Influence of an annealing treatment on the solid‐state grafting of styrene onto spherical isotactic polypropylene granules

The main place of solid‐state graft polymerization in polypropylene (PP) granules has been believed to be the amorphous region of PP. In this work, the solid‐phase morphology of nascent spherical PP (N‐PP) granules was found to be markedly changed by an annealing treatment. The crystallinity of PP granules was almost doubled after annealing at 150°C for 12 h, whereas the porosity of the granules was unchanged. Solid‐state grafting polymerizations of styrene initiated by tert‐butyl perbenzoate in both N‐PP and annealed polypropylene (A‐PP) granules were compared under different reaction conditions. The formation of gel in the product could be completely depressed at a low concentration of the initiator when A‐PP granules were used as the matrix and graft‐polymerized at 120°C. Both the introduction of styrene and the annealing treatment of the PP granules led to a depression of polymer degradation in the process of the grafting reaction. However, using A‐PP as the matrix caused an increase in the grafting degree at a relatively high concentration of the initiator. A reduction in the amorphous phase in the PP granules was thought to be the main reason for the effects of the annealing treatment on the structure of the graft polymerization products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. I. Polymerization experiments

Grafting of vinyl monomers onto isotactic polypropylene (iPP) in the solid state, that is, below the melting point, displays several advantages over melt or solution grafting processes, such as negligible degradation of the iPP and absence of any solvent. The final properties of such iPP modifications or actually compatibilized PP blends are dependent on the dispersion of the new polymer into the iPP matrix, which is controlled to a large extent by the degree of grafting versus the amount of free homopolymer formed. In the present work, the solid‐state modification of iPP by styrene has been investigated from the point of view of the monomer polymerization behavior. In order to determine the styrene conversion and the distribution of the newly formed PS phase along the radius of the iPP powder particles, the reaction products were characterized by infrared (FTIR) and Raman spectroscopy. Fractionation of the reaction products via selective solvent extraction allowed the determination of the grafting efficiency (Φ). It was shown that besides the grafted PS two additional types of PS are formed, that is, free PS homopolymer in the pores of the PP powder and free PS in the amorphous PP phase. Phi shows an optimum as a function of the feed peroxide composition and the feeding rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3279–3291, 2003     

Solid‐state graft polymerization of styrene in spherical polypropylene particles in the presence of montmorillonite

In this work, cetyltrimethyl ammonium bromide and methacryloyloxyethyhrimethyl ammonium chloride were used to prepare organophilic montmorillonite (O‐MMT). Then, polypropylene (PP)–clay nanocomposites were prepared by the in situ grafting polymerization of styrene (St)‐containing O‐MMT onto PP with tert‐butyl perbenzoate as an initiator in the solid state. Fourier transform infrared spectroscopy, gel permeation chromatography, transmission electron microscopy, and X‐ray diffraction were applied to study the structure of the layered silicate and modified PP. The surfaces of the composites and, thus, the distribution of the clay in the PP matrix were characterized by scanning electron microscopy. The rheology and mechanical properties were studied and are discussed. According to the characterization results, OMMT and St were already grafted onto the PP main chain. Also, the intercalated structure of montmorillonite could be stabilized, and a stable exfoliated structure could be attained. Namely, intercalated PP/OMMT nanocomposites were obtained. The rheological results clearly show that these PP/OMMT nanocomposites had long‐chain‐branched structures. The peroxide modification of PP had minor effects on the tensile and bending strengths of the modified PP; however, this modification resulted in a significant reduction in the impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Solid‐state modification of isotactic polypropylene (iPP) via grafting of styrene. II. Morphology and melt processing

Grafting of vinyl monomers onto isotactic polypropylene (iPP) in the solid state represents a convenient route to chemically modify iPP and, consequently, its properties. Solid‐state modification can be carried out on iPP powder directly from the polymerization reactor. The modified powder is then processed in the melt, usually with the addition of fillers and/or additives, to obtain the final product. In this work we have studied the effect of melt processing on the morphology of solid‐state polymerized PP/polystyrene (PS) blends, i.e., of a iPP powder previously modified in the solid‐state with styrene (St) and optionally in the presence of divinylbenzene (DVB). A series of samples containing different amounts of PS and displaying different grafting efficiencies were investigated before and after processing in the melt. Transmission electron microscopy, scanning electron microscopy, and solid‐state NMR were used to investigate the morphology on different length scales. It was shown that PS coalescence during processing can be hindered, thereby stabilizing the initially polymerized iPP/PS blends morphology. Indeed, reducing the PS amount in the blend or increasing the grafting efficiency resulted in less coalescence of the PS domains. Crosslinking of the PS phase during the solid‐state polymerization resulted also in a very fine but heterogeneous morphology. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 575–583, 2005     

