High-molecular-weight polyethyleneimine conjuncted pluronic for gene transfer agents

In order to enhance the gene delivery efficiency and decrease cytotoxicity of polyplexes, copolymers consisting of branched polyethyleneimine (PEI) 25 kDa grafted with Pluronic (F127, F68, P105) were successfully synthesized using a simple two-step procedure. The copolymers were tested for cytotoxicity and DNA condensation and complexation properties. Their polyplexes with plasmid DNA were characterized in terms of DNA size and surface charge and transfection efficiency. The complex sizes were below 300 nm, which implicated their potential for intracellular delivery. The Pluronic-g-PEI exhibited better condensation and complexation properties than PEI 25 kDa. The cytotoxicity of PEI was strongly reduced after copolymerization. The Pluronic-g-PEI showed lower cytotoxicity in three different cell lines (Hela, MCF-7, and HepG2) than PEI 25 kDa. pGL3-lus was used as a reporter gene, and the transfection efficiency was in vitro measured in HeLa cells. Compared with unmodified PEI 25 kDa Pluronic-g-PEI showed much higher transfection efficiency. These results demonstrate that polyplexes prepared using a combined strategy of surface crosslinking and grafted with Pluronic seem to provide promising properties as stable, high transfection efficiency vectors.     

Nanosegregated polymeric domains on the surface of Fe3O4@SiO2 particles

Multifunctional, biocompatible, and brush‐grafted poly(ethylene glycol)/poly(ε‐caprolactone) (PEG/PCL) nanoparticles have been synthesized, characterized, and used as vehicles for transporting hydrophobic substances in water. For anchoring the polymer mixed brushes, we used magnetic‐silica particles of 40 nm diameter produced by the reverse microemulsion method. The surface of the silica particle was functionalized with biocompatible polymer brushes, which were synthesized by the combination of “grafting to” and “grafting from” techniques. PEG was immobilized on the particles surface, by “grafting to,” whereas PCL was growth by ROP using the “grafting from” approach. By varying the synthetic conditions, it was possible to control the amount of PCL anchored on the surface of the nanoparticles and consequently the PEG/PCL ratio, which is a vital parameter connected with the arrangement of the polymer brushes as well as the hydrophobic/hydrophilic balance of the particles. Thus, adjusting the PEG/PCL ratio, it was possible to obtain a system formed by PEG and PCL chains grafted on the particle's surface that collapsed in segregated domains depending on the solvent used. For instance, the nanoparticles are colloidally stable in water due to the PEG domains and at the same time are able to transport, entrapped within the PCL portion, highly water‐insoluble drugs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2966–2975     

Size- and Surface- Dual Engineered Small Polyplexes for Efficiently Targeting Delivery of siRNA

Though siRNA-based therapy has achieved great progress, efficient siRNA delivery remains a challenge. Here, we synthesized a copolymer PAsp(-N=C-PEG)-PCys-PAsp(DETA) consisting of a poly(aspartate) block grafted with comb-like PEG side chains via a pH-sensitive imine bond (PAsp(-N=C-PEG) block), a poly(l-cysteine) block with a thiol group (PCys block), and a cationic poly(aspartate) block grafted with diethylenetriamine (PAsp(DETA) block). The cationic polymers efficiently complexed siRNA into polyplexes, showing a sandwich-like structure with a PAsp(-N=C-PEG) out-layer, a crosslinked PCys interlayer, and a complexing core of siRNA and PAsp(DETA). Low pH-triggered breakage of pH-sensitive imine bonds caused PEG shedding. The disulfide bond-crosslinking and pH-triggered PEG shedding synergistically decreased the polyplexes’ size from 75 nm to 26 nm. To neutralize excessive positive charges and introduce the targeting ligand, the polyplexes without a PEG layer were coated with an anionic copolymer modified with the targeting ligand lauric acid. The resulting polyplexes exhibited high transfection efficiency and lysosomal escape capacity. This study provides a promising strategy to engineer the size and surface of polyplexes, allowing long blood circulation and targeted delivery of siRNA.     

