Properties of cured polymer

Polymer modifiers that influence the polymer structure in some way are widely used for regulation of the properties of cured polymers and to produce composite materials with specified chracteristics. For mix-... 

The industrial value of furfuryl alcohol is a consequence of its low viscosity, high reactivity, and the outstanding chemical, mechanical, and thermal properties of its polymers, corrosion resistance, nonburning, low smoke emission, and exceUent char formation. The reactivity profile of furfuryl alcohol and resins is such that final curing can take place at ambient temperature with strong acids or at elevated temperature with latent acids. Major markets for furfuryl alcohol resins include the production of cores and molds for casting metals, corrosion-resistant fiber-reinforced plastics (FRPs), binders for refractories and corrosion-resistant cements and mortars. 

Two kinds of monomers are present in acryUc elastomers backbone monomers and cure-site monomers. Backbone monomers are acryUc esters that constitute the majority of the polymer chain (up to 99%), and determine the physical and chemical properties of the polymer and the performance of the vulcanizates. Cure-site monomers simultaneously present a double bond available for polymerization with acrylates and a moiety reactive with specific compounds in order to faciUtate the vulcanization process. 

Microstructure. Whereas the predominate stmcture of polychloroprene is the head to tail /n7 j -l,4-chloroprene unit (1), other stmctural units (2,3,4) are also present. The effects of these various stmctural units on the chemical and physical properties of the polymer have been determined. The high concentration of stmcture (1) is responsible for crystallization of polychloroprene and for the abiUty of the material to crystallize under stress. Stmcture (3) is quite important in providing a cure site for vulcanization, but on the other hand reduces the thermal stabiUty of the polymer. Stmctures (3),(4), and especially (2) limit crystallization of the polymer. 

Accelerators may be added to improve the physical properties of the polymer when needed. Where high modulus or low oil swell is required, thiocarbanihde is the preferred accelerator, with a cure time of 60 min at 100°C. Tetraethyl thiuram disulfide and sodium dibutyl dithiocarbamate are preferred for high tensile strength and cured at 121°C. 

Silicone adhesives are generally applied in a liquid and uncured state. It is therefore the physical and chemical properties of the polymers, or more precisely of the polymer formulation, that guide the various processes leading to the formation of the cured silicone network. The choice of the cure system can be guided by a variety of parameters that includes cure time and temperature, rheological properties in relation with the application process, substrates, the environment the adhesive joints will be subjected to and its subsequent durability, and of course, cost. 

When formulating a silicone adhesive, sealant, or coating, based on hydrosilylation addition cure, one must consider the following properties of the uncured product pot life, dispensing technique, rheology, extrusion rate, cure performance. These characteristics directly affect the processing properties of the polymer base or crosslinker parts. The degree of cure conversion at the temperature of interest is determined by properties such as tack free time, cure profile and cure time. Once... 

The final physical properties of thermoset polymers depend primarily on the network structure that is developed during cure. Development of improved thermosets has been hampered by the lack of quantitative relationships between polymer variables and final physical properties. The development of a mathematical relationship between formulation and final cure properties is a formidable task requiring detailed characterization of the polymer components, an understanding of the cure chemistry and a model of the cure kinetics, determination of cure process variables (air temperature, heat transfer etc.), a relationship between cure chemistry and network structure, and the existence of a network structure parameter that correlates with physical properties. The lack of availability of easy-to-use network structure models which are applicable to the complex crosslinking systems typical of "real-world" thermosets makes it difficult to develop such correlations. 

The important item is that this coating can be applied at room temperature and cured at 90 °C and gives a clear film with optical quality. Typical properties of inorganic polymers (hardness) and organic polymers (coating as a lacquer and low temperature processing) could be combined in one and the same polymer. 

Studies were performed to demonstrate the effects of process variables such as light intensity, cure time, initiator concentration, and fiber loading on the evolution of the mechanical properties of the polymers and composites. Even with moderate incident light intensities (less than 500 mW/cm2) and high fiber loadings (60 wt.% random fibers) the photopolymerizations proceed to completion in minutes and exhibit mechanical properties equivalent to samples prepared by traditional... 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

The unsaturated side chain of the SoyOx repeating units could be used for cross-linking well-defined P(EtOx)-.yfaf-(SoyOx) copolymers. Thus, the effect of cross-linking on the thermal properties of the polymers was investigated. The thermal properties of the synthesized P(EtOx)-.yfaf-(SoyOx) copolymers before and after UV-curing are illustrated in Fig. 18. 

The reaction of curing the epoxy-amine system occurring in the diffusion-controlled mode has little or no effect on the topological structure of the polymer 74> and on its properties in the rubbery state. However, the diffusion control has an effect on the properties of glassy polymers 76 78). 

Cure — A process of changing the properties of a polymer by a chemical reaction (condensation, polymerization, or addition). In elastomers it means mainly cross-linking or vulcanization. 

Shieh JY, Wang CS. Synthesis of novel flame retardant epoxy hardeners and properties of cured products. Polymer 2001 42 7617-7625. 

The electron beam may be used in the printing industry to cure coatings but the energy available by this means is too great for surface treatment and such exposure would affect the bulk properties of the polymer. 

Curing of epoxy thermosets requires a knowledge of the chemical kinetics and the crosslinking reactions. This information is necessary to optimize the cure cycle. The parameters that define the cure cycle ultimately determine the crosslink density and the final physical properties of the polymer. In addition to temperature, these parameters include the rate of temperature increase, the number of stages in the cure, the hold temperature at each stage, the pressure at which cure takes place, and the time allotted for the cure cycle. These parameters are usually determined empirically. Once the kinetics are understood and the actual chemistry behind the cure is established, these cure cycle parameters can be chosen based on the desired end properties. Usually the cure cycle seeks to establish a certain degree of cure that is in line with the expected final properties. 

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