In-situ photopolymerization of oriented liquid-crystalline acrylates, 3. Oriented polymer networks from a mesogenic diacrylate

Synthesis, mesomorphism, orientation and photo-initiated chain crosslinking of the liquid-crystalline diacrylate 1,4-phenylene bis{4-[6-(acryloyloxy)hexyloxy]benzoate} ( 1 ) are studied. Monomer 1 exhibits a broad nematic phase between 108 and 155°C and a monotropic smectic phase below 88°C. The monomer is uniaxially oriented in its nematic phase at a substrate which has been coated with polyimide and unidirectionally rubbed with tissue. At the transition temperature to the smectic phase the order parameter is measured to be 0,7. During polymerization, the ordering of the mesogens is frozen-in, yielding a uniaxially crosslinked network. The clear films of oriented poly( 1 ) exhibit a birefringence Δn between 0,12 and 0,15, depending on the polymerization temperature. In the highest oriented state of 1 a small reduction of the degree of order is observed during the crosslinking reaction, whereas at higher temperatures and lower ordering of 1 , the uniaxially orientation increases upon reaction. A special feature of the oriented networks is that the ordering is maintained while heating at high temperatures. The polymerization of the acrylate groups in the mesomorphic phases proceeds fast and to high conversion. Below 90°C the polymerization behaviour is similar to that of conventional isotropic diacrylates. Above 90°C the polymerization reaction of the liquid-crystalline diacrylate proceeds faster than that of an isotropic diacrylate.     

The laser-flash-initiated polymerization as a tool of evaluating (individual) kinetic constants of free-radical polymerization, 2. The direct determination of the rate of constant of chain propagation

When a polymerizable system is subjected to periodic light flashes, which induce the formation of primary radicals, a pseudostationary state is established which is characterized by a periodic profile of the (polymer) radical concentration. Within such a period of length t₀ the radical concentration will decay according to a second-order rate law. At the end of this period the radicals, which have escaped termination up to this moment, have propagated up to a chain length L₀ = t₀·k_p·c_M, k_p representing the propagation rate constant and c_M the monomer amount concentration. When the next flash arrives these radicals are opposed to a strongly increased overall concentration of radicals which leads to an enhanced probability for their termination. As a consequence the formation of dead polymer molecules with a chain length close to L₀ is favoured. The chain-length distribution of polystyrene prepared under such pseudostationary conditions, which was evaluated by gel permeation chromatography, in fact exhibits such a peak. The analysis of the theoretical distribution curves, derived in this communication, reveals that it is easily possible to correlate this peak to L₀, independently of the mode of termination (disproportionation or combination). Thus, a method of evaluating k_p is derived without any reference to the termination rate constant k_t and largely independent of all features which usually cause problems in the evaluation of k_p and k_t (such as primary radical termination etc.). The experimental results agree fairly well with the data reported in literature, especially with those obtained from the number of particles and the rate of polymerization in emulsion systems.     

Evaluation of three-dimensional scaffolds prepared from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) for growth of allogeneic chondrocytes for cartilage repair in rabbits

Articular cartilage repair using tissue engineering approach generally requires the use of an appropriate scaffold architecture that can support the formation of cartilage tissue. In this investigation, the potential of three-dimensional scaffolds made of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was evaluated in rabbit articular cartilage defect model. Engineered PHBHHx cartilage constructs inoculated in vitro with rabbit chondrocytes for 30 days were examined. Subsequently the constructs inoculated with chondrocytes for 10 days were selected for transplantation into rabbits. After 16 weeks of in vivo implantation, both the engineered cartilage constructs and the bare scaffolds were found to be filled the defects with white cartilaginous tissue, with the engineered constructs showing histologically good subchondral bone connection and better surrounding cartilage infusion. Owing to pre-seeded chondrocytes in the PHBHHx scaffolds, better surface integrality and more accumulation of extracellular matrix (ECM) including type II collagen and sGAG were achieved in the engineered cartilage constructs. The repaired tissues possessed an average compressive modulus of 1.58MPa. For comparison, the defects without repair treatments still showed defects with fibrous tissues. These results demonstrated that PHBHHx is a useful material for cartilage tissue engineering.     

