Enlargement of the glass transition range in compatible polymer blends

Abstract Analysis of glass transition temperature ( T g ) ranges for compatible polymer blends defined by differential thermal analysis traces for the onset temperature ( T g, i ) and the final temperature ( T g, f ) of the glass transition shows the well‐known increase in width when compared with the T g ranges of the blend components. This enlargement of the T g range is generally attributed to local composition fluctuations; from a comparison of the effects in blends of polystyrenes (PS/PS) of different molecular weights the influence of an increase of the ratio of weight‐ to number‐average molecular weights M̄ w / M̄ n , because of interactions between the blend components (hetero‐interactions) has to be considered, too. Poly(methyl vinyl ether) (PVME)/PS blends are characterized by a peculiar behaviour, the increase in the width of the T g range being at least three‐fold larger than for all other blends studied. This is valid for all blends with a molecular weight of the PS component higher than 10000. Local incompatibilities suggested by enthalpy relaxation and by dynamic mechanical measurements may be responsible for the observed unusual enlargement of the T g range in the blends with 50–75 wt.‐% PS.