The three-dimensional structures of hyperbranched materials have made them attractive in many important applications. However, the preparation of hyperbranched materials remains challenging. The hyperbranched materials from addition polymerization have gained attention, but are still confined to only a low level of branching and often low yield. Moreover, the complication of synthesis only allows a few specialized monomers and inimers to be used. Here we report a 'Vinyl Oligomer Combination' strategy; a versatile approach that overcomes these difficulties and allows facile synthesis of highly branched polymeric materials from readily available multi-vinyl monomers, which have long been considered as formidable starting materials in addition polymerization. We report the alteration of the growth manner of polymerization by controlling the kinetic chain length, together with the manipulation of chain growth conditions, to achieve veritable hyperbranched materials, which possess nearly 70% branch ratios as well as numerous vinyl functional groups.

Branched water-soluble copolymers were obtained by direct radical crosslinking copolymerisation of acrylic acid or acrylamide and N,N'-methylenebisacrylamide at high solid content in the presence of an O-ethylxanthate as a reversible chain transfer agent.

A new type of photocatalyzed Cu-based atom transfer radical polymerization (ATRP) is described, involving directly the light absorption of the activator form of the copper complex Cu(I). The selected catalyst was bis(1,10-phenanthroline)copper(I), Cu(phen) 2 + , due to its intense absorption in the visible domain, which permitted to use very soft irradiation conditions, consisting of a simple household blue LED at 0.9 W. An excellent control over the polymerization of methyl methacrylate (MMA) in dimethylformamide (DMF) was observed under irradiation in these conditions, using ethyl α-bromophenylacetate (EBPA) as the initiator, with polydispersity indexes (PDI) as low as 1.10 while using low catalyst content (80 ppm). The proposed mechanism implies first the formation under irradiation of the excited state of the activator form of the complex Cu(I)*. It can then rapidly undergo the oxidative quenching of the alkyl bromide, which results in its conversion into the deactivator form of the complex Cu(II)−Br along with the generation of a propagating radical. The setting up of the ATRP equilibrium ensues. Additionally, it was possible to complete the catalysis mechanism by adding triethylamine (TEA), which permitted a faster polymerization, thanks to a faster regeneration of the activator Cu(I). An excellent control over the polymerization was also observed in the presence of TEA, with PDI as low as 1.06. The addition of TEA allowed also to use a catalyst loading as low as 20 ppm, while maintaining a good controllability.

International audienceA new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiations (lights ranging from 457 to 532 nm). A ring-opening polymerization (ROP) of an epoxy monomer was easily promoted through the interaction between nIr and an iodonium salt (Iod) upon light. The addition of N-vinylcarbazole (NVK) enhances the performance. In radical polymerization, nIr can be efficient in combination with phenacyl bromide (PBr) and optionally an amine: these photoinitiating systems work according to an original oxidative cycle and a regeneration of nIr is observed. A control of the methyl methacrylate polymerization (conducted under a 462 nm light) with 1.2–1.6 polydispersity indexes was displayed. Surface modifications by direct laser write was also easily carried out for the first time through surface re-initiation experiments, i.e. the dormant species being reactivated by light in the presence of nIr; the polymer surfaces were analyzed by XPS. The chemical mechanisms were examined through laser flash photolysis, NMR, ESR and size exclusion chromatography experiment

Poly(vinyl acetate) (PVAc) nanogels are synthesized by a radical crosslinking copolymerization (RCC) in solution of vinyl acetate and divinyl adipate (DVA) or 2,4,6‐tris(allyloxy)‐1,3,5‐triazine (TAT) as the crosslinker, in the presence of a xanthate as a reversible chain transfer agent. Higher concentrations of crosslinker and lower concentrations of xanthate produce PVAc nanogels of higher molar masses, for a given concentration of xanthate and for a fixed concentration of crosslinker, respectively. The xanthate end‐groups allow for the synthesis of ‘second generation’ nanogels through a subsequent RCC from precursors. The chemical cleavage of the crosslinks yields individual poly(vinyl alcohol) chains, which attests that the length of the constitutive chains is controlled by the xanthate.magnified image