Synthesis and characterization of solid‐phase graft copolymer of polypropylene with styrene and maleic anhydride

Polypropylene (PP) was modified by solid‐phase graft copolymerization with maleic anhydride (MAH) and styrene (St), using benzoyl peroxide as the initiator and xylene as the interfacial agent. Effects of various factors such as monomer concentration, monomer ratio, initiator concentration on grafting percentage, and acid value were investigated. The graft copolymer was characterized by Fourier transform infrared, pyrolysis gas chromatography—mass spectroscopy, and dynamic mechanical analysis, and the intrinsic viscosity of the extractive from the reaction product was investigated. The results showed that the grafting percentage and acid value of the graft copolymer of PP with two monomers (MAH and St) were considerably higher than those of the graft copolymer of PP with MAH alone. The graft segments were shown to be the copolymer of St and MAH with a substantial molecular weight. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2482–2487, 2000     

Radiation‐induced graft copolymerization of 2‐vinylpyridine and styrene onto isotactic polypropylene fiber

Isotactic polypropylene fiber (IPP) was graft‐copolymerized using 2‐vinyl pyridine (2‐VP) and styrene (sty) as the monomers by the mutual irradiation method in air. The percentage of grafting was determined as a function of various reaction parameters and it was found that the maximum grafting of 2‐VP (114%) and sty (76%) was obtained at an optimum dose of 1.08 × 10⁴ and 0.64 × 10⁴ Gy using 1.8 × 10⁻² mol of 2‐VP and 4.3 × 10⁻² mol of sty, respectively. The graft copolymers were characterized by differential scanning calorimetric analysis and isolation of the grafted chains from the grafted iPP samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2959–2969, 1999     

Plasma‐induced,solid‐state polymerization of N‐isopropylacrylamide

The radio‐frequency plasma‐initiated polymerization of N‐isopropylacrylamide (NIPAM) in the solid state was performed. The isolated linear polymer was characterized by ¹³C‐NMR, ¹H‐NMR, and Fourier transform infrared spectroscopy, and the effects of selected operational plasma parameters (discharge power and time) on the conversion rates were studied. Reversible transitions at the volume‐phase‐transition temperatures of the swelled poly(N‐isopropylacrylamide) hydrogels were investigated by differential scanning calorimetry. The surface morphologies before and after plasma treatment were followed by scanning electron microscopy. With the obtained X‐ray diffraction results, we propose a solid‐state plasma polymerization mechanism for the NIPAM. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of polypropylene graft copolymers from a hydroxyl‐groups‐containing polypropylene precursor via atom‐transfer radical polymerization

Isotactic polypropylene graft copolymers, isotactic[polypropylene‐graft‐poly(methyl methacrylate)] (i‐PP‐g‐PMMA) and isotactic[polypropylene‐graft‐polystyrene] (i‐PP‐g‐PS), were prepared by atom‐transfer radical polymerization (ATRP) using a 2‐bromopropionic ester macro‐initiator from functional polypropylene‐containing hydroxyl groups. This kind of functionalized propylene can be obtained by copolymerization of propylene and borane monomer using isospecific MgCl₂‐supported TiCl₄ as catalyst. Both the graft density and the molecular weights of i‐PP‐based graft copolymers were controlled by changing the hydroxyl group contents of functionalized polypropylene and the amount of monomer used in the grafting reaction. The effect of i‐PP‐g‐PS graft copolymer on PP‐PS blends and that of i‐PP‐g‐PMMA graft copolymer on PP‐PMMA blends were studied by scanning electron microscopy. Copyright © 2006 Society of Chemical Industry     

