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In 1940, the first all-hydrocarbon elastomer containing limited olefinic functionality, butyl rubber, was announced. Because of its resistance to em-brittlement on aging, cracking on exposure to ozone, its impermeability to gases, and high damping capacity, this elastomer found use in inner tubes, cable insulation and miscellaneous hose, grommet, and gasket applications, generally lumped together as mechanical goods. It was the chemist's desire to prepare elastomers from other simple, inexpensive olefins, varying the structure to meet property requirements and using limited functionality to accommodate vulcanization. But no such preparative scheme was found, and, instead, attention was turned to modifications of known, substantially saturated hydrocarbon polymers to effect elastomeric properties and vulcanizability or to prepare elastomers from other raw materials, typical examples being Hypalon (chlorosulfonated, low density polyethylene) and polymers derived from epoxides and acrylates. However, K. Ziegler and coworkers pursued the matter of dimerization or oligomerization of olefins with metal alkyls until a breakthrough was made, and the catalyst system now known as Ziegler or Mulheim catalysts was discovered. This basic discovery, initially applied to the polymerization of ethylene, was expanded by Natta and his group and others to preparation of entirely new polymer structures. And, while attention was initially devoted to the preparation of miscellaneous stereoregular, crystalline homopolymers from simple olefins, it was virtually axiomatic that it would inevitably turn to the preparation of elastomeric copolymers. So, like the development of butyl rubber from polyisobutylene, ethylene/propylene elastomers (EPM) were followed by their olefin-containing terpolymers (EPDM), all of which are commercially prepared today. The Nobel Prize Award addresses by each of these aforementioned men trace the history of this important step forward in organometallic catalysis and polymer science.

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Li?id,en, New Jersey 07'036 synopsis X-ray, differential scanning calorimeter, and density measurements of the degree of crystallinity have been made on ethylene-propylene copolymers which range in composition from 60 to 100 mole-~. ethylene. At 23'C the degree of crystallinity was found to vary from zero to approximately 75 w e % in a regular manner with composition. A systematic difference exists between the x-ray and heat of fusion measurements if a simple two-phase model is assumed in order to calculate the per cent crystallinity from heats of fusion. The apparent heat of fusion of the crystalline fraction detected by the x-ray method is aslow as 30 cal/g.It issuggested that large surface or defect energies are present. The broad melting behavior of the samples is also consistent with such a description of the system. This discrepancy increases with comonomer content.Density, differential scanning calorimetry (DSC) , and x-ray techniques are used on samples with identical thermal history, and thus the study has generated a novel set of data for ethylene propylene copolymers. 0%. EXPERIMENTALThe ethylene to propylene ratio in all of the polymers studied was determined by infrared spectroscopy (Beckman IR 5A). The ratios of peaks at 4400,1160, and 720 cm-I were used. This method was calibrated by using W-tagged polymers prepared by the same catalyst system which was used to prepare the copolymers discussed here.

Size exclusion chromatography (SEC) is a widely used method for determining the molecular weights of polymer molecules. SEC calibration is often achieved using the “universal calibration” technique, which assumes hydrodynamic volume is the sole determinate of retention time. Recent work has demonstrated the failure of this approach when molecular weights are small (<5000) and particularly in the oligomer range. In order to explore the theoretical reasons for this failure, molecular dynamics (MD) simulations have been used to compute the partition coefficients as a function of pore size for oligomeric series of three polymers:  polyethylene (PE), polyisobutylene (PIB), and polystyrene (PS). The molecular weight ranges studied were from dimers up to 500 g/mol for PE and up to 1000 g/mol for PIB and PS. MD simulation was used to generate a large number of configurations of the various oligomers. These configurations were then used to compute the partition coefficients of the species in cylindrical pores of varying diameters. The MD model of the oligomers included all atoms explicitly and all internal degrees of freedom. Solvent was not included specifically but the configurations were generated under phantom chain conditions for longer range interactions that are appropriate to the ϑ solvent conditions that prevail for short molecules. The variation of partition coefficient with pore size for a given oligomer could be described well by assigning an effective hard-sphere radius, called here the retention radius, to the molecule. The retention radii for an oligomer series were found to correlate well with the radii of gyration. There were however significant differences in the retention radii vs radii of gyration correlations among the three series studied. At the same radius of gyration, the retention radii order is found to be PS > PIB > PE. This order agrees with experimental SEC data for retention times for these oligomer series. The differences are attributed to asphericity of individual configurations enhancing the effects of substituent size. The approach of the mean-square radius of gyration and mean-square end-to-end distance dependence on chain length to limiting long-chain behavior is discussed. It is found that the limiting proportionality to chain length has not been reached in the molecular weight ranges studied. A comparison of the use of the intrinsic viscosity−molecular weight product ([η]M) as a measure of radius of gyration, the radius of gyration determined independently, and the retention radius from simulation as criteria for equal retention times is made. The errors in molecular weight determination resulting from the use of each of the three criteria are discussed. The retention radius from simulation is found to be a significantly better criterion for retention time than the [η]M product or directly determined radius of gyration.