Nanometer-scale porosity is being introduced into low-k dielectrics in an attempt to achieve inter-level metal insulators with permittivities less than 2.0. It has proven extremely difficult to describe pore formation and to characterize the porous structure. This work investigates pore formation in a polyphenylene low-k dielectric based on pyrolysis of a porogen (27 vol %) in a polyphenylene matrix. One unique aspect presented here is the characterization of the nanoscale structure at various stages of pore formation through the use of a deuterated porogen. The combination of X-ray reflectivity (XRR) and smallangle neutron scattering (SANS) is found to be a powerful technique for describing porogen degradation and pore formation in nanoporous materials. The average radius of the porogen domains was approximately 60 Å with a relatively broad size distribution. During degradation the smaller porogen domains collapse, while the larger domains yield stable pores. This collapse of the relatively large number of smaller domains results in a significant reduction in film thickness, a porosity that is significantly smaller than the porogen content, a pore size distribution that is narrower than the porogen domain size distribution, and an average pore size of approximately 80 Å.

The modification of porous PVC particles by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within the PVC particles is presented. The modifying crosslinked polymers are polystyrene (PS) crosslinked with DVB (divinyl benzene), polymethyl methacrylate (PMMA) crosslinked with ethylene glycol dimethacrylate (EGDMA), and styrene‐MMA copolymer crosslinked with DVB. The modified PVC particles characterization includes polymerization yield, non‐extractables, 13C solid‐state CPMAS NMR, porosity measurements and also morphology and dynamic mechanical behavior (DMTA). The levels of nonextractable fractions found and 13C solid‐state CPMAS NMR results are indicative of low chemical interaction in the semi‐IPN PVC particles. Particle porosity levels and SEM observations indicate that styrene and MMA mainly polymerize within the PVC particles' bulk and just small amounts in the pores. MMA polymerization in the PVC pores is as crusts covering the PVC pore surfaces, whereas styrene polymerization in the PVC pores is by filling the pores. Dynamic mechanical studies show that tanδ and the storage modulus curves are influenced by the incorporation of PS and XPS but not by the incorporation of PMMA and XPMMA.

In‐situ polymerization is the polymerization of one monomer in the presence of another polymer. It can be performed by sequential emulsion polymerization, or by reactions in the melt, in the solid phase, or in solution. The current report describes two methods to obtain poly(vinyl chloride) (PVC) modification through polymerization of a monomer absorbed in commercial porous suspension‐type PVC particles. The generated modified PVC products differ significantly in their structure and properties. The first approach includes absorption of a monomer/peroxide solution within porous suspension‐type PVC particles, followed by polymerization/crosslinking in the solid state at 80°C in an aqueous stabilizer‐free dispersion. The monomer/crosslinker pairs selected are styrene/DVB (divinyl benzene), methylmethacrylate/EGDMA (ethylene glycol dimethacrylate), butyl acrylate/EGDMA, and ethylhexyl acrylate/EGDMA. The influence of composition and nature of the polymerizing/crosslinking constituents on the modified PVC particle structure was studied by microscopy methods, porosity measurements, and dynamic mechanical behavior (DMTA). The level of molecular grafting between PVC and the modifying polymer was determined by solvent extraction experiments. This work shows that the different monomers used represent distinct courses of monomer transport through the PVC particles. The characteristics of the modified PVC particle indicate that the polymerization/crosslinking process occurs in both the PVC bulk, i.e., within the walls constituting a particle, and in the PVC pores. No indication of chemical intermolecular interaction within the modified PVC particles was found. In the second approach, a solution of monomer, initiator, and a crosslinking agent is absorbed in commercial suspension‐type porous PVC particles, thus forming a dry blend. This dry blend is subsequently reactively polymerized in a twin‐screw extruder at an elevated temperature, 180°C, in the molten state. The properties of the reactively extruded PVC/PMMA blends are compared with those of physical blends at similar compositions. Owing to the high polymerization temperature, short‐chain polymers are formed in the reactive polymerization process. Reactively extruded PVC/PMMA blends are transparent, form single‐phase morphology, have a single Tg, and show mechanical properties comparable with those of the neat PVC. The resulting reactively extruded PVC/PMMA blends have high compatibility. J. Vinyl Addit. Technol. 10:109–120, 2004. © 2004 Society of Plastics Engineers.

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The present study describes modification of porous PVC particles by polymerization of a monomer/crosslinker/ peroxide solution absorbed within the PVC particles. The modifying crosslinked polymers include butyl acrylate (BA) crosslinked with ethylene glycol dimethacrylate (EGDMA) and ethylhexyl acrylate (EHA) crosslinked with EGDMA. The monomer solution is blended with the PVC particles by dry-blending. The monomer absorbed particles are then polymerized in a stabilizerfree aqueous dispersion-polymerization. The modified semi-IPN PVC particles have better stability than the neat PVC particles in packed columns for absorption of halo-organics from water, etc. The modified semi-IPN PVC particles are melt processable and thus have the potential of being interesting and useful modified rigid PVC materials.The modified PVC particles characterization includes polymerization yield, non-extractables and porosity measurements and also morphology and dynamic mechanical behavior (DMTA).PBA and PEHA polymerization has shown high yield levels. The high conversion of BA and EHA within the particle, is partly due to their low solubility in water.The levels of non-extractable fractions found are indicative of low chemical interaction between the polyacrylate/PVC phases in the particle. The modified PVC particle's porosity levels indicate that BA and EHA partly polymerize within the PVC particles' bulk and partly in the pores as crusts covering the PVC pore surfaces. This finding is supported by SEM observations of unetched and etched freeze fractured surfaces. Higher crosslinking levels of the polyacrylate modification promote compatibility with the PVC particles' bulk. DMTA measurements show two loss modulus peaks for the 0.5%EGDMA blends in the glass transition temperature region, suggesting imcompatibility. However, at 5%EGDMA a single transition is found exhibiting enhanced compatibility owing to the high degree of crosslinking, which prevents phase separation.