Durairaj Baskaran

Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium (P5+) as counterion in tetrahydrofuran

A novel metal-free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) cation with the 1,1-diphenylhexyl (DPH–) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between –20 and +20°C using a flow tube reactor provide nearly linear first-order time-conversion plots with half-lives below 0.1 s, a linear dependence of the number-average degree of polymerization, and rather narrow molecular weight distributions (Mw/Mn ≈ 1.2). 13C NMR measurements on a model of the active chain end (the P5+ salt of ethyl isobutyrate) in THF-d8 show 15 and 25 ppm upfield shifts of the α-carbon compared to the dimers and tetramers of the lithium ester enolate, respectively, indicating a non-aggregated structure and an increased charge density on the α-carbon.

Preparation of Polyurethane Microspheres via Dispersion Polycondensation Using Poly(1,4-isoprene)-block-poly(ethylene oxide) as Steric Stabilizer

A novel dispersion polymerization of a diisocyanate and a diol for the preparation of spherical polyurethane particles is reported. An amphiphilic block copolymer, namely, poly(1,4-isoprene)-block-poly(ethylene oxide) was used as a steric stabilizer. Monodisperse spherical particles were obtained in the size range from 0.2 to 2.0 μm. The polyurethane particle formation was dependent on the concentration of the steric stabilizer, the block segment molecular weight and the nature of dispersion medium. The polyurethane particles were stabilized by a mechanism involving physical adsorption of the steric stabilizer on the surface of the growing particle.

Polypeptide Grafted Hyaluronan: Synthesis and Characterization

Poly(l-leucine) grafted hyaluronan (HA-g-PLeu) has been synthesized via a Michael addition reaction between primary amine terminated poly(l-leucine) and acrylate-functionalized HA (TBAHA-acrylate). The precursor hyaluronan was first functionalized with acrylate groups by reaction with acryloyl chloride in the presence of triethylamine in N,N-dimethylformamide. (1)H NMR analysis of the resulting product indicated that an increase in the concentration of acryloylchoride with respect to hydroxyl groups on HA has only a moderate effect on functionalization efficiency, f. A precise control of stoichiometry was not achieved, which could be attributed to partial solubility of intermolecular aggregates and the hygroscopic nature of HA. Michael addition at high [PLeu-NH(2)]/[acrylate](TBAHA) ratios gave a molar grafting ratio of only 0.20 with respect to the repeat unit of HA, indicating grafting limitation due to insolubility of the grafted HA-g-PLeu. Soluble HA-g-PLeu graft copolymers were obtained for low grafting ratios (<0.039) with <8.6% by mass of PLeu and were characterized thoroughly using light scattering, (1)H NMR, FT-IR, and AFM techniques. Light scattering experiments showed a strong hydrophobic interaction between PLeu chains, resulting in aggregates with segregated nongrafted HA segments. This yields local networks of aggregates, as demonstrated by atomic force microscopy. Circular dichroism spectroscopy showed a β-sheet conformation for aggregates of poly(l-leucine).

Micellar-cluster association of ureidopyrimidone functionalized monochelic polybutadiene

A series of monochelic polybutadienes with a ureidopyrimidone terminal group (MPBd-UPy) has been synthesized using anionic polymerization and chain-end transformation. Monochelic polybutadiene with two UPy terminal groups, MPBd-(UPy)2, has also been synthesized to study the effect of chain-end concentration on hydrogen bonding association. The transformation of the precursor ω-hydroxyl terminated polybutadiene into the ureidopyrimidone functionality via the reaction with 1-(6-isocyanatohexyl)-3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl) urea (UPy-NCO) turns free-flowing liquid samples into a semi-solid, viscous material, due to the well-known quadruple hydrogen bonding ability of UPy. The dimerization association of MPBd-UPy has been studied thoroughly using size exclusion chromatography, intrinsic viscosity and dynamic light scattering. Solutions of MPBd-UPy exhibit a high Huggins parameter, 0.40 0.63, depending on the molecular weight and the number of UPy groups at the chain-end. Studies reveal that along with hydrogen bonded dimers, (MPBd-UPy)2, they also aggregate intermolecularly to form star-like micelles that are in equilibrium with the dimers. The presence of multiple populations with Rh as high as 700 nm, which decreases with increasing temperature in toluene has been identified. The UPy aggregated micellar clusters have distinct endothermic transitions in the solid-state and atomic force microscopy studies show the presence of micellar-clusters forming a well-defined assembly of fibrous like parallel lines on a mica surface.

Asymmetrical self-assembly from fluorinated and sulfonated block copolymers in aqueous media

Block copolymers of fluorinated isoprene and partially sulfonated styrene form novel tapered rods and ribbon-like micelles in aqueous media due to a distribution of sulfonation sites and a large Flory–Huggins interaction parameter. A combination of microscopy, light scattering, and simulation demonstrates the presence of these unique nanostructures. This study sheds light on the micellization behavior of amphiphilic block polymers by revealing a new mechanism of self-assembly.

