74 research outputs found
Amphiphilic Statistical Copolymers from Catalytic Chain Transfer as Reactive Surfactants in Emulsion Polymerization
Get PDFStatistical copolymers of methacrylic acid (MAA) and methyl methacrylate (MMA), butyl methacrylate (BMA), or lauryl methacrylate (LMA) were synthesized via cobalt(II)-mediated catalytic chain transfer polymerization (CCTP) and used as macromonomeric stabilizers in the emulsion polymerization of MMA. By varying the composition, length, and concentration of the macromonomers, we were able to tune the particle size, molar mass, and rheological behavior of the latexes. Most latexes stabilized with macromonomers containing BMA and LMA showed rheological properties such as small yield stress and shear thinning behavior similar to those of binders for coating applications
The solution copolymerization of styrene and maleic anhydride in a continuous stirred tank reactor and its theoretical modelling
No full textThe synthesis of copolymers with a narrow chemical composition distribution (CCD) often requires a technological solution to overcome composition drift. Among the possible solutions, polymerization in a continuous stirred tank reactor (CSTR) is one of the most elegant. During steady state operation, the CCD is only determined by the statistical nature of the copolymerization without any broadening as typically observed in batch reactions. In this contribution, the mathematical description of the copolymerization of styrene and maleic anhydride in a CSTR is provided and experimental data are used to estimate reactivity ratios as well as to describe the copolymer composition as a function of steady state conversion
Synthesis of polymer-vesicle latex particles through an ATRP-based approach
Get PDFThe synthesis of polymer-vesicle latex particles by using extruded vesicles of dimethyldioctadecyl ammonium bromide (DODAB) via an atom transfer radical polymerization–based approach is reported. Cryo-TEM characterization revealed the growth of polymer from one side of the vesicle, and the final morphology of the resulting particles was affected by monomer feed composition. Protrusions or nanocapsules were synthesized when MMA:BA:EGDMA or MMA were used, respectively. Furthermore, it was found that the co-oligomer composition and chain length affect the resulting morphologies of the particles. Graphical abstract: [Figure not available: see fulltext.
In situ stabilizer formation from methacrylic acid macromonomers in emulsion polymerization
Get PDFOligomers of methacrylic acid containing a propenyl ω-endgroup (i.e. MAA-macromonomers) were synthesized by cobalt-mediated catalytic chain transfer polymerization and used as precursors to stabilizers in emulsion polymerization. It was found that only in those polymerizations in which these precursors were sufficiently quickly converted into amphiphilic molecules, via a type of polymerization induced self-assembly (PISA) mechanism, stable emulsion polymerization could be carried out. This process was too slow in the emulsion polymerization of methyl methacrylate (MMA) and in order to obtain stable latexes, the addition of a conventional surfactant (sodium dodecyl sulphate, SDS) was necessary. In the emulsion polymerization of butyl acrylate, however, reactions with the macromonomers were faster and because of the more hydrophobic nature of BA (as compared to MMA), stabilizers were sufficiently quickly formed in situ and stable latexes were produced without the need for additional SDS. Also the emulsion polymerization of butyl methacrylate (BMA), which reacts via the same "sulfur-free RAFT" mechanism as MMA, could be carried out in the absence of SDS because of the greater hydrophobicity of the monomer. Copolymerizations of MMA with >30% of BA or 85% BMA also resulted in stable latexes without the addition of SDS. The synthesized macromonomers and in situ formed copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy and MALDI-ToF MS
Synthesis and rheological characterization of latexes stabilized by methacrylic acid containing macromonomers
No full textA range of copolymers of methacrylic acid (MAA) macromonomers prepared by cobalt-catalyzed chain transfer and methyl methacrylate (MMA) and/or butyl acrylate (BA) was synthesized and used as a stabilizer in the emulsion polymerization of MMA. Although clear differences were observed in polymerization rates using the different MAAx-MMAy stabilizers, these differences were not as clearly reflected in the particle sizes nor in the rates per particle. However, a clear difference between these systems and those stabilized by MAAx-BAy was observed. The latter systems were all characterized by much smaller particle sizes and corresponding higher rates of polymerization. In addition, the molar masses in the latter systems were all significantly larger than those obtained in the MAAx-MMAy stabilized system, in which the stabilizers act as "sulfur-free" RAFT agents. Interestingly, the prepared latexes showed a range of appearances varying from "milky" to "gel-like" depending on the used stabilizer. The MAAx-BAy stabilized latexes had, in general, a lower viscosity and a significantly smaller (if any) yield stress than the MAAx-MMAy stabilized latexes, and in the latter case the rheological behavior was found to depend on the block lengths in and concentration of the stabilizer
