1,4-Polybutadienes with Pendant Hydroxyl Functionalities by ROMP: Synthetic and Mechanistic Insights

The reactivity of <i>cis</i>-3,4-bis­(hydroxymethyl)­cyclobutene derivatives bearing free and protected hydroxyl groups during ring-opening metathesis polymerization (ROMP) was investigated using ruthenium-based initiators. It was found that the ROMP of <i>cis</i>-4-benzyloxymethyl-3-hydroxymethylcyclobutene (<b>1</b>) using highly reactive initiators containing <i>N</i>-heterocyclic carbenes as nonlabile ligands leads to well-defined polymers while <i>cis</i>-3,4-bis­(hydroxymethyl)­cyclobutene (<b>2</b>) was reluctant to polymerize under the same conditions. Kinetic studies were performed to assess a number of critical reaction parameters: initiator structure, solvent, and temperature. The results demonstrate that Grubbs’ second- and third-generation catalysts are the best initiators to prepare well-defined 1,4-polybutadienes containing simultaneously free and protected hydroxyl side groups with predictable molecular weights (up to 40 000 g mol^–1) and narrow molecular weight distributions. Besides, low values of <i>k</i>_p/<i>k</i>_i (the ratio of the rate constant of propagation to the rate constant of initiation) were found for the ROMP of monomer <b>1</b> with Grubbs’ second-generation catalyst in chloroform or THF as the solvent, demonstrating a living process. The so-obtained polymers having hydroxyl side groups are an ideal platform to prepare original well-defined graft copolymers through the grafting-from strategy

An Orthogonal Modular Approach to Macromonomers Using Clickable Cyclobutenyl Derivatives and RAFT Polymerization

A series of cyclobutene-based macromonomers derived from monomethyl ether poly­(ethylene oxide) (PEO), poly­(ethyl acrylate) (PEA), poly­(<i>N</i>-isopropylacrylamide) (PNIPAM), and PEO-<i>b</i>-PNIPAM were synthesized by “click” copper-catalyzed azide–alkyne cycloaddition (CuAAC) and reversible addition–fragmentation chain transfer (RAFT) polymerization. First, original di- and trifunctional cyclobutene precursors with azido, alkyne and/or chain transfer agent were successfully obtained and fully characterized. Azido- and alkyne-functionalized cyclobutenes were then conjugated with modified PEO bearing azido or alkyne groups, resulting in cyclobutene-based PEOs in quantitative conversions as ascertained by NMR spectroscopy and MALDI–TOF mass spectrometry. The new chain transfer agent-terminated cyclobutene was used to mediate the RAFT polymerization of ethyl acrylate and <i>N</i>-isopropylacrylamide. Well-defined polymers with controlled molecular weights (<i>M</i>_n = 3700–11 500 g·mol^–1) and narrow molecular weight distributions (PDI = 1.06–1.14) were thus obtained that retain the cyclobutene functionality, demonstrating the orthogonality of the RAFT process toward the cyclobutenyl insaturation. Combination of CuACC and RAFT polymerization was used to afford PEO-<i>b</i>-PNIPAM block copolymer functionalized by a cyclobutene end-group

High Molar Mass Poly(1,4-butadiene)-<i>graft</i>-poly(ε-caprolactone) Copolymers by ROMP: Synthesis via the Grafting-From Route and Self-Assembling Properties

Well-defined high molar mass poly­(1,4-butadiene)-<i>g</i>-poly­(ε-caprolactone) (PBu-<i>g</i>-PCL) graft copolymers were prepared through the grafting-from route by the combination of ring-opening metathesis polymerization (ROMP) and organocatalyzed ring-opening polymerization (ROP). The synthesis route relies on the ROMP of <i>cis</i>-4-benzyl­oxymethyl-3-hydroxy­methyl­cyclobutene initiated by ruthenium-based Grubbs’ catalysts followed by organocatalyzed ROP of ε-caprolactone initiated by the hydroxyl side groups of the backbone using 1,5,7-triaza­bicyclo[4.4.0]­dec-5-ene (TBD) as the catalyst. The reported strategy provides PBu-<i>g</i>-PCL having a strictly poly­(1,4-butadiene) backbone with the highest molar mass reported up to now (<i>M</i>_n > 10⁶ g mol^–1). Self-assembling properties of the resulting PBu-<i>g</i>-PCL graft copolymer were investigated using small-angle X-ray scattering (SAXS) in toluene solution and in the solid state

