The incorporation of multilayer toughness modifiers to glassy polymers proceeds frequently by kneading the polymers in a molten state. This process influences the primary structure of the modifier and the properties of the blend in dependence on a shear stress intensity. In this article, we compare the properties of polymer materials prepared from a multilayer poly(methyl methacrylate) core, butyl acrylate copolymer interlayer, and methyl methacrylate copolymer shell particles {P[MMA-(BAC-co)-(MMA-co)]} by press-molding from powder and from polymer obtained by stirring a melt of this powder in the chamber of a Brabender mixer (200 degrees C, 60 rpm, 10 min). The powder is obtained from a latex by coagulation after polymer synthesis in emulsion. Tensile testing shows different responses of the particle polymers when crosslinked in the middle layer by diallylphthalate (DAP) or by triallylcyanurate (TAC). Although many of the properties of the samples with DAP are improved by kneading, the presence of TAC in polymer particles led mostly to less desirable properties. The maximum percent strain in the polymer with 4.2 wt % of DAP upon shearing increases from 27% to 50%. In the samples with 4.5% TAC the maximum percent strain falls from 39% to 7%. Comparison of Young's modulus E for identical samples shows an analogous effect : a shift from 429 MPa to 638 MPa and from 624 MPa to 548 MPa. The design of the polymer particles used in this work leads to the conclusion that stress during kneading induces a partial desintegration of the crosslinked cage around the particle core. Thus, the varied behaviors of polymers used in this study are connected with the BAC-co network structure and its transformations during the shear stress treatment of the initial polymer material.