Thermal diffusion and molecular weight calibration of poly(ethylene-co-vinyl acetate)s by thermal field-flow fractionation

Copolymer characterization is accomplished with respect to measurement of thermal diffusion coefficient (D_T) and molecular weight determination by thermal field-flow fractionation. The examined copolymers are the eight poly(ethylene-co-vinyl acetate)s [P(E-V)] having different compositions of vinyl acetate ranging from 25 to 70% and the molecular weight from 110,000 to 285,000, and three polyvinyl acetate standards as component homopolymer. The carrier solvents are tetrahydrofuran, toluene, and chlorobenzene which have different viscosities and thermal conductivities. Measured D_T values vary from 1.36 × 10^?8 to 5.97 × 10_?8 cm²/(s . K) which are dependent on the composition of copolymers and types of carriers. These values increase linearly with the increase of weight percent of vinyl acetate. It is possible to estimate D_T values of polyethylene from the extrapolated intercept in the plots of D_T vs. vinyl acetate wt % of copolymer. Tetrahydrofuran is found to be the appropriate carrier solvent for the separation of P(E-V) copolymers since D_T varies greatly with the increase of wt % in THF. Attempts are made to correlate the measured retention data with molecular sizes of copolymers for the construction of the molecular weight calibration curve. Good correlations (r² ≥ 0.931) are found in which D/D_T values of polymers vary inversely with the product of hydrodynamic volume by weight ratio of vinyl acetate. Based on this relationship, the unknown molecular weight of copolymer sample can be determined from component homopolymers for which standards are readily available. © 1995 John Wiley & Sons, Inc.     

High molecular weight monodisperse polystyrene microspheres prepared by dispersion polymerization,using a novel bifunctional macromonomer

A novel bifunctional vinyl‐terminated polyurethane macromonomer was applied to the dispersion polymerization of styrene in ethanol. Monodisperse polystyrene (PS) microspheres were successfully obtained above 15 wt % of macromonomer relative to styrene. The steep slope from the reduction of the average particle size reveals that the macromonomer can efficiently stabilize higher surface area of the particles when compared with a conventional stabilizer, poly(N‐vinylpyrrolidone). The stable and monodisperse PS microspheres having the weight‐average diameter of 1.2 μm and a good uniformity of 1.01 were obtained with 20 wt % polyurethane macromonomer. The grafting ratio of the PS calculated from ¹H NMR spectra linearly increased up to 0.048 with 20 wt % of the macromonomer. In addition, the high molecular weights (501,300 g/mol) of PS with increased glass transition and enhanced thermal degradation temperature were obtained. Thus, these results suggest that the bifunctional vinyl‐terminated polyurethane macromonomer acts as a reactive stabilizer, which gives polyurethane‐grafted PS with a high molecular weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3566–3573, 2005     

Fabrication and chemical surface modification of nanoporous silicon for biosensing applications

In this work, porous silicon (PS) films with varied porosity (68–82%) were formed on the p-type, boron-doped silicon wafer (100) by the electrochemical anodisation in an aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities (I _d) ranging from 20–70 mA cm^?2, respectively. Biofunctionalisation of the PS surface was carried out by chemically modifying the surface of PS by the deposition of 3-aminopropyltriethoxysilane thermally leading to high density of amine groups covering the PS surface. This further promotes the immobilisation of immunoglobulin (human IgG and goat anti-human IgG binding) on to the PS surface. Formation of nanostructured PS and the attachment of antibody–antigen to its surface were characterised using photoluminescence (PL), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, respectively. The possibility of using these structures as biosensors has been explored based on the significant changes in the PL spectra before and after exposing the PS optical structures to biomolecules. These experimental results open the possibility of developing optical biosensors based on the variation of the PL position of the PL spectra of PS-based devices.     

