Extracting force fields for disordered polymeric materials from neutron scattering data

We present a new approach that allows the determination of force-field parameters for the description of disordered macromolecular systems from experimental neutron diffraction data obtained over a large Q range. The procedure is based on a tight coupling between experimentally derived structure factors and computer modelling. We separate the molecular potential into non-interacting terms representing respectively bond stretching, angle bending and torsional rotation. The parameters for each of the potentials are extracted directly from experimental data through comparison of the experimental structure factor and those derived from atomistic level molecular models. The viability of these force fields is assessed by comparison of predicted large-scale features such as the characteristic ratio. The procedure is illustrated on molten poly(ethylene) and poly(tetrafluoroethylene).

Cinnamate ester containing liquid crystalline side chain polymers

The synthesis of methacrylate esters of 4-cyanophenyl-(4-(ω-hydroxyalkyloxy)) cinnamates, with spacer lengths of 2 and 6 methylene units and the synthesis of the corresponding acrylate ester with a spacer of 2 methylene units are described. The methacrylate monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with the analogous benzoate monomer of spacer length 6. The acrylate ester could not be polymerized successfully under the same reaction conditions. Polymers were characterized by NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermo-optic observations. Of the monomers prepared, only the cinnamate with a hexamethylene spacer shows a mesophase, seen on supercooling of the melt. All of the polymers prepared were liquid crystalline, with smectic behavior predominating in the polymethacrylates with the longer spacer group. A narrow nematic region is seen just below the clearing temperature with a range of 3–9°C, nematic character is increased in the copolymer series with the degree of incorporation of the cinnamate monomer with the spacer group of length 2.

Approaches to the synthesis of novel photoactive side chain liquid crystalline polymers containing analogues of the cinnamate ester group

A series of chain liquid crystalline copolymers of 4-cyanophenyl 4′-(6-methacryloyloxyhexyloxy)benzoate and 2-methacryloyloxyethyl β-(1-naphthyl)-propenoate were prepared by free radical polymerization. The corresponding polyacrylates could not be prepared in the same way and an alternative method was used for their preparation involving the synthesis of copolymers of the mesogenic monomer and 2-hydroxyethyl acrylate followed by treatment of the resulting polymers with β-(1-naphthyl)propenoyl chloride. The materials are of interest as photoactive liquid crystalline polymers. The effect of introducing a bulky nonmesogenic group into a liquid crystalline copolymer generally lowers the clearing temperature and raises Tg but also gives rise to contrasting phase behaviour in these two series of polymers. Polymethacrylates which show mesomorphism have sharp transitions and continue to exhibit a highly ordered smectic phase over the bulk of their liquid crystal range. Polyacrylates, on the other hand, exhibit a weakening and broadening-out of their thermal transitions consistent with a lowering of order. These results emphasize the effect of the polymer backbone on phase behaviour.

Polysialic acid as a drug carrier: evaluation of a new polysialic acid–epirubicin conjugate and its comparison against established drug carriers

This paper explores the potential of polysialic acid (PSA) as a carrier for low molecular weight anticancer drugs. A PSA–epirubicin (Epi) conjugate was synthesized and compared against Epi conjugates containing established carriers, namely: N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers, poly(ethylene glycol) (PEG) and polyglutamic acid (PGA). Biological assessments in the breast cancer cell line MCF-7 and in the anthracycline resistant MCF-7/DX showed that the PSA–Epi conjugate had the highest activity (40% and 30% cell death in the two cell lines at 1 mM Epi equiv., respectively). FACS studies confirmed internalization of all conjugates by cholesterol-dependent endocytosis. PSA–Epi showed release of Epi (40% at 5 h) when incubated with lysosome extracts. In vivo evaluation showed that all conjugates had a significantly longer half-life compared to free Epi. This study also allowed an investigation on the effect of the polymeric carrier on the biological activity of a conjugate, with the biodegradability of the carrier emerging as an important feature.