Chain-length dependent termination in pulsed-laser polymerization, 7. The evaluation of the power-law exponent b from the chain-length distribution in the low frequency (single-pulse) limit for the reference systems styrene and methyl methacrylate in bulk at 25°C

The chain-length distribution (CLD) was examined for polymers prepared by “low frequency pulsed laser polymerization” (LF-PLP), i. e. for very long pulse separations in the so-called “low frequency” or “single pulse limit”. The data were fitted to the theoretical CLD which could be derived in a closed form for a chain-length dependent rate coefficient k_t and the parameter b that characterizes this chain-length dependence was determined by this fitting procedure. b values close to 0.2 were obtained for styrene as well as for MMA, indicating a moderate chain-length dependence of k_t at low conversions. This result, which is in good agreement with data evaluated by other methods in our laboratory, points to the fact that under these conditions end-segment diffusion is the rate-determining step in bimolecular termination. Factors like moderate chain transfer to monomer and uncertainties with respect to the mechanism of termination (combination or disproportionation) appear to have very little influence on this result.     

Characterization of a PE-g-LCP compatibilizer,prepared by reactive blending of acrylic acid grafted polyethylene (PE) and a semiflexible liquid crystalline polymer (LCP)

Novel graft copolymers (PE-g-LCP) consisting of polyethylene (PE) backbones and liquid crystalline polymer (LCP) branches, synthesized via reactive blending of acrylic acid functionalized PE (Escor 5000 and Escor 5001 by Exxon) with a semiflexible LCP (SBH by Eniricerche S.p.A.; mole ratio sebacic acid (S): 4,4′-dihydroxybiphenyl (B): 4-hydroxybenzoic acid (H) = 1 : 1 : 2) have been characterized by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The isothermal crystallization, the morphology, and the crystalline structure of the crude reactive blending products (COPLE and COPHE) and of their fractions soluble in boiling toluene and xylene and of the residue have been investigated. It has been shown that the isothermal crystallization rate of PE segments of the copolymers decreases from toluene fractions to xylene insoluble fractions, however, these segments preserve their crystallizability even in SBH-rich copolymers. LCP does not lose its mesophase behaviour when bonded to the PE backbone and the morphology of the copolymers is not homogeneous. It is characterized by two types of structure typical of both copolymer segments. There are no interactions in the crystal phase or co-crystallization between the copolymer segments, forming separate crystalline phases. The results have been interpreted by a sufficient length of crystallizable segments of PE and SBH grafts and by a random distribution of SBH grafts along the PE backbone. The latter effect is more pronounced for PE-g-SBH copolymers based on higher molar mass functionalized PE (Escor 5001). It has been assumed that the compatibilization activity of these copolymers towards polyethylene/SBH blends is due not only to the identical chemical structure of the copolymer segments and the corresponding blend components but also to the similarity of their crystalline structure, crystallization behaviour, and morphology.     

Mathematical properties of polydisperse systems, 3. Calculation of molecular weight distribution from light scattering on gaussian polymer coils. Inversion by means of a nonlinear fit

The molecular weight distribution (MWD) of a high polymer is calculated from a weakly perturbed Zimm-plot of the classical light scattering on dilute solutions of Gaussian polymer coils (theta state). A typical Zimm-plot is simulated corresponding to the measurements of high accuracy as would be obtained by using the laser photometer described by Hack and Meyerhoff. The accuracy as published by these authors for small dissymmetries is used. Two numerical methods for calculating the MWD are briefly described and tested, both using an empirical formula for the Laplace image of the calculated MWD.     

