Poly(vinyl acetal) resin compositions, layers and interlayers having enhanced properties

An interlayer comprising:

• a first resin layer comprising a first poly(vinyl acetal) resin and a first plasticizer;
• and
• a second resin layer adjacent to said first resin layer, said second resin layer comprising a second poly(vinyl acetal) resin and a second plasticizer,
• wherein said interlayer meets at least one of the following criteria (i) through (iii) below
• (i) said first poly(vinyl acetal) resin comprises at least 5 weight percent of residues of i-butyraldehyde, based on the total weight of aldehyde residues of said first poly(vinyl acetal) resin, and said second poly(vinyl acetal) resin comprises at least 10 weight percent of residues of an aldehyde having 6 or fewer carbon atoms, based on the total weight of aldehyde residues of said second poly(vinyl acetal) resin, wherein the refractive index of said first resin layer is at least 0.002 lower than the refractive index of a comparable polyvinyl n-butyral) resin layer, and wherein the residual hydroxyl content of said second poly(vinyl acetal) resin is not more than 12 weight percent and the difference between the residual hydroxyl content of said first poly(vinyl acetal) resin and the residual hydroxyl content of said second poly(vinyl acetal) resin is at least 2 weight percent;
• (ii) said first poly(vinyl acetal) resin comprises at least 5 weight percent of residues of i-butyraldehyde, based on the total weight of aldehyde residues of said first poly(vinyl acetal) resin, and said second poly(vinyl acetal) resin comprises at least 10 weight percent of residues of an aldehyde having more than 6 carbon atoms, based on the total weight of aldehyde residues of said second poly(vinyl acetal) resin, wherein the residual hydroxyl content of said second poly(vinyl acetal) resin is at least 0.25 weight percent higher than the residual hydroxyl content of said first poly(vinyl acetal) resin, and wherein the amount of said second plasticizer in said second resin layer is at least 10 parts per hundred resin (phr) higher than the amount of said first plasticizer in said first resin layer;
• and
• (iii) neither of said first and said second poly(vinyl acetal) resins comprise residues of i-butyraldehyde and said second resin layer has a glass transition temperature that is at least 3° C. lower than the glass transition temperature of a comparable poly(vinyl n-butyral) resin layer,
• wherein the difference between the refractive index of said first resin layer and the refractive index of said second resin layer is not more than 0.010, and said interlayer has a haze value less than 5 percent.