Trifunctional organolithium initiator for living anionic polymerization in hydrocarbon solvents in the absence of polar additives

A novel hydrocarbon-soluble trifunctional organolithium initiator, with no polar-additive requirements, has been synthesized for use in anionic polymerization. The complete synthesis of the unsaturated tri-diphenylethylene compound, 4,4,4-(ethane-1,1,1-triyl)tris(((3-(1-phenylvinyl)benzyl)oxy)benzene) (I), is described and the efficiency of the new initiator is evaluated using 1H NMR and Nano-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (NALDI-TOF MS). Activation of precursor I, was performed in situ using stoichiometric amounts of sec-BuLi in benzene. Three-arm polystyrene and polyisoprene stars with narrow molecular weight distributions were obtained in the case of relatively high total anion concentration, [sec-BuLi]0 > 3.8 × 10−3 mol L−1 (3 × [I]0). At low total anion concentrations, uncontrolled molecular weight and broad/bimodal distributions were obtained, plausibly attributed to the presence of partially solvated aggregation dynamics complicating the propagation. The ‘living’ nature of the polymerization was confirmed by the sequential polymerization of styrene, and isoprene. The viscometric branching factor g′ values of the final branched polymers were measured and compared to g′ values of three-arm stars reported in the literature.

Poly(styrene-graft-hyperbranched polyglycidol): synthesis and solution behavior of a hyperbranched polyelectrolyte

This work presents a three-step synthetic procedure to obtain a hypergrafted copolymer composed of a glassy backbone with flexible branched pendant segments. The desired hypergrafted structure was obtained by using a polyfunctional macroinitiator, linear poly(styrene-co-4-hydroxystyrene), to yield polystyrene-graft-hyperbranched polyglycidol with randomly placed branch junctions. Atomic force microscopy, dynamic light scattering, and viscometry probed the aggregation and viscometric behavior of the polymer in DMF and DMF–LiBr solutions. The polymer exhibited polyelectrolyte behavior demonstrated by a large increase in the reduced viscosity prior to neutralization with LiBr salt. Additionally, conformational changes were observed by dynamic light scattering in both the average aggregate size and aggregate population with the addition of LiBr salt.

The tracer diffusion coefficient of soft nanoparticles in a linear polymer matrix

The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and are often difficult to determine experimentally. To address this shortcoming, we have developed a novel method to determine the tracer diffusion coefficient of soft polystyrene nanoparticles in a linear polystyrene matrix. Monitoring the interdiffusion of soft nanoparticles into a linear polystyrene matrix provides the mutual diffusion coefficient of this system, from which the tracer diffusion coefficient of the soft nanoparticle can be determined using the slow mode theory. Utilizing this protocol, the role of nanoparticle molecular weight and rigidity on its tracer diffusion coefficient is provided. These results demonstrate that the diffusive behavior of these soft nanoparticles differ from that of star polymers, which is surprising since our recent studies suggest that the nanoparticle interacts with a linear polymer similarly to that of a star polymer. It appears that these deformable nanoparticles mostly closely mimic the diffusive behavior of fractal macromolecular architectures or microgels, where the transport of the nanoparticle relies on the cooperative motion of neighboring linear chains. The less cross-linked, and thus more deformable, nanoparticles diffuse faster than the more highly crosslinked nanoparticles, presumably because the increased deformability allows the nanoparticle to distort and fit into available space.

Anionic Polymerization of Polar Vinyl Monomers

This chapter reports on the kinetics and mechanisms of the anionic polymerization of polar vinyl monomers, in particular alkyl methacrylates and acrylates as well as N,N-dialkylacrylamides and vinylpyridines.

Evaluation of line-edge/line-width roughness of directed self-assembled PS-b-PMMA patterns using coarse-grained molecular dynamics simulation

In recent years, Directed-Self Assembly (DSA) of block copolymers (BCPs) has gained relevance as a promising ‘bottomup’ technique to produce nano-lithographic patterns. To make DSA a reliable and robust technique, much of the research is focused on reducing defectivity and mitigating Line Edge Roughness (LER) and Line Width Roughness (LWR) of the pre-and post-etched polymer blocks. High roughness values often inhibit the smooth functioning of the transistors by constraining the electron flow through the spaced channels. It is thus crucial to develop novel modeling and simulations techniques for DSA to harness the full potential of this technique and thus meet the ITRS roadmap LER standards. In our recent work, we have outlined our CGMD framework and the subsequent etching methodology used to produce line space patterns created by lamellae forming polystyrene-block-polymethyl methacrylate (PS-b-PMMA) with periods of about 28 nm, on a patterned Liu-Nealey (LiNe) flow substrate. In this paper, we present a comparative study of the experimental LER / LWR calculations with our coarse-grained molecular dynamics (CGMD) simulation results. We employ highly parallelized supercomputing resources on a full-scale system with a detailed topographical substrate and exact matching of the BCP molecular weight. The simulations offer us a 3-D profile of the BCP domains and the subsequent resist pattern formed after etching, thus providing us with roughness estimates across the film thickness for three process stages: anneal, pre-etch and post-etch. Additionally, we also evaluate the edge morphology in the Fourier domain by generating power spectral density curves.