Structure and Properties Relationships of Epoxy Resins Part 1: Crosslink Density of Cured Resin: (II) Model Networks Properties

Abstract

Carefully designed resin precursors of high purity, viz. N,N‐bis‐(2,3‐epoxypropyl)‐N',N‐dimethyl‐4,4′‐diaminodiphenylenemethane (G2A) and N,N‐bis‐(2,3‐epoxypropyl)‐N,N‐dimethyl‐4,4′‐diamino‐diphenylenemethane (G2S) were used in combination with N,N,N',N‐tetrakis‐(2,3‐epoxypropyl)‐4,4′‐diaminodiphenylene methane, TGDDM, and cured with stoichiometric amounts of 4,4′‐diamino‐diphenylene methane (DDM) to produce networks with a range of controlled crosslink density. The tensile moduli E of the networks in the rubbery state, at Tg+30°C, Tg+45°C and Tg+60°C, were measured using a thermal mechanical analyser. Using the statistical theory of rubber elasticity and the observed values of E, the number average molecular weights between crosslink points Mc for the cured resins were deduced. The experimental Mc values were then compared with those derived by calculations based on a probabilistic model of the network proposed by Chu and Seferis.1 The experimental Mc values were 2.5 to 5.5 times larger than the calculated ones. The differences were attributable to a consumption of only 40% of the available secondary amino hydrogen via epoxy‐amine reaction. A direct relationship was established between the glass transition temperature and the crosslink density 1/Mc for the resins, and the dynamic mechanical properties were studied. The thermal stability of cured resins studied by thermo‐gravimetric analysis indicated an enhancement of stability as 1/Mc was reduced. The amount of water absorbed by cured resin was directly proportional to 1/Mc.

Amino Acids as Bio-Based Curing Agents for Epoxy Resin: Correlation of Network Structure and Mechanical Properties

“…However, aliphatic structures increase the mobility of network segments, which leads to increased toughness, i.e., increased and [ 19 ]. Typically, a high cross-link density is associated with high , modulus, and strength, while the thermoset’s toughness decreases [ 22 , 23 ]. Since the thermal and mechanical properties of thermosets depend on the network structure, and as there are 22 proteinogenic -amino acids that all possess distinct structures [ 8 ], it would be interesting to see the effect of structural differences in the curing agent on the thermoset’s properties.…”

The preparation and characterization of crosslinked polytriazoles with different network grids

“…As well known, the crosslinked structures of a resin had a great influence on its properties 7–10. Investigation on the effect of the molecular structure and crosslinking character of a crosslinked network on properties would give an effective guide for the design and preparation of a new crosslinkable resin.…”

New autophotosensitive semiaromatic hyperbranched polyimides with excellent thermal stabilities and low birefringences

“…A value of Φ = 1 may be used for a good order-of-magnitude prediction. 22 With the experimental values of E ′ reported in Figure 5, the concentration of elastic chains could be determined. Cross-link density derived using equation (1) was ranged from 1.72 × 10 −4 mol/cm 3 to 2.47 × 10 −4 mol/cm 3 (Table 1).…”