Interconnected macroporous polymers can be made by polymerisation of emulsion templates consisting of an aqueous phase and a monomer phase (typically styrene and divinylbenzene) in which the aqueous (internal) phase is in the form of drops and the monomer phase is the continuous phase between the drops. Until recently it was thought that interconnected macroporous polymers could only be produced from the polymerisation of high internal phase emulsion (HIPE) templates with an internal phase level exceeding 74 vol%. Improvement of the poor mechanical performance, characteristic of such macroporous polymers, was achieved simply by increasing the material density of the macroporous polymer. However, this required a reduction in the internal phase volume of the emulsion template. Polymerisation of the continuous organic phase of emulsion templates with an internal phase volume ranging from 84 vol% to 70 vol% resulted in the production of poly(merised)HIPEs, polymerisation of medium internal phase emulsions with internal phase volume ranging from 70 vol% to 30 vol% in polyMIPEs and polymerisation of a low internal phase emulsion with an internal phase volume of 25 vol% in a polyLIPE. The resulting macroporous polymers were characterised in terms of mechanical and structural properties as well as gas and mercury permeability. Compression tests show that mechanical properties improved as the material density was increased. Gas and mercury permeability measurements show that as the internal phase volume of the emulsion template is reduced, the permeability of the resultant macroporous polymer is also reduced. However, surprisingly even macroporous polymers produced from low internal phase emulsion templates (25 vol%) were permeable with a gas permeability of 2.6 Â 10 À14 m 2 indicating that polyLIPEs are still interconnected macroporous polymers. Reconstruction modelling of the transport properties of porous materials shows that the permeability of a porous material with similar structures to that of the macroporous polymers increases exponentially with the porosity.

No abstract

In a previous paper (Grof, Z.; Kosek, J.; Marek, M. Morphogenesis model of growing polyolefin particles. AIChE J., accepted), we have introduced the model of the morphological evolution of polyolefin particles in catalytic polymerization reactors. The model considers the polyolefin particle to consist of a large number of microelements with viscoelastic interactions acting among them. Here we present the results of the systematic mapping from the parametric space of catalyst activity, reaction conditions, mass transport resistance, and viscoelastic properties of polyolefins into the space of possible morphological developments, such as the formation of hollow particles, particles with macrocavities, regular or irregular replication of particle shape during its growth, highly porous or compact particles, the formation of fine particles, etc. The predicted particle morphologies are compared with experimental findings. We focus on the effect of temperature on the morphogenesis of polyolefin particles and identify the reaction conditions leading to the disintegration of the growing particle into fine particles, which is the unwanted phenomenon observed in industrial reactors. The causes of different pore space morphologies of Ziegler−Natta and metallocene-born polyolefin particles are also investigated.

A recently developed method is used for the analysis of structures of planar disordered granular assemblies. Within this method, the assemblies are partitioned into volume elements associated either with grains or with more basic elements called quadrons. Our first aim is to compare the relative usefulness of description by quadrons or by grains for entropic characterization. The second aim is to use the method to gain better understanding of the different roles of friction and grain shape and size distributions in determining the disordered structure. Our third aim is to quantify the statistics of basic volumes used for the entropic analysis. We report the following results. (1) Quadrons are more useful than grains as basic ''quasiparticles'' for the entropic formalism. (2) Both grain and quadron volume distributions show nontrivial peaks and shoulders. These can be understood only in the context of the quadrons in terms of particular conditional distributions. (3) Increasing friction increases the mean cell size, as expected, but does not affect the conditional distributions, which is explained on a fundamental level. We conclude that grain size and shape distributions determine the conditional distributions, while their relative weights are dominated by friction and by the pack formation process. This separates sharply the different roles that friction and grain shape distributions play. (4) The analysis of the quadron volumes shows that Gamma distributions, which are accepted to describe foamlike structures well, are too simplistic for general granular systems. (5) A range of quantitative results is obtained for the ''density of states'' of quadron and grain volumes and calculations of expectation values of structural properties are demonstrated. The structural characteristics of granular systems are compared with numerically generated foamlike Dirichlet-Voronoi constructions.

The growth of polyolefin particles in heterogeneous catalyzed polymerization reactors is simulated often by reaction-transport models that introduce certain ad hoc effecti®e spatial scales to the description of particle morphology and transport processes inside the particles. Because predicti®e capabilities of such models with respect to particle morphogenesis are limited, a multiscale model of a growing particle is de®eloped. Maximum rele®ant information can be systematically extracted from particle microscopy images using the method of reconstructed porous media. The spatially 3-D replicas of the particle pore space allow to calculate the effecti®e transport and mechanical properties. Two new modeling techniques approximate catalyst particle fragmentation: Delaunay triangulation generalized into a 3-D space with non-Euclidean metrics and disconnection of the skeleton representation of the solid phase. Predicti®e mesoscopic modeling of particle morphogenesis is also discussed.