Metal-free strategies for the synthesis of functional and well-defined polyphosphoesters

in Macromolecules (2012), 45(11), 4476-4486

We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of ... [more ▼]

We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of organocatalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]undec-5-ene (TBD), and a bicomponent thiourea−tertiary amine catalyst. Each of these catalysts is efficient to produce linear polyphosphoesters (PPEs) from CPMs but with different sensitivity toward transesterification side reactions. The strong basicity of DBU is sufficient to activate an alcohol initiating the polymerization in the absence of any other cocatalyst. Nevertheless, side chain transfer reactions leading to branched and/or cyclic polymeric structures are observed, especially for high monomer conversion. Unlike DBU, TBD is a dual catalyst activating both the alcohol and the monomer. This dual activation allows shorter polymerization time, but SEC analyses of polyphosphates reveal bimodal molecular weight distribution due to chains coupling. Finally, a mixture of DBU and thiourea (TU) appears by far the most efficient catalyst to carry out fast and controlled polymerization while minimizing transesterification reactions, even at near-complete conversion. Compared with polymerizations carried out with Sn(Oct)2 as a metal catalyst, the control of polymerization is much better so that it is possible to prepare polyphosphoesters (PPEs) with molecular weight close to 70 000 g mol−1 and polydispersity index below 1.10. Simultaneous activation by TU of both CPMs and the alcohol group of the initiator by DBU proves to be an effective and robust ROP catalytic system to synthesize polymers with predictable molecular weight and narrow polydispersity. The chain extension experiments through the use of hydroxy end- capped PPEs as macroinitiators confirm the controlled/living nature of the DBU/TU-catalyzed ROP of CPMs and pave the way to the synthesis of block copolymers based on polyphosphates. [less ▲]

Synthesis and thermal properties of linear amphiphilic diblock copolymers of L-lactide and 2-dimethylaminoethyl methacrylate

in Macromolecules (2011), 44(13), 5209-5217

A well-defined series of nine poly(l-lactide)-b-(2-dimethylaminoethyl methacrylate) (PLLA-b-PDMAEMA) linear diblock copolymers with low polydispersity were prepared by ring-opening polymerization of LLA ... [more ▼]

A well-defined series of nine poly(l-lactide)-b-(2-dimethylaminoethyl methacrylate) (PLLA-b-PDMAEMA) linear diblock copolymers with low polydispersity were prepared by ring-opening polymerization of LLA using 4-isopropylbenzyl alcohol and tin octoate as the initiating system, conversion of the OH-terminated PLLA into Br-terminated macroinitiators (5, 13, and 19 kg/mol), followed by atom transfer radical polymerization of DMAEMA (to obtain one-half, equal, and twice the molecular weight of each PLLA block). Compositional analysis and molecular weight characterization were done using NMR, SEC–LS, TGA, polarimetry, and PDMAEMA quaternization/precipitation to test for residual PLLA homopolymer. DSC investigations indicate that low molecular weight amorphous PLLA or PDMAEMA blocks (less than or equal to ca. 5000 g/mol) are miscible in the second block. Compared to the parent PLLA homopolymers, PLLA crystallization in the block copolymers is significantly retarded, whereas the degree of crystallinity is only mildly affected and melting points are reduced only for the low molecular weight miscible blocks. [less ▲]

Effective cobalt-mediated radical coupling (CMRC) of poly(vinylacetate) and poly(N-vinylpyrrolidone) (co)polymer precursors

in Macromolecules (2010), 43(6), 2801-2813

Cobalt-mediated radical coupling (CMRC) is successfully applied to poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) precursors for the first time. The coupling process is based on addition ... [more ▼]

Cobalt-mediated radical coupling (CMRC) is successfully applied to poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) precursors for the first time. The coupling process is based on addition of isoprene onto polymer chains preformed by controlled radical polymerization with cobalt complexes (CMRP). The extents of coupling were high (>90%) to moderate (75-80%) for PVAc and PNVP precursors, respectively. Effects of the length of the polymer precursors and conditions used in the polymerization step on the coupling efficiency are discussed. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) analyses conducted on the coupling products demonstrate the preferential insertion of two isoprene units in the final polymers. The CMRC mechanistic proposal, supported by DFT calculations, is based on this microstructure feature. Finally, illustration of the macromolecular engineering potential of this technique is given by the preparation of symmetrical PVAc-b-PNVP-b-PVAc triblock copolymers starting from the corresponding PVAc-b-PNVP-[Co] diblock copolymer. [less ▲]