Graft copolymerization of thiophene onto polystyrene synthesized via nitroxide‐mediated polymerization and its polymer − clay nanocomposite

A new strategy for graft copolymerization of thiophene onto a polystyrene (PSt) backbone by a multi‐step process is suggested and the effects of an organoclay on the final properties of the graft copolymer sample are described. For this purpose, first poly(styrene‐co‐4‐chloromethyl styrene) [P(St‐co‐CMSt)] was synthesized via nitroxide‐mediated polymerization. Afterwards, the chlorine groups of P(St‐co‐CMSt) were converted to thiophene groups using the Kumada cross‐coupling reaction and thiophene‐functionalized PSt multicenter macromonomer (ThPStM) was synthesized. The graft copolymerization of thiophene monomers onto PSt was initiated by oxidized thiophene groups in the PSt chains after addition of ferric chloride (FeCl₃), an oxidative catalyst for polythiophene synthesis, and FeCl₃‐doped polythiophene was chemically grafted onto PSt chains via oxidation polymerization. The graft copolymer obtained was characterized by ¹H NMR and Fourier transform infrared spectroscopy, and its electroactivity behavior was verified under cyclic voltammetric conditions. Finally, PSt‐g‐PTh/montmorillonite nanocomposite was prepared by a solution intercalation method. The level of dispersion of organoclay and the microstructure of the resulting nanocomposite were probed by means of XRD and transmission electron microscopy. It was found that the addition of only a small amount of organoclay (5 wt%) was enough to improve the thermal stabilities of the nanocomposite.© 2013 Society of Chemical Industry     

Synthesis of functional polypropylene via solid‐phase grafting soft vinyl monomer and its mechanism

Solid‐phase grafting of a soft vinyl monomer, butyl methylacrylate (BMA), onto polypropylene (PP) matrixes with 2,2′‐azobisisobutyronitrile (AIBN) as initiator was carried out to enhance the polarity of polymer. Soft vinyl monomer was a novel notion in grafting modification of PP. Effects of swell time, BMA concentration, AIBN concentration, grafting reaction time, and temperature on grafting percentage (G_p) and grafting efficiency (G_e) were examined. The optimal conditions of grafting reaction were obtained: swell time of 60 min, BMA concentration of 6 wt %, AIBN concentration of 0.05 wt %, reaction temperature of 85°C, and reaction time of 2 h. The grafting samples were investigated by such characterization techniques as Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscope (SEM) analysis. FTIR results indicated that BMA was actually grafted onto PP backbone. TGA results showed that the decomposition temperature increases with addition of BMA into PP backbone. SEM results indicated that the surfaces of PP‐g‐BMA had a markedly bumpy texture, whereas the pure PP surface was very smooth. Water contact angle results showed that the polarity and hydrophilicity of PP were improved effectively. Compared with the traditional monomer MAH, G_p, and G_e, melt flow rate and mechanical property results all indicated that the soft vinyl monomer had a many advantages in the modification of PP. In the end, the mechanism of solid grafting was discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of crystallinity on solid‐state polymerization of poly(ethylene terephthalate)

There has been a widely held assumption that the solid‐state polymerization (SSP) rate of poly(ethylene terephthalate) (PET) decreases with increasing crystallinity. Several published articles that purported to prove this assumption were based on faulty experiments. Therefore, a proper experimental procedure has been used to study the true effects of crystallinity on the SSP of PET. The results show that, for PET in pellet and powder forms, the SSP rate increases with increasing crystallinity. This is because an increase in the crystallinity results in increased end‐group concentration in the amorphous phase, where SSP reactions take place, and decreased concentrations of inactive end groups trapped inside the crystals, thereby increasing the rates of end‐group collision and reactions. These positive effects outweigh the negative effect of the increased byproduct‐diffusion resistance because of the increase in crystallinity. As the particle size of PET is increased beyond a critical value of about 7 mm, the SSP rate actually decreases with increasing crystallinity because of the excessively increased byproduct‐diffusion resistance within the PET particles. However, this critical particle size is far greater than the pellet sizes of commercial PET resins. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 623–632, 2006     

Grafting of poly(N‐isopropylacrylamide) onto nylon and polystyrene surfaces by atmospheric plasma treatment followed with free radical graft copolymerization

