Multiblock Copolymers in the Compatibilization of Polystyrene and Poly(methyl methacrylate) Blends:  Role of Polymer Architecture

Abstract

An asymmetric double cantilever beam (ADCB) was utilized to determine the ability of a series of styrene and methyl methacrylate copolymers with varying architectures to compatibilize the polystyrene/poly(methyl methacrylate) interface. Diblock, triblock, pentablock, and heptablock multiblock copolymers with similar molecular weights were compared to a random copolymer. When the surface is saturated with copolymer, PS/PMMA interfaces compatibilized with pentablock copolymers [S-M-S-M-S(30) and M-S-M-S-M(30)] were the strongest, followed by triblock [S-M-S(50) and M-S-M(50)] and then diblock [S-M(100)]. The least blocky structures, heptablocks [S-M-S-M-S-M-S( 21) and M-S-M-S-M-S( 21)] and random, provided the weakest interfaces under similar conditions. The ability of the multiblock copolymers to strengthen the PS/PMMA interfaces was attributed to multiple interface crossings and blocks of monomers that are able to anchor into the homopolymers. The results suggest that block lengths with molecular weight greater than 21 000 are required for adequate anchoring into the PS/PMMA homopolymer phases. Surprisingly, a dependence of the interfacial fracture toughness on copolymer composition was not observed for the multiblock copolymers studied. Both styrene-centered and methyl methacrylate-centered multiblock copolymers gave comparable results even though the compositions of the comparable copolymers differed greatly, as much as 70/30 to 30/70. In addition, increasing block lengths in multiblock copolymers of a given architecture increased interfacial adhesion.

The reinforcement of polystyrene and poly(methyl methacrylate) interfaces using alternating copolymers

“…This modification of the interface provides a mechanism to transfer stress across the phase boundary and increases the interfacial adhesion. These results agree with previous ADCB measurements on multi-block copolymers that contain block lengths that are shorter than the critical molecular weight for entanglements [34]. Results for these copolymers demonstrate that there was a continual increase in G c with an increase in copolymer layer thickness up to 100 nm.…”

“…This figure shows the interfacial toughness, G c of each modified interface as a function of copolymer layer thickness for the five P(S-alt-MMA) copolymers studied, where the error bars correspond to one standard deviation. The value of G c for a bare PS/PMMA interface measured by ADCB is reported in the literature as 3.4 J/m 2 [34,36]. Clearly, for all 5 alternating copolymers the value of G c increases with increased copolymer thickness at the interface.…”

“…The thickness of the copolymer films was controlled by the concentration of the solutions that varied from 0.85 -5.3 wt%. The correlation between solution concentration and the copolymer film thickness was determined using a nulling ellipsometer [34]. Dry PMMA strips were then placed on top of the bi-layer to complete the tri-layer samples.…”

“…The samples were then annealed for two hours at 150 8C under slight pressure (, 10 lb). The annealing time and temperature used in this studied were chosen to be consistent with similar studies of PS/PMMA interfaces reinforced with other P(S-co-MMA) structures for the purpose of comparing results [34,36].…”

“…The effectiveness of random copolymers to reinforce polymers interfaces has also been widely investigated [11,12,15,21,22,[33][34][35][36][37][38] and was found to be dependent on the monomer composition [22]. In the case of PðS f -ran-MMA 12f Þ; where f is the monomer composition, the compositionally asymmetric P(S 0.7 -ran-MMA) displayed the greatest reinforcement of the PS/PMMA interface out of a range of P(S-ran-MMA) compositions studied [21].…”