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External electric fields align nanostructured block copolymers by either rotation of grains or nucleation and growth depending on how strongly the chemically distinct block copolymer components are segregated. In close vicinity to the order-disorder transition, theory and simulations suggest a third mechanism: selective disordering. We present a time-resolved small-angle X-ray scattering study that demonstrates how an electric field can indeed selectively disintegrate ill-aligned lamellae in a lyotropic block copolymer solution, while lamellae with interfaces oriented parallel to the applied field prevail. The present study adds an additional mechanism to the experimentally corroborated suite of mechanistic pathways, by which nanostructured block copolymers can align with an electric field. Our results further unveil the benefit of electric field assisted annealing for mitigating orientational disorder and topological defects in block copolymer mesophases, both in close vicinity to the order-disorder transition and well below it.

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).

Free-radical polymerization of methyl methacrylate and styrene using conventional organic initiators in the room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) is rapid and produces polymers with molecular weights up to 10x higher than from benzene; both polymerization and isolation of products were achieved without using VOCs, offering economic as well as environmental advantages.

The room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, [C4mim][PF6] was found to be an efficient plasticizer for poly(methyl methacrylate), prepared by in situ radical polymerization in the ionic liquid medium; the polymers have physical characteristics comparable with those containing traditional plasticizers and retain greater thermal stability.

We carried out a large set of tests to establish a correlation between the molecular (network) structure (influenced by molecular weight, molecular weight distribution, and melt predeformation) and mechanical responses of several glassy polymers to uniaxial compression at different temperatures and different compression speeds. The experimental results show that to have ductile responses there must be an adequate chain network, afforded by the interchain uncrossability among sufficiently long chains. Specifically, polystyrene (PS) and poly(methyl methacrylate) of sufficiently low molar mass do not have chain network and are found to be very brittle. Binary PS mixtures are brittle at room temperature when the volume fraction of the high‐molecular‐weight component is sufficiently low (e.g., at and below 27.5%). Moreover, sufficiently melt‐stretched PS mixtures show brittle fracture when compressed along the same direction, along which melt stretching was made. All the experimental findings confirm that a robust chain network is also a prerequisite for yielding and ductile cold compression of polymer glasses, as is for extension. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 758–770 [ABSTRACT FROM AUTHOR]

Research on block copolymers (BCPs) has played a critical role in the development of polymer chemistry, with numerous pivotal contributions that have advanced our ability to prepare, characterize, theoretically model, and technologically exploit this class of materials in a myriad of ways in the fields of chemistry, physics, material sciences, and biological and medical sciences. The breathtaking progress has been driven by the advancement in experimental techniques enabling the synthesis and characterization of a wide range of block copolymers with tailored composition, architectures, and properties. In this review, we briefly discussed the recent progress in BCP synthesis, followed by a discussion of the fundamentals of self-assembly of BCPs along with their applications [ABSTRACT FROM AUTHOR]

Abstract: Melt stirring of non-functional polymers such as poly(ethylene oxide) dimethylether (PEO–Me) and polystyrene (PS–H) with multiwalled carbon nanotubes (MWNTs) in the absence of solvent for 48h induced a substantial amount of polymer adsorption on the MWNTs. The chloroform extraction of the reaction products using centrifugation yielded black colored solutions exhibiting UV absorbance corresponding to the presence of MWNTs. The adsorption of polymer was confirmed on the surfaces of solvent washed residual and recovered MWNTs from the reactions using thermogravimetric analysis (TGA) and FT-IR spectroscopy. Covalent grafting reactions carried out using hydroxyl-terminated PEO–OH and PS–OH with acid chloride containing MWNTs under identical melt stirring condition produced similar results. The presence of polymer on the residual and recovered MWNTs irrespective of the nature of the terminal groups indicates that the adsorption of polymers poses a problem in accurately determining the grafting efficiency. FT IR spectra of the PEO-g-MWNTs shows a substantial shift in CH stretching vibrations indicating a plausible weak intermolecular interaction with π electrons of the MWNTs. [Copyright &y& Elsevier]

A series of sodium poly(styrene sulfonate)[hyphen]block[hyphen]poly(4[hyphen]tert[hyphen]butylstyrene) (NaPSS[hyphen]b[hyphen]PtBS) copolymers and related homopolymers were characterized by Fourier transform infrared (FT[hyphen]IR) and nuclear magnetic resonance (NMR) spectroscopy. The homopolymers included polystyrene (PS), poly(4[hyphen]tert[hyphen]butylstyrene) (PtBS), sodium poly(4[hyphen]styrene sulfonate) (NaP4SS), sodium poly(styrene sulfonate) (NaPSS) with various sulfonation levels, and partially sulfonated PtBS (PtBSS). The structures of NaPSS and PtBSS were elucidated, and the effect of sulfonation level on the NaPSS FT[hyphen]IR spectrum was studied. The characteristic peaks for NaPSS and PtBSS in FT[hyphen]IR and NMR spectra were identified. [Copyright &y& Elsevier]