Stimuli‐responsive polymer materials (SRPs) have potential uses in drug delivery, tissue engineering, bioreactors, and cell‐surface adhesion control. Temperature‐responsive surfaces were fabricated by grafting poly(N‐isopropylacrylamide) (PNIPAM) onto nylon and polystyrene surfaces via a new procedure, i.e., He atmospheric plasma treatment followed by free radical graft copolymerization. The atmospheric plasma exhibits the activation capability to initiate graft copolymerization. The procedure is suitable for integration into a continuous manufacturing process. To reduce homopolymerization and enhance graft yield, Mohr's salt was added. The graft of PNIPAM was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy. Dramatic water contact angle increase was found for PNIPAM‐grafted polymers at about 32°C, indicating the temperature sensitivity of the grafted surface, i.e., the change of surface from hydrophilic to hydrophobic when temperature increases above the lower critical solution temperature (LCST). The addition of Mohr's salt enhances the grafting reaction and the magnitude of temperature sensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3614–3621, 2007     

Study of modified polypropylene nonwoven cloth. I. graft copolymerization of 4‐vinylpyridine onto polypropylene nonwoven cloth by preirradiation method

Polypropylene (PP) nonwoven cloth was grafted with 4‐vinylpyridine (4‐VP) by a preirradiation method. The effects of preirradiation conditions on the mechanical properties of preirradiated PP nonwoven cloth and the percentage of grafting (Pg) of 4‐VP onto the preirradiated PP nonwoven cloth were systematically investigated. The results indicated that the mechanical properties of preirradiated PP nonwoven cloth decreased with increasing irradiation dose and that the Pg was greatly affected by the concentration of monomer, irradiation dose, grafting reaction temperature, and the addition of inhibitor and inorganic acid in the grafting reaction system. The grafted nonwoven cloth samples were characterized using IR spectroscopy and SEM. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1861–1868, 2000     

Post‐extrusion solid‐state polymerization of fully drawn polyester yarns

Post‐extrusion solid‐state polymerization (SSP) of a commercial fully drawn filament yarn (FDY) of poly(ethylene terephthalate) was carried out at 220°C, 230°C, and 240°C for a duration of 30 min to 2 h under inert atmosphere. Molecular weight of the solid‐state polymerized polyester filaments was increased from 1.67 × 10⁴ gm/mol to a maximum of 2.61 × 10⁴ gm/mole for the sample subjected to 240°C for 2 h. The kinetics of the SSP in the highly oriented crystalline FDY polyester filaments was investigated using an empirical relation between initial molecular weight and time of SSP and was found to be greatly enhanced, compared to amorphous unoriented polyester chips. Though the free annealing (i.e., under no tension) of samples at high temperature during solid‐state polymerization had a detrimental effect on the orientation of the FDY yarn, the simultaneous increase in the molecular weight compensated the loss in mechanical properties to a great extent. Application of tension during SSP was found to improve the mechanical properties of the SSP yarn by a small value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5113–5122, 2006     

Kinetics of the solid‐state polymerization of nylon‐6

The kinetics of the thermally induced solid‐state polymerization (SSP) of nylon‐6 were examined in both a fixed‐bed reactor and a rotary reactor. Factors such as the regulator content, the reaction temperature and time, the particle size, the type and geometry of the nylon‐6 prepolymer, the nitrogen gas flow rate, the water content of the nitrogen gas flow, and the polymerization process were studied. The results showed that the regulator content, the reaction temperature and time, and the particle size were the primary factors, and that the others were negligible. Moreover, the SSP rate and number‐average molecular weight (M_n) increased with increasing reaction temperature and time and decreasing particle size. The SSP rate and M_n had maximum values with increasing regulator content in an experimental range of 0.03–0.07 wt %. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 616–621, 2002; DOI 10.1002/app.10341     

Solid‐state polymerization of poly(ethylene terephthalate). I. Experimental study of the reaction kinetics and properties