Stoichiometric silicon carbide from borate‐catalyzed polymethylsilane–polyvinylsilane formulations

Polymethylsilane (PMS) and polyvinysilane (PVS) were prepared by Wurtz condensation of chlorosilanes and characterized by spectroscopy (¹H, ¹³C and ²⁹Si NMR, and infrared), viscosity and GPC analysis. Mixtures of the PMS and PVS were prepared and stabilized with 2,6‐di‐t‐butyl‐4‐methylphenol (BHT; 0.5 wt%) to which was added a catalytic amount of tris­(trimethylsilyl)borate, B(OSiMe₃)₃ (BTMS; 2 wt% by weight). The resulting liquid materials were pyrolyzed to 950 °C and to 1400 °C under argon. The formulation, composed of 60% PMS / 40% PVS / 2% BTMS, was pyrolyzed and gives nearly stoichiometric silicon carbide in 73% yield. The pyrolyzate was analyzed spectroscopically at intermediate stages in order to study its thermal transformations and the influence of the boron catalyst. The ceramic obtained from the formulation 60% PMS / 40% PVS / 2% BTMS shows good stability at 1500 °C under oxygen. Copyright © 1999 John Wiley & Sons, Ltd.     

Patterning nanocluster polystyrene brushes grafted from initiator cores on silicon surfaces by lithography processing

In this study, we formed grafted polystyrene (PS) brushes possessing nanocluster structures through atom transfer radical polymerization from initiator cores presented on Si surfaces that had been generated using reactive ion etching (RIE). We established the surface grafting polymerization kinetics of the nanoclustered PS chains on the Si surfaces to fit their experimentally determined thickness (ellipsometry) and number-average molecular weight (M _n) of “free” PS (gel permeation chromatography). The propagation rate (k _p) and active grafting species deactivation rate (k _d) were obtained from reactions involving styrene concentrations from 0.2 to 2 M. We also used scanning electron microscopy to observe the morphologies of the PS grafted to the surfaces after various reaction times at various styrene concentrations. The PS brushes grafted onto the Si surfaces under styrene concentrations of 0.2, 0.5, 1, and 2 M exhibited clustered structures having cluster diameters of 12, 28, 42, and 45 nm, respectively; from these observations, we calculated the critical grafting density. In addition, we generated highly dense, well-defined patterns of PS on patterned Si(100) surfaces through the use of a very-large-scale integration process involving electron beam lithography and RIE. We employed the RIE system to generate a high density of reactive species at the bottom of the trenches for graft polymerization. After 21 h of grafting, AFM imaging revealed dense line patterns of nanoclustered PS.     

Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes

Desorption/ionization on silicon (DIOS) mass spectra of model ionic dyes methylene blue (MB⁺Cl^?) and methyl orange (Na⁺MO^?) were studied using p⁺ type‐derived porous silicon (PS) free layers. As‐prepared PS (PS‐H), the PS thermally oxidized at 300 °C (PS‐OX), PS with chemically grafted cation‐exchanging alkylsulfonic acid (PS‐SO₃H) and anion‐exchanging propyl‐octadecyldimethylammonium chloride (PS‐ODMA⁺Cl^?) groups was tested as ionization platforms. Two mechanisms of the methylene blue desorption/ionization were found: (1) the formation of [MB + H]^+? ion due to the reduction/protonation of MB⁺, which is predominant for PS‐H and PS‐OX platforms and (2) direct thermal desorption of the MB⁺ cation, prevailing for PS‐SO₃H. The fragmentation of the cation is significantly suppressed in the latter case. The samples of PS‐SO₃H and PS‐ODMA⁺ Cl^? efficiently adsorb the dyes of the opposite charge from their solutions via the ion‐exchange. Consequent DIOS MS studies allow to detect only low fragmented ions (MB⁺ and MO^?, respectively), demonstrating the potential of the ion‐exchange adsorption combined with DIOS MS for the analysis of ionic organic compounds in solutions. Copyright © 2009 John Wiley & Sons, Ltd.     

A facile strategy to modify TiO2 nanoparticles via surface‐initiated ATRP of styrene

A core‐shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n‐TiO₂) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface‐initiated atom transfer radical polymerization (ATRP) at 90 °C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, ¹H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core‐shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO₂‐PS nanocomposites exhibited higher glass transition temperature (T_g) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface‐attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1782–1790, 2010     

Effect of nano‐polystyrene (nPS) on thermal,rheological, and mechanical properties of polypropylene (PP)