One-Step Synthesis of Azlactone-Functionalized SG1-Based Alkoxyamine for Nitroxide-Mediated Polymerization and Bioconjugation

The one-step synthesis of azlactone-functionalized SG1-based alkoxyamine (AzSG1) for the design of functional polymers by nitroxide-mediated polymerization (NMP) is reported. At 347.7 K, its dissociation rate constant, <i>k</i>_d, was determined to be 2.72 × 10^–4 s^–1, leading to an activation energy, <i>E</i>_a, of 119.5 kJ mol^–1, which represents the lowest value ever reported for a secondary SG1-based alkoxyamine without any activation by an external stimulus. This was ascribed to enhanced stabilization of the released radical compared to other secondary alkyl radicals. The AzSG1 alkoxyamine was successfully used for the NMP for styrene, <i>n</i>-butyl acrylate, and methyl methacrylate with the addition of a small amount of acrylonitrile as a comonomer, without the need for free SG1. In all cases, first-order kinetics, good control with low dispersities (<i><i><i>Đ</i></i></i> = 1.2–1.4), and high living chain fractions (LF ∼90%) were obtained. As a proof of concept, the conjugation of azlactone-functionalized polymers to benzylamine and lysozyme was successfully demonstrated. This work may be of high interest for conjugation as the azlactone functionality is also known to react with other nucleophiles such as alcohols or thiols

ROMP-based Glycopolymers with High Affinity for Mannose-Binding Lectins

Well-defined, highly reactive poly(norbornenyl azlactone)s of controlled length (number-average degree of polymerization DPn̅ = 10 to 1,000) were made by ring-opening metathesis polymerization (ROMP) of pure exo-norbornenyl azlactone. These were converted into glycopolymers using a facile postpolymerization modification (PPM) strategy based on click aminolysis of azlactone side groups by amino-functionalized glycosides. Pegylated mannoside, heptyl-mannoside, and pegylated glucoside were used in the PPM. Binding inhibition of the resulting glycopolymers was evaluated against a lectin panel (Bc2L-A, FimH, langerin, DC-SIGN, ConA). Inhibition profiles depended on the sugars and the degrees of polymerization. Glycopolymers from pegylated-mannoside-functionalized polynorbornene, with DPn̅ = 100, showed strong binding inhibition, with subnanomolar range inhibitory concentrations (IC50s). Polymers surpassed the inhibitory potential of their monovalent analogues by four to five orders of magnitude thanks to a multivalent (synergistic) effect. Sugar-functionalized poly(norbornenyl azlactone)s are therefore promising tools to study multivalent carbohydrate–lectin interactions and for applications against lectin-promoted bacterial/viral binding to host cells

New Cross-Linkable Polymers with Huisgen Reaction Incorporating High μβ Chromophores for Second-Order Nonlinear Optical Applications

We report herein the synthesis, the functionalization, and the successful radical polymerization of very nonlinear optical (NLO) active push–pull polyene chromophores (CPO). Second, the thermal Huisgen cyclo-addition cross-linking reaction was implemented, and it proved to be fully compatible with a polyene-based push–pull chromophore. Toward this goal, PMMA-<i>co</i>-CPO-3 and two cross-linkable polymers (PCC1-CPO-3 and PCC2-CPO-3) were first prepared and characterized by a modified Teng and Man technique performed in transmission. These first series of polymers were not compatible with the applied poling conditions because an irreversible film degradation was systematically observed at a temperature significantly lower than the cross-linking temperature. Consequently, a second series of polymers was prepared, in which the cross-linking temperature was decreased by functionalizing acetylenic moieties with ester electron withdrawing groups, which decrease the activation energy of the thermal Huisgen cyclo-addition. These new polymers were stable until the cross-linking reaction, and they exhibit bulk electro-optic coefficients (<i>r</i>₃₃) until 41 pm/V at 1.5 μm. Furthermore, it was shown that the Huisgen cross-linking reaction is compatible with such push–pull polyene-based chromophores, and it systematically enhances the stability of the electro-optic activity because chromophore orientation was maintained up to 96 °C against 70 °C for the same uncross-linked polymer