Amphiphilic PEG‐grafted poly(ester‐carbonate)s: Synthesis and diverse nanostructures in water

Novel biodegradable amphiphilic graft copolymers containing hydrophobic poly(ester‐carbonate) backbone and hydrophilic poly(ethylene glycol) (PEG) side chains were synthesized by a combination of ring‐opening polymerization and “click” chemistry. First, the ring‐opening copolymerization of 5,5‐dibromomethyl trimethylene carbonate (DBTC) and ε‐caprolactone (CL) was performed in the presence of stannous octanoate [Sn(Oct)₂] as catalyst, resulting in poly(DBTC‐co‐CL) with pendant bromo groups. Then the pendant bromo groups were completely converted into azide form, which permitted “click” reaction with alkyne‐terminated PEG by Huisgen 1,3‐dipolar cycloadditions to give amphiphilic biodegradable graft copolymers. The graft copolymers were characterized by proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectra and gel permeation chromatography measurements, which confirmed the well‐defined graft architecture. These copolymers could self‐assemble into micelles in aqueous solution. The size and morphologies of the copolymer micelles were measured by transmission electron microscopy and dynamic light scattering, which are influenced by the length of PEG and grafting density. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Plasmid DNA complexation with phosphorylcholine diblock copolymers and its effect on cell transfection

We examined a series of novel cationic MPC-based (2-methacryloyloxyethyl phosphorylcholine) copolymers as vectors for gene delivery, with emphasis on the assessment of the effects of the charge ratio (administered via pH variation) on the complex (polyplex) formation and the subsequent transfection efficiency. A combination of electrophoresis, dynamic light scattering, and small angle neutron scattering was used to characterize the structure and charge distribution of the polyplexes formed between the copolymer and the luciferase plasmid DNA. Polymers with larger hydrophobic side chains had lower p K a values and tended to aggregate more strongly. For a given copolymer, electrostatic interaction was the main driving force for the formation of the nanopolyplexes. When the cationic copolymers were in excess, the majority of the polyplexes formed was neutral, and only a small faction of them carried net positive charges. Polyplexes formed under excess copolymer protected the DNA from restriction enzyme digestion. As the copolymers were weak polyelectrolytes, the pH had a distinct effect on the structure and charge distribution of the polyplexes formed. Below the p K a, the copolymers were found to bind with the plasmid DNA in the form of unimers, while above the p K a, the copolymers self-aggregated and complexed with DNA in the form of micelles. It was subsequently found that unimer/DNA polyplexes were far more effective in the transfection of HEK293 cells than micellar DNA polyplexes. The results thus revealed that different hydrophobicities of the side chains in the copolymer series led to different nanostructuring and charge characteristics, which had a consequential effect on the transfection efficiency. This study provided useful insight into the molecular processes underlying polyplex formation and demonstrated a strong link between structural and physical properties of polyplexes and cell transfection efficiency.     

Synthesis of Double Hydrophilic Block Copolymers Poly(2-isopropyl-2-oxazoline-b-ethylenimine) and their DNA Transfection Efficiency

Gene delivery is now a part of the therapeutic arsenal for vaccination and treatments of inherited or acquired diseases. Polymers represent an opportunity to develop new synthetic vectors for gene transfer, with a prerequisite of improved delivery and reduced toxicity compared to existing polymers. Here, the synthesis in a two-step's procedure of linear poly(ethylenimine-b-2-isopropyl-2-oxazoline) block copolymers with the linear polyethylenimine (lPEI) block of various molar masses is reported; the molar mass of the poly(2-isopropyl-2-oxazoline) (PiPrOx) block has been set to 7 kg mol⁻¹. Plasmid DNA condensation is successfully achieved, and in vitro transfection efficiency of the copolymers is at least comparable to that obtained with the lPEI of same molar mass. lPEI-b-PiPrOx block copolymers are however less cytotoxic than their linear counterparts. PiPrOx can be a good alternative to PEG which is often used in drug delivery systems. The grafting of histidine moieties on the lPEI block of lPEI-b-PiPrOx does not provide any real improvement of the transfection efficiency. A weak DNA condensation is observed, due to increased steric hindrance along the lPEI backbone. The low cytotoxicity of lPEI-b-PiPrOx makes this family a good candidate for future gene delivery developments.     