Hot (at 120 °C) and dry (20% relative humidity) operating conditions benefit fuel cell designs based on proton exchange membranes (PEMs) and hydrogen due to simplified system design and increasing tolerance to fuel impurities. Presented are preparation, partial characterization, and multi-scale modeling of such PEMs based on cross-linked, sulfonated poly(1,3-cyclohexadiene) (xsPCHD) blends and block copolymers with poly(ethylene glycol) (PEG). These low cost materials have proton conductivities 18 times that of current industry standard Nafion at hot, dry operating conditions. Among the membranes studied, the blend xsPCHD-PEG PEM displayed the highest proton conductivity, which exhibits a morphology with higher connectivity of the hydrophilic domain throughout the membrane. Simulation and modeling provide a molecular level understanding of distribution of PEG within this hydrophilic domain and its relation to proton conductivities. This study demonstrates enhancement of proton conductivity at high temperature and low relative humidity by incorporation of PEG and optimized sulfonation conditions. [ABSTRACT FROM AUTHOR]

Abstract: Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(l-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(l-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks. [Copyright &y& Elsevier]

Abstract: Temperature induced conformational changes of poly(p-oligo(ethylene glycol) styrene) (POEGS) in aqueous solutions were investigated by small angle neutron scattering (SANS), neutron transmission and dynamic light scattering (DLS). The molecular weight of the polymer studied was 9400g/mol with a polydispersity index of 1.18 and each repeat unit of the polymer had four ethylene glycol monomer segments. The polymer was water soluble due to the hydrophilicity of the OEG side chains and these solutions showed lower critical solution temperature (LCST) depending on the concentration of the polymer. Measurements of solution behavior were made as a function of temperature in the range of 25–55°C for three polymer concentrations (0.1wt%, 0.3wt%, and 1.8wt%). Neutron transmission measurements were used to monitor the amount of polymer which precipitated or remained in solution above the cloud point temperature (T CP). DLS revealed the presence of large clusters in all solutions both below and above T CP while SANS provided information on the structure and interactions between individual chains. It was found that in the homogeneous region below T CP the shape of individual polymers in solution was close to ellipsoidal with the dimensions R a =37Å and R b =14Å and was virtually independent of temperature. The SANS data taken for the most concentrated solution studied (1.8wt%) were fit to the ellipsoidal model with attractive interactions which were approximated by the Ornstein–Zernike function with a temperature-dependent correlation length in the range of 24–49Å. The collapse of individual polymers to spherical globules with the radius of 15Å above T CP was observed. [Copyright &y& Elsevier]

MALDI-TOF MS was used to study the end-group distribution of a series of poly(m-phenyleneisophthalamide) oligomers which were synthesized using various mole percent ratios of diamine to diacid chloride (90:10, 80:20,70:30,60:40,50:50,40:60,30:70,20:80, and 10:90) to clarify results obtained in previous work published in this journal. Oligomers synthesized with excess diamine or excess diacid chloride were found to contain abundances of amine or carboxylate end groups, respectively, as expected. Oligomers synthesized with equal molar ratios of reactants produced cyclic species which were also found in a previous publication as an oligomer in commercially produced, high molecular mass Nomex. [ABSTRACT FROM AUTHOR]

A novel synthetic biodegradable oligomer based upon methacrylated aminocaproyl maleamic acid (MACMA), was synthesized and characterized. Injectable and in situ crosslinkable polymer networks were formulated by copolymerization of MACMA with triethyleneglycol dimethacrylate (TEGDMA). In addition, composites composed of MACMA, TEGDMA and beta-tricalcium phosphate (β-TCP) were prepared. The networks and composites were initiated by photo- and redox-polymerization, respectively. The initial compressive (CS) and diametral tensile strengths (DTS) of these materials were determined and used to evaluate the effects of MACMA/TEGDMA ratios on the degradation behavior of the materials. The neat resin networks exhibited initial CS values ranging from 6.7 to 284.2 MPa and the composites demonstrated initial DTS values ranging from 2.8 to 20.8 MPa and CS values ranging from 19.1 to 119.5 MPa. During the course of degradation the polymer neat resins lost 51%, 69% and 61% of their initial CS after 3 weeks for the MACMA/TEGDMA ratios at 25/75, 50/50 and 75/25, respectively. The resin with the MACMA/TEGDMA ratio of 75/25 completely degraded after 6 months. The composite with the MACMA/TEGDMA ratio of 25/75 exhibited a significant increase in CS after an initial decrease for 7 days and then lost 57% of its initial CS after 3 months. The composite composed of poly(MACMA) homopolymer showed a complete degradation after 21 days. [Copyright &y& Elsevier]

A method of off-line coupling of thin layer chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (TLC/MALDI-TOF MS) was used to study a synthetic procedure that produces well-defined hydroxyl-end-capped polymers. The TLC separation is based on the structure of the end group of the polymer and is not affected by the degree of polymerization. MALDI-TOF mass spectral analysis of these TLC fractions confirmed their structures. [Copyright &y& Elsevier]