Joining efforts of nitroxide-mediated polymerization (NMP) and cobalt-mediated radical polymerization (CMRP) for the preparation of novel ABC triblock Copolymers

in Macromolecules (2009), 42(22), 8604-8607

Synthesis of highly functionalized poly(alkyl cyanoacrylate) nanoparticles by means of click chemistry

in Macromolecules (2008), 41(22), 8418-8428

A general methodology was proposed to prepare highly functionalized poly(alkyl cyanoacrylate) nanoparticles by means of Huisgen 1,3-dipolar cyclo-addition, the so-called click chemistry. To achieve this ... [more ▼]

A general methodology was proposed to prepare highly functionalized poly(alkyl cyanoacrylate) nanoparticles by means of Huisgen 1,3-dipolar cyclo-addition, the so-called click chemistry. To achieve this goal, different protocols were investigated to obtain azidopoly(ethylene glycol) cyanoacetate of variable molar mass, followed by a Knoevenagel condensation−Michael addition reaction with hexadecyl cyanoacetate to produce a poly[(hexadecyl cyanoacrylate)-co-azidopoly(ethylene glycol) cyanoacrylate] (P(HDCA-co-N3PEGCA)) copolymer, displaying azide functionalities at the extremity of the PEG chains. As a proof of concept, model alkynes were quantitatively coupled either to the P(HDCA-co-N3PEGCA) copolymers in homogeneous medium followed by self-assembly in aqueous solution or directly at the surface of the preformed P(HDCA-co-N3PEGCA) nanoparticles in aqueous dispersed medium, both yielding highly functionalized nanoparticles. This versatile approach, using alkyl cyanoacrylate derivatives, opened the door to ligand-functionalized and biodegradable nanoparticles with “stealth” properties for biomedical applications. [less ▲]

Synthesis of novel well-defined poly(vinyl acetate)-b-poly(acrylonitrile) and derivatized water-soluble poly(vinyl alcohol)-b-poly(acrylic acid) block copolymers by cobalt-mediated radical polymerization

in Macromolecules (2008), 41(7), 2353-2360

Poly(vinyl acetate)−Co(acac)2 macroinitiators, prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc), were used to synthesize well-defined poly(vinyl acetate)-b-poly(acrylonitrile ... [more ▼]

Poly(vinyl acetate)−Co(acac)2 macroinitiators, prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc), were used to synthesize well-defined poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) block copolymers. Different solvents and temperatures were tested for the polymerization of the acrylonitrile segment by cobalt-mediated radical polymerization (CMRP), and copolymers with low polydispersity were obtained provided that dimethylformamide was used as solvent at 0 °C. The mechanism of control was assumed to change from a degenerative chain transfer mechanism for the VAc polymerization to a reversible-termination process for the AN polymerization. The hydrolysis of the ester groups of the PVAc block and the nitrile groups of the PAN sequence of the copolymer by potassium hydroxide in an ethanol/water mixture provided the double hydrophilic and pH-responsive poly(vinyl alcohol)-b-poly(acrylic acid) block copolymer. Finally, the pH responsiveness of these copolymers was demonstrated by DLS pH titration with formation of aggregates at pH < 3. [less ▲]

Amphiphilic poly(vinyl acetate)-b-poly(N-vinylpyrrolidone) and novel double hydrophilic poly(vinyl alcohol)-b-poly(N-vinylpyrrolidone) block copolymers prepared by cobalt-mediated radical polymerization

in Macromolecules (2007), 40(20), 7111-7118

Well-defined amphiphilic block copolymers of poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) were synthesized by cobalt-mediated radical polymerization (CMRP). The NVP polymerization ... [more ▼]

Well-defined amphiphilic block copolymers of poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) were synthesized by cobalt-mediated radical polymerization (CMRP). The NVP polymerization initiated by poly(vinyl acetate) end-capped by the cobalt(II)acetylacetonate complex met the criteria of controlled polymerization, i.e., first-order kinetic in NVP, increase of the molar mass with the NVP conversion, and narrow molar mass distribution. Therefore, the length of the two blocks can be tuned by the [VAc]/[Co(acac)(2)] and the [NVP]/[PVAc] ratios for the synthesis of the macroinitiator and the polymerization of the second monomer, respectively. These amphiphilic PVAc-b-PNVP block copolymers were easily converted into the double hydrophilic PVOH-b-PNVP counterparts by selective methanolysis of the PVAc block. These two types of copolymers were prone to self-association into micelles in appropriate solvents. [less ▲]

