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Copolymers of hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPMA) with styrene and with methyl methacrylate have been studied. Variations in nature and composition have been correlated, both with the total equilibrium water content of the resultant hydrogel and with the more detailed water binding behaviour as revealed by differential scanning calorimetry studies. Differential scanning calorimetry enables the relative proportions of non-freezing and freezing water to be determined and, in addition, enables the fine structure of the melting endotherm to be observed. Particular interest centres around the ability to produce hydrogels in which all freezing water has been eliminated by progressive incorporation of non-hydrophilic monomer or crosslinking agent (ethylene glycol dimethacrylate). Distinct differences are observed between hydrophilic acrylates and methacrylates in the relative effects of temperature on the equilibrium water contents of their respective copolymer series.

5-Phenyl-1,3-dioxolan-2,4-dione (the anhydrocarboxylate derivative of mandelic acid) has been shown to undergo polymerisation in the presence of tertiary organic bases such as pyridine in a reaction that has somewhat unusual characteristics. Thus, although the reaction in nitrobenzene shows first-order kinetic dependence on both monomer and pyridine over a reasonable concentration range, the pyridine is not consumed and does not appear to control the molecular weight of the resultant polymer. The most important factor in controlling molecular weight is the presence of adventitious moisture which enters into the polymerisation process producing poly-α-esters that are hydroxyl/carboxyl terminated. The rate of polymerisation increases progressively as pyridine is replaced by 2-methylpyridine and 2,6-dimethylpyridine but decreases dramatically when 2-methoxypyridine is used, indicating the importance of the basicity of the attacking species. The results are interpreted in terms of the interaction of the basic nitrogen and the C-4 ring carbonyl leading to the formation of a transient charge transfer complex which subsequently decomposes to form pyridine, carbon dioxide and the α-lactone. The chain growth process involves the interaction of the α-lactone with any nucleophiles present which control the molecular weight and nature of the end groups.

The design and evaluation of Friedel-Crafts polymers as electrical insulants is discussed with particular reference to materials based on p-xylylene glycol dimethyl ether and terphenyl. The general synthetic procedure for these applications normally consists of two idealised stages. The first involves the formation of a soluble, linear or branched polymer. The second consists of its conversion, sometimes after isolation and compounding operations, to a cross-linked material at a controllable rate in a moulding or film-forming reaction. A variety of catalysts and reaction conditions were examined, of which SnC14 and the so-called ball clays (a range of kaolin-based minerals varying in acidity and iron content) proved to be the most interesting. The structures of the polymers at various stages of the reaction leading to the final cross-linked product are discussed together with the properties of the resultant materials.

Some of the problems and advantages in the use of non-hydrogel polymers in contact lenses are discussed together with studies on a series of such polymers which have potential advantages over the established material, poly(methyl methacrylate), in that they are both more flexible and more oxygen-permeable. Of the polymers examined which are all too hydrophobic for direct use, poly(4-methylpent-l-ene) proved to be the most readily modified in such a way that its surface became sufficiently wettable to sustain a coherent tear film without reducing its optical qualities to an unacceptable level. The ‘dissolved’ and ‘gaseous’ oxygen permeability coefficients of this polymer were studied as a function of film thickness, surface hydrophilicity and temperature. A pronounced boundary layer effect was observed in ‘dissolved’ oxygen permeability studies, although this decreased as the surface was treated to make it more wettable (as indicated by the equilibrium advancing water contact angle). The ‘gaseous’ permeability coefficients of oxygen were found to be some 4-6 times greater than those for nitrogen. A discontinuity corresponding to the glass transition temperature was observed at 28°C with both permeants and apparent activation energies for permeation were determined both above and below this temperature.

The use of anhydrosulphite and anhydrocarboxylate derivatives of α-pentafluorophenyl-α-hydroxypropanoic acid as precursors in the formation of fluorine-containing poly α-esters is described. Kinetic studies have enabled the nature of the competing mechanisms to be determined and compared with those occurring in the hydrocarbon analogues. The pentafluorophenyl group markedly enhances the susceptibility of both ring systems to hydroxyl-initiated polymerisation and in the case of the anhydrocarboxylate this is the only viable polymerisation mechanism under the conditions described here. Although polymerisation of the anhydrosulphites is possible, purification of both the phenyl, and especially the pentafluorophenyl substituted monomer, is more difficult than in the case of either alkyl substituted anhydrosulphites or phenyl and pentafluorophenyl substituted anhydrocarboxylates. For this reason anhydrocarboxylate polymerisation represents the preferred route to pentafluorophenyl substituted poly α-esters. The characterisation of the polymers produced is discussed.

