Structure and Properties of Cured Resins

Since the characteristic grouping of the resins discussed in this chapter largely disappears on cross-linking it is difficult to make simple generalisations relating structure to properties. 

Being cross-linked, the resin will not dissolve without decomposition but will be swollen by liquids of similar solubility parameter to the cured resin. The chemical resistance is as much dependent on the hardener as on the resin since these two will determine the nature of the linkages formed. The acidic hardeners form ester groups which will be less resistant to alkalis. 

The main skeleton of the resins themselves has generally good chemical resistance 

The thermal properties of the resin are dependent on the degree of cross-linking, the flexibility of the resin molecule and the flexibility of the hardener molecule. Consequently the rigid structures obtained by using cycloaliphatic resins or hardeners such as pyromellitic dianhydride will raise the heat distortion temperatures. 

The resins are somewhat polar and this is reflected in the comparatively high dielectric constant and power factor for an insulating material. 

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Non-glycidyl ether epoxides Diluents, Rexibilisers tmd other Additives Structure and Properties of Cured Resins Applications... 

Studies of the dependence of EEC properties obtained as above on the formation method showed that the precipitated finely dispersed rubber that is not bonded to the epoxy matrix does not endow it with high mechanical characteristics. When reactive oligomers are applied with high-temperature cure, there is a sharp enhancement of the modifying efficiency, accounting for the more intensive separation of the phases in the system and for the increase of the yield of the epoxy rubber copolymer. Thus, the structure and properties of epoxy resins modified by rubbers are mainly determined by the mode of system curing, but the quantitative relationships between curing mode and final properties have not been sufficiently studied. 

The structure and properties of epoxy resins cured with MA have been compared with a variety of other... 

Ozonization of lignin forms derivatives of muconic acid that have the unique chemical structure of conjugated double bonds with two carboxyl groups. These derivatives have great potential for chemical modification. The ozonized lignin of white birch was soluble in epoxy resin at 120°C, and the free carboxyl groups were found to react with epoxide. This paper discusses developmental work on the preparation of pre-reacted ozonized lignin/epoxy resins the dynamic mechanical properties of cured resins and preliminary results of the application of these resins as wood adhesives. 

Although the processing and final physical properties of epoxy-curing agent systems depend primarily on their chemical composition and degree of cure, the corresponding relations are often empirical or semiempirical and are not well understood. The tie between the cure chemistry and structure and properties of the cured resins consists in the theoretical and experimental study of network formation as a function of the depth of cure. 

Habermeier also pointed out the ready synthesis of hydantoins from aldehydes or ketones the substituents in the 5-position of the ring were thus determined by the carbonyl compound used as starting material. Most of the examples cited had methyl, ethyl, or cyclopentamethylene substitution in the 5-position. Data were presented on the properties of cured resins with these substituents and with a broad variety of the other structural features mentioned. 

The influence of surfactants on the formation of microdiscontinuities. The structure and properties of the cured polyester resin are determined to a great extent by the compatibilily of the system s copolymerizing components. Let us therefore consider the possibility of regulating their compatibility with the help of surfactants. 

In this article, recent developments in the formation and properties of epoxy layered silicate nanocomposites are reviewed. The effect of processing conditions on cure chemistry and morphology is examined, and their relationship to a broad range of material properties elucidated. An understanding of the intercalation mechanism and subsequent influences on nanocomposite formation is emphasized. Recent work involving the structure and properties of ternary, thermosetting nanocomposite systems which incorporate resin, layered silicates and an additional phase (fibre, thermoplastic or rubber) are also discussed, and future research directions in this highly active area are canvassed. 

Consider now the effect of surfactant on the properties of the initial and the cured polyester resins. Such systems show a number of parti-cul lr features. The structure and properties of the cured polyester resins are determined to a great extent by the compatibility of the copolymerizing components of the system. There is almost no information on the possibility of controlling this compatibility by means of surfactant, which is why it is of great interest to study the influence of surfactant upon the thermodynamics of compatibility of the components of the cured polyester resin, as well as the effect of this compatibility on the molecular mobility of the polymeric chains and on the physical-mechanical properties of the polymer. 

