A polymethyl methacrylate polymer, prepared by the emulsion technique, was fractionated three times to obtain essentially homogeneous fractions. The intrinsic viscosities and weight average molecular weights were determined in an ideal solvent at 23°C. and in nonideal solvents at 25°C. The constants K and a in the conventional modified equation [η] = KMa were determined. The intrinsic viscosity in an ideal solvent was found to fit closely over the molecular range studied with the relation [η]θ = KM1/2. Light scattering measurements giving root‐mean‐square distance between ends of a polymer chain were carried out. It was shown that these results support both Kuhn's relation (r̄2)1/2 ≈︁ M0.50 and Flory's relation (r̄2)3/2 = M[η]/2.1 × 1021 in an ideal solvent. In a nonideal solvent only Flory's relation was found to be in agreement with the experimental results. The values of volume expansion factor α3 ratios A2M italicw2/(r̄2)3/2 and A2Mw/[η] in a nonideal solvent and the value of the ratio [η]/M1/2 in an ideal solvent showed that the polymer molecules were expanded beyond their random flight dimensions in a nonideal solvent.
The elasticity of polymer melts is of major concern in the processing of plastics. It is usually reflected by dimensional changes. Since the swelling of polymer extrudates depends on the capillary dimensions and the volumetric flow rate, the blow-up must be examined over a range of conditions, Of course, the swelling is also dependent on polymer structure. Consequently, variations in materials and operating conditions necessitate changes in tooling. This paper describes the swelling behavior of several different polymer types and illustrates that viscosity measurements can not be used to predict elasticity.
SynopsisThe stability of poly(viny1 chloride), as measured by thermogravimetric analysis, is significantly different from that of other thermoplastics. It is shown that the onset of weight loss can be correlated with the development of color in a processed resin. It is further shown that the ingredients within a rigid polyvinyl chloride compound drastically alter its thermal behavior. The effect of lubricant and stabilizer on the degradation of poly(viny1 chloride) is stressed.The processing of thermoplastic materials usually requires reasonably high temperature stability (up to 300°C.) of polymers. It is apparent that all resins do not behave similarly ( Fig. 1) and, since this is also true of single resins from different sources or of different batches of a resin from the same source, it is necessary to be able to distinguish or determine the differences in thermal stability. Thermogravimetric analysis (TGA) affords an excellent method by which this may be accomplished. Most of the common resins (e.g. , polyethylene and polystyrene) have a single weight-loss mechanism or reaction. This is not true, however, of resins such as polyvinyl chloride (PVC). PVC is especially vulnerable to changes in thermal conditions due to the chlorine groupings, and thus its weight-loss process is somewhat different (see Fig. 1).The thermal instability of PVC can be followed by a three-step weightloss thermogram on the TGA. This degradation procedure is identified as follows (Fig. 2): A is the region of dehydrochlorination (weight loss of 50-60y0), B is the evolution of simple hydrocarbons formed by cyclization and chain scission (weight loss of 15-3oyO), and C is a gradual evolution of the more complex degradation compounds.'r2The initial formation of conjugated bonds (caused by the evolution of HCl) imparts a coloring to the PVC compound that is quite unfavorable to the processer. Since PVC compounds are mixtures of PVC resin and additives such as lubricants, stabilizers, and modifiers, it is necessary to understand the influence of these additives 011 the stability of the material. It is the purpose of this paper to demonstrate the use of the TGA technique *
The preparation of a completely isopropylated polystyrene by polymerization of p‐isopropylstyrene monomer is described. This polymer was autoxidized in cyclohexane with lauroyl peroxide to give a material of good reproducibility and high purity. Methyl methacrylate was successfully grafted to the polymeric hydroperoxide by using a sugar‐containing recipe. Homopolymer was separated from the graft copolymer by extraction. Evidence for grafting was obtained from solubility and fractionation behavior, as well as from light‐scattering and viscosity measurements.
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