Polystyrene nanoparticles (nPS) in the range of 10–100 nm with spherical shape were synthesized by oil/water (o/w) microemulsion process. In this process ammonium persulfate (APS) as an initiator, sodium dodecyl sulphate as a surfactant and n‐pentanol as cosurfactant were used. Isolated nPS was characterized by FTIR and ¹H NMR spectroscopy. DSC studies of nPS showed higher T_g as compared to bulk PS. The effect of lower weight percentage (wt%) of nPS on the mechanical, rheological, and thermal properties of PP was investigated. The blends were prepared individually on brabender plastograph by incorporating nPS of ～60 nm with different wt% of loading (i.e., 0.10–0.5%). It was shown from the experimental results that thermal, rheological, and mechanical properties were increased as the polymer particles blended with PP. Blends with 0.25 wt% loading of nPS exhibit better properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of PP chains as recorded by improvement in crystallinity of PP with the addition of nPS as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of bulk chain coupling reactions. III. Reaction between bisoxazolines or bisoxazlines and carboxy-terminated oligomers

2,2′-Bis(2-oxazoline) and 2,2′-bis[5,6-dihydro-(4H)-1,3-oxazine] have been used as chain coupling reagents ( CC ) and reacted in the bulk with α,ω-dicarboxy-poly(2,2′-oxydiethylene adipate) ( PS ) or with α,ω-dicarboxy-polyamide 12 ( PA ). The reactions have been followed by viscosimetry, titration of COOH groups and ¹H- and ¹³C-NMR spectroscopy. Either with the PS/CC or PA/CC systems, or with the model system dodecanoic acid ( DA )/ CC , the reactions were fast, since in most cases 80% conversion was reached after 15 min reaction. The expected DA dimer or high molar mass PA or PS polymers were obtained. No significant side reaction has been detected. The thermal stability of the resulting polymers is higher than that of starting oligomers. Due to the introduction of CC units in the chains, the crystallinity of PA/CC is slower than that of starting PA . © 1995 John Wiley & Sons, Inc.     

Effects of active silicon uptake by rice on 29Si fractionation in various plant parts

Rice (Oryza sativa L.) accumulates large amounts of silicon which improves its growth and health due to enhanced resistance to biotic and abiotic stresses. Silicon uptake and loading to xylem in rice are predominantly active processes performed by transporters encoded by the recently identified genes Lsi1 (Si influx transporter gene) and Lsi2 (Si efflux transporter gene). Silicon deposition in rice during translocation to upper plant tissues is known to discriminate against the heavier isotopes ²⁹Si and ³⁰Si, resulting in isotope fractionation within the plant. We analyzed straw and husk samples of rice mutants defective in Lsi1, Lsi2 or both for silicon content and δ²⁹Si using isotope ratio mass spectrometry (IRMS) and compared these results with those for the corresponding wild‐type varieties (WT). The silicon content was higher in husk than in straw. All the mutant rice lines showed clearly lower silicon content than the WT lines (4–23% Si of WT). The δ²⁹Si was lower in straw and husk for the uptake defective mutant (lsi1) than for WT, albeit δ²⁹Si was 0.3‰ higher in husk than in straw in both lines. The effect of defective efflux (lsi2) differed for straw and husk with higher δ²⁹Si in straw, but lower δ²⁹Si in husk while WT showed similar δ²⁹Si in both fractions. These initial results show the potential of Si isotopes to enlighten the influence of active uptake on translocation and deposition processes in the plant. Copyright © 2009 John Wiley & Sons, Ltd.     

Sub‐glass‐transition temperature interface formation between an immiscible glass rubber pair

We used neutron reflectivity to measure the interfacial width in the immiscible system polystyrene/poly(n‐butyl methacrylate) (PS/PnBMA). Measurements were made on the same samples at temperatures ranging from below the glass‐transition temperature (T_g) of PS to slightly above. We observed significant broadening of the interface at temperatures below the T_g of PS, indicating chain mobility below the bulk T_g value. The interfacial width exhibited a plateau at a value of 20 Å in the temperature range of 365 K < T < 377 K. A control experiment involving hydrogenated and deuterated PS films (hPS/dPS) showed no such broadening over the same temperature region. The results are consistent with a reduction of the T_g of PS in the interfacial region of ～20 K. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2664–2670, 2001     

Monoisotopic varieties of silicon and germanium with a high chemical and isotopic purity

