Chemical irregularities such as side chain branches or comonomers in an otherwise regular polymer influence its crystallization. In most polymer systems, these chemical defects are randomly distributed along the chain, and it is difficult to understand in detail their effect on crystallization. We have examined three precision polymers prepared by acyclic diene metathesis (ADMET) polymerization. This synthesis ensures exact placement of the chain defects; here they are all separated by 20 CH 2 units. The polymers are two polyphosphoesters with a phosphate or phosphonate group in the main chain and one polyethylene with butyl branches. Although the alkyl part is identical for all three polymers, their thermal and crystal properties differ noticeably. By means of differential scanning calorimetry, X-ray scattering, and transmission electron microscopy, we characterize the lamellar crystals and correlate our findings to the observed difference in thermal behavior.

The model of the molecular weight distribution (MWD) of polypropylene produced in a loop reactor is established. The simulated MWD data of the polymers produced in steady-state polymerizations agree with the actual data collected from certain plant. The simulated weight-average molecular weight data also agree with the plant data in start-up processes. Furthermore, the model can be used to simulate the influence of the operation parameters on the MWD of the polymers produced in the steady-state polymerizations as well as the dynamic polymerizations. The simulated results of the steady state polymerizations show the MWD width of polypropylene decreases with the increase of both the propylene flow and the hydrogen flow, but increases with the increase of the catalyst flow. We also find the weight fraction of the polymers with short chains increases with the increase of both the propylene flow and the hydrogen flow, meanwhile, a small shift of the MWD curve to long chains can also be found as the catalyst flow increases. In the dynamic polymerizations, simulations indicate the MWD width and the weight fraction of the polymers with long chains all decrease in both of the start-up process and the end-up process of the polymerizations

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