The polymerization of cyclopentene in the presence of an unsaturated ester led to the synthesis of low-molecular-weight polypentenamer with a terminal functional group by ringopening metathesis polymerization using WCl6/AlEtCl2/EtOH as catalyst. Unlike most reactions of this nature the efficiency of the catalyst system is high because the ester used possesses an electron withdrawing group, the trichloromethyl group. The presence of this group ensures that the complex formed between the metal carbene complex and the ester group is reduced in stability and catalyst concentrations normally used for ring-opening metathesis polymerizations can be used (mole ratio W : CP = 1 : 1000), the concentrations of ester being quite high (mole ratio ester : CP = 1 : 5). Under these conditions reasonably high yields of liquid polymers are obtained.

The complex series of reactions that takes place between WCl6 and cyclopentene was studied spectroscopically. The products of reaction remain soluble when chlorobenzene is used as solvent. A number of intermediates was observed and the kinetics of formation and removal of these was studied in detail. A complex series of reactions was postulated to account for these changes and the significance of each reaction to the overall scheme was determined by computer simulation of the changes that occur. One of the products has particular significance in the scheme of reactions since it is believed that this species is eventually responsible for the monometallic initiation of the polymerization of cyclopentene. The reaction was also studied gas chromatographically when it was shown that the reaction is accompanied by the formation of a complex mixture of products. One of these products was shown to have the mass spectrum that would be expected of 3-chlorocyclopentene and a reaction scheme that would account for its formation is postulated. The reactions involved in the generation of centres active towards the formation of polypentenamer were considered for both monometallic and bimetallic (WCl6/AlR3) catalyst.

The interaction of nitrogen monoxide (nitric oxide, NO) with pyrolysed polyacrylonitrile (PANP) has been examined together with the feasibility of the use of PANP based catalysts for the removal of small quantities of NO from the exhaust systems of internal combustion engines. Kinetic studies indicated that PANP was capable of interacting with and removing NO from an inert carrier gas and that the initial specificity of this interaction was little affected by hydrogen, hydrocarbons, carbon monixide or oxygen, the initial rates of removal being appreciably higher than those obtainable with conventional inorganic catalysts or graphitised carbon. The activation energy and kinetic features of the reaction suggested that the interaction involved the odd electron nature of NO and the free spin generated at the polymer surface. Once adsorbed the nitric oxide decomposes to form dinitrogen oxide (N2O) which is further reduced to nitrogen with concurrent assimilation and rearrangement of oxygen within the polymer structure. As a result the PANP gradually loses its capacity to adsorb and decompose NO. In addition, it appears that the structural features which promote the oxidative instability of PANP also govern its NO removal ability. Consequently, the lifetime and therefore practical utility of these systems is governed by the limits of oxidative stability and catalytic capacity.

The ‘dissolved’ oxygen permeabilities (Pd) of a range of hydrogels have been studied at 25 and 34°C (the temperature of the eye). At both temperatures the equilibrium water content (W) was found to be the major controlling factor in determining oxygen permeability and log (Pd) was found to be linearly related to W. The values of Pd at 34°C were found to be approximately twice those at 25°C throughout the range of water contents studied. Available information on corneal oxygen consumption rates is used as a basis for the prediction of oxygen permeability/thickness requirements in continuous wear lenses. These data lead in turn to predicted minimum equilibrium water contents for hydrogels in this, type of application.