Nonviral gene delivery using poly‐D/L aspartate‐diethylenetriamine cationic polymers and polyethylene glycol: A two‐step approach

Cationic polymers have received much attention as promising nonviral vectors for gene transfer. However, development of polymers with low cell toxicities and high transfection efficiencies continue to be a significant problem and a major hurdle to their success. Poly‐D /L aspartate‐diethylenetriamine poly(D /L Asp‐DET) polymers were synthesized and evaluated as nonviral gene delivery agents. Poly(D /L Asp‐DET) polymers display endosome buffering capacity. The polymers condense plasmid DNA above N:P ratios of 1 and form polyplex particles of ～50–100 nm, with zeta potentials between neutral and +40 mV. Transmission electron microscopy shows the polyplexes to be uniform in size and shape. Polyplexes maintain the structural integrity of DNA following incubation in nucleases and also show high transfection efficiencies with minimal toxicity in both HCT‐116 and PC‐3 cell culture. However, it is found that these poly(D /L Asp‐DET)/DNA polyplexes immediately aggregate in salt and serum conditions, making them unsuitable for use in vivo. Therefore, the polyplexes were further modified by covalent addition of polyethylene glycol (PEG). Introduction of this second step produces PEG‐polyplexes of uniform size (below 100 nm), with neutral zeta potentials that are also stable in both salt and serum conditions. These results suggest poly(D /L Asp‐DET) cationic polymers as potentially safe and efficient nonviral gene delivery agents. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

End‐grafting copolymers of styrene and 4‐vinylpyridine on an interacting solid surface

Copolymers of styrene and 4‐vinylpyridine with a styrene fraction f varying from 1 to 0 were grafted onto a silicon substrate in the melt. The grafting reaction and the stability of the grafted chains were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopy. The thickness and surface morphology of the grafted copolymer layers were characterized with ellipsometry and atomic force microscopy (AFM). The copolymer chains were successfully grafted to the surface of the silicon substrate by a reaction between the hydroxyl groups of the nitroxide moiety at the end of the copolymers and the silanol groups on the surface of the silicon wafer. A measurement of the thickness of the grafted copolymer layers showed that the ratio of grafted‐layer thickness to the unperturbed chain radius of gyration decreased with the increasing fraction of 4‐vinylpyridine in the copolymer; this indicated that the grafted layer was strongly attracted to the substrate. In addition, an accelerated grafting process was observed at grafting times ranging from 48 to 72 h for pure poly(4‐vinylpyridine) and copolymers with f values of 0.3 and 0.5. AFM observation revealed that the grafted layers densely and homogeneously covered the silicon substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1332‐1343, 2005     

Design of Well‐Defined Monofunctionalized Poly(3‐hexylthiophene)s: Toward the Synthesis of Semiconducting Graft Copolymers

The post‐functionalization of poly(3‐hexylthiophene) (P3HT) via various synthetic routes is reported. Well‐defined and monofunctionalized ω‐thiol‐terminated P3HT, ω‐carboxylic acid‐terminated P3HT, ω‐acrylate‐terminated P3HT, and ω‐methacrylate‐terminated P3HT are obtained in high yields through a straightforward procedure. From those, different novel P3HT‐based graft copolymers are synthesized following two routes: “grafting onto” and “grafting through” (macromonomer polymerization) methods. The synthesis of three types of graft copolymers is described. Each one has “rod” P3HT‐grafted side chains on a “coil” main chain, which can be polyisoprene, poly(vinyl alcohol), or poly(butyl acrylate). Each copolymer is characterized by size‐exclusion chromatography and NMR.     

