Monodisperse macromolecules – A stepping stone to understanding industrial polymers

AbstractPolymers synthesized via anionic polymerization have proved important to our fundamental understanding of the processing, that is rheology and crystallisation, of bulk commodity polymers. The role of monodisperse hydrogenated polybutadienes as models for linear and branched polyethylene is examined. Systematic studies of the effects of long-chain branching, using well-defined “comb” materials have improved our understanding of how the number and length of branches affect the rheological properties and how these features impact on their crystallization behaviour. A combination of techniques including rheology, Small Angle X-ray Scattering (SAXS), and birefringence measurements have provided insight into role of linear long chains in the formation of oriented morphologies during the crystallization of hydrogenated polybutadiene blends of controlled polydispersity leading to the development of a quantitative model

Fludarabine, cytarabine, granulocyte colony-stimulating factor, and idarubicin with gemtuzumab ozogamicin improves event-free survival in younger patients with newly diagnosed aml and overall survival in patients with npm1 and flt3 mutations

Purpose To determine the optimal induction chemotherapy regimen for younger adults with newly diagnosed AML without known adverse risk cytogenetics. Patients and Methods One thousand thirty-three patients were randomly assigned to intensified (fludarabine, cytarabine, granulocyte colony-stimulating factor, and idarubicin [FLAG-Ida]) or standard (daunorubicin and Ara-C [DA]) induction chemotherapy, with one or two doses of gemtuzumab ozogamicin (GO). The primary end point was overall survival (OS). Results There was no difference in remission rate after two courses between FLAG-Ida + GO and DA + GO (complete remission [CR] + CR with incomplete hematologic recovery 93% v 91%) or in day 60 mortality (4.3% v 4.6%). There was no difference in OS (66% v 63%; P = .41); however, the risk of relapse was lower with FLAG-Ida + GO (24% v 41%; P < .001) and 3-year event-free survival was higher (57% v 45%; P < .001). In patients with an NPM1 mutation (30%), 3-year OS was significantly higher with FLAG-Ida + GO (82% v 64%; P = .005). NPM1 measurable residual disease (MRD) clearance was also greater, with 88% versus 77% becoming MRD-negative in peripheral blood after cycle 2 (P = .02). Three-year OS was also higher in patients with a FLT3 mutation (64% v 54%; P = .047). Fewer transplants were performed in patients receiving FLAG-Ida + GO (238 v 278; P = .02). There was no difference in outcome according to the number of GO doses, although NPM1 MRD clearance was higher with two doses in the DA arm. Patients with core binding factor AML treated with DA and one dose of GO had a 3-year OS of 96% with no survival benefit from FLAG-Ida + GO. Conclusion Overall, FLAG-Ida + GO significantly reduced relapse without improving OS. However, exploratory analyses show that patients with NPM1 and FLT3 mutations had substantial improvements in OS. By contrast, in patients with core binding factor AML, outcomes were excellent with DA + GO with no FLAG-Ida benefit

The effect of PEO length on the self-assembly of poly(ethylene oxide)−tetrapeptide conjugates prepared by “Click” chemistry

Two series of poly(ethylene oxide)−tetrapeptide conjugates have been prepared using a “Click” reaction between an alkyne-modified tetra(phenylalanine) or tetra(valine) and various azide-terminated poly(ethylene oxide) (PEO) oligomers. Three different PEO precursors were used to prepare these conjugates, with number-average molecular weights of 350, 1200, and 1800 Da. Assembly of mPEO−F4−OEt and mPEO−V4−OEt conjugates was achieved by dialysis of a THF solution of the conjugate against water or by direct aqueous rehydration of a thin film. The PEO length has a profound effect on the outcome of the self-assembly, with the F4 conjugates giving rise to nanotubes, fibers, and wormlike micelles, respectively, as the length of the PEO block is increased. For the V4 series, the propensity to form β-sheets dominates, and hence, the self-assembled structures are reminiscent of those formed by peptides alone, even at the longer PEO lengths. Thus, this systematic study demonstrates that the self-assembly of PEO−peptides depends on both the nature of the peptides and the relative PEO block length

Shear-Induced Crystallization in blends of Model Linear and Long-Chain Branched Hydrogenated Polybutadienes