The surface and mechanical properties of copolymers of hydroxyalkyl acrylates and methacrylates have been examined by a variety of techniques. This work is complementary to earlier parts of this series which describe the effect of copolymer structure on water binding properties. Water structure has been demonstrated to exert a profound effect upon mechanical properties whether measured in compression or in tension. In particular, water that is characterized by differential scanning calorimetry as ‘freezing’ water is observed to have a marked plasticizing effect upon the gel, whereas ‘non-freezing’ water has little such effect. Similarly, the ‘freezing’ water produces a more marked effect on thermally induced transitions. Two distinct transition points are observed as a result of its presence. One corresponds to the freezing point of water and the other to a glass transition temperature, whose value depends upon the proportion of ‘freezing’ or ‘plasticizing’ water in the gel. Several predictive and direct measurement techniques have been used to study the surface properties of the copolymers in both hydrated and dehydrated states. Taken together they have established a sound understanding of the way in which polar and dispersive components of surface free energy vary as a function of copolymer composition and water content. Use of protein adsorption and fibroblast cell interaction techniques demonstrate that biological phenomena respond to changes at a molecular level which current macroscopic surface energy techniques are unable to discern.

Prolonged controlled release of drugs from polymeric matrices is now well established. In contrast, however, release of macromolecules presents more difficulties and in consequence is less well studied and relatively rarely discussed in the literature. The processes of biodegradation and bioerosion which are important in this field have been exploited in other types of surgical device for some years. This review brings together the literature on various aspects of the bioerosion of polymers containing ester groups, with particular emphasis on release and degradation studies that might form a basis for the design and selection of controlled macromolecular release systems. Polymers discussed include the poly(alpha esters) -including poly(lactic acid) and polyfglycolic acid) —, poly(3-hydroxybutyrate), polydioxanes, polyoxalates, polylactones, polyester hydrogels and the polyanhydride/poly(ortho ester) series.

Patients will be selected wearing PMMA ora hard gas permeable lens, who are having particular problems. The problems designated are: a poor or non wetting contact lens surface with or without accompanying punctuate epithelial erosions. These patients will be refitted with a lower wetting angle material; and the effects of wear on the contact lens surface, and on the cornea, willbe discussed.

The release of a series of surrogate drugs from bioerodible polyhydroxybutyrate-polyhydroxyvalerate copolymer matrices has been investigated. Release was found to be dependent not only on drug loading but also on the porosity of the drug-polymer matrix. Release was affected significantly by the addition of porosigens, notably microcrystalline cellulose and lactose. At low porosigen levels release was matrix controlled and independent of solution hydrodynamics. Release from the matrices was independent of solution pH, except where the drug had different solubility in gastric and intestinal fluids. This is therefore a system which in its primary drug release function is not governed by the degradation or erosion of the polymer but which is ultimately biodegradable and bioabsorbable.

The reaction of C(5) phenyl-substituted 1,3-dioxolan-2,4-diones with a series of alcohols has been studied in order to obtain quantitative information relating to the role of hydroxyl initiation in the polymerization of these compounds. Results relating to both the effect of C(5) substitution and the structure of the attacking alcohol are presented. The reactions are secondorder (first-order with respect to each component) and show some of the kinetic features associated with monosubstituted 1,3,2-dioxathiolan-4-one-2-oxides. Structural effects are adequately represented in terms of Taft σ* and Es substituent constants. Of the parameters describing the properties of the reaction medium, the donicity concept was found to give the best correlation with rate data. It is considered that hydroxyl initiation will contribute to a relatively small extent in the polymerization of 5,5-diphenyl-1,3-dioxolan-2,4-dione and 5-methyl, 5-phenyl-1,3-dioxolan-2,4-dione but will form the basis for the major chain-growth process in 5-phenyl-1,3-dioxolan-2,4-dione.

The permeability, to lithium, potassium, sodium and calcium chlorides, of a series of hydrogel membranes based principally on copolymers of 2-hydroxyethyl methacrylate has been studied. These copolymers yield homogeneous hydrogels whose water-binding properties vary regularly between those of the relevant comonomers. Changes of this type, which are most readily characterized by the ratio of freezing to non-freezing water determined by differential scanning calorimetry, reflect in some ways the water structure-making and structure-breaking properties of the transported anions and cations themselves. The role of these and related size exclusion phenomena in governing membrane permeability is discussed in comparison with transport models that depend simply upon the volume fraction of water within the system.

