Telechelic polymers — precursors to high solids coatings

Coating industry concerns for energy and environmental cost in formulation suggest high solids coatings as an alternative. The use of 100% active coatings, wherein the polymeric binder precursor has functional groups on the chain ends, is rationalized. However, the use of liquid ‘telechelic’ polymer requires the knowledge of syntheses for understanding of fluid properties, cures and physical properties after cure. Synthesis techniques control these end results through their influence on type and amount of functionality, chain configurations and by-products.

As the techniques for making carboxy- or hydroxy-telechelic polyesters or hydroxy-telechelic polyethers have been the object of considerable study and review, this review deals with syntheses based upon addition polymers. The synthesis methods' impact on functionality (type and amount) is emphasized. Fluid property expectations are also noted, and analysis techniques summarized. Currently commercial polymers are cited with notation as to recommended cure and uses. A Summary of cure studies, mostly with emphasis on the applications (e.g. rocket propellant binders, sealants, coatings and so on) is also included.

The conclusions are that current problems with rheology, cure rates and chemistry, and final coating properties may be overcome by appropriate research. These efforts are already under way in some segments of the industry, and high solids coatings or 100% active coatings will be a growing factor in the market place. The prime objective of this review is to gather some of the pertinent information on synthesis, properties and application of the telechelic polymers as a guide to the research on high solids coatings.     

Scanning electron microscopy — energy dispersive x-ray analysis of cement constituents — some cautions

Application of SEM-EDXA instrumentation to rough fracture surface specimens of cement systems should be carried out with due regard to certain inherent problems. Data indicate that the effective lateral spread of the x-ray source may be as much as 1.5 μm. Theoretical calculations and experimental evidence are supplied indicating that variations in take-off and incidence angles can cause significant variations in ratios of peak heights obtained for a given composition, but that if the take-off angle is restricted to the range between 60° and 90° and the incidence angle to between 45° and 90° acceptable results may be obtained. The problems involved in compositional analysis are discussed; it is suggested that the operator maintain awareness of geometric and other possible sources of error and avoid recording spectra in areas that may be subject to such difficulties.     

Polythiocarbamate polymers II.—Optimum conditions for synthesis

Polythiocarbamate polymers have been prepared from a prepolymer containing terminal isocyanate groups, obtained from reaction of a low molecular weight thiol-terminated polymer with a diisocyanate. The prepolymer was chain extended and crosslinked with diols. and triols. Optimum conditions for prepolymer formation were established. Void formation in prepolymer is avoided by use of antioxidants but is difficult to prevent in the crosslinked material. Isocyanate appeared to be consumed in a reaction other than directly with thiol, and a water-forming oxidation may be involved. A crosslinking reaction involving the thiocarbamate hydrogen and isocyanate appears to be favoured, contrary to results with carbamates. The nature of an isocyanate and catalyst complex is discussed.     

Bioactive polymers XXIX—immobilisation of α-amylase on Biozan R

The immobilisation of α-amylase (E.C.3.2.1.1) on Biozan R with dicyclohexyl carbodiimide as an activator has been studied. The reaction was proved to be influenced by the enzyme support and activator support ratios as well as by the reaction duration. The function correlating the coupled enzyme activity with process parameters was derived by processing the experimental results obtained by means of a second order, composite, centrate, rotatable experimental design, using the multiple regression method. The activity of the coupled enzyme was dependent on the temperature and pH of the incubation reaction. The Michaelis-Menten constant is higher for the immobilised enzyme as compared with the free one.     

Glass transition temperatures of poly N — (N — alkyl)—maleimides

The glass transition temperatures (T_gs) of a series of poly N-(n-alkyl) maleimides covering only the even members with side chains ranging in length from ethyl to n-octadecyl have been studied from room temperature to above T_g. T_gs and thermal quantities have been determined from the specific volume-temperature relations only for the higher (n=8, 10, 12, 14, 16 and 18, where n = no of CH₂) members of the series. However for the lower ones (n = 2, 4, 6, 8 and 10) T_gs have been detected from heat capacity-temperature traces of differential scanning calorimetry diagrams by extrapolation to zero rate of heating. Accurate consistency was found in the values (n = 8 and 10) determined by both experimental methods. T_gS of these polymers continuously decrease as the number of methylene groups in the side chain is increased, and they have been correlated with the size of the n-alkyl group in the side chain. The results are in accord with a previously studied series concerning the effect of a long side chain on the T_g of a comb-like polymer in the amorphous state. T_gs of poly N-(n-alkyl) maleimides encompassing a wide range of methylene group content (n = 2, 4, 6, 8, 10 and 12) have been examined according to the Gordon-Taylor-Wood extrapolation with the objective of ascertaining the T_g of polyethylene (PE). Our approach of ignoring higher members of the homologous series in this extrapolation appears to be old and well known and it has been variously ascribed to different authors. Extrapolation of T_g values to 100% amorphous PE gives a T_g of 200/pm 10 °K in complete agreement with recent predictions made by Boyer from different sources of data. The Simha-Boyer free volume quantity Δa. T_g decreases slowly with the methylene group content in the longer terms (n = 8, 10, 12, 14, 16 and 18) of the series presumably because of a reduction in the polarity or an in-chain crankshaft loss mechanism which generates free volume in the glassy state, as stated by Boyer. T_gs do not correlate very well with the contributions of the atomic groups to the cohesive energy density (c.e.d.) so it can be concluded that c.e.d. is not the only factor determining T_g. However, a somewhat improved relationship might be obtained by taking into account the steric hindrance effect according to an approach made by Hayes.     

