Degradable Copolymer Nanoparticles from Radical Ring-Opening Copolymerization between Cyclic Ketene Acetals and Vinyl Ethers

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Using apparent molecular weight from SEC in controlled /living polymerization and kinetics of polymerization

Apparent molecular weights from size exclusion chromatography, that is molecular weights relative to standards of a nature different to that of the polymer sample being studied, are frequently used. We use calculations corresponding to realistic cases to provide guidelines for situations when, and to what extent, apparent molecular weights (MWs) can be meaningful. In controlled polymerization, we show how, without due care, use of apparent MW, could lead to the incorrect conclusion that the reaction was not controlled, whereas the true MWs would be close to theoretical values. We show here that the quality of the eluent as a solvent for the standard and the polymer sample is a good indication of the accuracy and the significance of the apparent polydispersity index. Accurate Mark–Houwink–Sakurada parameters are of limited availability, but the data about solvent quality available in handbooks or available from static light scattering measurements. Apparent Mn is of no use in controlled polymerization if simple simulations as performed in this work do not validate their use. The determination of transfer constants by the Mayo plot can be performed using apparent Mn without introducing any significant error, contrary to apparent weight-average molecular weight Mw or apparent ln number distribution

Macromol. Rapid Commun. 13/2015.

International audienceFront Cover: Nitroxide-mediated polymerization (NMP) of methacrylic esters is still a great challenge in the field of polymer science. This Feature Article will first discuss the reasons why this class of monomers-the most representative one being methyl methacrylate-is usually poorly controlled by NMP, and will then present the most successful strategies to control their polymerization. NMP-derived materials comprising uncontrolled methacrylate segments will also be covered. Further details can be found in the article by E. Guegain, Y. Guillaneuf, and J. Nicolas* on page 1227

Investigation of the End Group Fidelity at High Conversion during Nitroxide-Mediated Acrylate Polymerizations

International audienceThe impact of formation of midchain radicals?and more specifically the follow up reactions of ?-scission and macromonomer addition to propagating macroradicals stemming from this process?on the nitroxide-mediated polymerization of acrylates have been studied via kinetic modeling with the software package Predici on the example of butyl acrylate polymerization at 120 °C. Only small influences of the midchain radical formation on the livingness of the process is observed, however, large effects must be envisaged by the (reverse) scission reaction at high monomer-to-polymer conversions. A significant loss of livingness, depending on the temperature, monomer and initiator concentration must be expected at elevated stages of polymerizations. For a polymerization at 120 °C and a target chain length of 100, less than 75% livingness of the polymer product can be expected at 80% conversion. From this point of polymerization on, significant broadening of the overall polymer product is predicted in accordance to literature data and eventually the chain-length?conversion relation is lost at the end of reaction

Simulation of radical polymerization of methyl methacrylate at room temperature using a tertiary amine/BPO initiating system

International audienceThe decomposition kinetics of the initiation reaction between benzoyl peroxide and a tertiary amine, either dimethyl-p-toluidine or dihydroxyethyl-p-toluidine, was studied by infrared spectroscopy and an Arrhenius plot was established. Based on these results, a model was developed for the polymerization of methyl methacrylate at room temperature. The model used both free volume and empirical models for propagation, termination and several side reactions. The model described the conversion for a very broad range of reaction conditions and the results were in good agreement with the experimental data. This study showed significant differences between dimethyl-p-toluidine and dihydroxyethyl-p-toluidine with respect to the gel time and the molar mass of poly(methyl methacrylate)

New experimental procedure to determine the recombination rate constants between Nitroxides and Macroradicals

A new experimental procedure for the determination of the recombination rate constant, kc, between a propagating macroradical and a nitroxide is proposed. It is based on a single pulse−pulsed lamp polymerization where the main chain growth breaking event between two consecutive pulses is the recombination of the macroradicals with the nitroxide. The recovered polymer is analyzed by size exclusion chromatography, and the parameters of the molar mass distribution are used to determine kc, in a similar way as that traditionally applied in the determination of the chain transfer rate constants, i.e., the Mayo method using the number- or weight-average degrees of polymerization and the full chain length distribution method. We named the technique RNR−PLP−SEC for radical nitroxide recombination−pulsed lamp polymerization−size exclusion chromatography. The particular polystyryl macroradical−SG1 nitroxide system was tested to validate it. To apply a consistency check, the experimental parameters have been varied according to the recommendations made by the IUPAC for the measurements of the propagation rate constants via PLP. The recombination rate constant kc was measured over a temperature range where no cleavage of the formed alkoxyamine might occur. At 40 °C kc = 2.6 × 105 L mol-1 s-1, and the value increased from 1.1 × 105 L mol-1 s-1 at 15 °C to 4.0 × 105 L mol-1 s-1 at 82 °C. The extrapolation at 120 °C led to 5.3 × 105 L mol-1 s-1, in good agreement with the values already reported in the literature

Radical Ring-Opening Polymerization: Scope, Limitations, and Application to (Bio)Degradable Materials

International audienceCyclic monomers bearing either vinyl or exomethylene groups have the ability to be polymerized through a radical pathway via a ring-opening mechanism (addition fragmentation process), leading to the introduction of functionalities in the polymer backbone. Radical ring-opening polymerization (rROP) combines the advantages of both ring-opening polymerization and radical polymerization, that is the preparation of polymers bearing heteroatoms in the backbone but with the ease and robustness of a radical process. This current review presents a comprehensive description of rROP by detailing: (0 the various monomers that polymerize through rROP; (ii) the main parameters that govern the rROP mechanism; (iii) the copolymerization by conventional or controlled/living radical polymerization between rROP monomers and traditional vinyl monomers to obtain copolymers with advanced properties; (iv) the different applications (low shrinkage materials and pieparation of (bio)degradable materials) of rROP monomer-containing materials, and (v) the main alternatives to rROP to induce degradability to materials obtained by a radical polymerization

Novel polymer synthesis methodologies using combinations of thermally - and photochemically-induced nitroxide mediated polymerization

The combination of thermally- and photochemically-induced polymerization using light sensitive alkoxyamines was investigated. The thermally driven polymerizations were performed via the cleavage of the alkoxyamine functionality, whereas the photochemically-induced polymerizations were carried out either by nitroxide mediated photo-polymerization (NMP2) or by a classical type II mechanism, depending on the structure of the light-sensitive alkoxyamine employed. Once the potential of the various structures as initiators of thermally- and photo-induced polymerizations was established, their use in combination for block copolymer syntheses was investigated. With each alkoxyamine investigated, block copolymers were successfully obtained and the system was applied to the post-modification of polymer coatings for application in patterning and photografting