Quiescent and shear-induced crystallizations were performed on several well-defined linear monodisperse hydrogenated polybutadiene blends with a high-molecular-weight long-chain branched (LCB) combshaped additive. The connection between microscopic molecular motion and crystallization kinetics has been quantitatively studied with respect to the formation of either isotropic or oriented shish kebab crystal morphology using time-resolved X-ray scattering techniques. Using a constant preshear rate, the addition of small amounts of LCB combs to the sample blends, at concentrations below and just above the overlap concentration c*, has significantly increased the crystallization rates compared to quiescent conditions. However, only one blend showed the formation of an oriented shish kebab morphology. Also, for these model blends, the transition between isotropic and oriented crystals occurs quite sharply between 5 and 10%, which is around c*. We explain these data by using a shish formation mechanism in which, to form shish kebabs, the combs must be mutually overlapping and the comb Weissenberg number must be in the strong stretch regime

Soft hydrogels from nanotubes of poly(ethylene oxide)−tetraphenylalanine conjugates prepared by click chemistry

A new poly(ethylene oxide)−tetraphenylalanine polymer−peptide conjugate has been prepared via a “click” reaction between an alkyne-modified peptide and an azide-terminated PEO oligomer. Self-assembled nanotubes are formed after dialysis of a THF solution of this polymer−peptide conjugate against water. The structure of these nanotubes has been probed by circular dichroism, IR, TEM, and SAXS. From these data, it is apparent that self-assembly involves the formation of antiparallel β-sheets and π−π-stacking. Nanotubes are formed at concentrations between 2 and 10 mg mL−1. Entanglement between adjacent nanotubes occurs at higher concentrations, resulting in the formation of soft hydrogels. Gel strength increases at higher polymer−peptide conjugate concentration, as expected

On the mechanism of formation of vesicles from poly(ethylene oxide)-block-poly(caprolactone) copolymers

Micelles, worm-like micelles and vesicles were prepared from poly(ethylene oxide)-b-poly(caprolactone) block copolymersvia a solvent switch method, and characterised by light scattering, X-ray scattering and cryo-transmission electron microscopy. The volume fraction of ethylene oxide, as the hydrophilic part in these polymers, determined the morphology in dilute solution, with spherical micelles, worm-like micelles, vesicles and precipitate being formed as the volume fraction decreased. The mechanism by which vesicles were formed in these systems during sequential dilution of the initial THF-rich solution with water was probed. It was shown that vesicles formed via a sequence of morphologies. The transitions between different self-assembled structures were followed using dynamic cryo-TEM. The behaviour of the PEO-b-PCL system was compared with the well-studied poly(acrylic acid)-b-poly(styrene) system; the behaviour was shown to differ in the final stage during the transition from worm-like micelles to vesicles

Neutron flow-mapping: Multiscale modelling opens a new experimental window

Small-angle neutron scattering (SANS) has delivered significant insight into the rich and varied phenomena seen in the non-linear dynamics of entangled polymers. The lengthscales accessible by SANS are ideally matched to the strongly lengthscale-dependent relaxation in entangled polymers. This, in turn, has facilitated a detailed and challenging test for models of molecular rheology. Here, we review experimental techniques, along with the multiscale modelling required to predict these measurements. This approach has enriched our understanding of monodisperse linear polymers, model linear–linear blends and branched polymers. We also indicate potential future directions for this fruitful approach

Control of the Porous Structure of Polystyrene Particles Obtained by Nonsolvent Induced Phase Separation

Porous polystyrene microspheres were produced by a process of nonsolvent induced phase separation (NIPS) from ternary polymer–solvent–nonsolvent (polystyrene–toluene–ethanol) systems and characterized by scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS) techniques. This study provides evidence for a link between the structural morphology of the porous polystyrene particles and the polystyrene concentration in the initial solutions. A reciprocal relationship between pore diameter and polymer concentration was observed for the systems with the polymer amount below the critical chain overlap concentration, <i>C</i>*. Above <i>C</i>*, this relationship breaks down. The reciprocal relationship between porosity and polymer concentration can be used to facilitate the fine control of the void size. We demonstrate that the observed reciprocal relationship between pore diameter and polymer concentration correlates well with the relative amount of nonsolvent present in the system at the onset of the phase separation process. The pore size can be reduced and, consequently, the pore surface area can be increased either by reducing the polymer concentration in the initial solution or by decreasing the polymer molecular weight in the sample composition