The permeability of hydrated poly(2-hydroxyethyl methacrylate) membranes to a series of mono- and divalent cations in the form of their chlorides has been examined. These initial studies indicate that a simple relationship involving some function of the size of the hydrated cation is unable to provide a basis for understanding the transport process. This view is confirmed by the results of studies of the permeation of a single cation (potassium) in the presence of a series of anions. Indeed, anion variation proved to exert an appreciably greater effect than did cation variation. The results are discussed in terms of the structure-making and structure-breaking potential of the ions and the various ways in which such properties have been correlated or measured. The structure-making or structure-breaking properties of an ion appear, to a degree, to be subsumed in the experimentally determined partition coefficient of a salt between solution and membrane. This enables the residual diffusion coefficient to be calculated and provides a reasonable basis for correlation with the hydrodynamic radii of the individual ions.

The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3, 7.4 and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up.

The use of thermoplastics, elastomers and hydrogel polymers in contact lens applications is discussed in terms of the balance of properties required for the lens to function in a satisfactory manner. Although there are several thermoplastics that would appear to offer advantages over poly(methyl methacrylate), the most widely used polymer, the inherent disadvantages are in each case too great. The clarity, toughness, physiological inactivity and ease of fabrication are shared by many polymers, but its critical surface tension governing as it does the maintenance of a coherent tear film on the lens surface is unique amongst materials that are otherwise acceptable. The development of hydrogel polymers is discussed in terms of the potential use of this group of polymers in lenses designed for continuous as distinct from daily wear. The specific requirements of such a lens are considered in the light of the properties possessed by the cornea. Apart from the optical properties of thin (∼0.2 mm) sections of material, the most important parameters are oxygen permeability (since the cornea is avascular a relatively high permeability is required), mechanical properties (the material must be soft enough to avoid discomfort but rigid enough to resist deformation during eyelid movement) and surface hydrophilicity (most conveniently described in terms of the critical surface tension phenomena).

The syntheses of anhydrosulphite and anhydrocarboxylate derivatives of tartronic acid are described. These compounds, more correctly named 5-carboxy-1,3,2-dioxathiolan-4-one-2-oxide and 5-carboxy-1,3-dioxolan-2,4-dione have been shown to undergo polymerization and copolymerization to poly-α-esters containing the tartronic acid residue, characterized by the presence of a pendant carboxyl group. Thermal polymerization of the anhydrosulphite appears to proceed in a substantially identical manner to other members of the series in which the monomer decomposes by a first order process to yield an α-lactone which polymerizes by a rapid chain growth reaction. Because the rate of thermal polymerization of tartronic acid anhydrosulphite is much more rapid than simple alkyl substituted anhydrosulphites, copolymerization favours the former residues. More successful copolymerization was achieved by the use of tertiary base initiators and the anhydrocarfaoxylate derivative of tartronic acid. The polymers and copolymers described are of potential value in the synthesis of drug-carrying biodegradable matrices or more hydrophilic analogues of poly(glycolic acid) which combine the known bioerodibility of the moiety with that presence of a pendant carboxyl group.

Synthetic hydrogels are a versatile range of materials which are of value in several biomedical applications, particularly those where permeability is important. Because the equilibrium water content of the gel governs permeability processes and has a marked influence on other important properties, the permeability requirements of a material often influence other aspects of its behaviour. The design of hydrogels for contact lenses demands an understanding of these interrelationships and thus provides a valuable basis for extending hydrogel design to other applications.

The effect of C-5 phenyl substituents on the thermal decomposition of the 1,3-dioxolan-2,4-dione ring has been examined. Unlike the dimethyl-substituted ring, 5-methyl-5-phenyl-1,3-dioxolan-2,4-dione decomposes smoothly in dry nonhydroxylic solvents to yield polymer and carbon dioxide. The introduction of a second C-5 phenyl substituent produces a similar but more rapid decomposition, with the added complication of a competing ring fragmentation leading to ketone formation. An analogy is drawn between the observed behavior of the phenyl-substituted 1,3-dioxolan-2,4-diones and that of the previously studied 1,3,2-dioxanthiolan-4-one 2-oxides. These monomers therefore provide another example of the thermal polymerisation mechanism first observed with 5,5-dimethyl-1,3,2-dioxathiolan-4-one 2-oxides. In these reactions the rate-determining step is the first-order ring-scission process leading to the formation of an α-lactone intermediate. This intermediate then takes part in a very rapid chain-growth process which governs the characteristics of the polymer formed.

