Self-immolative polymers (SIPs) are unique macromolecules that are able to react to multiple types of environmental influences by giving amplified response outputs. When triggering moieties installed at SIP chain ends are activated by their corresponding stimuli, a spontaneous head-to-tail depolymerization ensues, often involving multitopic release of small molecules. SIP designs have evolved a high degree of modularity in each of their functional components, enabling a broad range of utility and applications-driven tuning.
Methods for the synthesis, properties and applications of alkyl 2-cyanoacrylates are surveyed. The reactions of alkyl 2-cyanoacrylates with various nucleophiles (thiols, alcohols, diols, hydrogen sulfide, phosphines, etc.) including a new reaction involving insertion of isocyanates into the C=C bonds in the adducts of alkyl 2-cyanaocrylates with trialkylphosphines are considered. The prospects for the use of alkyl 2-cyanoacrylates in organic synthesis, in the chemistry of polymers and in the chemistry of adhesives are described. The bibiolgraphy includes 177 references.
The conditions for the Knoevenagel synthesis of 2-cyanoacrylates containing double and triple bonds in the alkoxycarbonyl group have been studied. It was found that the esters are formed in 10–70 % yields by the condensation of the respective cyanoacetates with formaldehyde in the 1∶1 ratio in the presence of piperidine, followed by the pyrolysis of the oligomers formedin vacuo at 170–200 °C in the presence ofpara-toluenesulfonic acid.
The properties of 2-cyanoacrylates are considered. The geometric structure of 2-cyanoacrylic acid and its 1-adamantylmethyl ester is established by X-ray diffraction methods. Two methods for expanding the temperature range of the service lives of adhesives based on crosslinked 2-cyanoacrylates are considered. The first method is based on the incorporation of unsaturated carbon-carbon bonds into ester fragments of alkyl 2-cyanoacrylates followed by crosslinking via these bonds.
Cyanoacrylates are solvent free adhesives that cure rapidly when pressed into a thin film between two surfaces. Their ease availability and use in various formulations made them attractive to manufacturers a wide variety of medical devices. Unfortunately, earlier generations of cyanoacrylates had several limitations, such as poor thermal resistance and peel strength. Subsequent developments in cyanoacrylate technology have greatly expanded the performance of these adhesives.
The glass transition temperatures of the poly(alkyl α-cyanocrylates) were determined by the dilatometric technique, and some of the values were checked by differential thermal analysis. The data indicate that the Tg's appear to decrease with increase in the size of the alkyl group, for a given molecular weight range. It was also found that the Tg of poly(methyl or butyl α-cyanoacrylate) increased with molecular weight. All cyanoacrylates, excepting methyl and ethyl esters, formed only low molecular weight polymers in aqueous surroundings.
Various developments in the synthesis of alkyl 2-cyanoacrylates, their analytical and test methods, adhesive compositions for different applications including those in the medical field, handling and storage, and health and safety hazards are reviewed.
Twenty-six alkyl, alkenyl, cycloalkyl, and substituted alkyl 2-cyanoacrylates were synthesized in the pure state. The purity was determined by gas-liquid chromatography, and a correlation between the log retention time and the number of carbons in the compounds within the homologous series was deduced. Their physical properties such as parachor and molar refraction were determined and the data were fitted to a linear relation to the number of carbons present in the ester within a homologous series of cyanoacrylates.
The effect the curing conditions on the properties of adhesive joints formed using cyanoacrylate-based adhesives is investigated. The temperature dependences of relative rigidity and mechanical loss tangent are studied by torque analysis for poly(ethyl-, allyl-, allyloxyethyl-, allyloxyisopropyl-, propargyloxyethyl-, and propargyl-) cyanoacrylates after their thermal treatment in the temperature range of 20–250°C. The glass transition parameters of polycyanoacrylates and the dependence of the curing intensity on the structure of initial monomers and polymers are determined.
Cyanoacrylate polymers are commercially important materials as structural ad- hesives. They combine rapid curing and high strength and are widely used to bond a diverse range of substrate surfaces, including metals, ceramics, plastics, rubbers, and biologically derived materials. The corresponding monomers were first isolated in 1947 by Ardis at B. F. Goodrich (1). Subsequently, Eastman Ko- dak patented them as adhesive compositions in 1957 (2) and the first commer- cial adhesive formulation, based on methyl 2-cyanoacrylate, was introduced in 1958 (3).
