12 research outputs found
Block and multi block copolymers via SF-RAFT : utilising macromonomers as chain transfer agents
The objective of this work is to investigate and expand the use of methacrylic macromonomers as chain transfer agents. Although chain transfer activity had been demonstrated previously, the limits of the technique have not been fully explored. As such, a new approach for the efficient synthesis of methacrylic polymers in emulsion is presented, aiming at fully exploiting the vinyl end-group of the CCTP-derived macromonomers and consequently their chain transfer activity. Moreover, the preparation of higher MWt copolymers as well as more complex structures (e.g. triblocks etc) by this method will be investigated as research so far has only been focusing on certain degrees of polymerisation, mainly resulting in diblock copolymers of relatively low MWt. In addition, macromonomers based on diverse methacrylic monomers will be employed, as most studies to date have focused on a narrow monomer pool. In parallel, another aspect of radical polymerisation in the presence of macromonomers is the livingness of the system. Even though living-like characteristics have been observed, previous studies did not reach definitive conclusions, according to the generally set criteria of livingness.
At the same time, the use of macromonomers as precursors for comb-like polymers will be described. Despite the technique being known and well-reported, the aim is to successfully employ solvents that satisfy the needs of automotive applications, such as mineral oil. In detail, both the macromonomer synthesis and the subsequent comb formation will be attempted in this solvent. A similar approach has not been reported so far. It needs to be noted, that this part is an ongoing work with the Lubrizol Corporation and as such it only demonstrates a few initial steps towards developing materials with interesting properties and applications
Copper mediated reversible deactivation radical polymerization in aqueous media
Key advances within the past 10 years have transformed copper mediated radical polymerization from a technique which was not very tolerant to protic media into a range of closely related processes capable of control over the polymerization of a wide range of monomers in pure water at ppm catalyst loadings; yielding water soluble macromolecules of desired molecular weight, architecture and chemical functionality, with applications ranging from drug delivery to oil field recovery. In this review we highlight and critically evaluate the synthetic methods that have been developed to control radical polymerization in water using copper complexes, identify future areas of interest and challenges still to be overcome
Copper mediated polymerization without external deoxygenation or oxygen scavengers
Overcoming the challenge of rigorous deoxygenation in copper mediated controlled radical polymerization processes (e.g. ATRP), we report a simple Cu(0)‐RDRP system in the absence of external additives (e.g. reducing agents, enzymes etc.). By simply adjusting the headspace of the reaction vessel, a wide range of monomers, namely acrylates, methacrylates, acrylamides and styrene, can be polymerized in a controlled manner yielding polymers with low dispersities, near‐quantitative conversions and high end group fidelity. Significantly, this approach is scalable (~ 125 g), tolerant to elevated temperatures, compatible with both organic and aqueous media and does not rely on external stimuli which may limit the monomer pool. The robustness and versatility of this methodology is further demonstrated by the applicability to a number of other copper mediated techniques including conventional ATRP and light‐mediated approaches
Methacrylic block copolymers by sulfur free RAFT (SF RAFT) free radical emulsion polymerisation
We demonstrate the use of sulfur free reversible addition-fragmentation chain transfer polymerisation (RAFT as a versatile tool for the controlled synthesis of methacrylic block and comb-like copolymers. Sulfur free RAFT (SF-RAFT) utilises vinyl terminated macromonomers obtained via catalytic chain transfer polymerisation (CCTP) of methacrylates as a chain transfer agent (CTA), and thus precluding adverse aspects of the RAFT such as toxicity of dithioesters. We have synthesised a range of narrow dispersity block copolymers (Đ < 1.2) and comb-like macromolecules by employing emulsion polymerisation allowing for the preparation of relatively large quantities (~50 g) of the above mentioned copolymers promptly and straightforwardly. Copolymers were characterised using 1H NMR, size exclusion chromatography (SEC), thermogravimetric analysis (TGA) and matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF-MS) techniques
Ultra-low volume oxygen tolerant photoinduced Cu-RDRP
We introduce the first oxygen tolerant ultra-low volume (as low as 5 μL total reaction volume) photoinduced copper-RDRP of a wide range of hydrophobic, hydrophilic and semi-fluorinated monomers including lauryl and hexyl acrylate, poly(ethylene glycol methyl ether acrylate) and trifluoroethyl (meth)acrylate. In the absence of any external deoxygenation, well-defined homopolymers can be obtained with low dispersity values, high end-group fidelity and near-quantitative conversions. Block copolymers can be efficiently synthesized in a facile manner and the compatibility of the system to larger scale polymerizations (up to 0.5 L) is also demonstrated by judiciously optimizing the reaction conditions. Importantly, the online monitoring of oxygen consumption was also conducted through an oxygen probe and the role of each component is identified and discussed