The solid‐state polymerization (SSP) reaction kinetics of poly(ethylene terephthalate) were investigated in connection with the initial precursor intrinsic viscosity (IV; molecular weight). Evaluations were performed with otherwise equivalent precursors melt‐polymerized to IVs of 0.50, 0.56, and 0.64 dL/g. The changes in the molecular weight and other properties were monitored as functions of the reaction times at solid‐state temperatures of 160–230°C. Precursors with higher initial molecular weights exhibited higher rates of SSP than those with lower initial values, as discussed in connection with the levels of crystallinity and the carboxyl and hydroxyl end‐group composition. Activation energies decreased at temperatures above 200°C, and this indicated a change in the SSP reaction mechanism. At temperatures of 200–230°C, similar activation energies were required for the polymerization of all three precursors. Lower temperature polymerizations, from 160 to 200°C, required higher activation energies for all precursors, with the 0.50‐IV material requirement almost twice as high as that calculated for the higher IV precursors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 197–212, 2003     

Modification of acrylonitrile‐butadiene‐styrene terpolymer by graft copolymerization with maleic anhydride in the melt. II. Properties and phase behavior

The graft copolymerization of maleic anhydride (MAH) onto acrylonitrile‐butadiene‐styrene terpolymer (ABS) using dicumyl peroxide and benzoyl peroxide as the binary initiator and styrene as the comonomer in the molten state was described. The properties and phase morphologies of the modified products (ABS‐g‐MAH) were studied. The results indicate that the melt flow index (MFI) of ABS‐g‐MAH increases with the increase of MAH content, the initiator concentration, and the screw speed, whereas the MFI decreases with the increase of temperature. The impact strength and the percentage elongation of ABS‐g‐MAH both decreased and the tensile strength of ABS‐g‐MAH increased slightly as the grafting degree increased. The phase inversion behavior of the modified product was observed by transmission electron microscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2834–2839, 2004     

Structure and mechanism of functional isotactic polypropylene via in situ chlorination graft copolymerization

This paper discusses the structure and mechanism of maleic anhydride (MAH) grafted onto isotactic polypropylene (iPP) via in situ chlorination graft copolymerization (ISCGC). The molecular structure of the grafted iPP was characterized using ¹H NMR and ¹³C NMR spectroscopy, viscosity‐average molecular weight and gel content. The structure of un‐grafted MAH present in the reaction system was investigated using Fourier transform infrared spectroscopy in order to explore the grafting of MAH on iPP. The main side‐reactions, including iPP chain scission and crosslinking, during the grafting reaction were explored. From the experimental results obtained, the reason for controlled macromolecular chain degradation and crosslinking of grafted iPP in ISCGC is proposed. Based on the structural characterization of the grafted polymer, the mechanism of grafting onto iPP obtained via ISCGC was deduced. Mechanical properties, both static and dynamic, of grafted iPP were also investigated and the results showed that the properties of the material changed due to grafted MAH. Copyright © 2011 Society of Chemical Industry     

Preparation of PTT/clay nanocomposites with solid‐state polymerized polytrimethylene terephthalate

To enhance the effectiveness of polytrimethylene terephthalate (PTT) for the preparation of clay‐based nanocomposites by melt intercalation and to upgrade the mechanical performance of these materials, solid‐state‐polymerization (SSP) experiments with neat PTT were carried out at 190, 200, and 210°C prior compounding to increase the average molecular weight and, based on this, the melt viscosity of this polymer. The progress of SSP was registered by time dependent sampling of intrinsic viscosity data. From this, activation energy of 180.6 kJ mol^?1 was calculated. A characteristic sublimate formed during these SSP‐reactions was identified by mass‐spectroscopy to be a mixture of cyclic oligomers containing 2, 3, 4, and 5 monomeric units. The melt viscosity of neat PTT(SSP) could be increased from ～ 460 to 15,000 Pa s^?1. Therefore, tensile strength and Young's modulus were improved by 3.5 and 9%, respectively. Manufacturing of PTT(SSP) and the modified nanoclay was carried out with a corotating twin‐screw‐extruder at 230°C. A concentration of 3% of the inorganic filler component in the composites was aimed at. Compared with the data of virgin PTT, tensile strength, and modulus of the PTT(SSP)‐based nanocomposites could be enhanced by ～ 9 and 40%, respectively. Additionally, a SSP‐reaction of the nanocomposite prepared with non‐pretreated PTT and nanoclay was performed at 210°C to test the robustness of the matrix polymer PTT against the influences of the nanofiller. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013