We presented the results on the preparation of high-purity monoisotopic varieties of silicon and germanium. The process involves the separation of isotopes in the form of SiF₄ and GeH₄ by centrifugation, ultrapurification of volatile compounds, and preparation of poly and single crystals. The attained degree of isotopic and chemical purities of single crystals obtained was shown. The content of the main isotope in the single crystals of ²⁸Si is >99.99% and those in the single crystals of ²⁹Si and ³⁰Si are >99.9%. The specific resistivity of the ²⁸Si single crystals is ～1 kOhm cm and those of ²⁹Si and ³⁰Si are about 100–150 Ohm cm. The samples of the ⁷⁶Ge single crystals have the main isotope content of >88 at.% and the difference concentration of electrochemically active impurities of 5·10¹⁰ cm^?3. The main isotope content in the ⁷⁴Ge polycrystal is 99.93 at.%. The optical and thermophysical properties of the isotope-enriched silicon and germanium single crystals were measured, which suggest a significant effect of the isopotic composition on thermal capacity, thermal conductivity, luminiscence, and light absorption.     

The interface effect on the lithiation of silicon/graphene composites: The first principles study

To reveal the interaction mechanism between lithium (Li) and silicon/graphene (Si/Gra) interface at the atomic scale, it was calculated that the energy band structure, density of states, charge transfer, radial distribution function and Li diffusion coefficient based on the first principles. The results indicated that the volume expansion of Si was effectively limited by the Si/Gra interface during Li insertion. There appeared the interface effect of Si/Gra on the combination of Li and Si atoms, according to the longer Li-C (2.9 Å) and the larger electron cloud near the Li atom at the Si/Gra interface. The better diffusion channel for Li atoms was constructed at the Si/Gra interface, due to the lower diffusion energy barrier (0.42–0.44 eV) and higher diffusion coefficient (D_Li = 0.784 × 10⁻⁴ cm²/s) for Li⁺ diffusion.     

Investigation of thermal properties of some basalt samples in Egypt

This work aims in studying the temperature dependence of the thermal properties (thermal diffusivity, k, specific heat, C _p and thermal conductivity, ) of some basalt group samples, collected from different regions in the eastern desert of Egypt. The thermal properties of these samples were measured in the temperature range from r.t. to 900 K. The average values of the thermal conductivity of these investigated samples lie in the range from 0.4·10^–3 to 2.01·10^–3 cal cm^–1 s^–1 K^–1. This means that these samples are considered as thermal insulating materials. The thermogravimetric analysis (TG) confirmed that these investigated samples are dry rocks. X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed that these rock samples have a crystalline phase, the peaks of XRD have a small change in their location as a result of heat treatment. This behaviour was attributed to the oxidation and firing of some minerals after the heat treatment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and morphology of model PS‐b‐PDMS copolymers

True model linear poly(styrene‐b‐dimethylsiloxane) PS‐b‐PDMS copolymers were synthesized by using sequential addition of monomers and anionic polymerization (high‐vacuum techniques), employing the most recent experimental procedures that allow the controlled polymerization of each monomer to obtain blocks with controlled molar masses. The model diblock copolymers obtained were analyzed by using different techniques, such as size‐exclusion chromatography, ¹H NMR, Fourier transform infrared spectroscopy, small angle X‐rays scattering (SAXS), and wide angle X‐rays scattering (WAXS). The PS‐b‐PDMS copolymers obtained showed narrow molar mass distribution and variable PDMS content, ranging from 2 up to 55 wt %. Compacted powder samples were investigated by SAXS to reveal their structure and morphology changes on thermal treatment in the interval from 30 to 200 °C. The sample with the highest PDMS content exhibits a lamellar morphology, whereas two other samples show hexagonally packed cylinders of PDMS in a PS matrix. For the lowest PDMS content samples, the SAXS pattern corresponds to a disordered morphology and did not show any changes on thermal treatment. Detailed information about the morphology of scattering domains was obtained by fitting the SAXS scattering curves. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3119–3127, 2010     

Preparation and properties of polycarbonate/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites

Octaphenylsilsesquioxane (PH‐POSS) and octa(γ‐methacryloxypropyl)silsesquioxane (MA‐POSS) were successfully synthesized by hydrolytic condensation of phenyltrichlorosilane and γ‐methacryloxypropyltrimethoxysilane, and characterized by Fourier transform infrared (FT‐IR), ¹H and ²⁹Si nuclear magnetic resonance (NMR), and matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrum. Morphology, degradation behavior, thermal, and mechanical properties of hybrid composites were studied by transmission electron microscopy (TEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), surface contact angle (SCA), tensile, and impact testing. Domains of PH‐POSS and MA‐POSS dispersed in the matrix with a wide size distribution in a range of 0.1–0.5 µm, while PH‐POSS exhibited a preferential dispersion. Because of the possible homopolymerization of MA‐POSS during the melt blending, the glass transition temperature of polycarbonate (PC)/MA‐POSS composites remained nearly unchanged with respect to PC/PH‐POSS composites that showed a depression of T_g due to the plasticization effect. It is interesting to note that the incorporation of POSS retarded the degradation rates of PC composites and thus significantly improved the thermal stabilities. Si? O fractions left during POSS degradations were a key factor governing the formation of a gel network layer on the exterior surface. This layer possessed more compact structures, higher thermal stabilities, and some thermal insulation. In addition, percentage residues at 700°C (C₇₀₀) significantly increased from 10.8% to 15.8–22.1% in air. Fracture stress of two composites showed a slight improvement, and the impact strength of them decreased monotonically with the increase of POSS loading. Copyright © 2011 John Wiley & Sons, Ltd.     

On a proposed radiation-induced polaronic hole in silicon dioxide

Ab-initio self-consistent-field molecular-orbital (SCF MO) Hartree–Fock (HF) calculations using the STO-3G, 6-31G, and 6-31G* basis sets, were performed to model quasi-tetrahedral silicon species in silicon dioxide. Mostly nine-atom clusters, [Si(OH)₄]^qt, with charge number q_t = 0 or + 1, were studied. The positions of the Si and O atoms were varied to achieve minimum total energies, while the protons were held fixed in the O-(neighboring)Si direction to simulate the rigid crystal surroundings. The α-quartz-type local symmetry C₂ was found to be retained for the neutral cluster, but not for the ionic one. The unrestricted HF calculations indicate that the latter paramagnetic centre, (q_t = +1), has its spin population almost entirely on one short-bonded oxygen ion bonded weakly to its neighboring Si, and is quite high in energy (9.55 eV with 6-31G) compared to the diamagnetic centre (q_t = 0). The ionization energy is much higher than the self-trapping potential of the polaronic hole, a fact which may account for the failure so far to observe a [SiO₄]⁺¹ center in quartz by means of continuous-wave electron paramagnetic resonance spectroscopy. Calculations on the [SiO₄]⁺¹ center agree well with ultraviolet spectra, and with the [hole portion of a] proposed radiation-induced exciton in quartz. The hole in [Si(OH)₄]⁺¹ can be shifted from a short-bonded to a long-bonded oxygen to give the excited state [Si(OH)₄]_es⁺¹. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [Si(OSiH₃)₄]^qt. Comparisons with the known isoelectronic species [AlO₄]⁰ were carried out.     

Thermal characterization of montmorillonite clays saturated with various cations

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li⁺, Cs⁺, NH₄⁺, Mg²⁺ and Al³⁺. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ΔE. Decreases in c-axis basal spacing (d ₀₀₁) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003     

Photoinitiated polymerization of methacrylic monomers in a polystyrene matrix: Kinetic,mechanistic, and structural aspects

The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6‐hexanediol dimethacrylate (HDDMA) and 2‐ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matrix were studied. The aggregation state, vitreous or rubbery, of the monomer/matrix system and the intermolecular strength of attraction in the monomer/matrix and growing macroradical/matrix systems are the principal factors influencing the kinetics and mechanism. For the PS/HDDMA system, where a relatively high intermolecular force of attraction between monomer and matrix and between growing macroradical and matrix occurs, a reaction‐diffusion mechanism takes place at low monomer concentrations (<30–40%) from the beginning of the polymerization. For the PS/EHMA system, which presents low intermolecular attraction between monomer and matrix and between growing macroradical and matrix, the reaction‐diffusion termination is not clear, and a combination of reaction‐diffusion and diffusion‐controlled mechanisms explains better the polymerization for monomer concentrations below 30–40%. For both systems, for which a change from a vitreous state to a rubbery state occurs when the monomer concentration changes from 10 to 20%, the intrinsic reactivity and k_p/k_t^1/2 ratio (where k_p is the propagation kinetic constant and k_t is the termination kinetic constant) increase as a result of a greater mobility of the monomer in the matrix (a greater k_p value). The PS matrix participates in the polymerization process through the formation of benzylic radical, which is bonded to some extent by radical–radical coupling with the growing methacrylic radica, producing grafting on the PS matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2049–2057, 2001