Search for nonoxidative,hydrogen-abstracting initiators useful for melt grafting processes

Using organic peroxide initiators in the melt grafting of monomers containing amino groups onto polyethylenes is known to cause serious discoloration of the resulting polymers. To eliminate the discoloration while preserving the controlled degree of grafting, a nonoxidative and hydrogen-abstracting initiator with appropriate thermal stability is needed. In this study, the hydrogen-abstracting capability of three azo initiators with suitable decomposition rates in the melt grafting temperature ranges was evaluated using polyethylene cross-linking and polypropylene degradation experiments (called “hydrogen-abstracting experiments”). Among the three azo initiators tested, only a phenylazo initiator, 2 - phenylazo - 2,4 - dimethyl - 4 - methoxyl - valeronitrile (V-19), demonstrated strong hydrogen-abstracting capability from polymer backbones. These three azo initiators were used in the melt grafting of 2 - (N, N - dimethylamino) ethyl methacrylate (DMAEMA) and 2-(N-t -butylamino) ethyl methacrylate (tBAEMA) onto a linear low-density polyethylene (LLDPE). In agreement with the results obtained from the hydrogen-abstraction experiments, only V-19 led to a considerable amount of grafting of both DMAEMA and tBAEMA onto LLDPE. As expected, polymers grafted with V-19 showed significantly reduced discoloration compared with those grafted with peroxide initiators. Further examination of the grafting results indicated that the initiator efficieny, defined as the number of grafted monomer units per radical generated from initiator decomposition, was higher with the phenylazo initiator than with peroxide initiators. The hydrogen-abstracting capability of the phenyl free radical generated from the decomposition of V-19 was estimated to be higher than peroxide and methyl free radicals produced in the decomposition of peroxide initiatros. © 1993 John Wiley & Sons, Inc.     

Functionalization of polyolefins with maleic anhydride in melt state through ultrasonic initiation

The functionalization reaction of high-density polyethylene (HDPE), linearly low-density polyethylene (LLDPE), polypropylene (PP) and EPDM rubber with maleic anhydride (MAH) in melt state through ultrasonic initiation was studied. The effect of ultrasonic intensity on the percentage of grafting, viscosity-average molecular weight, melt flow rate and gel content of the functionalized products were investigated by means of chemical titration, Fourier-transform infra-red spectroscopy (FT-IR), intrinsic viscosity and melt flow rate, etc. The molecular structures of the functionalized products prepared via ultrasonic initiation and via peroxide initiation were characterized by ¹H NMR spectroscopy. The results show that the functionalization reaction of HDPE, LLDPE and EPDM with MAH can be realized by ultrasonic initiation. This reaction mainly consists of the chain scission under ultrasonic irradiation, the end chain reaction of the produced macroradicals with MAH, and the terminated reaction of the produced succinyl radicals with the macroradicals or H* radicals through recombination or dismutation. The functionalized product through ultrasonic initiation mainly consists of the products containing an anhydride ring attached to the chain terminus. And the products prepared through peroxide initiation mainly contain an anhydride ring grafted on the side chain.     

亚甲基丁二酸接枝LDPE

利用反应挤出技术制备了低密度聚乙烯(LDPE)/亚甲基丁二酸接枝物。研究了引发剂种类及用量对接枝率和接枝物熔体流动速率(MFR)的影响。结果表明：采用引发剂L-101的接枝率最高,添加ω(L-101)为0．2％时．接枝率即可接近90％,接枝的同时伴有交联,接枝物的MFR从LDPE的16g／10min下降到2g／10min左右。     

Reactor Modeling of Gas‐Phase Polymerization of Ethylene

A model is developed for evaluating the performance of industrial‐scale gas‐phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low‐density and high‐density polyethylene grades. A pseudo‐homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks‐in‐series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed.     

