Simulating The Hydrolysis Process Of Poly(Lactic Acid) And The Mechanism Of The Molecular Chain Scission

In recent years, biodegradable polymer materials based on natural renewable resources-polylactide have solved the environmental problems which derived from petroleum resources. These polymer materials completely degraded in the natural environment have been extensively studied by polymer scientists. But the degradation processes of these materials are slow and complex. It will be hard to discuss only using the polymer disciplines and even difficult to touch the main core of the scientific issues. Furthermore, it seems more whimsical to directly observe the dynamic degradation process on the molecular level.The modern computer science and technology have changed the ever-changing human lifestyle, and will also have a profound impact on other science areas. It is possible to establish a novel interdisciplinary research method by effective integration of computer science and polymer science. This will open new areas of research. Therefore, we propose to construct a computer simulation platform based on the experiment results of the polymer science to describe the dynamic degradation process of biodegradable polymers, such as poly(lactic acid).The computer method which is used to describe the biodegradable polymer dynamic degradation process is the key of this research. We believe that starting from the molecular weight of the polymer is a good approach. The greatest different of the polymer from a small molecule compound is the molecular weight. Polymers usually have a very large molecular weight (the molecular chain length), which can be seen as the collection of homologues. The molecular weight of the polymer is not an exact value, but rather an average distribution. The dynamic process of the polymer degradation means the decrease of the average molecular weight of the polymer and the change of molecular weight distribution. Such average molecular weight and its distribution changing are closely related to the structure of the molecular chains and their degradation mechanism.Therefore, a specific distribution function (or degradation experiments results) is used to describe the molecular weight distribution of the polymer chains. Through the parameters of the factors which affecting the polymer scission, a high dimensional parameter statistical model is constructed to describe the polymer dynamic degradation. Assuming the degradation process of the polymer is a discrete event. Considering both of the accuracy of the sampled data and the efficiency of calculation, the statistical distribution functions of the polymer degradation obtained by the experiment will be computed. With obtaining several degradation parameters a computer simulation platform was built for the study of the poly(lactic acid) dynamic degradation process.The hydrolysis of poly(lactic acid) was used for the polymer chain scission model. Monte Carlo chemical kinetic model was used to compute the changes of the polymer chains in the hydrolysis process. The method obtained the factor which influence of the change of the molecular chain lengths in the degradation reaction. Different from the experimental studies, in this article we discussed a competitive relationship between the long chain and the short chain which were in the same system, which cannot be solved by experimental approach. It is found that during the hydrolysis process of amorphous poly(lactic acid), the ratio of the reaction probability of the long chain molecules and the short chain equal to their molecular weight ratio of 0.4-th power. That is, the long chain molecules are more prone to scission. In the hydrolysis process of the extended-chain crystalline poly(lactic acid), the exponent is a time-related variable. As the degradation proceeds, the exponent reduced from 1 to 0.7. Meanwhile, in the degradation reaction, the long chain is still more prone to scission than the short chain. The article also attempts to simulate the hydrolysis of crystalline poly(lactic acid).This article also studied the solution of the degradation kinetics equation to simulate the process of the polymer chain broken. The Method of Lines (MoL) was used to solve the kinetic equation with integral-differential equation. A very general kinetics domaint equation was obtained. This equation can be used for an arbitrarily initial molecular weight distribution, or applicable to a variety of complex degradation kinetics. The molecular weight distribution curve obtained from the calculation can be compared with the experimental results. The method has an accurate simulation result even if the degradation products have a very low molecular weight.