| The ability of alternating and random copolymers, containing styrene (S) and methyl methacrylate (MMA), to modify polystyrene (PS)/poly(methyl methacrylate) (PMMA) interfaces was investigated. The ability of P(S-alt-MMA) to reinforce PS/PMMA interfaces was examined using the asymmetric double cantilever beam tests (ADCB) and specular neutron reflectivity (NR). P(S-alt-MMA) copolymers were tested using ADCB where the interfacial fracture toughness, Gc, was measured as a function of both copolymer layer thickness and weight average molecular weight (Mw). Results demonstrate that Gc increases with copolymer layer thickness for all Mw.; The effect of copolymer Mw and composition on its ability to segregate to the d-PMMA/d-PS interface out of a homopolymer matrix was examined using NR. The interfacial excess, Z*, of P(S-alt-MMA) that varied in Mw and P(Sf-ran-MMA1-f) that in monomeric composition, f, was monitored as a function of copolymer Mw and composition at 150°C. The dynamic evolution of the Z* was observed to be dependent on the copolymer miscibility in the polymer matrix. For miscible blends, the copolymer Z* growth scaled to t1/2, which is indicative of diffusion limited growth of a polymer wetting layer. The equilibrium Z* and time were then used to calculate the inter-diffusion coefficients for P(S-alt-MMA) with Mw equal to 8.50 × 104; 9.60 × 104; and 1.08 × 105g/mole and P(S0.33-ran-MMA) and P(S0.50-ran-MMA) with M w equal to 8.90 × 104 and 1.28 × 10 5g/mole, respectively. The mutual and inter-diffusion coefficients, effective friction coefficients, and the relaxation times for the alternating and compositionally symmetric copolymers were observed to scaled to M w−1.85, Mw0, and M w2.8; respectively. However, P(S0.33-ran-MMA) demonstrated slower diffusive behavior in the d-PMMA matrix. This was attributed to an increase in copolymer MMA composition, which was observed to increase the effective friction coefficient of the copolymer.; For immiscible blends, the copolymer Z* growth scaled to t1/4 , which is indicative of the coalescence of phase separated domains at an interface. This type of behavior was observed for P(S-alt-MMA) with Mw of 4.97 × 105 and 2.55 × 10 6 g/mole and P(S0.64-ran-MMA) out of both d-PMMA and d-PS. It was determined that the Z* growth was attributed to Rouse dynamics or Ostwald ripening. |