High performance polyester-based materials

Biaxially oriented films produced from semi-crystalline, semi-aromatic polyesters are utilised extensively as components within various applications, including the specialist packaging, flexible electronic and photovoltaic markets. However, the thermal performance of such polyesters, specifically poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalate) (PEN), is inadequate for several applications that require greater dimensional stability at higher operating temperatures. The work described in this project is therefore primarily focussed upon the copolymerisation of rigid comonomers with PET and PEN, in order to produce novel polyester-based materials that exhibit superior thermomechanical performance, with retention of crystallinity, to achieve biaxial orientation. Rigid biphenyldiimide comonomers were readily incorporated into PEN and poly(butylene-2,6-naphthalate) (PBN) via a melt-polycondensation route. For each copoly(ester-imide) series, retention of semi-crystalline behaviour is observed throughout entire copolymer composition ratios. This phenomenon may be rationalised by cocrystallisation between isomorphic biphenyldiimide and naphthalenedicarboxylate residues, which enables statistically random copolymers to melt-crystallise despite high proportions of imide sub-units being present. In terms of thermal performance, the glass transition temperature, Tg, linearly increases with imide comonomer content for both series. This facilitated the production of several high performance PEN-based biaxially oriented films, which displayed analogous drawing, barrier and optical properties to PEN. Selected PBN copoly(ester-imide)s also possess the ability to either melt-crystallise, or form a mesophase from the isotropic state depending on the applied cooling rate. An equivalent synthetic approach based upon isomorphic comonomer crystallisation was subsequently applied to PET by copolymerisation with rigid diimide and Kevlar®-type amide comonomers, to afford several novel high performance PET-based copoly(ester-imide)s and copoly(ester-amide)s that all exhibited increased Tgs. Retention of crystallinity was achieved in these copolymers by either melt-crystallisation or thermal annealing. The initial production of a semi-crystalline, PET-based biaxially oriented film with a Tg in excess of 100 °C was successful, and this material has obvious scope for further industrial scale-up and process development.

Equilibrium behavior of symmetric ABA triblock copolymer melts

Melts of ABA triblock copolymer molecules with identical end blocks are examined using self-consistent field theory (SCFT). Phase diagrams are calculated and compared with those of homologous AB diblock copolymers formed by snipping the triblocks in half. This creates additional end segments which decreases the degree of segregation. Consequently, triblock melts remain ordered to higher temperatures than their diblock counterparts. We also find that middle-block domains are easier to stretch than end-block domains. As a result, domain spacings are slightly larger, the complex phase regions are shifted towards smaller A-segment compositions, and the perforated-lamellar phase becomes more metastable in triblock melts as compared to diblock melts. Although triblock and diblock melts exhibit very similar phase behavior, their mechanical properties can differ substantially due to triblock copolymers that bridge between otherwise disconnected A domains. We evaluate the bridging fraction for lamellar, cylindrical, and spherical morphologies to be about 40%–45%, 60%–65%, and 75%–80%, respectively. These fractions only depend weakly on the degree of segregation and the copolymer composition.

Effective interaction between monolayers of block copolymer compatiblizer in a polymer blend

The stability of ternary blends of two immiscible homopolymers and a block copolymer compatiblizer depends crucially on the effective interaction between the copolymermonolayers that form between the unlike homopolymer domains. Here, the interaction is calculated for blends involving A and B homopolymers of equal size with ABABdiblock copolymers of symmetric composition using both self-consistent field theory (SCFT) and strong-segregation theory (SST). If the homopolymers are larger than the copolymer molecules, an attractive interaction is predicted which would destroy the blend. This conclusion coupled with considerations regarding the elastic properties of the monolayer suggests that the optimum size of the homopolymer molecules is about 80% that of the copolymer molecule. A detailed examination of the theory demonstrates that the attraction results from the configurational entropy loss of the homopolymer molecules trapped between the copolymermonolayers. We conclude by suggesting how the monolayers can be altered in order to suppress this attraction and thus improve compatiblization.

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.

Synthesis of biodegradable polyhydroxyalcanoate copolymer from a renewable source by alternate feeding

Polyhydroxyalcanoates copolymers with 3-hydroxybutirate (3HB) and 3-hydroxyvalerate (3HV) co-monomers, P3(HB-co-x%HV), were produced in fed-batch culture by Ralstonia eutropha DSM428 using fructose as a single carbon source in the first step and adding propionic acid in the second step by alternating feeding. Polymer yield was 0.18 g/L with a content of 24 mol% of the 3HV fraction determined by H-1 NMR. NMR measurements indicated that the polymer obtained is isotactic. The copolymer attained 35% of crystallinity according to X-ray diffraction measurements, and two (020) planes were observed. Thermal behavior presented melting temperature at 154 degrees C and the crystallization temperature was 65 degrees C. A glass transition temperature was observed at -10 degrees C. Average molecular weight measured by GPC was 4.9 x 10(5) Dalton. Isothermal radial growth rates of spherulites of P3(HB-co-24%HV) were studied. All experimental facts and the analysis of the sequence distribution of diads and triads of 3HB and 3HV units led to the conclusion that it is not a completely statistical random copolymer once it contains different types of segments. POLYM.