The use of nitrogen- and carboxyl-containing monomers in conjunction with hydroxyalkyl acrylates and methacrylates enables hydrogels having equilibrium water contents in the range 30–90% to be obtained. Although such systems are described in the patent literature, the effect of structural variation on properties is not well recognized. In this paper, the effect of copolymer composition on equilibrium water content is discussed, together with the way in which water structure within the polymer varies. Although weakly interacting monomer pairs, such as hydroxyethyl methacrylate and vinylpyrrolidone, produce steady and predictable changes in polymer properties as a function of compositional variation, the same is not true of monomers that possess appreciable hydrogen-bonding capability. In such cases, typified by acrylamide-methacrylic acid and acrylamide-acrylic acid, hydrogen bonding between the constituent monomers produces the most marked structural effects at around equimolar feed ratios. The resultant interaction is reflected in equilibrium water content, mechanical properties and surface properties. The effect of composition on these properties (as measured by micropenetrometry and surface energy analyses) is discussed together with the results of more structure-specific biological probe experiments.

The thermal degradation of poly(cyclopentylidene carboxylate) and poly(cyclohexylidene carboxylate) has been studied over the temperature range 200–500°C by using a combination of kinetic and analytical techniques. The results obtained indicate the simultaneous operation of mechanisms previously observed with different compounds in the series. Thus kinetic studies by thermogravimetric analysis and characterization of the products formed suggest the occurrence of an essentially first-order hydrogen abstraction process with superimposed random scission reactions in the early stages. The main products are cyclopenten-1-carboxylic acid and cyclohexen-1-carboxylic acid, respectively. This corresponds to the behavior previously observed in the degradation of poly(3-pentylidene carboxylate). On the other hand, in-line pyrolysis directly linked to a gas chromatograph clearly indicates the production of cyclopentanone and cyclohexanone and, more importantly in the case of poly(cyclopentylidene carboxylate), the formation of dicyclopentyl glycollide. The appearance of these products in addition to the unsaturated acids suggests that some degradation occurs by the intramolecular ester-interchange process previously postulated for poly(methylene carboxylate) and poly(isopropylidene carboxylate). The associated thermodynamic parameters and relative quantities of the different products observed by gas-chromatographic methods indicate that the hydrogen-abstraction process predominates.

Present knowledge relating to the effect of fluoroaromatic residues on the properties of polymers and the limited literature on the synthesis and properties of fluorine-containing polyesters are briefly discussed. The use of α-hydroxy carboxylic acid anhydrosulphites in the preparation of poly α-esters is described, together with the potential use of this route in the evaluation of the effect of fluoroaromatic substituents on the properties of these polymers. Details of a series of new Grignard syntheses of α-pentafluorophenyl-α-hydroxy carboxylic acids from the commercially available bromopentafluorobenzene and of the conversion of these acids to the anhydrosulphites via the reaction of thionyl chloride on the anhydrous cupric salts of the acids are presented. In this way a series of intermediates has been synthesised from which new fluorine-containing polymers may be prepared.

The Farol-Weissenberg rheogoniometer has been used to follow molecular weight changes during the degradation of certain poly-α-esters in the melt state. By observing the change in melt viscosity at low shear rates it had been shown that the decomposition of the poly(isopropylidene carboxylate) is substantially first-order with respect to the molecular weight of the residual polymer. The derived kinetic parameters are in good agreement with those previously obtained by other techniques. This provides a substantial piece of supporting evidence for the view that degradation takes place predominantly by intramolecular ester interchange involving the formation of 1,1,4,4,-tetramethylglycollide. The introduction of β-chlorine atoms into the polymer structure leads to a more complex degradation pattern. Thus the presence of a single β chlorine atom per repeat unit, as in poly(3-chloro-2-methyl-2-hydroxypropionic acid) leads to a substantially similar dependence on molecular weight with the added complication of progressive crosslinking which becomes more apparent in later stages of the reaction. This crosslinking reaction plays an increasingly important part as the extent of chlorination of the polymer is increased. In addition, the presence of chlorine leads to an increased sensitivity of the degradation reaction to the presence of oxygen.