New chitin-based polymer hybrids, 3. Miscibility of chitin-graft-poly(2-ethyl-2-oxazoline) with poly(vinyl alcohol)

The miscibility of blends of poly(vinyl alcohol) (PVA) with chitin-graft-poly(2-ethyl-2-oxazoline) ( 1 ) and poly(2-ethyl-2-oxazoline) homopolymer (PEtOZO) was investigated. Calorimetric results showed a single glass transition temperature (T_g) in the entire range of compositions for both blend systems, which indicated that PVA is miscible with both the graft copolymer 1 and PEtOZO. The T_g of PVA is also shifted to lower temperature upon blending with the graft copolymer 1 . IR analysis revealed the existence of specific interactions via hydrogen bonding between the hydroxyl groups in PVA and the carbonyl groups in the poly(2-ethyl-2-oxazoline) side chain of graft copolymer 1 . The results show that the interaction of graft copolymer 1 with PVA is increased by introduction of longer poly(2-ethyl-2-oxazoline) side chains. Thermal decomposition (TG) measurements supported the compatibility of PVA with graft copolymer 1 and with PEtOZO, and showed that the thermal stability of PVA is improved upon blending with 1 or PEtOZO.     

New polymer syntheses, 92. Biodegradable,thermotropic copolyesters derived from β-(4-hydroxyphenyl)propionic acid

Binary copolyesters were prepared by polycondensation of the trimethylsilylester of acetylated β-(4-hydroxyphenyl)propionic acid (HPPA) with acetylated 4-hydroxybenzoic acid (HBA), vanillic acid (VA), 6-hydroxy-2-naphthoic acid (HNA), 4-hydroxycinnamic acid (HCA) or 4′-hydroxybiphenyl-4-carboxylic acid (HBCA). Only the binary copolyester derived from 4-hydroxybenzoic acid proved to be enantiotropic nematic, whereas all other binary copolyesters were more or less crystalline and infusible. Furthermore eight ternary copolyesters were prepared, which all proved to be soluble and thermotropic. ¹³C NMR spectroscopy proved a random nature of the sequences of the copolyesters, which were only obtained when transesterification catalysts such as Ti(OiPr)₄ or MgO were used for the polycondensations. Optical microscopy revealed that five of the eight copolyesters form a homogeneous nematic phase above 220 or 250°C. However, in three cases the nematic melt contained crystalline particles which did not melt below 400°C. According to the WAXS powder patterns and DSC measurements most binary and ternary copolyesters are semicrystalline and form an imperfect orthorhombic crystal lattice. In three cases, the solid phase is best described as a hexagonal columnar mesophase.     

The laser flash-initiated polymerization as a tool of evaluating (individual) kinetic constants of free radical polymerization, 1. Outline of method and first results

A method is presented which allows the determination of k_p/k_t-values in free radical polymerization. It is based on measurements of the (average) rate of polymerization under pseudostationary conditions, the polymerization being initiated by laser flashes of short duration. For ρk_t t₀ ? 1 (ρ being the additional polymer radical concentration produced by each laser flash, k_t the bimolecular termination constant between polymer radicals, k_p the rate constant of chain propagation, t₀ the time separating two successive laser flashes) k_p/k_t may be obtained as the slope of a linear plot of the fractional conversion per flash vs. ln t₀. Dividing the intercept by the slope yields ln (pk_t). Thus, if p is accessible, separation of k_p/k_t-data into its individual constituents may be accomplished without making any use of stationary polymerization data. Application of this method to the polymerization of styrene sensitized by benzoin or AIBN at 25°C gives k_p/k_t-values of 1,0 · 10^?6 which are in fair agreement with those obtained by other methods.     

An investigation of HAP/organic polymer composite coating prepared by electrochemical co-deposition technique (II) characterization of XRD, SEM and mechanic properties]

Electrodeposition hydroxyapatite(HAP) coatings of ceramics were studied by Nano Indent. The bonding force between the coating and metal substrate was distinctly increased. The experiments about XPS and SIMS showed that there is the act of organic polymer enriching at negative. It ensues that minor organic polymer is compounded to HAP coatings at molecular level and forms that HAP/Organic polymer compound coating.     

