Improving polymeric microemulsions with block copolymer polydispersity

Recent experiments have demonstrated that block copolymers are capable of stabilizing immiscible homopolymer blends producing bicontinuous microemulsion. The stability of these polymeric alloys requires the copolymer to form flexible, nonattractive monolayers along the homopolymer interfaces. We predict that copolymer polydispersity can substantially and simultaneously improve the monolayers in both of these respects. Furthermore, polydispersity should provide similar improvements in systems, such as colloidal suspensions and polymer/clay composites, that utilize polymer brushes to suppress attractive interactions.

Investigation by Combined Solid-State NMR and SAXS Methods of the Morphology and Domain Size in Polystyrene-b-Polyethylene Oxide-b-Polystyrene Triblock Copolymers

The microphase structure of a series of polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid-state NMR, DSC, wide and small angle X-ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethyleneoxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and (1)H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:55-64,2010

Correlations between Conjugation Length, Macromolecular Dynamics, and Photophysics of Phenylene-Vinylene/Aliphatic Multiblock Copolymers

This work reports a detailed spectroscopy study of a series of multiblock conjugated nonconjugated copolymers built by p-phenylene vinylene type units (PV) and octamethylene spacers, namely, poly(1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene) (LaPPS18). The relative proportions of the PV and aliphatic segments were estimated on the basis of solid-state NMR and Raman spectroscopy. The overall structure was characterized by wide angle X-ray diffraction; H-1 wide-line dipolar chemical shift correlation (DIPSHIFT), and centerband-only detection of exchange (CODEX) NMR data, that together with glass transition temperatures allowed us to identify the groups involved in the molecular dynamics. These different structural properties were used to explain the photoluminescence properties in terms of peak position and spectral profile

Clay-containing block copolymer nanocomposites with aligned morphology prepared by extrusion

Clay-containing nanocomposites of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) copolymers having cylindrical domains were obtained by melt extrusion using a tape die. One type of sample (SEBS-MA) had maleic anhydride attached to the middle block. Two types of organoclays were added, namely Cloisite 20A and Cloisite 30B. Small angle X-ray scattering and transmission electron microscopy (TEM) analyses showed that the addition of 20A clay to SEBS and SEBS-MA resulted in nanocomposites with intercalated and partially exfoliated structures, respectively. The addition of 30B clay to SEBS and SEBS-MA promoted the formation of composites containing relatively large micron-sized and partially exfoliated clay particles, respectively. Our TEM analysis revealed that clay particles embedded in SEBS are preferably in contact with the polystyrene cylindrical domains, while in SEBS-MA they are in contact with the maleated matrix. The extrusion processing promoted alignment of the axes of the polystyrene cylinders along the extrusion direction in all samples, and the basal planes of the clay particles were mostly parallel to the main external surfaces of the extruded tapes. © 2013 Society of Chemical Industry.

Synthese und Untersuchung des Aggregationsverhaltens von Oligo(p-benzamid)-Rod-Coil-Blockcopolymeren

In dieser Arbeit wird das erste Beispiel einer automatisierten Oligo(p-benzamid)synthese beschrieben. Die auf diese Weise synthetisierten Oligo(p-benzamid)e wurden zu verschiedensten Block-co-polymeren umgesetzt und, nach Abspaltung der p-Methoxybenzylschutzgruppe, die Lösungsaggregation der resultierenden Rod-Coil Block-co-polymere mithilfe der Transmissionselektronen-Mikroskopie untersucht.

Selective Formation of Diblock Copolymers Using Radical Trap-Assisted Atom Transfer Radical Coupling

Polystyrene (PSt) radicals and poly(methyl acrylate) (PMA) radicals, derived from their monobrominated precursors prepared by atom transfer radical polymerization (ATRP), were formed in the presence of the radical trap 2-methyl-2-nitrosopropane (MNP), selectively forming PSt-PMA diblock copolymers with an alkoxyamine at the junction between the block segments. This radical trap-assisted, atom transfer radical coupling (RTA-ATRC) was performed in a single pot at low temperature (35 degrees C), while analogous traditional ATRC reactions at this temperature, which lacked the radical trap, resulted in no observed coupling and the PStBr and PMABr precursors were simply recovered. Selective formation of the diblock under RTA-ATRC conditions is consistent with the PStBr and PMABr having substantially different K-ATRP values, with PSt radicals initially being formed and trapped by the MNP and the PMA radicals being trapped by the in situ-formed nitroxide end-capped PSt. The midchain alkoxyamine functionality was confirmed by thermolysis of the diblock copolymer, resulting in recovery of the PSt segment and degradation of the PMA block at the relatively high temperatures (125 degrees C) required for thermal cleavage. A PSt-PMA diblock formed by chain extenstion ATRP using PStBr as the macroinitiator (thus lacking the alkoxyamine between the PSt-PMA segements) was inert to thermolysis. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3619-3626

