Block or graft copolymers have gained much interests recently, not only because of their general application as compatibilizers in blends with thermodynamically immiscible polymer pairs [1], but also of many special and important characteristics of themselves, such as the formation of self assembly morphologies, which can be used for drug delivery, nanoreactor and molecular templating, etc. [2, 3]. In general, copolymers can be prepared by ionic polymerization [4], controlled radical polymerization [5] and some other special polymerization methods [6, 7]. However, for some specific polymer pairs, such as polypropylene (PP) and polyamide 6 (PA6), it is still a challenge to prepare premade PP-g-PA6 copolymer. Although, maleic anhydride can react with the end amino group of PA6 and in situ forming PP-g-PA6 graft copolymer at the phase interface when maleic anhydride modified PP (PP-g-MAH) is used as an interfacial compatibilizer in PP and PA6 blends [8, 9], the amount of such copolymer is too small to be extracted out because of the relatively low grafting degree of MAH on PP. Preparing such kind of copolymers is still unpractical so far. Recently, Leibler et al. [10] successfully increased the MAH content by preparing the poly (ethylene-ethylacrylate-MAH) copolymer (PE-1) before blending with PA6. They have extracted the PE-1-g-PA6 copolymer out from the blending system in their work. In this communication, we will report another novel exploration of preparing PP-g-PA6 copolymers through reactive blending. Isotactic-PP homopolymer was purchased from Montell (Profax 6331, melt index 10 dg/min at 230 C, density 902 kg/m). Dicumyl peroxide (DCP), e-caprolactam, adipic acid, 3-isopropenyl-a,a0-dimethylbenzene isocyanate (TMI), x-aminocaproic acid and m-cresol were obtained from Aldrich Co. Ltd. Formic acid, xylene and acetone were purchased from Riedel-de Haen. All the chemicals are reagent grade and used as received. PA6 ‘‘end-functionalized’’ by unsaturated double bonds (PA6-TMI) was synthesized by condensation polymerization under the protection of nitrogen gas. Condensation polymerization of e-caprolactam was initiated by x-aminocaproic acid at 260 C. The molecular weight was adjusted by stoichiometrically adding adipic acid into the polymerization system. At the end of polymerization, a certain amount of 3-isopropenyl-a,a-dimethylbenzeneisocyanate (TMI) was added into the polymeric melt. The isocyanate group in TMI will react with the end carboxyl (COOH) group of PA6 to form amide [11], which will result in the TMI attachment to the PA6 molecular chain ends (PA6-TMI). About 50 ml of m-cresol was added to terminate all the reaction and drop down the system temperature to room temperature. After precipitated in acetone, filtrated and dried in a vacuum oven at 85 C for 48 h, end functional PA6 powder were stored in a dry box for further blending with PP. The molecular weight of end functionalized PA6 was measured by relative viscosity method. Table 1 lists the PA6 samples with and without TMI end functionalization used in this experiment. PP/PA6 blend was prepared by reactive blending of PP and the PA6-TMI using DCP as initiator. Melt blending was performed in a Brabender internal mixer at 230 C for 5 min. The blend weight ratio employed was PP/PA6D. Shi R. K. Y. Li (&) Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong e-mail: aprkyl@cityu.edu.hk
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Apr 18, 2013
Xi-Qiang Liu + 5
Open Access