Studies on salts of amine‐containing polymers with benzoic acids. III. Poly(N,N‐dimethylaminoethyl methacrylate‐g‐polyethylene) with benzoic acids

Poly(N,N‐dimethylaminoethyl methacrylate) [poly(DMAEMA)] was grafted onto a commercial polyethylene film by means of γ‐irradiation, and the grafted films were reacted with various liquid‐crystal‐forming benzoic acids. When polymeric salts consisting only of poly(DMAEMA) and the benzoic acids were heated, dissociation of salts was observed, but with poly(DMAEMA) grafted onto polyethylene films, salt dissociation or crystallization of dissociated acids could be avoided, and interesting morphologies, including liquid‐crystal phases, were observed for the systems of benzoic acids–poly(DMAEMA‐g‐polyethylene). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 972–978, 2000     

Functionalization of high density polyethylene with maleic anhydride in the melt state through ultrasonic initiation

Grafting of maleic anhydride (MAH) onto high density polyethylene (HDPE) performed in the melt state through ultrasonic initiation by a laboratory‐scale ultrasonic extrusion reactor was studied in this paper. The effect of sonic intesity on the amount of grafted MAH, viscosity‐average molecular weight and melt flow index of the grafted product was investigated. The results show that the ultrasonic waves can obviously decrease the molecular weight of the grafted product and cause the increase of the amount of grated MAH, implying that the grafting reaction consists of the chain scission and the grafting reaction of the produced macroradicals with MAH. The percentage of grafting of the product amounts to 0.6%; its melt‐flow index is between 0.5 and 2.0 g/10 min, depending upon ultrasonic intensity, MAH content and grafting temperature. Compared with the method of peroxide initiation, in this method the crosslinking reaction can be prevented easily through the allocation of ultrasonic intensity. The mechanical properties of the improved HDPE/GF composite produced by ultrasonic initiatives are higher than in those produced by peroxide initiatives.     

Kinetics of surface grafting on polyisoprene latexes by reaction calorimetry

The two-component redox-initiation system, cumene hydroperoxide (CHP) and tetraethylene pentamine (TEPA), was used to polymerize dimethylaminoethyl methacrylate (DMAEMA) in the presence of synthetic polyisoprene latexes. The modified latex particles are postulated to possess a ‘hairy layer’ of surface-grafted poly(DMAEMA) chains formed via an abstraction reaction between cumyloxy radicals and the isoprene moieties present in the seed polymer. The modified latexes exhibited enhanced colloidal stability to low pH, and dynamic light scattering showed that the apparent particle size was sensitive to pH. The rate of polymerization was followed by reaction calorimetry. No steady-state polymerization was observed, with a continual increase in the number of propagating chains at all initiator feed rates investigated. The data for particle size and colloidal stability, together with the calorimetric data, are consistent with radical production at the particle surface, and with abstraction near the interface being a rare event. Further, there is evidence that radical production by the redox couple is relatively slow. While this ‘topology-controlled’ reaction is responsible for the formation of the hairy layer and latex stability, the dominant polymerization process appears to be the formation of ungrafted poly(DMAEMA) in the water phase.     

Synthesis and characterization of glycerol dimethacrylate cross-linked polymethyl methacrylate: a resin for solid phase peptide synthesis

The new glycerol dimethacrylate cross-linked polymethyl methacrylate polymer support (GDMA-PMMA) for solid phase synthesis is presented. The synthesis of GDMA-PMMA resin is based on the cross-linking of GDMA with methyl methacrylate by free radical polymerization, affording a polymer containing ester and secondary hydroxyl groups. The polymer was prepared using benzoyl peroxide as initiator either via bulk polymerization or via suspension polymerization in polyvinyl alcohol, the latter yielding a beaded resin. The polymerization reaction was investigated with respect to the effect of amount of cross-linking agent in order to vary the swelling, loading and the mechanical stability of the resin. The polymer was characterized by FT-IR and ¹³C CP MAS NMR spectroscopic techniques. The solvent uptake of the polymer was studied in relation to cross-linking and compared with Merrifield resin. The stability of the resin was tested in various synthetic conditions used in solid phase peptide synthesis. The resin was derivatized with chloro and amino functional groups. The C-terminal amino acid incorporation, Nα-Fmoc deprotection, acylation reactions and removal of target peptide from the support were optimized. The efficiency of the resin was demonstrated by synthesizing leucyl-alanyl-glycil-valine, alanine-alanine-alanine-alanine, acyl carrier protein (65-74) and retro-acyl carrier protein (74-65) fragments under optimal conditions and is compared with Merrifield resin. The purity of the peptides was checked by HPLC and identities were established by amino acid analysis and mass spectroscopic techniques.     

