Interfaces in Diblocks: A Study of Miktoarm Star Copolymers

We study AB$_n$ miktoarm star block copolymers in the strong segregation limit, focussing on the role that the AB interface plays in determining the phase behavior. We develop an extension of the kinked-path approach which allows us to explore the energetic dependence on interfacial shape. We consider a one-parameter family of interfaces to study the columnar to lamellar transition in asymmetric stars. We compare with recent experimental results. We discuss the stability of the A15 lattice of sphere-like micelles in the context of interfacial energy minimization. We corroborate our theory by implementing a numerically exact self-consistent field theory to probe the phase diagram and the shape of the AB interface.Comment: 12 pages, 11 included figure

Long-Term Outcomes in Percutaneous Radiofrequency Ablation for Histologically Proven Colorectal Lung Metastasis

Introduction To evaluate the long-term outcome of image-guided radiofrequency ablation (RFA) when treating histologically confirmed colorectal lung metastasis in terms of overall survival (OS), progression-free survival (PFS) and local tumour control (LTC). Materials and Methods Retrospective single-centre study. Consecutive RFA treatments of histologically proven lung colorectal metastases between 01/01/2008 and 31/12/14. The primary outcome was patient survival (OS and PFS). Secondary outcomes were local tumour progression (LTP) and complications. Prognostic factors associated with OS/ PFS were determined by univariate and multivariate analyses. Results Sixty patients (39 males: 21 females; median age 69 years) and 125 colorectal lung metastases were treated. Eighty percent (n = 48) also underwent lung surgery for lung metastases. Mean metastasis size (cm) was 1.4 ± 0.6 (range 0.3–4.0). Median number of RFA sessions was 1 (1–4). During follow-up (median 45.5 months), 45 patients died (75%). The estimated OS and PFS survival rates at 1, 3, 5, 7, 9 years were 96.7%, 74.7%, 44.1%, 27.5%, 16.3% (median OS, 52 months) and 66.7%, 31.2%, 25.9%, 21.2% and 5.9% (median PFS, 19 months). The LTC rate was 90% with 6 patients developing LTP with 1-, 2-, 3- and 4-year LTP rates of 3.3%, 8.3%, 10.0% and 10.0%. Progression-free interval < 1 year (P = 0.002, HR = 0.375) and total number of pulmonary metastases (≥ 3) treated (P = 0.037, HR = 0.480) were independent negative prognostic factors. Thirty-day mortality rate was 0% with no intra-procedural deaths. Conclusion The long-term OS and PFS following RFA for the treatment of histologically confirmed colorectal lung metastases demonstrate comparable oncological durability to surgery

Microphase separation in block co- and terpolymers of novel macromolecular architectures

The synthesis of model miktoarm stars of the A2B, A3B, (AB)2(BA)2 and ABC (A:polyisoprene, B: polystyrene C: poly (methyl methacrylate)) was achieved by using anionic polymerization techniques and controlled chlorosilane chemistry. The microphase separation was studied by TEM, SAXS and image simulation. In the case of A2B and A3B miktoarm star copolymers, the morphology results are in agreement with the newly and after the experimental results developed theory of Milner. One of the symmetric in composition inverse block copolymers ((AB)2(BA)2) shows the OBDD morphology due to the special spatial arrangements of the arms. The first morphological results of ABC miktoarm star terpolymer show interesting future

Microphase separation in model 4-miktoarm star copolymers of the AB3 type

The order-disorder transition has been studied in two AB3 miktoarm stars of styrene and isoprene with SAXS and rheology. A mean-field theory has been developed to treat the most general case of miktoarm stars: AmBn (m ≠ n) which provides the phase stability criteria and the static structure factor in the disordered phase. The theory predicts a maximum in the critical value of χNt (Nt = NA + nNB) as a function of the number of arms n in ABn, for n = 3. This maximum arises from a delicate balance between the stretching free energies of the A and B blocks forming the miktoarm stars. The theoretical predictions for the phase stability and the structure factor have been tested experimentally, using SAXS, and the interaction parameter has been extracted. The latter exhibits a weak T-independence which is consistent with fluctuation effects near the transition. Further evidences for the existence of fluctuations at temperatures above and below the transition are provided by (i) the nonlinearity of the inverse peak intensity vs inverse temperature, in the disordered state, and (ii) the existence of metastable states in the ordered state. All SAXS peak parameters were discontinuous at the order-to-disorder transition, revealing a first-order transition

Model nonlinear block copolymers: Synthesis, Characterization, Morphology

The synthesis of well-defined, near monodisperse, nonlinear block copolymers of the A2B (3-miktoarm star copolymers), A3B (4-miktoarm star copolymers), (AB)2(BA)2 (inversed 4-miktoarm star block copolymers), and A3BA3 (bridged miktoarm star copolymers) types is described. A is polyisoprene (PI) and B is polystyrene (PS). The synthetic approach involves the reaction of methyltrichlorosilane or tetrachlorosilane with monofunctional or difunctional macroanions of B under conditions unfavorable to chain coupling or linking, followed by addition of the monofunctional macroanion A. Characterization was carried out by size exclusion chromatography, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, and NMR and UV spectroscopy. Microphase separation was studied by transmission electron microscopy and small-angle x-ray scattering. Comparison with the corresponding linear block copolymers showed that the macromolecular architecture not only strongly affects the morphological domain borders but can introduce new morphologies as well

Architecturally-induced tricontinuous cubic morphology in compositionally symmetric miktoarm starblock copolymers

We report the synthesis and morphological characterization of a miktoarm block copolymer architecture: (PSαM-PIM)n-(PSM-PI αM)n, where M ∼ 20 000, n = 1, 2, and the arm asymmetry parameter α = 1, 2, or 4 (α is the ratio of the outer block molecular weight to that of the inner block). These block copolymers are symmetric in overall composition and exhibit n- and α-dependent microdomain morphologies. Alternating lamellae are observed for linear tetrablocks (n = 1), α = 1, 2, 4, and for inverse starblock (n = 2), α = 1, 2. An architecturally-induced morphological transition from lamellae to a tricontinuous cubic structure is observed with n = 2 and α = 4. The formation of the tricontinuous cubic microdomain structure in this compositionally symmetric system is thought to relieve the overcrowding of the four peripheral PS-PI junctions by providing a curved intermaterial dividing surface with a triply periodic microdomain structure, allowing some bridging by the interior blocks of the miktoarm star

Conformation of A2B and A3B miktoarm star copolymers in dilute solutions

The dimensionless ratio σG, expressing quantitatively the effects of heterointeractions between unlike units on the conformational properties of copolymers, has been determined experimentally by intrinsic viscosity analysis for the A2B and A3B miktoarm stars in various solvent conditions. In the case of symmetric samples (where the lengths of A and B arms are the same) in a common good solvent, the values of the required Flory parameter Φ for homopolymer stars with three and four arms were used. For the other cases and solvent conditions, Φ was determined by extended Monte Carlo calculations which provide a lower bound of this quantity. The experimental values of σG are compared with the results obtained by Monte Carlo simulations and recent renormalization group predictions