Structure and properties of a semifluorinated diblock copolymer modified epoxy blend

in Macromolecules (2007), 40(11), 4068-4074

Novel nanostructured thermosetting materials have been prepared by modification of an epoxy resin with a semifluorinated diblock copolymer, poly(heptadecafluorodecyl acrylate)-b-poly(caprolactone), PaF-b ... [more ▼]

Novel nanostructured thermosetting materials have been prepared by modification of an epoxy resin with a semifluorinated diblock copolymer, poly(heptadecafluorodecyl acrylate)-b-poly(caprolactone), PaF-b-PCL. In a first step, the phase behavior and linear viscoelasticity of PaF-b-PCL were investigated. According to the segregation regime, no order-order transitions were detected, being the order-disorder transition temperature beyond the degradation temperature. Atomic force microscopy (AFM) images of the block copolymer after different thermal treatments revealed that self-assembly takes place into spherical nanodomains, which is consistent with the copolymer composition. This block copolymer was further used to prepare a nanostructured thermoset blend with an epoxy resin. DSC and DMA analysis reveals microphase separation of PaF block from the epoxy-rich phase after curing. The PaF block self-assembled into wormlike and spherical micelles in the thermoset system. This nanostructured blend presented unique surface properties showing high hydrophobicity (upsilon = 109 degrees) and low surface energy (17 mN/m). [less ▲]

Combination of ring-opening polymerization and "click chemistry": Toward functionalization and grafting of poly(epsilon-caprolactone)

in Macromolecules (2007), 40(4), 796-803

A straightforward strategy is proposed for the derivatization of poly(epsilon-caprolactone) (PCL). First, statistical copolymerization of alpha-chloro-epsilon-caprolactone (alpha-Cl-epsilon-CL) with ... [more ▼]

A straightforward strategy is proposed for the derivatization of poly(epsilon-caprolactone) (PCL). First, statistical copolymerization of alpha-chloro-epsilon-caprolactone (alpha-Cl-epsilon-CL) with epsilon-caprolactone (epsilon-CL) was initiated by 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP). In a second step, pendent chlorides were converted into azides by reaction with sodium azide. Finally, duly substituted terminal alkynes were reacted with pendent azides by copper-catalyzed Huisgen's 1,3-dipolar cycloaddition, thus a "click" reaction. According to this strategy, pendent hydroxyl and acrylate groups and atom transfer radical polymerization (ATRP) initiators were successfully attached to PCL. Similarly, amphiphilic graft copolymers were prepared by cycloaddition of an alkyne end-capped poly(ethylene oxide) (PEO) onto the azide substituents of the copolyester. The dependence of the grafting yield on the experimental conditions of the "click" reaction, i.e., temperature, solvent, and catalyst, was investigated. This strategy is very versatile because a large variety of aliphatic polyesters can be easily synthesized from a single precursor, easily prepared from commercially available compounds, merely by changing the alkyne involved in the Huisgen's 1,3-dipolar cycloaddition. Last but not least, PCL subsituted by azide groups does not have to be isolated after substitution of chlorides by sodium azide, and the "click" reaction can be carried out in a "one-pot" process. [less ▲]

Cobalt-mediated radical polymerization (CMRP) of vinyl acetate initiated by redox systems: Toward the scale-up of CMRP

in Macromolecules (2006), 39(24), 8263-8268

A redox initiating system was developed in order to bypass 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70) as the initiator of the cobalt-mediated radical polymerization (CMRP) of vinyl acetate ... [more ▼]

A redox initiating system was developed in order to bypass 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70) as the initiator of the cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) in the presence of cobalt(II) acetylacetonate (Co(acac)(2)). It is indeed a problem to stock up with V70 because of needed storage at -20 degrees C during transportation. This paper reports on the controlled CMRP of VAc initiated by ascorbic acid combined with either lauroyl peroxide or benzoyl peroxide at 30 degrees C. Substitution of citric acid for ascorbic acid results in faster polymerization whereas the polymerization control is maintained. All these improvements facilitate the implementation of the vinyl acetate CMRP and open the door to the scale-up of the process. [less ▲]