Polyplex Particles Based on Comb‐Like Polyethylenimine/Poly(2‐ethyl‐2‐oxazoline) Copolymers: Relating Biological Performance with Morphology and Structure

The present contribution is focused on feasibility of using comb‐like copolymers of polyethylenimine with poly(2‐ethyl‐2‐oxazoline) (LPEI‐comb‐PEtOx) with varying grafting densities and degrees of polymerization of PEI and PEtOx to deliver DNA molecules into cells. The copolymers form small and well‐defined particles at elevated temperatures, which are used as platforms for binding and condensing DNA. The electrostatic interactions between particles and DNA result in formation of sub‐100 nm polyplex particles of narrow size distribution and different morphology and structure. The investigated gene delivery systems exhibit transfection efficiency dependent on the copolymer chain topology, shape of the polyplex particles, and internalization pathway. Flow cytometry shows enhanced transfection efficiency of the polyplexes with elongated and ellipsoidal morphology. The preliminary biocompatibility study on a panel of human cell lines shows that pure copolymers and polyplexes thereof are practically devoid of cytotoxicity.     

Manifestation of side-chain interactions in solution properties of “loose” PI-graft-PMMA molecular brushes

The molecular properties of polymer brushes composed of polyimide with polymerization degree 50 and loosely grafted poly(methyl methacrylate) chains of variable length (PI-graft-PMMA) were studied by viscometry, dynamic light scattering, and equilibrium electro-optical Kerr effect methods in a diluted solution. It was established that the intrinsic viscosity and hydrodynamic dimension of PI-graft-PMMA copolymers increase when the electro-optical Kerr constant decreases with the elongation of PMMA side chains in the range of 40–110 monomer units. The observed difference in the solution properties of the copolymers was explained by their side-chain interactions in spite of a large distance between the neighboring grafting points typical of “loose brushes.” A strong effect of the chain rigidity and dipole structure on solution properties of the studied samples was demonstrated. The Kuhn segment lengths for PI-graft-PMMA copolymers were estimated to vary in the range 3.8–12.1?nm.     

Synthesis,characterization, and micellization of PCL‐g‐PEG copolymers by combination of ROP and “Click” chemistry via “Graft onto” method

Biodegradable and biocompatible PCL‐g‐PEG amphiphilic graft copolymers were prepared by combination of ROP and “click” chemistry via “graft onto” method under mild conditions. First, chloro‐functionalized poly(ε‐caprolactone) (PCL‐Cl) was synthesized by the ring‐opening copolymerization of ε‐caprolactone (CL) and α‐chloro‐ε‐caprolactone (CCL) employing scandium triflate as high‐efficient catalyst with near 100% monomer conversion. Second, the chloro groups of PCL‐Cl were quantitatively converted into azide form by NaN₃. Finally, copper(I)‐catalyzed cycloaddition reaction was carried out between azide‐functionalized PCL (PCL‐N₃) and alkyne‐terminated poly(ethylene glycol) (A‐PEG) to give PCL‐g‐PEG amphiphilic graft copolymers. The composition and the graft architecture of the copolymers were characterized by ¹H NMR, FTIR, and GPC analyses. These amphiphilic graft copolymers could self‐assemble into sphere‐like aggregates in aqueous solution with diverse diameters, which decreased with the increasing of grafting density. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Blue-emitting PEGylated hyperbranched PAMAM: transformation of cross-linked micelles to hollow spheres controlled by the PEG grafting density

Here we reported the synthesis of polyethylene glycol 2000 monomethyl ether (PEG)ylated hyperbranched poly (amido amine) (h-PAMAM-g-PEG) and the study of an elaborate control over the structure transition by solvents. The double hydrophilic hyperbranched copolymers could form micelles with h-PAMAM core and solvophilic PEG shell in tetrahydrofuran (THF). It was found that the micellization stage was prolonged if more PEG chains were anchored onto h-PAMAM cores. After cross-linking the h-PAMAM cores, well-dispersed hollow spheres were obtained when the micelles were transferred into water from THF. More grafted PEG chains on h-PAMAM may prohibit the creation of a hollow cage upon the swelling of the hydrophilic h-PAMAM cores. Such engineered hollow spheres also retained the pH-sensitive fluorescence characteristic, identical with the luminescent behavior of the free h-PAMAM molecules. H-PAMAM-g-PEG hollow spheres with pH-sensitive fluorescence have a potential application as a drug delivery vehicle for chemotherapy.     

