| Abstract
| - The fracture toughness Gc ofepoxy/high-impact polystyrene (HIPS) interfaces wasmeasuredas a function of grafting chain density Σ of carboxylic acidterminated deuterated polystyrene (dPS-COOH) chains of various degrees of polymerization N. ThedPS chains penetrate into the bulk HIPSwhereas the −COOH end functional group is chemically bonded to theepoxy. For short chains, e.g., N= 160, no effective entanglements can be formed between the dPSchains and the PS matrix of the HIPS,and thus no enhancement in Gc over that of abare interface. For longer chains, N = 410, theinterfacefails by chain pullout from the PS matrix of HIPS at low Σ.There is a transition from chain pullout tocrazing above an areal chain density Σ† ≈ 0.025chains/nm2 at this chain length. For very longchains,e.g., N = 1860, even though each chain is well entangled,the maximum grafting density achievable isvery low and such an interface fails by scission of the chains so thatthe interface fracture toughness isalso low. Large values of Gc are observedat intermediate chains lengths where both effectiveentanglements can be formed and a large Σ can be achieved. Underthese conditions, the interface failsinitially due to the formation of crazes in the HIPS side of theinterface and the subsequent breakdownof one of these crazes at the interface. As Σ increases, themechanism of interface failure undergoes atransition from scission of the bridging chains before craze formationto a mechanism where crazingoccurs and is followed by craze failure. The critical areal chaindensity at which this transition occurs,Σc, is independent of N and is found to be∼0.015 chains/nm2 for the epoxy/HIPS system. Themaximumgrafting density achievable is observed to decrease linearly withincreasing N, and the optimum interfaceadhesion appears to be achieved with N around 1000. Theresults are compared with those of epoxy/PSinterfaces for which the PS has a higher crazing stress and thus ahigher Σc ∼ 0.03 chains/nm2.
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