The use of highly conjugated organic polymers as heterogeneous catalysts is reviewed as part of a series of papers relating to their use in reactions involving oxides of nitrogen. The polymers which have been examined and the types of catalysed reaction so far recorded are described. In general the structural features, including extensive conjugation, which are considered important for catalytic activity and selectivity, are also responsible for their high thermal stability. The presence of hetero-atoms, a high stable concentration of delocalised electrons and semiconductivity, have each been proposed as primary requisites for catalytic activity.

5-Methyl-5-propyl-1,3,2-dioxathiolan-4-one 2-oxide (MPAS) and 5-methyl-5-isopropyl-1,3,2-dioxathiolan-4-one 2-oxide (MiPAS), which are isomers of the previously studied 5,5-diethyl-1,3,2-dioxathiolan-4-one 2-oxide (DEAS), have been synthesized and their polymerizability compared with that of the last compound. The two unsymmetrically substituted monomers polymerize by a mechanism which is substantially identical to that of their symmetrically substituted counterpart. In dry nonhydroxylic solvents the rate-determining process is the primary scission of the ring, which takes place with elimination of sulfur dioxide and concurrent ring contraction to form an α-lactone intermediate. In this reaction, the parent acid, produced by reaction of the monomer with adventitious traces of moisture, acts as the initiating species. The resultant polymers are all hydroxyl/carboxyl-terminated, but, whereas those derived from the two unsymmetrically substituted monomers are amorphous and readily soluble in a variety of organic solvents, those derived from the diethyl-substituted ring have been shown to be highly crystalline materials which dissolve in very few solvents. The relative polymerization rates are illustrated by the first-order rate constants for decomposition in nitrobenzene at 90°C: DEAS, 20.1 × 10−5 sec−1; MiPAS, 11.0 × 10−5 sec−1; MPAS, 9.7 × 10−5 sec−1. The role of the substituents in determining the magnitude of these constants is discussed in terms of both the Thorpe-Ingold effect and electron donation at C-5.

The thermal degradation of two β-chlorinated versions of poly(isopropylidene carboxylate) has been studied by the combined thermogravimetric and gas evolution techniques described previously. Poly(3-chloro-2-methyl-2-hydroxypropionic acid) was found to decompose by a predominantly first-order process which was characterized by kinetic parameters similar to those obtained for poly(isopropylidene carboxylate). These are interpreted in terms of an intramolecular ester-exchange process. As the reaction proceeds intermolecular elimination of hydrogen chloride leads to crosslinking and ultimately to the formation of a carbonaceous char. This process is much more marked in the randomly β-chlorinated analog of poly(isopropylidene carboxylate). With this polymer, drastic deviation from first-order behavior is observed in thermogravimetric results, even in the early stages of reaction. Gas evolution analysis, being more influenced by degradation fragments having an appreciable vapor pressure, yields reasonable first-order data and indicates that the intramolecular interchange mechanism is still an important process. In general, the introduction of β-chlorine atoms is seen to reduce the rate of thermal decomposition of poly-α-esters.

The thermal degradation of poly(3-pentylidene carboxylate) has been studied kinetically over the temperature range 200–300°C using thermogravimetry, gas evolution analysis, and rheogoniometry together with isolation and analysis of the reaction products. The observed behavior is completely different from that previously reported for poly(isopropylidene carboxylate) and poly(methylene carboxylate). Whereas in the latter cases the decomposition occurs by a first-order intramolecular ester interchange process characterized by an activation energy in the region of 27 kcal mole−1, poly(3-pentylidene carboxylate) decomposition occurs by random chain scission superimposed on a first-order hydrogen abstraction process. The activation energy associated with this decomposition reaction is in the region of 47 kcal mole−1, and the major degradation products are cis- and trans-2-ethyl crotonic acid.