Investigation of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) blends, 3. Permeation properties of polymer blend membranes

Dense membranes made of poly(vinyl alcohol) (PVA) and poly(N-vinyl-2-pyrrolidone) (PVP) blends of different compositions were studied in gas-sweeping permeation of a water-ethanol mixture containing 10 wt.-% of water. When the PVP content increases, the steady-state permeation flux and the water content in the permeate show sudden changes at ca. 30–40 wt.-% of PVP in the membrane: the flux increases drastically, while the water selectivity of the membrane falls to a much lower level. The diffusion coefficients of both water and ethanol, as determined from the permeation flux changes in the transient regime, exhibit a large increase when the PVP content exceeds 30 wt.-%, and this accounts for the flux increase. The fall in the permeation selectivity is shown to be due to a strong decrease in the sorption selectivity. The threshold of the change corresponds approximately to the PVP content at which PVA crystallites no longer exist in the blend. A further study on the states of water in the blend membranes by differential scanning calorimetry made it possible to relate these changes with a change in the interactions of water with hydrophilic sites in the polymer blend when the PVP content changes.     

Polymerization of 3,3-bis (chloromethyl) oxetane catalyzed by i-Bu3Al in bulk. I. The conditions of high polymer formation

The high temperature (up to 220°C.) polymerization of 3,3-bis(chloromethyl)oxetane catalyzed by i-Bu₃Al was investigated. The conversion-time curves are of the autocatalytic type and the molecular weight increases lineary with conversion up to the point at which for lower temperatures, e.g. 60–80°C., the whole polymer becomes insoluble. An alternative explanation of this phenomenon is proposed; the formation of insoluble product is related to the entanglement of macromolecules of very high molecular weight and or macrocycle formation in the degradative chain transfer to polymer. The phenomenon of insoluble products formation was never observed at higher temperatures (> 150°C.). The dependence of molecular weight on catalyst and impurity concentrations as well as on the polymerization temperature was investigated. It was shown that the high molecular weight product (\documentclass{article}\pagestyle{empty}\begin{document}$\overline {DP}$\end{document} = 1000–1500) can be produced at 180–220°C. even at rather high impurity level.     

BK virus (BKV) quantification in urine samples of bone marrow transplanted patients is helpful for diagnosis of hemorrhagic cystitis, although wide individual variations exist.

BACKGROUND: Hemorrhagic cystitis (HC) in allogeneic bone marrow transplanted (BMT) patients is associated with BK virus (BKV) reactivation manifested as BK viruria. However, since 77-90% of all adult BMT patients excrete BKV, viral reactivation alone cannot be responsible for HC. Recently, a significant overrepresentation of C-->G mutations in the Sp1 binding site in the non-coding control region (NCCR) of BKV was shown to be present in HC patients and absent in non-HC patients. OBJECTIVES: We aimed to investigate if this mutation resulted in excessive BKV excretion in HC patients. STUDY DESIGN: A Real-Time PCR was developed and used to quantify BKV in urine samples from 21 patients with HC, with and without the mutations, as well as from patients without HC. RESULTS: Quantification of BKV was successful in 18 of 21 urine patients (six with and six without C-->G mutations) and six patients without HC. A mean of 3.0 x 10(6) BKV copies/microl was detected in urine samples of HC patients with C-->G mutations, compared to a mean of 1.5 x 10(6) BKV copies/microl in HC patients without C-->G mutations and a mean of 1.0 x 10(6) BKV copies/microl in patients without HC. The obtained differences were however not statistically significant, due to one individual non-HC patient with an extremely high BKV copy number. Nevertheless, while 50% of the samples in the HC groups expressed 1 x 10(6) copies/microl or more, only one of the samples in the non-HC group contained a virus quantity higher than 5 x 10(5) copies. CONCLUSIONS: Although we could not confirm that the C-->G mutations in the Sp1 site of BKV were responsible for an increased viral load in patients with HC, our data suggest that levels of BKV above 10(4) copies/microl may indicate a risk for HC.     

Detection of varicella-zoster virus (VZV) DNA in clinical samples from patients with VZV by the polymerase chain reaction.

A polymerase chain reaction system for the detection of varicella-zoster virus was established. Of 25 nucleotides, 4 oligonucleotide pairs (regions of thymidine kinase, thymidylate synthetase, glycoprotein I, and immediate early gene) were synthesized. The first three oligonucleotide pairs could be used as primers on the basis of specific DNA amplification. Varicella-zoster virus DNA was amplified by this polymerase chain reaction system in 20 of 20 vesicle samples, 5 of 6 crusts, and 12 of 13 throat swabs collected from patients with clinical varicella.     

