The viscosities of samples of poly(methy1 methacrylate), PMMA, W' tJ narrow molecular weight distributions and with molecular weights in the range 1,75 . lo4 < M , < 1,60. lo6 were measured in methyl methacrylate, MMA, as solvent at 20,40, and 60 "C in the dilute and in the semi-dilute concentration regime. By extrapolation to zero polymer concentration the limiting viscosity numbers and therefrom the Mark-Houwink-Kuhn-Sakurada parameters for PMMA in MMA were obtained. In addition, unperturbed dimensions were determined from dilute solution viscosity data. Together with some published results for more concentrated solutions of PMMA in MMA the viscosities of the semi-dilute systems were analysed in terms of scaling theories. It was found that irrespective of temperature, polymer concentration, and molecular weight all data could be quite well fitted by a single master curve when the relative viscosity q/qo was plotted as a function of the product of the intrinsic viscosity and mass concentration [q] . c.No sharp transitions between different concentration regimes were observed, however, and the scaling law exponents for the entangled solution are significantly higher than predicted by theory. 0025-1 16)

The kinetic model given by Marten and Hamielec that describes the bulk polymerization of methyl methacrylate (MMA) and accounts for diffusion‐controlled termination and propagation was modified to include termination by combination and reaction diffusion and was then tested using isothermal conversion/time and molecular weight data obtained dilatometrically at various temperatures and with three different initiators. For each series of measurements two adjustable parameters were fitted to the conversion/time data. Excellent fits were obtained and the adjustable parameters were found to be the same for all concentration levels of the three initiators and to vary in a simple manner with temperature. The predicted molecular weight averages and molecular weight distributions were in satisfactory agreement with those found experimentally considering the difficulty of measuring high molecular weight PMMA by GPC. This model thus satisfies the specifications for a polymer reactor model that can be used to optimize commercial production systems.

SUMMARY:A model is proposed for the radical-induced polymerization of methyl methacrylate which combines concepts given in the literature. Consecutive steps for diffusion and reaction are used for both the propagation and the termination process, and the termination at higher degrees of conversion is dominated by reaction diffusion as described by Buback. The diffusional contributions to the processes are semi-empirically based on the free-volume theory, following a suggestion made by Marten and Hamielec, and the diffusion of the macroradicals is assumed to depend on the instantaneous molar mass (as representative for their chain length) and on the cumulative molar mass (representing the matrix of the dead polymer). With one fixed and four adjustable parameters, the model successfully not only describes the bulk polymerization but also takes account of the presence of solvent, chain transfer agent and pre-polymer.

Bei der Definition von kt halten wir uns an die im Angelsachsischen ubliche Beziehung fur die Abbruchgeschwindigkeit R, = 2kt[p7'.

Uber das Partialvolumen der Leerstellen in Polymeren gibt es in der Literatur eine Reihe von ). Sie fuhren zu Werten, die zwischen 0,025 und 0,07 schwanken. Als experimenteller Wert wird meist der von WILLIAMS, LANDEL und FERRY 2) aus Viskositatsdaten erhaltene angegeben; als Mittelwert fur eine Reihe von Hochpolymeren betragt er 0,025. Einen weiteren experimentellen Wert fur das Leerstellen-Volumen sollte man erhalten, wenn man das als frei von Leerstellen gedachte Partialvolumen des Polymeren in Losung mit dem spezifischen Volumen des festen Polymeren vergleicht. Dazu haben wir Dichtemessungen an Mischungen aus Polymethylmethacrylat (PMMA) und dessen Monomer (MMA) durchgefuhrt. Mischungen mit PMMA-Massenanteilen zwischen 0 und 0,4 wurden durch Auflosen von PMMA in MMA hergestellt, ihre Dichte wurde im DichtemeDgerat der Firma A. PAAR, Graz, nach KRATKY, LEOPOLD und STABINGER~) bei 20°C gemessen. Als Proben mit PMMA-Massenanteilen zwischen 0,8 und 1 ,O dienten ungetemperte Substanzpolymerisate. Ihre Dichte wurde pyknometrisch gemessen, ihre Zusammensetzung wurde durch DSC-Messungen uber die Polymerisationswarme des Restmonomer-Gehaltes bestimmt. Hierbei haben wir vorausgesetzt, da13 die Proben noch genugende Mengen an Radikalbildner enthielten, um alles MMA zu polymerisieren. Diese Annahme konnte durch gravimetrische und spektroskopische Bestimmung des Restmonomer-Gehaltes bestatigt werden. In Abb. 1 ist das spezifische Volumen gegen die Zusammensetzung aufgetragen. Oberhalb eines PMMA-Massenanteils von 0,8 weichen die MeDpunkte vom linearen Verlauf ab und geben fur reines PMMA einen Wert von 0,842 cm3 . 8-1, hingegen findet man durch Extrapolation des linearen Verlaufs ein Partialvolumen von 0,820 cm3 * g-1. Die Differenz 351