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) with a broad range of 3HV content at high yields by Burkholderia sacchari IPT 189

The biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from sucrose and propionic acid by Burkholderia sacchari IPT 189 was studied using a two-stage bioreactor process. In the first stage, this bacterium was cultivated in a balanced culture medium until sucrose exhaustion. In the second stage, a solution containing sucrose and propionic acid as carbon source was fed to the bioreactor at various sucrose/propionic acid (s/p) ratios at a constant specific flow rate. Copolymers with 3HV content ranging from 40 down to 6.5 (mol%) were obtained with 3HV yield from propionic acid (Y-3HV/prop) increasing from 1.10 to 1.34 g g(-1). Copolymer productivity of 1 g l(-1) h(-1) was obtained with polymer biomass content rising up to 60% by increasing a specific flow rate at a constant s/p ratio. Increasing values of 3HV content were obtained by varying the s/p ratios. A simulation of production costs considering Y-3HV/prop obtained in the present work indicated that a reduction of up to 73% can be reached, approximating US$ 1.00 per kg which is closer to the value to produce P3HB from sucrose (US$ 0.75 per kg).

Screening of bacteria to produce polyhydroxyalkanoates from xylose

Although xylose is a major constituent of lignocellulosic feedstock and the second most abundant sugar in nature, only 22% of 3,152 screened bacterial isolates showed significant growth in xylose in 24 h. Of those 684, only 24% accumulated polyhydroxyalkanoates after 72 h. A mangrove isolate, identified as Bacillus sp. MA3.3, yielded the best results in literature thus far for Gram-positive strains in experiments with glucose and xylose as the sole carbon source. When glucose or xylose were supplied, poly-3-hydroxybutyrate (PHB) contents of cell dry weight were, respectively, 62 and 64%, PHB yield 0.25 and 0.24 g g(-1) and PHB productivity (P(PHB)) 0.10 and 0.06 g l(-1) h(-1). This 40% P(PHB) difference may be related to the theoretical ATP production per 3-hydroxybutyrate (3HB) monomer calculated as 3 mol mol(-1) for xylose, less than half of the ATP/3HB produced from glucose (7 mol mol(-1)). In PHB production using sugar mixtures, all parameters were strongly reduced due to carbon catabolite repression. PHB production using Gram-positive strains is particularly interesting for medical applications because these bacteria do not produce lipopolysaccharide endotoxins which can induce immunogenic reactions. Moreover, the combination of inexpensive substrates and products of more value may lead to the economical sustainability of industrial PHB production.

Synthesis of azopolymers with controlled structure and photoinduced birefringence in their LB films

The molecular architecture of azopolymers may be controlled via chemical synthesis and with selection of a suitable film-forming method, which is important for improving their properties for practical uses. Here we address the main challenge of combining the photoinduced birefringence features of azopolymers with the higher thermal and mechanical stabilities of poly(methyl methacrylate) (PMMA) using Atom Transfer Radical Polymerization (ATRP) to synthesize diblock- and triblock-copolymers of an azomonomer and the monomer methyl methacrylate. Langmuir-Blodgett (LB) films made with the copolymers mixed with cadmium stearate displayed essentially the same optically induced birefringence characteristics, in terms of maximum and residual birefringence and time for writing, as the mixed LB films with the homopolymer poly[4-(N-ethyl-N-(2-methacryloxyethyl))amino-2`-chloro-4`-nitroazobenzene] (HPDR13), also synthesized via ATRP. In fact, the controlled architecture of HPDR13 chains led to Langmuir films that could be more closely packed and reach higher collapse pressures than the corresponding films obtained with HPDR13-conv synthesized via conventional radicalar polymerization. This allowed LB films to be fabricated from neat HPDR13, which was not possible with HPDR13-conv. The enhanced organization in the LB films produced with controlled azopolymer chains, however, led to a smaller free volume available for isomerization of the azochromophores, thus yielding a lower photoinduced birefringence than in the HPDR13-conv films. The combination of ATRP synthesis and LB technology is then promising to obtain optical storage in films with improved thermal and mechanical processabilities, though a further degree of control must be sought to exploit film organization while maintaining the necessary free volume in the films. (C) 2008 Elsevier Ltd. All rights reserved.

