Polymerization simulated start

Figures 7. Simulated start-up of vinyl acetate polymerization at low emulsifier level (0.01 mol/L H20) under closed-loop control with arbitrarily selected controller tuning constants and manipulation of initiator flow rate at 50°C conversion in R1—STD feedback (--------------------------) vs. DTC (----)...

R. H. Boyd and P. V. K. Pant, Polym. Prepr. ACS, Div. Polym. Chem., 30(2), 30 (1989). Atomistic Simulation of a Polymeric Glass Starting from an Equilibrated Liquid. 

Flory [6] estimated lO collisions between functional groups before a reaction in a typical step growth polymerization. Even in the case of rodlike molecules, the local dynamics are fast though reorientation is a very slow process. Clearly, a brute force simulation of the polymerization process starting with reactive monomers and allowing them to react to form polymers seems infeasible... 

The gas temperature accelerated the evaporatimi but it did not change the relative particle at which shell formation happened. This leads to the conclusimi that the shell formation is a (hying phenomenon and not a polymerization phenomenon, since higher temperatures would favor the reaction and an earher shell formation. This conclusicMi is in accordance with simulations carried out by Sackel et al. [35]. The authors described that the polymerization reacticni starts after shell formation because then the inner droplet temperature rises so that the initiator decomposes quantitatively. With that in mind, the starting point of the polymerization can be controlled by the amount of initial solvent. The following reaction is more a mass polymerization than a solution polymerization [36]. 

Addition of a core compound even in a batch wise polymerization makes the distribution narrower. This problem can simply be handled by TBP. If one starts with a core and the monomer is gradually added, the distribution can be narrowed even more [51, 83-87]. This follows from kinetic simulations. However, the monomer addition method has certain limits. It is effective for low molecular weights, so that B groups are almost absent in all initial larger molecules. Unless the monomer addition is infinitesimally slow, which is impractical, condensates by reactions between the monomers are formed containing B... 

Since about 15 years, with the advent of more and more powerfull computers and appropriate softwares, it is possible to develop also atomistic models for the diffusion of small penetrants in polymeric matrices. In principle the development of this computational approach starts from very elementary physico-chemical data - called also first-principles - on the penetrant polymer system. The dimensions of the atoms, the interatomic distances and molecular chain angles, the potential fields acting on the atoms and molecules and other local parameters are used to generate a polymer structure, to insert the penetrant molecules in its free-volumes and then to simulate the motion of these penetrant molecules in the polymer matrix. Determining the size and rate of these motions makes it possible to calculate the diffusion coefficient and characterize the diffusional mechanism. 

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