Nanofabrication of Surface-Enhanced Raman Scattering Device by an Integrated Block-Copolymer and Nanoimprint Lithography Method

The integration of block-copolymers and nanoimprint lithography presents a novel and cost-effective approach to achieving nanoscale patterning capabilities. The authors demonstrate the fabrication of a surface-enhanced Raman scattering device using templates created by the block-copolymers nanoimprint lithography integrated method.

Modeling the molecular weight distribution of block copolymer formation in a reversible addition-fragmentation chain transfer mediated living radical polymerization

Block copolymers have become an integral part of the preparation of complex architectures through self-assembly. The use of reversible addition-fragmentation chain transfer (RAFT) allows blocks ranging from functional to nonfunctional polymers to be made with predictable molecular weight distributions. This article models block formation by varying many of the kinetic parameters. The simulations provide insight into the overall polydispersities (PDIs) that will be obtained when the chain-transfer constants in the main equilibrium steps are varied from 100 to 0.5. When the first dormant block [polymer-S-C(Z)=S] has a PDI of 1 and the second propagating radical has a low reactivity to the RAFT moiety, the overall PDI will be greater than 1 and dependent on the weight fraction of each block. When the first block has a PDI of 2 and the second propagating radical has a low reactivity to the RAFT moiety, the PDI will decrease to around 1.5 because of random coupling of two broad distributions. It is also shown how we can in principle use only one RAFT agent to obtain block copolymers with any desired molecular weight distribution. We can accomplish this by maintaining the monomer concentration at a constant level in the reactor over the course of the reaction. (c) 2005 Wiley Periodicals, Inc.

Solution properties of star and linear poly(N-isopropylacrylamide)

The LCST transitions of novel N-isopropylacrylamide ( NIPAM) star polymers, prepared using the four-armed RAFT agent pentaerythritoltetrakis(3-(S-benzyltrithiocarbonyl) propionate) (PTBTP) and their hydrolyzed linear arms were studied using H-1 NMR, PFG-NMR, and DLS. The aim was to determine the effect of polymer architecture and the presence of end groups derived from RAFT agents on the LCST. The LCST transitions of star PNIPAM were significantly depressed by the presence of the hydrophobic star core and possibly the benzyl end groups. The effect was molecular weight dependent and diminished once the number of repeating units per arm >= 70. The linear PNIPAM exhibited an LCST of 35 degrees C, regardless of molecular weight; the presence of both hydrophilic and hydrophobic end groups after hydrolysis from the star core was suggested to cancel effects on the LCST. A significant decrease in R-H was observed below the LCST for star and linear PNIPAM and was attributed to the formation of n-clusters. Application of a scaling law to the linear PNIPAM data indicated the cluster size n = 6. Tethering to the hydrophobic star core appeared to inhibit n-cluster formation in the lowest molecular weight stars; this may be due to enhanced stretching of the polymer chains, or the presence of larger numbers of n-clusters at temperatures below those measured.

