No abstract

It is well known that in situ polymerization of various types of monomers in the presence of commercial ultrafine silica sols in either aqueous solution, [1][2][3][4][5] alcohol/water mixtures [6] or purely alcoholic media [7] (e.g., methanol or 2-propanol) leads to the formation of polymer-silica nanocomposite particles. Such colloidal particles have various potential applications, ranging from transparent, scratch-resistant, durable architectural coatings [8] to synthetic mimics for silicate-based micrometeorites [9] to new pH-responsive Pickering emulsifiers.

No abstract

Article:Fielding, L.A., Tonnar, J. and Armes, S.P. (2011) All-acrylic film-forming colloidal polymer/silica nanocomposite particles prepared by aqueous emulsion polymerization. Langmuir, 27 (17). 11129 -11144. ISSN 0743-7463 https://doi.org/10.1021/la202066n eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract. The efficient synthesis of all-acrylic, film-forming, core-shell colloidal nanocomposite particles via in situ aqueous emulsion copolymerization of methyl methacrylate with n-butyl methacrylate in the presence of a glycerol-functionalized ultrafine silica sol using a cationic azo initiator at 60 °C is reported. It is shown that relatively monodisperse nanocomposite particles can be produced with typical mean weight-average diameters of 140 -330 nm and silica contents of up to 39 wt. %. The importance of surface functionalization of the silica sol is highlighted and it is demonstrated that systematic variation of parameters such as the initial silica sol concentration and initiator concentration affect both the mean particle diameter and the silica aggregation efficiency. The nanocomposite morphology comprises a copolymer core and a particulate silica shell, as determined by aqueous electrophoresis, x-ray photoelectron spectroscopy and electron microscopy. Moreover, it is shown that films cast from n-butyl acrylate-rich copolymer/silica nanocomposite dispersions are significantly more transparent than those prepared from the poly(styrene-co-n-butyl acrylate)/silica nanocomposite particles reported previously. In the case of the aqueous emulsion homopolymerization of methyl methacrylate in the presence of ultrafine silica, a particle formation mechanism is proposed to account for the various experimental observations made when periodically sampling such nanocomposite syntheses at intermediate comonomer conversions.

Iodide does the job: Water‐soluble, harmless, cheap, and nonhazardous NaI was used in combination with K2S2O8 instead of I2 itself to produce an uncolored living poly(butyl acrylate) latex of controlled molecular weight by a single‐step polymerization process (see scheme for one polymerization pathway). Reactivation of the polymer then yielded a block‐copolymer latex. BuA=butyl acrylate.

The use of molecular iodine I 2 in controlled radical polymerization, called reverse iodine transfer polymerization, represents a new, straightforward way to prepare controlled macromolecular architectures. Herein, miniemulsion polymerization of styrene in the presence of molecular iodine has been successfully performed. The polymerization of styrene was initiated by bis(4-tert-butylcyclohexyl) peroxydicarbonate at T ) 60 °C with dodecyl sulfate sodium salt as surfactant and hexadecane as hydrophobe, yielding a stable and uncolored latex. A certain amount of iodine reacted with water to form hydroiodic acid, leading to an upward deviation of the experimental molecular weight from the theoretical value. However, when the iodine lost by hydrolysis was regenerated by continuous addition of hydrogen peroxide in acidic conditions, it led to the expected molecular weight (e.g., M n,SEC ) 7900 g mol -1 , M w /M n ) 1.46, styrene conversion ) 78%, M n,theoretical ) 7900 g mol -1 ). Hence, the molecular weight of the polymer chains could be accurately controlled by changing the concentration of iodine. Last, a chain extension was successfully performed in seeded emulsion polymerization, proving the living character of the polymerization.

Reverse iodine transfer polymerization (RITP) represents a new straightforward way to prepare controlled macromolecular architectures and relies on the use of molecular iodine (I2) as control agent. In this work, a one-step ab initio emulsion polymerization of n-butyl acrylate in the presence of molecular iodine has been successfully performed with potassium persulfate playing the dual role of radical initiator and oxidant. The polymerization was initiated by potassium persulfate at T = 85 °C with sodium 1-hexadecanesulfonate as surfactant, yielding a stable and uncolored latex. The hydrolytically disproportionated iodine was regenerated by potassium persulfate as oxidant (also serving as radical initiator), leading to the expected targeted molecular weight (e.g., butyl acrylate conversion = 99%, M n,theoretical = 10 100 g mol-1, M n,SEC = 9800 g mol-1, M w/M n = 1.8, particle diameter d p = 83 nm with a monomodal particle size distribution). The use of potassium persulfate as both radical initiator and oxidant offers a convenient way to overcome the upward deviation of the molecular weights due to hydrolytic disproportionation of iodine, which was a limitation for the implementation of the RITP process in dispersed aqueous media. The persulfate is able to regenerate iodine, and hence the molecular weight of the polymer chains can be accurately controlled by the concentration of iodine. Furthermore, a poly(butyl acrylate)-b-poly(butyl acrylate-co-styrene) block copolymer was synthesized in seeded emulsion polymerization, proving the living character of the polymerization.

Reverse iodine transfer polymerization (RITP) is a new controlled radical polymerization technique based on the use of molecular iodine I2 as control agent. This paper aims at presenting the basics of RITP and the strategy that we have followed for the development of this process in the past three years, from the validation in homogeneous solution polymerization up to recent results in heterogeneous aqueous polymerization processes. Typical examples of RITP of butyl acrylate in emulsion and RITP of styrene in miniemulsion are discussed.