PP/LDPE化学交联发泡的研究

聚丙烯(PP)熔融黏度较低,发泡过程中气泡容易从熔体中溢出。在PP中加入低密度聚乙烯(LDPE)和偶氮二异丙苯(DCP),提高PP交联度,从而大大提高PP的熔融黏度。研究了共混聚合物组分的种类和含量对PP交联度的影响。结果表明,在共混过程中,部分PP和LDPE分子在热作用下相互促进,产生了接枝交联;共混物比纯PP的泡孔结构优且发泡效果佳,当LDPE为70%,发泡剂为5%,DCP为0.36%时,PP的发泡效果最好。解决了PP发泡过程中出现的气孔塌陷现象。     

Photografting of acrylonitrile and methacrylic acid on polyethylene film under air atmosphere

Photografting of acrylonitrile (AN) and methacrylic acid (MAA) on low-density polyethylene film (thickness 70 μm), on which benzophenone was coated earlier, was investigated at 60°C in water medium under air atmosphere. In the case of AN monomer, where grafted polymer was formed predominantly, oxygen in the system promoted the formation of both grafted polymer and homopolymer. With MAA monomer, in which homopolymer was formed preferentially compared to the formation of grafted polymer, the formation of homopolymer was accelerated by the presence of oxygen while suppressing that of grafted polymer. The formation of polyethylene peroxides by photoirradiation seemed to be a factor for the accelerated polymerization under air atmosphere. It was found that additives such as hydrazine and metallic ions (Fe²⁺, Cu²⁺, and Ni²⁺) are useful for enhancing the photografting under air atmosphere. © 1993 John Wiley & Sons, Inc.     

Trace levels of mechanochemical effects in pulverized polyolefins

This research investigated the structural changes that occur on different polyethylene polymer systems as a result of a novel pulverization process called solid‐state shear pulverization (S³P). High‐density polyethylene, low‐density polyethylene, and two forms of linear low‐density polyethylene were run through a pulverizer under high shear conditions as well as low shear conditions. The physical properties were examined before and after the pulverization via melt index, melt rheology, GPC, and DSC, techniques. The low shear pulverization did not noticeably alter the physical properties of the polymers. In contrast, high shear pulverization did result in an increase in viscosity as observed by melt index and oscillatory shear experiments, although solid‐state and bulk properties as observed by DSC and GPC were not affected. These results indicate that a small amount of mechanochemically induced changes occur as a result of the pulverization process, including incorporation of a small amount of long‐chain branches randomly placed on a few of the polymer chains. No evidence of short‐chain branching resulting from S³P processing was found in these systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 671–679, 2001     

Two‐step degradation of high‐density polyethylene during multiple extrusion

Ensuing our recent studies on polyethylene stabilization,^1,2 further multiple extrusion experiments were carried out with a high‐density polyethylene (HDPE) polymer containing various amounts of a sterically hindered phenolic antioxidant. Discoloration, thermoxidative stability, and melt flow index (MFI) retention were measured by standard techniques; the functional group content of the polymer was determined by Fourier transform infrared (FTIR) spectroscopy, and rheological, as well as mechanical properties, were also measured. The results indicated that degradation and stabilization reactions take place according to two different mechanisms in the first and subsequent processing steps, respectively. Color development could be described well by the simple first‐order overall reaction kinetics proposed earlier, and color change could be related to the stability of the polymer. The existence of general correlations among the properties proved that all chemical reactions are interrelated. The reactions of the stabilizer lead to color development, while those of the polymer to a modification of its molecular architecture, which determines the rheological and mechanical characteristics of the product. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1596–1605, 1999     

