Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide-induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, 1 H NMR, and ESR. For the first time, the time-evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate-controlled step for the graft copolymerization. The results presented here revealed that the relative importance of graft copolymerization compared with homopolymerization mainly depended on the monomer solubility and reactivity, while the process parameters such as reaction temperature also influenced the reaction tendency.

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Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetic studies on reactive extrusion have been carried out because of the inherent difficulties, as expected. In this work, we have studied chain propagation kinetics on melt grafting using pre‐irradiated linear low density polyethylene (LLDPE) and three monomers, acrylic acid (AA), methacrylic acid (MAA), and methyl methacrylate (MMA), as the model system. We measured the apparent chain propagation rate coefficients of grafting (kp,g) and homopolymerization (kp,h) at an initial stage for the melt grafting by FT‐IR spectroscopy and electron spin resonance spectroscopy. It was observed that the convective mixing affected the rate coefficients. The magnitude of kp,h and kp,g were in the same order, but kp,h was slightly larger than kp,g. The kp,g of the three grafting systems increased in the order: LLDPE/MMA < LLDPE/MAA < LLDPE/AA. These results are explained in terms of phase separation, solubility, and inherent reactivity of the monomer.

Two sets of graft copolymers were prepared by grafting glycidyl methacrylate (GMA) or allyl (3-isocyanate-4-tolyl) carbamate (TAI) onto ethylene/propylene/diene terpolymer (EPDM) in an internal mixer. These graft copolymers were used as the compatibilizer to prepare the thermoplastic elastomers (TPEs) containing 50 wt % of poly(butylene terephthalate), PBT, 30 wt % of compatibilizer, and 20 wt % of nitrile-butadiene rubber, NBR. The indirect, two-step mixer process was chosen for dynamic curing. The TPEs were characterized by differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, tensile testing, and dynamic mechanical thermal analysis. It was found that this kind of TPEs possess enhanced toughness and stiffness when compared with the mechanical properties of binary blend EPDM/PBT; the compatibility between EPDM and PBT was improved when grafted EPDMs were used; EPDM-g-GMA and EPDM-g-TAI showed similar effects on the morphology and ultimate mechanical properties of TPEs. The indirect dynamic vulcanization has negative effect on the reactive compatibilization. Both indirect dynamic vulcanization and reactive compatibilization were crucial to obtain droplets of dispersed rubber phase in a continuous thermoplastic matrix. The above results are important for academic knowledge and industry applications.

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Rare earth oxide, neodymium oxide (Nd 2 O 3 ), -assisted melt free-radical grafting of maleic anhydride (MAH) on isotactic-polypropylene (i-PP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd 2 O 3 into reactive system leads to an enhancement of the grafting degree of MAH, along with an elevated degradation of i-PP matrix. When Nd 2 O 3 content is 4.5 mmol %, the increment of the grafting degree of MAH (maximally) is up to about 30% compared with that of the related system without adding Nd 2 O 3 , while the severest degradation of i-PP matrix simultaneously occurs. On the basis of the reaction mechanism of PPg-MAH proposed before, the sequence of b-scission and grafting reaction is discussed in detail. It is found that, for the reactive system studied, most tertiary macroradicals first undergo b-scission, and then, grafting reaction with MAH takes place at the new radical chain ends. The imported Nd 2 O 3 has no effect on the aforementioned reaction mechanism, whereas it enhances the initiating efficiency of the initiator, dicumyl peroxide (DCP). We tentatively explain the experimental results by means of synergistic effect between DCP and Nd 2 O 3 . It is calculated that the synergistic effect is maximal when the molar ratio of DCP to Nd 2 O 3 is approximately 1:6. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: [134][135][136][137][138][139][140][141][142] 2006