The use of reflectance techniques for the study of surface coatings is discussed and the applications of goniophotometry briefly reviewed. The necessary modifications to enable the Brice-Phoenix light scattering photometer to be used as a high sensitivity goniophotometer are described together with details of the application of the instrument to the study of point films. Results obtained with different types of coatings are presented in order to show typical effects of variation in, for example: pigmentation, application technique and environmental deterioration. The results are discussed in terms of the subjectively assessed “gloss” of the different coatings and the ways in which the features of the goniophotometric curves may be most effectively and compactly described. Goniophotometry is suggested as a potentially valuable and sensitive technique for the quantitative study of the early stages of deterioration of polymer films.

The success of synthetic polymers as biomaterials depends upon their interfacial properties and resultant interactions with cells and biological fluids in vivo. A useful experimental approach to defining requirements for biocompatibility is to study the mechanisms by which synthetic substrata influence eukaryote cell behaviour in culture. Here we present an overview of the relationships between physical and chemical substratum properties and cell behaviour on a range of synthetic polymers. We relate our results to theories of in vivo tissue compatibility.

An overview is presented of the use of hydrogel composites as biomaterials. These range from laminates or coatings (in which a homogeneous hydrogel is used in conjunction with a more mechanically stable substrate), through blends of hydrogels with synthetic hydrophobic polymers, to the use of two-component systems in which water enhances the compatibility of two structurally different polymers. Although synthetic hydrogels provide an ideal basis for materials of these types, naturally occurring hydrophilic polymers with their unique properties have a major contribution to make. It is in the clinical and patent literature, rather than journals dealing with polymers per se, that the vast majority of examples of the use of hydrogel composites are found. This review collects and comments on examples based on synthetic developments in this field during the last decade, particularly in relation to the development of wound dressings and implant materials.

The concept of the bionic man was most effectively brought to public attention in the 1970s by the American television series ‘The Six Million Dollar Man’. The programme centred around Steve Austin, an experimental plane test pilot who was reduced to a near-lifeless mutilated shell in a horrific crash. With the cry ‘we have the technology — we can rebuild him’ a team of scientists got to work and created the Bionic Man. No problems of rejection or failure of materials for him! The end result was a superhuman creature whose synthetic and electronic replacement parts far outperformed Mother Nature’s originals. The only hint of realism in the series came when the Bionic Man’s (non-bionic) girl friend jumped from a plane without the aid of a parachute. The scientists reluctantly performed a second series of operations to create the Bionic Woman. The programme producers, presumably to heighten pathos and avoid undue competition with the star of the show, permitted a hint of reality to creep in. The polymeric material encapsulating the electronic controls implanted in the girl’s brain caused a massive embolism and Jamie Summers died. Of course, we subsequently learned (when it was realised what hot commercial property the ‘Six Million Dollar Woman’ would be in her own television series) that she made an unexpected, miraculous recovery. There, at a stroke, the only resemblance in the series to real life problems in biomedical materials research disappeared.

The range and nature of the various clinical manifestations of hydrogel contact lens spoliations are considered. An indication of the present view of the occurrence, chemical composition and potential aetiology for discrete elevated deposits, organic and inorganic surface films, plaques and granular deposits, microbial spoliation, lens discolouration and other extrinsic factors is provided. The literature is principally concerned with the clinical manifestations of spoilation and most observations have been made on lenses that have become so severely spoiled as to be unwearable. No serious attempt has yet been made to identify those tear species responsible for the development of the various types of deposits or of the effects of variations in the bulk and lens chemistry, and also wear protocols on the formation of deposits.

Light, SEM and histochemical techniques were used to determine the architecture and composition of elevated deposits on a variety of commercial lenses of differing bulk and surface chemistries and wear protocols. Spoilt lenses were derived from controlled lens wear trials and additional clinical sources. Elevated deposits display a complex multilayered structure, unaffected by variations in wear protocol or bulk and surface chemistries. These deposits are predominantly composed of tear-derived lipids laid down in a well-defined fashion. The primary layer is composed of unsaturated lipids, whilst the secondary and tertiary layers are dominated by cholesterol and cholesterol esters. The composition and location of deposit components is unaffected by variations in, wear protocol, chemistry of the lens matrix, or tear composition of lens wearers. These findings suggest that unsaturated lipids are responsible for the biological interfacial conversion of hydrogel lenses, reducing their compatibility with the ocular environment.