Per B. Zetterlund

Controlled/Living Radical Polymerization in Dispersed Systems

2.6. Microemulsion Polymerization 3778 2.6.1. General Considerations 3778 2.6.2. Microemulsion NMP 3778 2.6.3. Microemulsion ATRP 3778 2.6.4. Microemulsion RAFT Polymerization 3779 2.6.5. ITP in Microemulsion 3779 2.7. Dispersion and Precipitation Polymerizations 3779 2.7.1. General Considerations 3779 2.7.2. NMP 3780 2.7.3. ATRP 3781 2.7.4. RAFT 3782 2.7.5. Dispersion ITP 3782 3. Cross-linking CLRP in Dispersed Systems 3783 3.1. General Considerations 3783 3.2. Cross-linking NMP 3783 3.3. Cross-linking ATRP 3784 3.4. Cross-Linking RAFT Polymerization 3784 3.5. Cross-Linking ITP 3784 4. Particle Morphology 3785 4.1. General Considerations 3785 4.2. Core-Shell Particles 3785 4.3. Hollow Particles 3785 4.4. Multilayered Particles 3786 5. Conclusions and Outlook 3787 6. List of Abbreviations 3788 7. Acknowledgments 3789 8. References 3789

Rapid and quantitative one-pot synthesis of sequence-controlled polymers by radical polymerization

A long-standing challenge in polymer chemistry has been to prepare synthetic polymers with not only well-defined molecular weight, but also precisely controlled microstructure in terms of the distribution of monomeric units along the chain. Here we describe a simple and scalable method that enables the synthesis of sequence-controlled multiblock copolymers with precisely defined high-order structures, covering a wide range of functional groups. We develop a one-pot, multistep sequential polymerization process with yields >99%, giving access to a wide range of such multifunctional multiblock copolymers. To illustrate the enormous potential of this approach, we describe the synthesis of a dodecablock copolymer, a functional hexablock copolymer and an icosablock (20 blocks) copolymer, which represents the largest number of blocks seen to date, all of very narrow molecular weight distribution for such complex structures. We believe this approach paves the way to the design and synthesis of a new generation of synthetic polymers.

Controlled/Living Radical Polymerization in Dispersed Systems: An Update.

This review is an extensive update to the comprehensive review on controlled/living radical polymerization (CLRP) in dispersed systems published in 2008.

Synthesis of multi-block copolymer stars using a simple iterative Cu(0)-mediated radical polymerization technique

In this communication, we describe a simple and highly efficient route to well-defined multi-block star copolymers based on copper(0)-mediated living radical polymerization. The technique involves a core first approach using a multi-functional initiator in connection with iterative copper(0)-mediated radical polymerization steps. Importantly, purification is not required between the successive chain extension steps as complete monomer conversion is reached before the addition of each consecutive monomer type.

Biomimetic radical polymerization via cooperative assembly of segregating templates

Segregation and templating approaches have been honed by billions of years of evolution to direct many complex biological processes. Nature uses segregation to improve biochemical control by organizing reactants into defined, well-regulated environments, and the transfer of genetic information is a primary function of templating. The ribosome, wherein messenger RNA is translated into polypeptides, combines both techniques to allow for ideal biopolymer syntheses. Herein is presented a biomimetic segregation/templating approach to synthetic radical polymerization. Polymerization of a nucleobase-containing vinyl monomer in the presence of a complementary block copolymer template of low molecular weight yields high molecular weight (M(w) up to ~400,000 g mol(-1)), extremely low polydispersity (≤1.08) daughter polymers. Control is attained by segregation of propagating radicals in discrete micelle cores (via cooperative assembly of dynamic template polymers). Significantly reduced bimolecular termination, combined with controlled propagation along a defined number of templates, ensures unprecedented control to afford well-defined high molecular weight polymers.

Optimization of the RAFT polymerization conditions for the in situ formation of nano-objects via dispersion polymerization in alcoholic medium

Hydrophilic polymer brushes based on poly(ethylene glycol) methyl ether acrylate (P(PEGA454)) or poly(ethylene glycol) methyl ether methacrylate (P(PEGMA475)), both having a trithiocarbonate end group, were prepared in water–dioxane (9 : 1) at 44 °C via RAFT polymerization, and subsequently used in RAFT dispersion polymerization of styrene in isopropanol at 90 °C. RAFT reaction conditions were first optimized to prepare P(PEGA454) and P(PEGMA475) macro-RAFT agents at high monomer conversions (>90%) and very low fraction of dead chains (<1%). The macro-RAFT agents were then shown to have similar efficiency in terms of reinitiating and controlling the polymerization of styrene in dispersion polymerization. Both polymer brushes allowed the preparation of well-defined amphiphilic diblock copolymers (P(PEGA454)-b-PS and P(PEGMA475)-b-PS) which self-assemble in situ into nano-objects with various morphologies. Using relatively long chain P(PEGA454) or P(PEGMA475) macro-RAFT agents (DP ≈ 75) leads to the formation of near uniform spherical nano-particles with diameters ranging from 30 to 140 nm, depending on the targeted DP of the PS block. In contrast, TEM and DLS studies demonstrated that using a shorter P(PEGA454) or P(PEGMA475) macro-RAFT agent (DP ≈ 20) enables the formation of worm-like micelles, vesicles and large compound vesicle morphologies, in addition to spheres. Cryo-TEM was used to confirm polymerization induced morphology transition, rather than morphologies obtained via self-assembly driven by selective solvent or solvent evaporation during the preparation of samples for characterization.