Universal conditions for the controlled polymerization of acrylates, methacrylates, and styrene via Cu(0)-RDRP
Atom transfer radical polymerization (ATRP) typically requires various parameters to be optimized in order to achieve a high degree of control over molecular weight and dispersity (such as the type of initiator, transition metal, ligand, solvent, temperature, deactivator, added salts, and reducing agents). These components play a major role when switching monomers, e.g., from acrylic to methacrylic and/or styrenic monomers during the synthesis of homo- and block copolymers as the stability and reactivity of the carbon centered propagating radical dramatically changes. This is a challenge for both “experts” and nonexperts as choosing the appropriate conditions for successful polymerization can be time-consuming and overall an arduous task. In this work, we describe one set of universal conditions for the efficacious polymerization of acrylates, methacrylates and styrene (using an identical initiator, ligand, copper salt, and solvent) based on commercially available and inexpensive reagents (PMDETA, IPA, Cu(0) wire). The versatility of these conditions is demonstrated by the near quantitative polymerization of these monomer families to yield well-defined materials over a range of molecular weights with low dispersities (∼1.1–1.2). The control and high end group fidelity is further exemplified by in situ block copolymerization upon sequential monomer addition for the case of methacrylates and styrene furnishing higher molecular weight copolymers with minimal termination. The facile nature of these conditions, combined with readily available reagents, will greatly expand the access and availability of tailored polymeric materials to all researchers
Copper-Mediated Polymerization without External Deoxygenation or Oxygen Scavengers
As a method for overcoming the challenge of rigorous deoxygenation in copper‐mediated controlled radical polymerization processes [e.g., atom‐transfer radical polymerization (ATRP)], reported here is a simple Cu0‐RDRP (RDRP=reversible deactivation radical polymerization) system in the absence of external additives (e.g., reducing agents, enzymes etc.). By simply adjusting the headspace of the reaction vessel, a wide range of monomers, namely acrylates, methacrylates, acrylamides, and styrene, can be polymerized in a controlled manner to yield polymers with low dispersities, near‐quantitative conversions, and high end‐group fidelity. Significantly, this approach is scalable (ca. 125 g), tolerant to elevated temperatures, compatible with both organic and aqueous media, and does not rely on external stimuli which may limit the monomer pool. The robustness and versatility of this methodology is further demonstrated by the applicability to other copper‐mediated techniques, including conventional ATRP and light‐mediated approaches.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083
One-pot sequence-controlled (SC) multiblock copolymers via copper-mediated polymerization
Over the past few years, the synthesis of sequence‐controlled (SC) multiblock copolymers has attracted considerable attention. Among the various polymerization techniques employed, copper mediated approaches have allowed access to both precisely controlled materials and also to fully optimized polymerization strategies. This provides additional access to the facile synthesis of less complex structures (e.g. diblocks and triblocks) that are routinely employed by the scientific community. This chapter aims to evaluate the main copper mediated radical polymerization techniques that can facilitate the synthesis of SC multiblock (≥ 5 blocks) copolymers and critically highlight the advancements of the field. Importantly, the potential and the limitations of each polymerization protocol will be critically evaluated and simplified with straightforward guidelines on the multiblock synthesis being further provided
Sequence-Controlled Methacrylic Multiblock Copolymers: Expanding the Scope of Sulfur-Free RAFT
Sulfur-free
reversible addition–fragmentation transfer polymerization
(SF-RAFT) in emulsion allows access to the synthesis of sequence-controlled
methacrylic multiblock copolymers. Herein, we expand the scope of
SF-RAFT emulsion polymerization by utilizing four different macrochain
transfer agents (mCTA) to mediate the synthesis of diblocks and sequence-controlled
methacrylic multiblock copolymers. Poly(methyl methacrylate) (pMMA),
poly(butyl methacrylate) (pBMA), poly(ethyl methacrylate) (pEMA),
and poly(benzyl methacrylate) (pBzMA) of a similar <i>M</i><sub>n</sub> (∼4300 g mol<sup>–1</sup>) were successfully
synthesized via catalytic chain transfer polymerization (CCTP) in
emulsion. The capability of these mCTAs to act as macroinitiators
was investigated through the synthesis of “<i>in situ</i>” diblock copolymers and was then expanded to the synthesis
of deca- and hexablock multiblock copolymers with varying degrees
of polymerization (DP<sub>n</sub> = 10–50 per block, <i>M</i><sub>n,total</sub> = 7000–55 000 g mol<sup>–1</sup>), yielding well-defined copolymers with controlled
molecular weights, quantitative conversions (>99%), and low dispersities
(<i>Đ</i> ∼ 1.2) without employing sulfur or
transition metal reagents