Methacrylic Copolymers: Observation of Near-Ideal Behavior using RAFT Polymerization

Abstract

We report the synthesis of model highly branched methacrylic copolymers by copolymerizing methyl methacrylate (MMA) with a disulfide-based dimethacrylate (DSDMA) branching comonomer via reversible addition-fragmentation chain transfer (RAFT) in toluene at 90°C using 1,1 0 -azobiscyclohexanecarbonitrile initiator and a cumyl dithiobenzoate (CDB) chain transfer agent. Selective cleavage of the disulfide bonds in the DSDMA branching comonomer using tributylphosphine leads to the formation of low polydispersity primary chains, as judged by gel permeation chromatography. The molecular weight distribution of these degraded chains is comparable to a RAFT-synthesized linear poly(methyl methacrylate) homopolymer prepared in the absence of any DSDMA brancher. This confirms that good control over the RAFT copolymerization is achieved under branching conditions and that the polydisperse highly branched chains simply comprise randomly coupled near-monodisperse primary chains, as expected. Moreover, HPLC analysis of the copolymerizing solution confirms that the consumption of DSDMA comonomer is close to that expected for a statistical copolymerization. The CDB efficiency is estimated to be 90% by GPC and 1 H NMR spectroscopy. Taking this into account and allowing for the incomplete comonomer conversions (typically 96-97%), our systematic variation of the proportion of DSDMA per primary chain indicates that this RAFT formulation conforms closely to classical Flory-Stockmayer theory. This near-ideal behavior is in marked contrast with earlier literature reports of strongly nonideal behavior, presumably because of significant levels of intramolecular cyclization. Our hypothesis is that this unwanted side reaction, which consumes the DSDMA brancher without leading to intermolecular branching, is suppressed in the present study because of the relatively high comonomer concentration (50% w/w) used in our RAFT syntheses.

Disulfide-Functionalized Diblock Copolymer Worm Gels

“…Although such high conversions are generally not advisable for RAFT macro-CTA syntheses, in this case it is essential because copolymerization of the second (pendent) methacrylate group on the DSDMA comonomer only occurs at high conversions. 32 A number-average molecular weight (M n ) of 14,000 g mol -1 and a reasonably low M w /M n of 1.26 was recorded for the G 54 -D 0.50 macro-CTA, indicating good RAFT control. A small high molecular weight shoulder was observed in the chromatogram, which was ascribed to a low level of branching for this statistical copolymer.…”

“…The first route involves statistical copolymerization of a bifunctional disulfide-based methacrylic monomer (DSDMA) with GMA during the macro-CTA synthesis. [31][32][33] Recently, we reported that, when copolymerized with a monofunctional methacrylic monomer in sufficiently dilute solution, DSDMA undergoes intramolecular cyclization rather than intermolecular branching. 29 Subsequent disulfide cleavage produces two 2-thioethyl methacrylate residues on the polymer backbone.…”

Facile one-spot synthesis of highly branched polycaprolactone

“…Hence, in spite of the fact that the synthetic strategies applied deliver poorer control over the molecular structure of these hyperbranched polymers when compared to "true" dendrimers, the economic and practical advantages from adopting these strategies are generally gained without significant negative impact upon the desired beneficial/differentiated material properties. 1,[3][4][5][6][7][8][9][10][11][12] In addition, these more affordable and accessible approaches have led to significant industrial interest targeted towards using these materials in larger scale applications such as imaging agents, reactive resins and industrial coatings. 1,[13][14][15] Compared to linear polymers, highly/hyper branched polymers often exhibit improved solubility, lower (melt) viscosity, higher density of functional-groups and have a more compact/globular structure.…”

“…solventless), controlled ROP mechanism. [3][4][9][10][11][12][31][32][33][34][35][36][37][38][39][40] The 'Strathclyde Method' was a pivotal early example of such a branching synthetic strategy and centred on the standard free radical (SFR) copolymerisation of monofunctional and difunctional vinyl monomers. [9][10][11][12] One of the main conclusions drawn from this work was that gelation, i.e.…”

“…[3][4][31][32][33][34][35][36][37][38][39][40] To further probe this effect, this report focussed on investigating the impact that controlled characteristics has upon the outcome of the Strathclyde strategy for the synthesis of highly branched PCL when applied to bulk conditions.…”