A mathematical model to describe the molecular weight and polydispersity index (Q) in poly(l-lactide) (PLLA) thermal degradation has been developed. Based on the random chain scission mechanism, effects of temperature and time on the molecular weight and polydispersity index are included in this model. It incorporates the degradation and recombination reaction of PLLA thermal degradation, while taking into account the equal probability assumption. The developments of molecular weight and polydispersity index of PLLA polymer in the thermal degradation process were investigated at temperature ranging from 180 -220°C, the experimental data show PLLA reaches its thermal degradation equilibrium in 2 h. The simulated results of this model are compared with the measured molecular weight and polydispersity index of the PLLA polymer. The changes of the molecular weight and polydispersity index in the PLLA thermal degradation can be predicted by this model.

A simulation model dealing with the kinetic behavior of the hydrolytic polymerization of c-caprolactam with bifunctional regulators has been proposed to analyse such characteristic data of the polymerization as the concentrations of caprolactam, endgroups, E-aminocaproic acid, cyclic dimer, and as well as conversion, numherand weight-average molecular weights, and polydispersity index. The calculated values based upon the model were found to be quite compatible with the observed values. It is found that the presence of more bifunctional acid leads to a lower equilibrium value of polydispersity index, unlike the case of monofunctional acid where the polydispersity index asymptotically reaches a value of 2, regardless of the amount of monofunctional acid initially added. ZUSAMMENFASSUNG:Ein Model1 zur Simulierung der Kinetik der hydrolytischen Polymerisation von E-Caprolactam mit bifunktionellen Molekulargewichtsreglem wird vorgeschlagen, um charakteristische Daten wie die Konzentrationen von Caprolactam, Endgruppen, E-Aminocapronsaure und cyclischem Dimeren sowie Umsatz, zahlen-und gewichtsmittlere Molekulargewichte und die Uneinheitlichkeit zu analysieren. Die anhand dieses Modells berechneten Werte stimmen gut mit den experimentellen Ergebnissen iiberein. Es wurde festgestellt, dal3 bei Venvendung bifunktioneller Saure als Regler mit zunehmender Reglerkonzentration die Uneinheitlichkeit abnimmt, wahrend sich mit monofunktioneller Saure als Regler die Uneinheitlichkeit mit steigender Reglerkonzentration asymptotisch einem Wert von 2 nahert.

A numerical method to seek a solution for the solid-state polycondensation (SSP) process has been proposed to analyze the mechanism of SSP. Results expound that, for the industrial SSP process of PET, the overall reaction rate in a single pellet is appropriately simulated by the diffusion and reaction rate jointly controlling the model. From the core to the surface the SSP rate increases monotonically due to a gradual reduction of the concentration of such by-products as ethylene glycol and water. However, the SSP rate at any location within the pellet is constrained between two purely reaction rate controlling cases. 0 1995

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A modified mathematical model based on the melting and recrystallization of an initial distribution of melting temperatures satisfactorily predicts the melting behavior of PET in differential scanning calorimetry. The simulated DSC curves produced in this work agreed fairly well not only with experimental DSC curves performed by Holdsworth et al., but also with the DSC traces provided by SSP PET pellets. The model, taking into account the initial distribution of melting points and the distribution of melting points for the recrystallized material, succeeded in analyzing the origin of dual endotherms of PET with various thermal histories, thereby elucidating the effect of changing crystallization temperature and time, the heating rate in the DSC heating scan, as well as the SSP process on the melting behavior of PET completely. Furthermore, it has been analytically proven that the crystallinity measured on a DSC diagram could not be equal to the weight percentage of crystalline state in the initial specimen. The deviation of the measured crystallinity, as observed relevant to the melting and recrystallization processes, is caused by the changes of the heat of fusion with the melting temperature as well as the difference of heat capacities of liquid and solidstate polymer.