Synthesis of polymers and copolymers of lactide through titanium initators

The research described in this thesis explored the synthesis tlnd characteristltion of biocompatible and biodegradable polymers of lactide through non-toxic titanium alkoxide nitiators. The research objectives focused on the preparation of polylactides in both solvent and solventless media, to produce materials with a wide range of molecular weights. The polylactides were fully characterised using gel permeation chromatography and 1H and 13C NMR spectroscopy. NMR spectroscopy was carried out in the study the reaction mechanisms. Kinetic studies of the ring opening polymerisation of lactide with titanium alkoxide initiators were also conducted using NMR spectroscopy. The objectives of this research were also focused on the enhancement of the flexibility of the polymer chains by synthesising random and block copolymers of lactide and ε-caprolactone using Ti(0-i-Pr)4 as an initiator, This work involved extensive characterisalion of the synthesised copolymers using gel permeation chromatography and 1H and 13C NMR spectroscopic analysis. Kinetic studies of the ring opening polymerisation of ε-caplrolactone and of the copolymerisation of lactide and ε-caprolactone with Ti(O-i-Pr)4 as an initiator were also carried out. The last section of this work involved the synthesis of block and star-shaped copolymers of lactide and poly(ethylene glycol) [PEG]. The preparation of lactide/PEG block copolymers was carried out by ring opening polymerisation of L-Iactide using Ti(O-i-Pr)4 as an initiator and hydroxyl-terminated PEG's with different numbers of hydroxyl groups as co-initiators both in solution and solventless media. These all-in-one polymersations yielded the synthesis of both lactide homopolymer and lactide/PEG block copolymer. In order to selectively synthesise copolymers of lactide and PEG, the experiment was carried out in two steps. The first step consisted of the synthesis of a titanium macro-initiator by exchanging the iso-propoxide ligands by PEG with different numbers of hydroxyl groups. The second step involved the ring opening polymerisation of lactide using the titanium macrocatalyst that was prepared as an initiator. The polymerisations were carried out in a solventless media. The synthesis of lactide/PEG copolymers using polyethylene glycol with amino terminal groups was also discussed. Extensive characterisation of the lactide block copolymers and macroinitiators was carried out using techniques such as, gel permeation chromatography (GPC), NMR spectroscopy and differential scanning calorimeter (DeS).

Block copolymer strategies for solar cell technology

A simple overview of the methods used and the expected benefits of block copolymers in organic photovoltaic devices is given in this review. The description of the photovoltaic process makes it clear how the detailed self-assembly properties of block copolymers can be exploited. Organic photovoltaic technology, an inexpensive, clean and renewable energy source, is an extremely promising option for replacing fossil fuels. It is expected to deliver printable devices processed on flexible substrates using high-volume techniques. Such devices, however, currently lack the long-term stability and efficiency to allow organic photovoltaics to surpass current technologies. Block copolymers are envisaged to help overcome these obstacles because of their long term structural stability and their solid-state morphology being of the appropriate dimensions to efficiently perform charge collection and transfer to electrodes.

Formation of sub-7 nm feature size PS-b-P4VP block copolymer structures by solvent vapour process

The nanometer range structure produced by thin films of diblock copolymers makes them a great of interest as templates for the microelectronics industry. We investigated the effect of annealing solvents and/or mixture of the solvents in case of symmetric Poly (styrene-block-4vinylpyridine) (PS-b-P4VP) diblock copolymer to get the desired line patterns. In this paper, we used different molecular weights PS-b-P4VP to demonstrate the scalability of such high χ BCP system which requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Bare Silicon Substrates were also modified with polystyrene brush and ethylene glycol self-assembled monolayer in a simple quick reproducible way. Also, a novel and simple in situ hard mask technique was used to generate sub-7nm Iron oxide nanowires with a high aspect ratio on Silicon substrate, which can be used to develop silicon nanowires post pattern transfer.

Double hydrophilic polyphosphoester containing copolymers as efficient templating agents for calcium carbonate microparticles

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Photoclickable surfaces for profluorescent covalent polymer coatings

The nitrile imine-mediated tetrazole-ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X-ray photoelectron spectroscopy and FT-IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation. Photoinduced nitrile imine-alkene 1,3-dipolar cycloaddition (NITEC) is employed to covalently bind well-defined polymers onto silicon oxide or cellulose. A diaryl tetrazole-functionalized molecule is grafted via silanization or amidification, respectively. Under UV light, a reactive nitrile imine rapidly forms and reacts with maleimide-functionalized polymers yielding a fluorescent linkage. Via a masking method, polymeric fluorescent patterns are achieved.

Development of polymers for Non-CAR resists for EUV lithography

Three strategies for approaching the design and synthesis of non-chemically amplified resists (non-CARs) are presented. These are linear polycarbonates, star polyester-blk-poly(methyl methacrylate) and comb polymers with polysulfone backbones. The linear polycarbonates were designed to cleave when irradiated with 92 eV photons and high Tg alicyclic groups were incorporated into the backbone to increase Tg and etch resistance. The star block copolymers were designed to have a core that is sensitive to 92 eV photons and arms that have the potential to provide properties such as high Tg and etch resistance. Similarly the polysulfone comb polymers were designed to have an easily degradable polymer backbone and comb-arms that impart favorable physical properties. Initial patterning results are presented for a number of the systems.