Polymethyl methacrylate molecular orientation

This chapter discusses the independent determination of parameters for a cluster entanglement network enabling the accurate description of the experimental data on the molecular orientation in polymethyl methacrylate. This confirms the validity of the earlier proposed structural model for the polymer amorphous state [1, 2]. 

When an amorphous polymer is stretched, the molecules may be preferentially aligned along the stretch direction. In polymethyl methacrylate and polystyrene, such molecular orientation may be detected by optical methods, which measure the small difference between the refractive index in the stretch direction and that in the perpendicular direction. 

Polymers that do not crystallise, such as polymethyl methacrylate, show a good correlation between the (low) degree of mechanical anisotropy and molecular orientation determined from birefringence. There is so much disorder that it seems unlikely that a significant proportion of the chains can achieve the high alignment of a crystalline polymer such as polyethylene. Other polymers such as polyethylene terephthalate, which have a... 

In the following sections, we shall discuss the effects of molecular weight, crack speed and molecular orientation on effective fracture surface energy, fracture energy and fracture toughness of glassy polymers. Polymethyl methacrylate will be used for illustration. Other variables, e.g., temperature, sampl thickness, etc., have been well discussed in the literature, we do not include them in this section. 

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