In order to impart these properties to the final product, very careful selection of the epoxide resin and hardener system, as well as all the other components of the formulation, is vitally important. As the cured material is crosslinked, the structure and properties of the original resin will be completely changed. The material will no longer be soluble without decomposition and its chemical resistance will depend as much upon the hardener selected as upon the epoxy resin. As an illustration of the dependency of the cured system upon the hardener, acid anhydride based hardeners offer excellent resistance to acid environments, whilst amine-type hardeners offer maximum resistance to alkaline environments. 

Ahmed, T.. and Funke, W.. Structure and properties of radiation cured unsaturated polyesters in absence of vinyl monomers, ACS Polymer Prept, Vol. 1, 34, 725, 1974. Pucic, I., and Ranogajec, E, DC electrical conductivity as a method for monitoring radiation curing of unsaturated polyester resins. 1. Measurement conditions and comparison with extraction analysis data. Radial. Phys. Chem., 46, 365, 1995. 

The thermal polymerization of reactive polyimide oligomers is a critical part of a number of currently important polymers. Both the system in which we are interested, PMR-15, and others like it (LARC-13, HR-600), are useful high temperature resins. They also share the feature that, while the basic structure and chemistry of their imide portions is well defined, the mode of reaction and ultimately the structures that result from their thermally activated end-groups is not clear. Since an understanding of this thermal cure would be an important step towards the improvement of both the cure process and the properties of such systems, we have approached our study of PMR-15 with a focus only on this higher temperature thermal curing process. To this end, we have used small molecule model compounds with pre-formed imide moieties and have concentrated on the chemistry of the norbornenyl end-cap (1). 

Table 11. Properties of ATI resins Uncured and cured Tgs as a function of the chemical structure (129)...

In measurements of physical properties of epoxy resins - and the epoxy-polyim-ide system will be included in this general categorization - the method of failure is of considerable interest. Gross flaws in the epoxy structure act as initiation points for cracks which typically propagate by the breaking crosslinks. Therefore the level of crosslinking and cure will have a significant influence on the physical properties determined. The incorporation of additives that typically... 

The general properties of cured and uncured epoxy resins are reviewed in Chap. 3. The chemical structures of the resin and curing agent will determine these physical properties. They will also determine, to a great extent, the surface chemistry and adhesion properties of the final product. 

The first category consists of unreactive diluents, and they may be considered mainly as plasticizers. Generally they do not increase flexibility, and often they result in the overall degradation of physical properties. The cured resin has reduced strength and hardness and could even exhibit a cheeselike structure. The second category consists of reactive diluents, and they can be considered as true flexibilizers. 

Structures and Dynamic Mechanical Properties of Epoxy Resins Cured... 

The factors determining the structure of cured resins and affecting the physical and mechanical properties are as follows ... 

A number of papers deals with the dynamic mechanical properties of cured epoxy resins1 -5) and with the effect of the structure of basic resins and the degree of cross-linking s 8>. 

Recently, the dynamic mechanical properties of the resins cured with a series of linear poly anhydrides having the structures shown in Table 5 were studied by Ramon41 . The dynamic mechanical properties are very similar to those of the resins cured with diamine hardeners as shown in Fig. 10. The relationships between the number of CH2 groups n and Tg Eire shown in Fig. 8. Tg drops rapidly below that of an alkyldiamine-cured resin as n increases. This is considered reasonable because, compared with the hardener.unit in an amine-cured resin, the acid anhydride segment existing in the main chain of the anhydride-cured resin is twice as long. 

The structure of DICY resembles that of diamine hardeners but the dynamic mechanical properties of the resin cured with DICY is far different from that of the diamine-cured resin in Fig. 2 (Figs. 13 and 14)47). 

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