Unimolecular Combination of an Atom Transfer Radical Polymerization Initiator and a Lactone Monomer as a Route to New Graft Copolymers

Abstract

The synthesis, polymerization, and copolymerization of a new cyclic ester, γ-(2-bromo-2-methyl propionyl)--caprolactone (3), containing a pendent-activated alkyl bromide functional group is described. This new compound serves as both a monomer for "living" ring-opening polymerization (ROP) as well as an initiator for the controlled atom transfer radical polymerization (ATRP). Three distinctive routes to poly( -caprolactone)-graft-poly(methyl methacrylate) copolymers were surveyed by either sequential or concurrent living polymerization procedures. The first approach involves the ROP of -caprolactone with various compositions of 3, followed by the polymerization of methyl methacrylate via ATRP from the activated alkyl bromide sites along the polyester backbone. Alternatively, R-lactone functional methyl methacrylate macromonomers were prepared by ATRP of methyl methacrylate initiated from 3. The macromonomers were copolymerized with -caprolactone via ROP to form the target graft copolymers. Finally, the graft copolymers could be prepared in a simple one-step approach by the concurrent polymerization of -caprolactone, 3, and methyl methacrylate together with the appropriate initiator for the ROP and the catalyst for the ATRP. The new monomer enabled new graft copolymers having an aliphatic polyester backbone with poly(methyl methacrylate) grafts of controlled molecular weight and narrow polydispersities (∼1.3). IntroductionThe renewed interest in the macromolecular engineering of poly(lactones) and related polyesters stems from the discovery that many organometallic compounds are effective initiators/catalysts for controlled ring-opening polymerization (ROP), 1 allowing the preparation of functional oligomers, random and block copolymers, and polymers with unique topology or architectural control. 1-4 For instance, asymmetric functionality can be introduced in a controlled way through the use of aluminum alkoxide initiators bearing functional alkoxide groups [Et 2 Al(ORX), where X is any functional group]. After hydrolytic deactivation of the active aluminum alkoxide growing species, R-X-ω-hydroxy poly-(lactone) telechelic chains are quantitatively and selectively recovered. The coupling of the telechelic macromonomers through block copolymerization provides a precise methodology to controlled macromolecular architecture. 2 Alternatively, dual "living" controlled polymerizations from a single initiating molecule without intermediate activation or transformation steps has been demon-

Synthesis of new substituted lactones by "click" chemistry

“…Hedrick et al synthesized an asymmetric inimer, 7-oxooxepan-4-yl 2-bromo-2-methylpropanoate 19, prone to ring-opening polymerization and to initiation of atom transfer radical polymerization (ATRP) (Scheme 6). 21 Initiation of ATRP by this inimer yielded a macromonomer that was ring-opening polymerized with formation of the parent graft copolymer. The sequence of reactions was reversed.…”

“…2 Nevertheless, the lack of pendant functional groups along the chains is a severe limitation for many applications. In order to tackle this drawback, the usual strategy relies on the ring-opening polymerization of lactones, duly substituted by a functional group 3,4 , e.g., pendant unsaturation, [5][6][7] alkyne, 8 protected carboxylic acid, 9 alcohol, 10,11 diol, 12 protected alcohol, 9,13-15 protected diol, 16 ketal, 17,18 ketone 19 and halogen 20,21 . Nevertheless, the synthesis of a new lactone requires a specific strategy.…”

Organocatalyzed ring-opening copolymerization of α-bromo-γ-butyrolactone with ε-caprolactone for the synthesis of functional aliphatic polyesters – pre-polymers for graft copolymerization

“…Between these two methods, copolymerization with functional monomers provides a high degree of functionality, together with a high degree of control. Therefore, much effort has been conducted, as early as 1999, εCL with a halogenated motif at the γ-position was synthesized [22]. Subsequently, α-, γ- and ω-substituted εCL were synthesized and used as functional monomers for lipase-catalyzed ring-opening polymerization [23].…”

Synthesis, characterization, and fluorescence of end‐functionalized polystyrene initiated by 4‐chloromethyl benzoic acid and ethyl 4‐chloromethyl benzenecarboxylate via ATRP

“…[1][2][3][4][5] In an ATRP, initiator always plays an important role to initiate the polymerization and determine the a-end of polymer. [6][7][8][9][10][11] Nowadays, various functionalized polymers with kinds of functional group at a-end have been obtained by using different initiators. For example, pyrene, anthracene end-functionalized macromonomers can be obtained by using initiators containing pyrene, anthracene group.…”