Jerzy Paprotny

Optical switching of coupled plasmons of Ag-nanoparticles by photoisomerisation of an azobenzene ligand

The optical switching of coupled plasmons of silver nanoparticles derivatised with a photoisomerisable azobenzene ligand is presented. It is shown that nanoparticle clusters, linked with an azobenzene dithiol molecule, display switchable optical properties. The photoisomerisation of the linker molecule was used to vary the separation between nanoparticles, which was monitored by changes in the UV-Vis-spectra of the plasmon band of adjacent nanoparticles. A red-shift due to the appearance of a coupled longitudinal plasmon band was observed resulting from the formation of nanoparticle clusters. The maximum absorbance wavelength of this secondary plasmon band was altered by isomerisation of the linker and the spectral changes observed were in good agreement with theory and earlier measurements for gold. Evidence of energy transfer between a nanoparticle and an azobenzene terminated monothiol attached to it was also observed in the UV-Vis spectra.

Synthesis of bulky bis(ether anhydride)s and poly(etherimide)swith bulky main-chain units

A series of bis(ether anhydride)s has been synthesized from very bulky bisphenols. Poly(ether imide)s have been synthesized from these bis(ether anhydride)s and two diamines in order to provide a series of poly(ether imide)s with bulky main-chain units. The polymers have been characterized in terms of molecular weight, solubility, glass-transition temperature and thermal stability in order to identify a series of high-performance polymers which are processable and potentially useful for applications which require soluble poly(ether imide)s for fabrication into, for example, gas separation membranes.

Synthesis of bis(ether nitrile)s and bis(ether acid)s from simplearomatic diols bymeta-fluoro displacement from3-fluorobenzonitrile

There is interest in synthesizing bis(ether acid)s and related compounds to use as monomers in order to prepare processable aromatic polymers, such as poly(ether amide)s and poly(ether ester)s. We have now found that it is possible to prepare efficiently bis(3-cyanophenoxy)phenylenes by fluoro displacement from 3-fluorobenzonitrile and phenylene diols or their derivatives, such as substituted catechols, and to convert those bis(ether nitrile)s to bis(3-carboxyphenoxy)phenylenes which can be used in the synthesis of poly(ether amide)s and poly(ether ester)s. Themeta-fluoro displacement is performed at elevated temperatures in N-methylpyrrolidinone.

Modification of polymers for cardiovascular applications—some routes to bioactive hydrophilic polymers

This paper is concerned with the activation of platelets by polymers, a key-process in the behaviour of prosthetic devices in contact with blood.Platelets are activated by contact with many different types of polymer surfaces, which must therefore be regarded as thrombogenic. Two procedures for reducing thrombogenicity are discussed: (i) the chemical attachment of inhibitors of platelet aggregation and (ii) gross modification of the nature of the surface, e.g. by making it more hydrophilic. For purposes of (i) the potent prostaglandin analogue BW 245C has been used, while for (ii) grafting of poly(ethylene glycol) (PEG) has been explored. Both methods give greatly reduced platelet adhesion inin vitro tests.The second part of the paper deals with the properties of adducts of inhibitors of platelet aggregation (BW 245C, dipyridamole) with water-soluble macromolecules [poly(N-vinyl pyrrolidone), PEG, dextran]. Adducts have been synthesized with terminal and side-chain coupling. On adduction the two inhibitors mentioned show opposite types of behaviour: the molar activity of BW 245C is dramatically reduced, but that of dipyridamole is significantly increased. Remarkable synergistic effects have been recorded for BW 245C adducts. These observations are interpreted in terms of differences in stereochemistry in the drug-receptor interactions.Appropriate chemical techniques for coupling are outlined, attention being drawn to the special uses of haloalkyl- and haloacyl-isocyanates and 2-isocyanatoethyl methacrylate as reagents.

Nitrodisplacement reactions and the synthesis of bis (ether anhydride) s from dihydroxynaphthalenes

Nitrodisplacement reactions between all ten dihydroxynaphthalenes and 4-nitrophthalodinitrile have been studied. Apart from 1,8-dihydroxynaphthalene, all dihydroxynaphthalenes undergo nitrodisplacement but only 1,5-, 2,3-, 2,6- and 2,7-dihydroxynaphthalenes give high yields of pure bis(ether dinitrile). The bisfether dinitriles produced in high yield were hydrolysed and converted to bis(ether anhydride) for subsequent synthesis of poly(ether imide)s. Success in nitrodisplacement correlates with high redox potentials for the dihydroxynaphthalenes, except for 1,8-dihydroxynaphthalene which probably fails to react because of steric constraints at the peri positions.

Synthesis and properties of poly (ether imide)s derived from dihydroxynaphthalenes

Polyether imides were synthesized from bisfether anhydrides derived from 1,5-, 2,3-, 2,6- and 2,7-dihydroxynaphthalenes and various aromatic diamines using a two-stage solution process, normally with chemical imidization. During the synthesis of polymers from the bis (ether anhydride) from 2,3-dihydroxynaphthalene and 4,4′-oxydianiline (4,4′-ODA), by both chemical and thermal imidization, small proportions of a relatively insoluble, infusible, crystalline solid were produced. It is proposed that this product is a cyclic oligomer. Solubilities of the polymers were assessed and, where sufficiently soluble, molecular weights were determined by gel permeation chromatography. Apart from polymers based on 2,3-naphthalene units, the polymers had limited solubilities. Glass-transition temperatures were determined; all were in excess of 220 °C, some were in excess of 300 °C. Several poly(ether imide)s based on ODA, were found to be thermally stable to 590 °C. Polymers based on the bis(ether anhydride) derived from 2,3-dihydroxynaphthalene gave strong solvent-cast films with high moduli extensions to break were modest except for the polymer from the diamine BAPB which extended to 150% prior to fracture.

Professor Bamford's research in the field of biomaterials

Professor Bamford was regarded by many as the greatest British polymer chemist of the twentieth century and when Bam passed away in November 1999 tribute was quite rightly made to his considerable achievements in the field of polymer science. The aim of this paper is to highlight Bams contribution to biomaterials research that occupied his attention for over 15 years after his official retirement. In particular a review of the synthetic methods employed by Bam for the modification of polymers to improve haemocompatibility and to function as affinity separation membranes for protein purification is presented.