Polyimides derived from bismethylolimides, 3. Synthesis and properties of poly(imide-urethane)s

Poly(imide-urethane)s having a methylene group between the imido and the oxycarbamoyl groups were synthesized by addition polymerization of bis(N-hydroxymethyl)imides and diisocyanates in hexamethylphosphoric triamide. Properties of the resulting poly(imide-urethane)s were studied in comparison with those of the corresponding poly(imide-urethane)s having no methylene group. The resulting carbamic ester linkage was found to be much more stable against nucleophiles compared with the carbamic ester linkage without the methylene group. However, there appeared to be not much difference in thermal stability between these two kinds of linkages.     

Study of the mechanism of propagation and transfer reactions in the polymerization of olefins by Ziegler-Natta catalysts, 3. Determination of the rate constants of chain transfer with an organo-alumimium cocatalyst

By quenching polymerization with tritium-labelled methanol the total number of the metal-polymer bonds in the polymerization of ethylene and propylene by Ziegler-Natta catalysts was determined. Using the propagation rate constants determined by quenching polymerization with ¹⁴CO the rate constants of chain transfer with AlEt₃ and Al(i-Bu)₃ and the activation energy of chain transfer with AlEt₃ were calculated.     

Anti-I-J alloantisera elicited by immunization of B10.A(3R) (I-Jb) mice with bone marrow-derived macrophages from B10.A(5R) (I-Jk) mice.

In this paper we describe production of alloantisera specific for determinants encoded by I-J gene loci expressed on macrophages. B10.A(3R) (I-Jb) mice were hyperimmunized with pure macrophages grown in vitro from bone marrow stem cells of congenic B10.A(5R) mice. The antisera contained predominantly IgM antibody that was non-adherent to protein-A-Sepharose with a minor component of IgG1, and IgG2a antibodies that were adherent to protein-A-Sepharose. The protein-A non-adherent antibody completely blocked the in vitro generation of humoral immune responses to sheep erythrocytes by spleen cell from B10.A(5R) mice and from inbred strains that share the I-Jk haplotypes, but did not alter the responses of spleen cells of the I-Jb haplotype. In the presence of complement, both protein-A adherent and protein-A non-adherent antibodies eliminated the capacity of B10.A(5R) spleen cells to generate humoral and proliferative responses, but the functional activity of B10.A(3R) cells was unaffected. These data indicate the I-Jk specificity of the antisera. The capacity of the anti-macrophage antibody to block humoral immune induction was removed by absorption with bone marrow-derived macrophages from B10.A(5R) mice, but not from B10.A(3R) mice. Further, the B10.A(5R) macrophages completely restored the humoral responses of antibody- and complement-treated B10.A(5R) spleen cells, but B10.A(3R) macrophages showed only partial restoration that was consistent with a factor-mediated allogeneic effect. These data demonstrate the specificity of our anti-I-J sera for macrophages and indicate that bone marrow-derived macrophages express surface I-J encoded molecules.     

Blood pressure is lowered by vitamin D (alphacalcidol) during long-term treatment of patients with intermittent hypercalcaemia. A double-blind, placebo-controlled study

There is epidemiologic evidence of a relationship between calcium deficiency and hypertension. The present study evaluated the effects of alphacalcidol, a synthetic analogue of active vitamin D, given to 29 patients with marginal, intermittent hypercalcaemia. Before therapy there was an inverse relationship between serum calcium levels and diastolic blood pressure (p less than 0.02). Treatment with 1 microgram alphacalcidol raised the serum calcium by 0.07 mmol/l during a 6-month, double-blind, placebo-controlled trial and caused a significant reduction of diastolic blood pressure by 9.2 mmHg compared with placebo (p less than 0.01). The study extends previous observations, in normocalcaemic subjects, of inverse relationships between serum calcium and blood pressure indicating a primary disturbance of calcium homeostasis in hypertension. The observation that a physiologic amount of active vitamin D has hypotensive effects agrees with such a concept and suggests a new principle for the treatment of hypertension.