Diamond — an adsorbent of a new type

Carbon-containing adsorbents are widely used in various industries, medicine, and pharmacology. The most abundant of them are activated coals, graphitized thermal carbon black, molecular sieves, etc. [Active Coals and their Industrial Applications (1984), 214]. Synthetic diamond presents a new class of carbon containing adsorbents. Diamond is a universal adsorbent that is characterized by chemical inertness and high strength. Another welcome effect is the possibility to modify and recover the diamond surface and, hence, to use the adsorbent repeatedly.     

A possible mechanism for cross-tie fibril generation in crazing of amorphous polymers

A possible mechanism for cross-tie fibril generation in crazes of amorphous polymers is proposed. Detailed finite element calculations are performed on an axisymmetric model of a single fibril inside the craze. These calculations suggest that the hydrostatic stress inside the fibril is large enough to cause cavitation and subsequent growth of initial imperfections inside the fibril. The calculations demonstrate that these cavities will then grow by local plastic flow around them, leading to a continuous network of main fibrils interconnected by cross-tie fibrils.     

Environmental stress cracking and crazing in polymers in terms of irreversible thermodynamics

The processes in environmental stress cracking and crazing in polymers are analysed in terms of the irreversible thermodynamics. The thermodynamic potential of the system composed of the polymer matrix at a flaw tip region and its environmental liquid is constructed as a function of the concentration of the liquid migrated in the matrix and the dilative stress due to stress concentration. A state of the system is represented by a point in the thermodynamic potential diagram. The paths of the state shifts leading to failure in the diagram are governed by the shapes of the thermodynamic potential curves, the liquid concentrations giving the potentials a minimum, the critical concentration and the breakdown concentrations here introduced. Various kinetic data of environmental stress cracking in low density polyethylenes can be understood by the unified picture. The predictions of the theory are also consistent with the reported kinetic nature of crazing.     

Cone calorimeter — an alternative calibration constant calculation

This paper focuses on an alternative method of calculating the calibration constant, C, used in the cone calorimeter. The alternative method is derived from the principles of thermochemistry. It is based on carbon dioxide measurements and implicit knowledge of water vapour and fuel mass loss and is independent of the oxygen concentration. In the final form, the equation for the alternative calibration constant is much simpler than the standard equation. An uncertainty analysis of the alternative technique is also presented in this paper and the alternative method was found to a have marginally lower uncertainty than the Standard method. Notwithstanding these advantages, the Standard method remains the preferred technique for calculating the calibration constant as it is based on the operating principle of the apparatus and includes an oxygen measurement term. However, the alternative method can be easily incorporated into software and act as a means for checkin/troubleshooting the cone calorimeter. Copyright © 2000 John Wiley & Sons Ltd.     

Synthesis and Electronic Spectra of Some Disperse Dyes Derived from N—2—Cyanoethyl—1,2,3,4—tetrahydroquinoline

Various monoazo dyes suitable for transfer printing have been prepared from N—2cyanoethyl—1, 2, 3, 4—tetrahydroquinoline and compared with the corresponding N—methyl (kairoline) derivatives. The presence of a β—cyanoethyl group brings about significant hypsochromic shifts of the first absorption band and leads to some improvement in light—fastness properties on polyester fibre.     

Reaction products of polyacrylonitrile with dicyandiamide — new flocculation agents —

A new flocculation agent is prepared by reaction of polyacrylonitrile with dicyandiamide in alkaline solution, followed by acid hydrolysis. The polymer contains guanamine-, N-carbimidoyl-N′-cyanoguanidine-, amido-, hydronaphthiridine-, and carboxylic-groups. In consequence of the alkaline and acidic groups present, the polymer shows polyampholytic properties and can be used as a primary flocculation agent. Fields of application are removal of contaminants dispersed in water, like waste, algae, bacteria and also in some cases dissolved substances like dyes, etc. Concepts of the flocculation activity and suggestions of application are discussed.     

Reactive polymers XIV. Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate — ethylenedimethacrylate

Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate - ethylenedi-methacrylate in variously concentrated sulphuric acid solutions was studied. An approximate activation energy of hydrolysis, 41 kJ mol^?1, was determined from the temperature dependences. For the sake of comparison the effect of pH on the degree of hydrolysis over the whole range of pH values was examined, and the importance of the results with respect to other reactions of the copolymer used was discussed.     

TNT — Equivalent

For engineering purposes, the effects of blast waves on various target structures can be estimated quite easily with the aid of TNT-equivalence. On the one hand, many experimental data are available on the blast damage done to structures, and on the other hand, the energy content of any source can be expressed in terms of an equivalent mass of TNT. The parameters involved in the propagation of a blast wave and in its interaction with target structures are discussed at some length in order to point out the inherent inaccuracies as well as the limits of applicability of the TNT-equivalence method.     

WOOLY — an expert system for the wool dyer

The knowledge acquired by many generations of dyers and by today's wool dyeing specialists can now be gathered and stored in databases. This has allowed the development of a computerised expert system capable of solving different standard tasks of the wool dyer. This is demonstrated by simulated screen displays.     

From cement to hardened paste — an elektrokinetic study

A new technique for the measurement of the zeta- potential of cement is applied to Portland cement and blastfurnace slag cement. It is now possible to measure the zeta-potential of hydrating cement under realistic conditions down to w/c-ratios of about 0.7. In addition the measurements have been extended to higher hydration times up to 28 days in order to study the electrochemical and electrokinetic aspects of the setting and hardening process of cement.