Controlled/living radical polymerization in nanoreactors: compartmentalization effects

Compartmentalization in nanoreactors, i.e. the confinement of reactants to monomer droplets or polymer particles with diameters in the approximate range 20–200 nm, may have a marked beneficial effect on the progression of a controlled/living radical polymerization based on the persistent radical effect such as nitroxide-mediated radical polymerization and atom transfer radical polymerization. Compartmentalization effects comprise the confined space effect, which acts to improve the control over the molecular weight distribution (narrower) and the segregation effect which results in increased livingness (end-functionality). Exploitation of nanoreactors thus offers novel means of improving the performance of controlled/living radical polymerizations.

Copper(0)-mediated radical polymerisation in a self-generating biphasic system

Herein, we demonstrate the synthesis of well-defined poly(n-alkyl acrylate)s via copper(0)-mediated radical polymerisation in a self-generating biphasic system. During the polymerisation of n-butyl acrylate in DMSO, the polymer phase separates to yield a polymer-rich layer with very low copper content (ICP-MS analysis: 0.016 wt%). The poly(n-butyl acrylate) has been characterized by a range of techniques, including GPC, NMR and MALDI-TOF, to confirm both the controlled character of the polymerisation and the end group fidelity. Moreover, we have successfully chain extended poly(n-butyl acrylate) in this biphasic system several times with n-butyl acrylate to high conversion without intermediate purification steps. A range of other alkyl acrylates have been investigated and the control over the polymerisation is lost as the hydrophobicity of the polymer increases due to the increase in alkyl chain length indicating that it is important for the monomer to be soluble in the polar solvent.

Polymerization induced self-assembly: tuning of nano-object morphology by use of CO2

Polymeric nano-objects of non-spherical morphology (e.g. rods, vesicles) have a range of potential applications, and it is thus of great interest to develop synthetic approaches that enable large scale production as well as fine tuning of the morphology. To this end, we have developed reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization in an alcoholic medium pressurized to low pressure (8.0 MPa) with CO2. It is demonstrated that the presence of CO2 has a profound effect on the morphology of the resulting polymer aggregates. In the presence of CO2, the formation of nano-objects with a high interfacial core/corona curvature is favoured relative to the corresponding system without CO2, e.g. rods are formed (with CO2) under conditions where vesicles (no CO2) would otherwise form. This is a convenient method for tuning the morphology without altering the recipe, and represents an attractive route to pure rod morphology, which is typically somewhat elusive.

Thermal and mechanical properties of polyurethanes derived from mono- and disaccharides

Department of Polymer Technology, Royal Institute of Technology, S-100 44 Stockholm, Sweden(Received 1 February 1996; revised version received 3 April 1996; accepted 8 July 1996)Abstract: Thermal and mechanical properties of polyurethane (PU) sheets pre-pared from the glucose/fructose/sucroseEpolyethylene glycol (PEG)Ediphenylmethane diisocyanate (MDI) system were examined by di†erential scan-ning calorimetry, thermogravimetry, dynamic mechanical analysis and tensiletests. The saccharide content was varied at a constant NCO : OH ratio of 1E0.The glass transition temperature increased with increasing saccharide(Tg)content. The incorporation of saccharides into the PU structure results in ahigher crosslinking density and a higher content of hard segments. The thermaldecomposition was dependent on the saccharide content, an increase leading to alower thermal decomposition temperature The dissociation of saccharide(Td).OH groups and NCO groups is a major part of the thermal decomposition ofthese PUs. Dynamic mechanical analysis revealed two kinds of relaxation: thehigh temperature relaxation corresponds to main chain motion and the other is alocal mode relaxation due to non-reacted isocyanate groups. The tensile stressand YoungIs modulus increased with the saccharide content.Key words: Polyurethane, mono- and di-saccharide, decomposition, glass tran-sition, DMA, tensile properties.* To whom all correspondence should be addressed¤ IRC in Polymer Science and Technology, University of Bradford, Bradford, BD7 1DP, UK.