The effect of maleic anhydride grafting efficiency on the flexural properties of polyethylene composites

Many authors have reported on the property enhancements possible by compounding high density polyethylene (HDPE) with fillers to produce composites. It is accepted that polyethylene combined with materials such as nanoclay or wood flour will not yield favorable properties unless a compatibilizing material is used to form a link. In this work, compatibilized HDPE was produced by grafting maleic anhydride (MA) to its backbone in a twin screw extruder using a peroxide initiated reactive process. Fourier transform infrared spectroscopy (FTIR) was used to examine the effects of varying peroxide and MA levels on the grafting percentage and it was found that a high percentage could be achieved. The gel content of each HDPE‐g‐MA batch was determined and twin bore rheometry analysis was carried out to examine the effects of crosslinking and MA grafting on the melt viscosity. These HDPE‐g‐MA compatibilizers were subsequently compounded with nanoclay and wood flour to produce composites. The composite materials were tested using a three point bending apparatus to determine the flexural modulus and strength and were shown to have favorable mechanical properties when compared with composites containing no compatibilizer. X‐ray diffraction (XRD) was used to examine the effects of grafted MA content on the intercalation and exfoliation levels of nanoclay composites. The results from XRD scans showed that increased intercalation in polymer nanoclay composites was achieved by increasing the grafted MA content. This was confirmed using a scanning electron microscope, where images produced showed increased levels of dispersion and reductions in nanoclay agglomerates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Melt spinning of conducting polymeric composites containing carbonaceous fillers

Fibers produced by melt spinning of conductive polymer composites are attractive for several applications; the main drawback is however reduced processability at high filler concentrations. Carbon nanotubes (CNTs) are considered suitable fillers for conductive polymer composites, replacing conductive grades of carbon black (CB). In this study, the fiber‐forming properties of conductive polymer composites based on a conductive grade of CB and two masterbatches with CNT in a polyethylene matrix were investigated. The CB was also used in a polypropylene matrix for comparison. The rheological properties of the filler‐containing melts in shear and their extensional behavior were evaluated. A piston‐driven device was used to extrude the molten materials through a capillary; different capillary geometries were tested. Fibers were produced at various draw ratios, and their conductivity was determined. To assess the ultimate extensibility, a modified Rheotens method was used. The results showed that a conductive CB grade can have a lower percolation threshold and higher conductivity than a material with CNT. Conductivity decreased with increasing melt draw ratio for both types of fillers. The spinnability of the materials decreased with increasing concentration of filler material and correlations were found between spinnability and melt elasticity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

MAH-g-LLDPE增容改性rPET/mLLDPE合金材料的研究

以马来酸酐接枝线性低密度聚乙烯(MAH-g-LLDPE)为相容剂,回收聚对苯二甲酸乙二醇酯(rPET)为基体材料,茂金属线性低密度聚乙烯(mLLDPE)为增韧材料,制备rPET/mLLDPE塑料合金材料。采用DSC、SEM分析MAH-g-LLDPE对rPET/mLLDPE结晶性能及断面相结构的影响,测试了rPET/mLLDPE材料的流变性能及力学性能。结果表明,mLLDPE的加入使得rPET/mLLDPE熔体结晶峰向右移动,结晶温度提高;MAH-g-LLDPE的加入,共混体系中rPET的玻璃化转变温度(tg)朝低温方向移动,rPET与mLLDPE相容性增强,相界面模糊,界面黏结力强,熔融塑化过程扭矩值增大。含5%MAH-g-LLDPE的rPET/mLLDPE材料,与纯rPET相比,其结晶温度(tc)提高24.73℃,断裂伸长率提高113.6%,缺口冲击强度提高66.48%,柔韧性和抗冲击性能较大幅度提高。     

