Eva Malmström

Synthesis of hyperbranched aliphatic polyethers via cationic ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane

Thermally initiated cationic ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane was carried out using benzyltetramethylenesulfonium hexafluoroantimonate as initiator. The resulting hydroxy-functional polyether was thoroughly analyzed by 1H and 13C NMR spectroscopy and found to have a hyperbranched architecture with a degree of branching of 0.4. The polyether was successfully employed as a multifunctional initiator for e-caprolactone. Molecular weight measurements on the polyether showed a narrow molecular weight distribution analyzed by SEC and MALDI-TOF (1.3 and 1.4, respectively).

ARGET ATRP for versatile grafting of cellulose using various monomers.

In recent years, cellulose-based materials have attracted significant attention. To broaden the application areas for cellulose, polymers are often grafted to/from the surface to modify its properties. This study applies ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization) when straightforwardly grafting methyl methacrylate (MMA), styrene (St), and glycidyl methacrylate (GMA) from cellulose in the form of conventional filter paper in the presence of a sacrificial initiator. The free polymer, formed from the free initiator in parallel to the grafting, was characterized by (1)H NMR and SEC, showing that sufficient control is achieved. However, the analyses also indicated that the propagation from the surface cannot be neglected compared to the propagation of the free polymer at higher targeted molecular weights, which is an assumption often made. The grafted filter papers were evaluated with FT-IR, suggesting that the amount of polymer on the surface increased with increasing monomer conversion, which the FE-SEM micrographs of the substrates also demonstrated. Water contact angle (CA) measurements implied that covering layers of PMMA and PS were formed on the cellulose substrate, making the surface hydrophobic, in spite of low DPs. The CA of the PGMA-grafted filter papers revealed that, by utilizing either aprotic or protic solvents when washing the substrates, it was possible to either preserve or hydrolyze the epoxy groups. Independent of the solvent used, all grafted filter papers were essentially colorless after the washing procedure because of the low amount of copper required when performing ARGET ATRP. Nevertheless, surface modification of cellulose via ARGET ATRP truly facilitates the manufacturing since no thorough freeze-thaw degassing procedures are required.

A novel processing aid for polymer extrusion: Rheology and processing of polyethylene and hyperbranched polymer blends

The use of hyperbranched polymers (HBPs) as a processing aid for linear low density polyethylene (LLDPE) was investigated. Various generation (or pseudo-generation) HBPs were used which had either 16 carbon atom alkanes or a mixture of 20/22 carbon atom alkanes on the end groups. In addition, the degree of end group substitution was studied. Blends of up to 10% HBP content were mixed via extrusion at 170 °C to produce 1 mm diameter fibers. Processability, surface appearance and the rheological properties of the blends were evaluated. It was found the power requirement for extrusion was significantly decreased as a result of reduced blend viscosity, and also, the mass flow rate for a given extruder speed was greater than virgin LLDPE for all HBP blends. Melt fracture and sharkskin of the blends was successfully eliminated, and minimal preprocessing time was required for the effect to take place. Surface analysis using x-ray photoelectron spectroscopy and transmission electron microscope techniques were per...

Macromolecular engineering via ‘living’ free radical polymerizations

The use of nitroxide-mediated ‘living’ free radical procedures as a synthetic tool for obtaining polymers with well defined and complex macromolecular architectures is discussed. The preparation of linear homo, block, and random co-polymers by ‘living’ free radical procedures have been demonstrated for a variety of systems and results in a significant increase in control over the macromolecular structure when compared to traditional free radical polymerization. The factors which affect the success of this novel synthetic approach will be reviewed and the advantages of ‘living’ free radical polymerization over other living polymerization techniques discussed. The synthesis and chemical stability of a wide range of unimolecular alkoxyamine initiators will also be demonstrated and their use in the preparation of complex macromolecular architectures such as hyperbranched polymers and hybrid dendritic-linear polymers illustrated.

Film blowing of linear low-density polyethylene blended with a novel hyperbranched polymer processing aid

The use of hyperbranched polymer (HBP) as a processing aid for linear low-density polyethylene (LLDPE) in the tubular film blowing process was investigated. Through the addition of HBP, sharkskin was successfully eliminated without significantly changing the overall physical properties of LLDPE films. Also, there was a minimum of 40% enhancement in processing rate with addition of 0.5 wt% HBP. The study showed that HBP and LLDPE are immiscible, and HBP has a tendency to migrate to the surface, subsequently, it seems to form a lubricating layer between the metal surfaces and the bulk material. This phase separation between HBP and LLDPE results in an HBP-rich surface, which has a high potential to create unique surface properties tailored to various applications. Rheological analysis indicated that excessive slip was present in HBP/LLDPE suggesting that the onset of slip is not the cause of sharkskin. On the contrary, it may be partially responsible for the elimination of sharkskin.

