Amorphous structure heat: Molecular structure from solution heats of polymethylmethacrylate in orthodichlorobenzene

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Abstract
The heats of solution in orthodichlorobenzene were measured as a function of temperature for both as‐reprecipitated and quenched atactic polymethylmethacrylate. The as‐reprecipitated curve decreases linearly with a slope of 0.096 cal/g°C from room temperature to 90°C, and above 110°C has a constant value of +1.5 cal/g. The quenched material data decreases linearly with a slope of 0.12 cal/g°C from room temperature to 55°C, jumps +2 cal/g at 55°C, and continues the linear decrease with a slope of 0.096 cal/g°C from 55 to 90°C. The data suggests that isotactic stereochemical impurities in the atactic material are able to crystallize at 55°C which is the Tg of i‐PMMA, and therefore must be associated as i‐PMMA islands in a rigid atactic‐syndiotactic PMMA matrix. This also suggests that the β transition in PMMA may be associated with the isotactic impurities