Target grafting of poly(2-(dimethylamino)ethyl methacrylate) to biodegradable block copolymers

A series of copolymers composed of methoxy poly(ethylene glycol) and a hydrophobic block of poly(ɛ-caprolactone-co-propargyl carbonate) grafted with poly(2-[dimethylamino]ethyl methacrylate) was synthesized by combining ring opening polymerization, azide-alkyne click reaction, and atom transfer radical polymerization (ATRP). Well-defined copolymers with a target composition and a tailored structure were achieved via the grafting from approach by using a single catalytic system for both click reaction and ATRP. Kinetic studies demonstrated the controlled/living character of the employed polymerization methods. The thermal properties and self-assembly in aqueous medium of the graft copolymers were dependent on their composition. The resulting polymeric materials showed low cytotoxicity toward L929 cells, demonstrating their potential for biomedical applications. This type of materials containing cationic side chains tethered to biocompatible and biodegradable segments could be the basis for promising candidates as drug and gene delivery systems.     

Polyiodized‐PCL as multisite transfer agent: Towards an enlarged library of degradable graft copolymers

Poly(ε‐caprolactone)‐based graft copolymers were prepared via a “grafting from” technique derived from iodine transfer polymerization. This copolymerization was done thanks to a poly(ε‐caprolactone‐co‐α‐iodo‐ε‐caprolactone) (PCL‐I), which was used as a multisite transfer agent. Styrene (Sty) and n‐butyl acrylate (n‐BuA) were firstly used as model monomers to establish the feasibility of using PCL‐I as multisite transfer agent, and investigate some general properties of the polymerization. The formation of PCL‐g‐PSty and PCL‐g‐P(n‐BuA) copolymers was confirmed by SEC and NMR analyzes of the copolymers before and after degradation of the PCL backbone. This method was extended to an acrylamide monomer, namely (N,N‐dimethyl) acrylamide (DMA), to prepare original amphiphilic copolymers with PCL as hydrophobic backbone and amido‐functionalized hydrophilic grafted chains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5006–5016, 2009     

Synthesis of densely grafted comblike copolymers

Densely grafted copolymers were synthesized using the “grafting from” approach via the combination of reversible addition‐fragment chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). First, a novel functional monomer, 2,3‐di(2‐bromoisobutyryloxy)ethyl acrylate (DBPPA), with two initiating groups for ATRP was synthesized. It was then polymerized via RAFT polymerization to give macroinitiators for ATRP with controlled molecular weights and narrow molecular weight distributions. Last, ATRP of styrene was carried out using poly(DBPPA)s as macroinitiators to prepare comblike poly(DBPPA)‐graft‐polystyrenes carrying double branches in each repeating unit of backbone via “grafting from” approach. Furthermore, poly(DBPPA)‐graft‐[polystyrene‐block‐poly(t‐BA)]s and their hydrolyzed products poly(DBPPA)‐graft‐[polystyrene‐block‐poly(acrylic acid)]s were also successfully prepared. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 362–372, 2008     

Crystallization behavior, thermal property and biodegradation of poly(3-hydroxybutyrate)/poly(ethylene glycol) grafting copolymer

The poly(3-hydroxybutyrate)(PHB)/poly(ethylene glycol)(PEG) grafting copolymer was successfully prepared by PHB and acrylate groups ended PEGM using AIBN as initiator. The crystallization behavior, thermal stability and environmental biodegradability of PHB/PEG grafting copolymers were investigated with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and Biodegradation test in vitro. In the results, all the grafting copolymers were found to show the X-ray diffraction arising from the PHB crystal lattice, while none of the PEG crystallized peaks could be found even though the graft percent reached 20%. This result indicated that PEG molecules were randomly grafted onto PHB chain. The thermal properties measured by DSC showed that the melting temperature(T_m) and glass transition temperature (T_g) were both shifted to lower temperature with the graft percent increasing, and this broadened the narrow processability window of PHB. According to TGA results, the thermal stability of the grafting copolymers is not changed compared to pure PHB. From the biodegradation test, it could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be adjusted by the PEG grafting ratio. In another words, the biodegradation profiles of PHB/PEG grafting copolymer can be controlled. These properties make PHB/PEG grafting copolymer have promising potential applications especially in agriculture fields.     