Adsorption of anionic amphiphilic polyelectrolytes onto amino-terminated solid surfaces

The adsorption behavior of several amphiphilic polyelectrolytes of poly(maleic anhydride-alt-styrene) functionalized with naphthyl and phenyl groups, onto amino-terminated silicon wafer has been studied by means of null- ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The maximum of adsorption, Gamma(plateau), varies with the ionic strength, the polyelectrolyte structure and the chain length. Values of Gamma(plateau) obtained at low and high ionic strengths indicate that the adsorption follows the ""screening-reduced adsorption"" regime. Large aggregates were detected in solution by means of dynamic light scattering and fluorescence measurements. However. AFM indicated the formation of smooth layers and the absence of aggregates. A model based on a two-step adsorption behavior was proposed. In the first one, isolated chains in equilibrium with the aggregates in solution adsorbed onto amino-terminated surface. The adsorption is driven by electrostatic interaction between protonated surface and carboxylate groups. This first layer exposes naphtyl or phenyl groups to the solution. The second layer adsorption is now driven by hydrophobic interaction between surface and chains and exposes carboxylate groups to the medium, which repel the forthcoming chain by electrostatic repulsion. Upon drying some hydrophobic naphtyl or phenyl groups might be oriented to the air, as revealed by contact angle measurements. Such amphiphilic polyelectrolyte layers worked well for the building-up of multilayers with chitosan. (C) 2010 Elsevier Ltd. All rights reserved.

Low cost selective sensor for carbonyl compounds in air based on a novel conductive poly(p-xylylene) derivative

A novel poly(p-xylylene), PPX, derivative bearing phenyl side groups was electrochemically synthesized in 85% yield. The polymer, poly(2-phenyl-p-xylylene) (PPPX), presented a major fraction (88%) soluble in common organic solvents. It showed to be thermally resistant up to 140 degrees C. UV-VIS analysis revealed an Egap of similar to 3.0 eV. Gas sensors made from thin films of CSA doped PPPX deposited on interdigitated electrodes exhibited significant changes in electrical conductance upon exposure to five carbonyl compounds: acetaldehyde, propionaldehyde. benzaldehyde, acetone and butanone. Three-dimensional plots of relative response vs. time of half-response vs. time of half-recovery showed good discrimination between the five carbonyl Compounds tested. (C) 2008 Elsevier B.V. All rights reserved.

Lysozyme binding to poly(4-vinyl-N-alkylpyridinium bromide)

The adsorption behavior of polycations at ionic strengths (1) ranging from 0.001 to 0.1 onto silicon wafers was studied by means of ellipsometry, contact angle measurements and atomic force microscopy (AFM). Polycations chosen were bromide salts of poly(4-vinylpyridine) N-alkyl quaternized with linear aliphatic chains of 2 and 5 carbon atoms, QPVP-C2 and QPVP-C5, respectively. Under 1 0.001 the reduction of screening effects led to low adsorbed amounts of QPVP-C2 or QPVP-C5 (1.0 +/- 0.1 mg/m(2)), arising from the adsorption of extended chains. Upon increasing l to 0.1, screening effects led to conformational changes of polyelectrolyte chains ill Solution and to higher adsorbed amount values (1.9 +/- 0.2 mg/m(2)). Advancing contact angle theta(a) measurements performed with water drops onto QPVP-C2 and QPVP-C5 adsorbed layers varied from (45 +/- 2)degrees to (50 +/- 5)degrees, evidencing the exposure of both hydrophobic alkyl groups and charged moieties. The adsorption of lysozyme (LYZ) molecules to QPVP-C5 layers was more pronounced than to QPVP-C2 films. Antimicrobial effect of LYZ bound to QPVP-C2 or QPVP-C5 layers or to Si wafers was evaluated with enzymatic assays using Micrococcus luteus as Substrates. The adsorption behavior of QPVP-C2 and QPVP-C5 at the water-air interface was studied by means Of surface tension measurements. Only QPVP-C5 was able to reduce water Surface tension. Mixtures of LYZ and QPVP-C5 were more efficient in reducing Surface tension than pure LYZ solution, evidencing co-adsorption at liquid-air interface. Moreover, antimicrobial action observed for mixtures of LYZ and QPVP-C5 was more pronounced than that measured for pure LYZ. Hydrophobic interaction between LYZ and QPVP-C5 ill Solution seems to drive the binding and to preserve LYZ secondary structure. (c) 2008 Elsevier Inc. All rights reserved.