Avoiding compositional drift during the RAFT copolymerization of N-(2-hydroxypropyl)methacrylamide and N-acryloxysuccinimide: towards uniform platforms for post-polymerization modification

Controlled radical polymerization techniques such as RAFT allow fine control over polymer molecular weight and architecture. These techniques, however, do not eliminate compositional drifts in copolymerizations, which are the consequence of differences in monomer reactivity and can lead to compositionally non-uniform polymers that may hamper establishing structure-property relationships. One way to avoid compositional drifts is to use controlled monomer feeding techniques. Using the N-(2-hydroxypropyl)methacrylamide/N-acryloxysuccinimide (HMPA/NAS) comonomer pair for a first proof-of-concept, this manuscript reports an alternative approach to avoid compositional drifts and generate uniform copolymers by judicious selection of the initial monomer feed composition and controlling monomer conversion. Screening the copolymerization kinetics and copolymer composition of HPMA/NAS copolymers generated under various reaction conditions revealed that RAFT copolymerization of HPMA and NAS in DMF with an initial feed of 30 mol% NAS only resulted in a minimal compositional drift. While these reaction conditions are specific to the NAS/HPMA comonomer pair studied here, this approach may be applied to other comonomer pairs as well. The reactive NAS groups in a poly(HPMA-stat-NAS) copolymer obtained via this strategy could be post-modified with near-quantitative conversion with a amine-functionalized crown ether, which illustrates the versatility of this protocol to generate uniform reactive scaffolds for further post-polymerization modification.

Maleimide-Functionalized Thiol Reactive Copolymer Brushes: Fabrication and Post-Polymerization Modification

Tugba Bilgiç Tune, Harm-Anton Klok

Polymer brushes that present side chain functional reactive groups are attractive platforms for the development of functional surface coatings. From the wide spectrum of possible postpolymerization modification reactions, thiol-based conjugation chemistries are particularly appealing as they can be performed reagent-less under mild conditions and can allow the site-selective conjugation of biomolecules. This manuscript reports a direct approach for the preparation of maleimide-functionalized polymer brushes. These brushes were obtained by surface-initiated atom transfer radical copolymerization of poly(ethylene glycol) methacrylate and a furan-protected, maleimide containing monomer, followed by a thermally induced retro DielsAlder reaction to unmask the maleimide groups. The feasibility of these brushes to serve as a platform for postpolymerization functionalization was explored in a series of model experiments using a variety of low molecular weight thiols, including a fluorescent dye and a thiol-modified biotin-derivative. The biotinylated brushes were subsequently used for the immobilization of streptavidin-coated quantum-dots. The copolymer brushes presented in this manuscript are attractive since they combine the nonbiofouling properties of the poly(ethylene glycol) methacrylate monomer with the chemoselective reactivity of the maleimide containing monomer, which makes them an attractive platform, e.g., for the immobilization of biomolecules.

American Chemical Society2014

Magnetic and electrostatic effects on the polymerization of water-soluble monomers

Ignacio Rintoul

Free radical polymerization is the most frequently used technique to produce synthetic polymers. They represent more than 25% of the total volume of materials made by the mankind. 3% thereof correspond to water soluble polymers with annual growth rates estimated as 8%. Therefore, everything contributing to progress of the radical polymerization of water soluble monomers may be evaluated as signicant. This thesis was devoted to identify the influence of magnetic (MF) and electrostatic interactions on the kinetics and mechanism of the radical polymerization of water soluble monomers. Acrylamide (AM), acrylic acid (AA), its ionized species, acrylate (A-), and diallyldimethylammonium chloride (DADMAC) were selected for homo and copolymerization case studies. Thermal and photochemically initiated polymerizations were performed varying the MF intensity, pH, ionic strength, monomer and initiator concentration, conversion degree, viscosity and temperature of the polymerization medium. The thesis reports the experiments, results, and conclusions thereof, increasing gradually the complexity of the polymerization system. It was demonstrated that an hybrid mechanism rules the persulfate initiated polymerization of AM also at 0.05

EPFL2006

High-temperature radical polymerization of methyl methacrylate in a continuous pilot scale process

Philip Nising

The present PhD thesis deals with the high temperature polymerization of methyl methacrylate in a continuous pilot scale process. The major aim is to investigate the feasibility of a polymerization process for the production of PMMA molding compound at temperatures in the range from 140 °C to 170 °C. Increasing the process temperature has the advantage of decreasing molecular weight and viscosity of the reaction mixture, thus allowing to reduce the addition of chain transfer agent and to increase the polymer content in the reactor. At the same time, the reaction rates are higher and the devolatilization is facilitated compared to low conversion polymerizations. Altogether, it leads to an improved space time yield of the process. However, increasing the process temperature also has an important impact on both, polymerization kinetics and polymer properties. The first two parts of this work are, therefore, dedicated to the self-initiation respectively the high temperature gel effect observed for the polymerization of MMA at the given temperature range. The self-initiation of MMA is mostly caused by polymeric peroxides that form from physically dissolved oxygen and the monomer, itself. The formation, decomposition and constitution of these peroxides are intensively studied and a formal kinetic is proposed for the formation and decomposition reaction. The polymerization of MMA is subject to a rather strong auto-acceleration, called gel effect, the intensity of which depends on process conditions and solvent content. There are several models proposed in the specialized literature to describe this phenomenon by modifying the termination rate constant as a function of conversion and temperature. The second part of this study contains the evaluation of these models with regards to their applicability to high temperature MMA polymerization as well as the development of a new variant of an existing model, which correctly describes the gel effect in the temperature range of interest as a function of polymer content, temperature and molecular weight. The advantage of this new variant is that it includes all other factors influencing the gel effect, i.e. chain transfer agent, initiator load, comonomer and solvent content, and that it is suitable for the description of batch and continuous processes. A complete kinetic model for the description of the high temperature copolymerization of MMA and MA, containing the results from the first two parts of this work, is established within the software package PREDICI® and validated by means of several series of batch polymerizations. In the third part of this work, a complete pilot plant installation for the continuous polymerization of MMA is designed and constructed in order to study the impact of increasing the reaction temperature on process properties and product quality under conditions similar to those of an industrial-scale polymerization. The pilot plant is based on a combination of recycle loop and consecutive tube reactor, equipped with SULZER SMXL® / SMX® static mixing technology. Furthermore, it is equipped with a static one-step flash devolatilization and a pelletizer for polymer granulation. At the same time, a refined method for inline conversion monitoring by speed of sound measurement is developed and tested in the pilot plant. By means of this technique it is possible to follow the dynamic behavior of the reactor and to measure directly the monomer conversion without taking a sample. The results of several pilot plant polymerizations carried out under different conditions are presented and the impact of temperature, comonomer and chain transfer agent on the thermal stability of the product is analyzed. From these results, the r-parameters for the copolymerization of MMA and MA at 160 °C as well as the chain transfer constant for n-dodecanethiol at 140 °C are determined. Finally, the pilot plant experiments are used to validate the kinetic model established beforehand in PREDICI® for the continuous copolymerization.

EPFL2006

High-temperature radical polymerization of methyl methacrylate in a continuous pilot scale process

Philip Nising

EPFL2006