Comparison of random and gradient amino functionalized poly(2‐oxazoline)s: Can the transfection efficiency be tuned by the macromolecular structure?

Poly(ethylene imine) can be considered as the gold standard for DNA delivery into cells in vitro, but severe cytotoxic side‐effects and inapplicability for targeted approaches in vivo urgently call for the design of new gene carriers. Since poly(2‐oxazoline)s (P(Ox)s) can be easily synthesized and modified, this polymer class might be ideal for the optimization of polymeric transfection processes. The utilization of 2‐methyl‐2‐oxazoline (MeOx) and 2‐ethyl‐2‐oxazoline (EtOx) is also known to be beneficial because these monomers were suggested to overcome solubility issues, mediate stealth behavior and, consequently, facilitate a reduction of cytotoxicity. A series of amino (AmOx) functionalized P(Ox) copolymers with either MeOx (gradient copolymers) or EtOx (random copolymers) was synthesized, deprotected and biochemically characterized regarding cytotoxicity, polyplex formation ability, cellular uptake, and transfection efficiency. Polymers with percentages of AmOx higher than 35 mol % showed stable polyplex formation and also an increase in cytotoxicity. All elucidated P(Ox)s revealed a poor transfection efficiency in both L929 and Hepa1‐6 cell lines. However, the investigations contribute to the understanding of the influence of stealth units (MeOx and EtOx) and their distribution within the polymer chain on selected properties of polyplexes and describe characteristics of amino functionalized P(Ox)s in different cell lines. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1210–1224     

Preparation of Clickable Poly(3‐hydroxyalkanoate) (PHA): Application to Poly(ethylene glycol) (PEG) Graft Copolymers Synthesis

A new synthesis of amphiphilic biodegradable copolymers consisting of hydrophobic poly(3‐hydroxyalkanoate) (PHA) backbone and hydrophilic poly(ethylene glycol) (PEG) units as side chains is described. Poly[(3‐hydroxyoctanoate)‐co‐(3‐hydroxyundecenoate)] (PHOU) was first methanolyzed and its unsaturated side chains were quantitatively oxidized to carboxylic acid. Esterification with propargyl alcohol led to an alkyne‐containing “clickable” PHA in 71% conversion. Its reactivity was successfully demonstrated by grafting azide‐terminated PEG chains of 550 and 5 000 g · mol⁻¹, respectively. All products were fully characterized using GPC, ¹H, and COSY NMR.

     

Reactive blending: inhomogeneous interface grafting in melts of maleinated polystyrene and polyamides

To be competitive, most blends need compatibilizers, usually copolymers with a blocky architecture, the chains of which cover the interfaces between the blend phases, refining the phase morphology and improving the interface strength. When the blend components are suitably functionalized, such copolymers can be conveniently generated in situ, in processes of reactive blending. Normally, graft copolymers are created. The polymer–polymer coupling proceeds exclusively in the interfaces. This interface grafting is (i) pivotal in the design of modern blend systems and (ii) an interesting route towards novel copolymers. The complex kinetics of interface grafting in blend melts have so far attracted little attention. In a model study, amino terminated polyamide 12 (PA) was grafted in the melt onto heavily maleinated polystyrene (SMA; S: styrene and MA: maleic anhydride). Anhydride and amino functions react at high temperatures fast and irreversibly by imide condensation. A series of SMA/PA blends differing in composition and PA chain lengths was investigated, with the aim of driving the grafting to high conversions so a pure graft copolymer SMAgPA would result, instead of an SMA/PA/SMAgPA blend. However, a pure copolymer was never obtained. The grafting remained incomplete, except with very short-chained PA and only at equal weight fractions of SMA and PA. More importantly, the SMA chains were never grafted evenly. Instead, “overgrafted” and “undergrafted” chains SMAgPA coexisted in one and the same product. It appears that the SMAgPA chains form an auto-inhibitory barrier in the interfaces that prevents random grafting. Grafting proceeds to high conversion only in SMA/PA blends with a co-continuous phase morphology where the interfaces are constantly torn apart and renewed, during melt blending, so the reaction is constantly reactivated. © 1998 John Wiley & Sons, Ltd.