Composition drift in radical copolymerization
Get PDFComposition drift in radical copolymerization is a topic of practical importance for the synthesis of homogeneous statistical copolymers and gradient copolymers, which generally does not receive much attention in most polymer chemistry textbooks. The aim of this paper is to provide a tutorial on the topic in which we provide some additional theory in a straightforward and accessible manner and show that composition drift can easily be described quantitatively. Furthermore we show how to circumvent composition drift in a semi-batch approach and by using a continuous stirred tank reactor (CSTR).</p
The Effect of Macromonomer Surfactant Microstructure on Aqueous Polymer Dispersion and Derived Polymer Film Properties
Get PDFWater-borne coatings were prepared from poly(methyl methacrylate-co-butyl acrylate) latexes using different methacrylic acid containing macromonomers as stabilizers, and their physical properties were determined. The amphiphilic methacrylic acid macromonomers containing methyl, butyl, or lauryl methacrylate as hydrophobic comonomers were synthesized via catalytic chain transfer polymerization to give stabilizers with varying architecture, composition, and molar mass. A range of latexes of virtually the same composition was prepared by keeping the content of methacrylic acid groups during the emulsion polymerization constant and by only varying the microstructure of the macromonomers. These latexes displayed a range of rheological behaviors: from highly viscous and shear thinning to low viscous and Newtonian. The contact angles of the resulting coatings ranged from very hydrophilic (<10°) to almost hydrophobic (88°), and differences in hardness, roughness, and water vapor sorption and permeability were found.</p
Morphology control of liposome - RAFT oligomer precursors to complex polymer nanostructures
Get PDF\u3cp\u3eDifferent types of butyl acrylate (BA)-co-acrylic acid (AA) oligomers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and mixed with extruded 200 nm dimethyldioctadecylammonium bromide vesicles. The resulting precursor structures form the basis for subsequent vesicle-templated polymerizations. Systematic variations in temperature, pH, oligomer length, and oligomer composition and their effects on precursor morphology were studied. Surprisingly, different morphologies were obtained, including capsules, protruded capsules, solid spheres, and multicompartment structures. For example, capsules and multicompartment structures were found to result from higher AA contents, and protruded capsules and solid particles resulted from lower AA contents. Subsequent chain extension of the RAFT oligomers resulted in polymer nanostructures resembling the precursor morphologies.\u3c/p\u3
Phosphate Triester Dynamic Covalent Networks
No full textDynamic covalent networks are a class of polymeric materials that combine the merits of classical thermosets and thermoplastics, in terms of mechanical properties and reprocessability, in one material. Various dynamic covalent chemistries have thus been implemented in polymeric materials with recent interests shifting toward chemistries that would allow rearrangements in network topology without the aid of external catalysts. Here we introduce transesterification in phosphate triesters as a new dynamic covalent chemistry in polymeric networks. A simple one-step synthetic strategy has been utilized to synthesize polytetrahydrofuran networks with phosphate triester cross-links. The materials showed finite viscous flow at elevated temperatures via transesterification at the cross-links without externally added catalyst. This approach provides an easy method for cross-linking OH-end-functionalized polyethers and has the potential for general use with other OH-functionalized polymers
Intramolecularly catalyzed dynamic polyester networks using neighboring carboxylic and sulfonic acid groups
Get PDFDynamic covalent bonds in a polymer network lead to plasticity, reshapability, and potential recyclability at elevated temperatures in combination with solvent-resistance and better dimensional stability at lower temperatures. Here we report a simple one-step procedure for the catalyst-free preparation and intramolecularly catalyzed stress-relaxation of dynamic polyester networks. The procedure is based on the coupling of branched OH-end functional polyesters (functionality ≥ 3) by pyromellitic dianhydride (PMDA) or 2,5-bis(methoxy-carbonyl) benzenesulfonic acid resulting in ester linkages with, respectively, a COOH or a SO3H group in a position ortho to the ester bond. This approach leads to an efficient external catalyst-free dynamic polyester network, in which the topology rearrangements occur via a dissociative mechanism involving anhydrides. The SO3H-containing network is particularly interesting, as it shows the fastest stress relaxation and does not suffer from unwanted additional transesterification reactions, as was observed in the COOH-containing network
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