Superhydrophobic and self-cleaning bio-fiber surfaces via ATRP and subsequent postfunctionalization

Superhydrophobic and self-cleaning cellulose surfaces have been obtained via surface-confined grafting of glycidyl methacrylate using atom transfer radical polymerization combined with postmodification reactions. Both linear and branched graft-on-graft architectures were used for the postmodification reactions to obtain highly hydrophobic bio-fiber surfaces by functionalization of the grafts with either poly(dimethylsiloxane), perfluorinated chains, or alkyl chains, respectively. Postfunctionalization using alkyl chains yielded results similar to those of surfaces modified by perfluorination, in terms of superhydrophobicity, self-cleaning properties, and the stability of these properties over time. In addition, highly oleophobic surfaces have been obtained when modification with perfluorinated chains was performed.

Synthesis of Polycaprolactone-Grafted Microfibrillated Cellulose for Use in Novel Bionanocomposites–Influence of the Graft Length on the Mechanical Properties

In the present work, microfibrillated cellulose (MFC) made from bleached sulfite softwood dissolving pulp was utilized to reinforce a poly(ε-caprolactone) (PCL) biopolymer matrix. To improve the dispersibility of the hydrophilic MFC in the nonpolar matrix and the interfacial adhesion in the composite material, we covalently grafted the MFC with PCL via ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). To be able to investigate the effect of the PCL graft length on the mechanical properties of the composite material, we performed ROP to different molecular weights of the grafts. Bionanocomposites containing 0, 3, and 10 wt % MFC were prepared via hot pressing using both unmodified and PCL grafted MFC (MFC-g-PCL) as reinforcement. PCL grafting resulted in improved dispersion of the MFC in a nonpolar solvent and in the PCL matrix. The mechanical testing of the biocomposites showed an improvement in the mechanical properties for the PCL grafted MFC in comparison to ungrafted MFC. It was also shown that there was an impact on the mechanical properties with respect to the PCL graft lengths, and the strongest biocomposites were obtained after reinforcement with MFC grafted with the longest PCL graft length.

Dendritic architectures based on bis-MPA : functional polymeric scaffolds for application-driven research

Dendritic polymers are highly branched, globular architectures with multiple representations of functional groups. These nanoscale organic frameworks continue to fascinate researchers worldwide and are today under intensive investigation in application-driven research. A large number of potential application areas have been suggested for dendritic polymers, including theranostics, biosensors, optics, adhesives and coatings. The transition from potential to real applications is strongly dictated by their commercial accessibility, scaffolding ability as well as biocompatibility. A dendritic family that fulfills these requirements is based on the 2,2-bismethylolpropionic acid (bis-MPA) monomer. This critical review is the first of its kind to cover most of the research activities generated on aliphatic polyester dendritic architectures based on bis-MPA. It is apparent that these scaffolds will continue to be in the forefront of cutting-edge research as their structural variations are endless including dendrons, dendrimers, hyperbranched polymers, dendritic-linear hybrids and their hybridization with inorganic surfaces.

Development of a new class of rate-accelerating additives for nitroxide-mediated ‘living’ free radical polymerization

Abstract Acylating agents have been identified as a new class of rate accelerating additives for nitroxide-mediated ‘living’ free radical polymerization. It is found that addition of 1 weight percent of acetic anhydride results in a significant decrease in the reaction time, 48 to 4 hours. This decrease in reaction time leads to greater control over the polymerization process with low polydispersity materials being obtained up to 150 000 a.m.u. A possible explanation for this effect is acylation of the alkoxyamine nitrogen leading to an increase in the lability of the CON bond.

The effect of degree of branching on the rheological and thermal properties of hyperbranched aliphatic polyethers

A series of hyperbranched aliphatic polyethers with different degree of branching (DB) and molecular weights have been studied with respect to their rheological and thermal properties. The DB was shown to affect the ability of the polymers to crystallize and thereby also the rheological properties of the polymers. A low DB resulted in semi-crystalline polymers with melting points between 100 and 130°C. The polymers with a higher DB were essentially amorphous and behaved as non-entangled Newtonian liquids in the molten state.