Addition of a block copolymer to polymer blends produced by cryogenic mechanical alloying

Cryogenic mechanical alloying is used to incorporate a poly(methyl methacry late-b-isoprene) (MI) diblock copolymer into blends of poly(methyl methacry late) (PMMA) and polyisoprene (PI). Mechanical milling of the copolymer pro motes a reduction in the molar mass of the M block, as discerned from glass transition temperature measurements performed by thermal calorimetry, and induces chemical crosslinking of the I block, as determined from sol-gel an alysis. These effects become more pronounced with increasing milling time. Morphological characterization of PMMA-rich PI/MI/PMMA blends by X-ray and electron microscopies reveals that the characteristic size scale of the min ority phase decreases with increasing MI content, as well as milling time. The nanostructural features observed in such blends are retained at relativ ely high MI concentrations during subsequent melt-pressing. Impact testing demonstrates that the blends become tougher upon addition of the MI copolym er, even at relatively low copolymer concentrations. Blend toughness likewi se increases with increasing milling time up to a point, beyond which phase inversion occurs within the ternary blends (the PI becomes continuous) and impact strength sharply decreases.