Abstract
The synthesis of vinyl bromobutanoate (VBr), a new vinyl acetate monomer derivative obtained by the palladium-catalyzed vinyl exchange reaction between vinyl acetate (VAc) and 4-bromobutyric acid is reported. The homopolymerization of this new monomer using the RAFT/MADIX polymerization technique leads to the formation of novel well-defined and controlled polymers containing pendent bromine functional groups able to be modified via postpolymerization modification. Furthermore, the copolymerization of vinyl bromobutanoate with 2-methylene-1,3-dioxepane (MDO) was also performed to deliver a range of novel functional degradable copolymers, poly(MDO-co-VBr). The copolymer composition was shown to be able to be tuned to vary the amount of ester repeat units in the polymer backbone, and hence determine the degradability, while maintaining a control of the final copolymers’ molar masses. The addition of functionalities via simple postpolymerization modifications such as azidation and the 1,3-dipolar cycloaddition of a PEG alkyne to an azide is also reported and proven by 1H NMR spectroscopy, FTIR spectroscopy, and SEC analyses. These studies enable the formation of a novel class of hydrophilic functional degradable copolymers using versatile radical polymerization methods.
Highlights
Initial studies by Bailey and co-workers that have been greatly expanded by numerous other groups have reported an alternative route for the synthesis of PCL-like polymers by radical ring-opening polymerization of the 7-membered cyclic ketene acetal (CKA), 2-methylene-1,3dioxepane (MDO).[27−39] This approach leads to a polymer that contains the same repeat units as conventional PCL synthesized by the ROP of CL (Scheme 1) and opens a new way of synthesizing functional
Only a few recent studies were focused on the use of reversible-deactivation radical polymerization (RDRP) techniques as a way to form controlled polymers from CKAs with targeted molecular weights as well as more complex polymer architectures.[42−48] Our group recently reported the copolymerization of MDO and vinyl acetate (VAc) using reversible addition−fragmentation chain transfer (RAFT) polymerization as a successful way to obtain welldefined and controlled functional copolymers of poly(MDO-coVAc) as well as the ability to form poly(NVP)-b-poly(MDO-coVAc) nanoparticles.[49]
After further investigation of the suitability of vinyl chloroacetate (VClAc) for the synthesis of Article degradable functional copolymers with MDO it was found that the copolymerization was limited to low monomer conversion; we propose that the poor stability of the propagating MDO radical and the subsequent chain transfer to VClAc monomer detrimentally affected the polymerization
Summary
Aliphatic polyesters represent the major class of polymers currently used in the biomedical field as a consequence of their ability to degrade in physiological conditions.[1,2] Their degradability allows them to be used in a vast range of applications from implantable and injectable drug delivery devices to tissue engineering scaffolds for bone replacement. = 35%, Mn (SEC, CHCl3) = 5.2 kDa, ĐM = 1.20, Mn (1H NMR) = 5.9 kDa. VBr and MDO monomers were dried and distilled over CaH2 before being degassed by three freeze pump thaw cycles. The polymer was purified by precipitation into cold hexane three times and dried in vacuo, Mn (1H NMR, CDCl3) = 9.12 kDa, Mn (SEC, CHCl3) = 6.8 kDa, ĐM = 1.24. A total of 16 scans from 600 to 4000 cm−1 were taken, and the spectra corrected for background absorbance
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