A new photocatalyzed atom transfer radical polymerization (ATRP) procedure starting directly from a copper­(II) bromine/phenanthroline (phen) mixture in the presence of triethylamine as a reducing agent is described. Under the irradiation of a compact blue LED lamp, the polymerization of methyl methacrylate (MMA) conducted to PMMAs with narrow molecular weights distributions (M w/M n ∼ 1.10). The good chain end fidelity of the products was validated in subsequent chain-extension experiments, using them as macroinitiators, either by conventional thermal ATRP or by photocatalyzed ATRP. The efficient reinitiation under light irradiation was also evidenced by a “light ON/OFF” experiment. The respective effects of several parameters on the polymerization kinetics were studied, including light intensity, the nature of the solvent, the molar ratio of the ligand, and the nature of the counterion. Besides the essential generation of the excited species [Cu­(phen)2]+*, which will undergo an oxidative quenching as the key step of this photocatalytic cycle, supplementary investigations by UV–vis spectroscopy revealed an additional role of light, which also favored the regeneration of the activator. This complementary contribution may consist in a light-triggered exchange of ligands involving minor Cu­(II) species, which absorb light in the blue wavelengths domain and are in equilibrium with [Cu­(phen)2Br]+ as the predominant Cu­(II) complex. Interestingly, this photocatalyzed ATRP mechanism exhibited a good tolerance to oxygen and inhibitors, as demonstrated by the efficient synthesis of PMMAs with relatively narrow molecular weights distributions (M w/M n < 1.30) in the presence of air and/or 4-methoxyphenol (MEHQ).

The mainstay of this description is a modeling of ''controlled/living'' chain growth crosslinking copolymerization (C/L CC) that is based on a simple equivalent kinetic scheme, resulting from assumptions consistent with an ideal C/L behavior. Analytical expressions of the double bond concentration according to reaction parameters are derived from the corresponding set of differential equations, and consideration of the respective values of the rate constants enables one to forecast the morphology of the branched polymers derived by C/L CC. The kinetic scheme is then enriched with a necessary distinction between intramolecular (cyclization) and intermolecular crosslinking which contribute to the formation of three-dimensional structures and to the increase of molar masses, respectively. This consideration leads to a key-equation governing C/L CC, which can be exploited in two ways. Its implicit integration coupled with a semi-empiric methodology gives an easy access to all the characteristic magnitudes of the products at complete conversion of the double bonds. An alternative approach implying a supplementary modeling of local concentration effects enables its numerical resolution. Modeled trends and predicted characteristic values are then successfully compared with experimental data which relate to xanthate-mediated radical CC. Specific reasons of dispersity related to the mechanism of CC are also discussed. Figure 4. Influence of the fraction of intermolecular/intramolecular crosslinks on the structure of the compounds for a ratio [crosslinks]/[constitutive chains] ¼ 1; both intra-and intermolecular crosslinkings are needed to form macromolecules having a network-like structure. 76 5316 POLY ET AL.

International audienceThis article reports on the presumably first use of iron complexes (FeC) as potential photocatalysts for controlled radical photopolymerization reactions (CRP2). Three compounds were designed and investigated. Good linear evolutions of the molecular weight (Mn) with the conversion were observed. A comparison was provided with a reference iridium (III) complex [Ir(ppy)3 where ppy stands for 2-phenylpyridine]. The on/off photopolymerization experiments highlight the presence of dormant species and a re-initiation on demand upon irradiation. This unique re-initiation property was used for the modification of surfaces (hydrophilic/hydrophobic properties) and surface patterning as well as the synthesis of a block co-polymer (PMMA-b-PBA). A comparative analysis of the behavior of these iron complexes in thermally and photochemically activated polymerization was provided. The chemical mechanisms were studied by steady state photolysis, laser flash photolysis, cyclic voltammetry, luminescence quenching, and electron spin resonance experiments. A catalytic cycle was proposed with two steps: (i) the oxidation of the FeC excited state by an alkyl halide and (ii) the reduction by the oxidized form (FeC°+) by an amine or the macroradicals leading to the regeneration of the catalyst