Melt grafting of 10‐undecenoic acid onto linear low density polyethylene

The melt grafting of 10‐undecenoic acid (UA) onto a linear low‐density polyethylene (LLDPE) was studied. The grafting reaction was performed in a thermoplastic mixer and 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane was used as initiator. The concentration of UA and peroxide ranged from 1 to 4% (w/w) and 0.025 to 0.1% (w/w), respectively. Evidence of the grafting of UA as well as its extent was determined by FTIR. Experimental results showed that the amount of UA grafted increases with both the UA and initiator concentrations. However, the greatest efficiency of grafting was found at the lowest concentration of UA investigated. The grafting efficiency ranged from 8 to 40%. The dynamic linear viscoelastic properties of the original polymer and the grafted materials were evaluated at different frequencies at 160°C using a dynamic rotational rheometer. The modification process affected the melt elasticity and viscosity of the LLDPE. When the original polymer was modified only with peroxide both properties increased with respect to those of the original material. However, when UA was grafted onto LLDPE, the resulting polymers displayed values of elastic moduli and viscosity lower than those of the polymer modified with peroxide. Moreover, when a concentration of 4% of UA was used, the values of those properties were even lower than those corresponding to the original LLDPE. These observations combined with the data obtained from the GPC results suggest that scission reactions may be favored by the presence on UA. In contrast with previous observations, the thermal properties measured by DSC were only slightly altered. The fusion temperature of the modified polymers was slightly lower than that corresponding to the original polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2303–2311, 2004     

Grafting of glycidyl methacrylate onto high‐density polyethylene with reaction time in the batch mixer

The melt grafting of glycidyl methacrylate (GMA) onto high‐density polyethylene (HDPE) in the presence of free radical initiators was investigated in the batch mixer. The graft content was determined with the titration and FTIR spectroscopy. The graft content increased with the increase of peroxide and initially introduced GMA concentration. Increase of the grafted GMA content resulted in decrease of the melt index. Interestingly, there was a sudden drop of GMA grafting content with the reaction time. It is assumed that depolymerization of GMA have taken place over the ceiling temperature. The crystallinity of the prepared glycidyl methacrylate grafted high density polyethylene (HDPE‐g‐GMA) was determined by the measurement of the heat of fusion. GMA grafted site acted as defect and crystallinity of the HDPE‐g‐GMA decreased with the increase of grafting reaction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Autohesive properties of polyolefins photografted with hydrophilic monomers

In an attempt to provide polyolefins such as low‐ and high‐density polyethylene and polypropylene with autohesive properties, hydrophilic monomers such as methacrylic acid (MAA), acrylic acid (AA), and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) were photografted onto their surfaces. The wettabilities of the grafted plates stayed constant above full coverage of the substrate surfaces with grafted polymer chains, except for the AA‐grafted plates. The amount of absorbed water for the grafted layers formed increased with an increase in the number of grafted polymer chains. The autohesive strength increased with an increase in the wettability and water absorptivity of the grafted plates as well as the temperature and load on heat pressing. For all grafted plates substrate breaking at autohesive strength measurements was observed for grafted amounts 2–3 times as much as those at adhesive strength measurements. The substrate breakings for the HDPE and PP plates photografted with AA and DMAEMA at adhesive strength measurements were observed at lower grafted amounts compared with those photografted with MAA. This study has made it clear that the photografting of hydrophilic monomers onto polyolefin materials can markedly enhance autohesivity without any adhesives as well as the adhesivity for high grafted amounts. Therefore, polyolefin materials with improved autohesivity and adhesivity can be widely applied in adhesive fields, including for novel uses. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2244–2252, 2003     

Radiation‐modified copolymer for the extraction of metal ions from water

The modification of heavy‐duty polyethylene films was carried out through the graft copolymerization of acrylamide and vinyl acetate mixtures of different compositions with the simultaneous radiation method. The influence of the synthesis conditions (the irradiation dose, comonomer composition, and dilution) on the degree of grafting was investigated. The grafted samples were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, and differential scanning calorimetry. The effect of the grafting degree on the thermal stability of the modified polymer was examined. The extraction of heavy and toxic metals such as cadmium, cobalt, copper, nickel, and lead by the modified heavy‐duty polyethylene was evaluated, and the metal‐ion uptake by the grafted and chemically treated samples seemed better than that of the grafted and untreated ones. Both the rate and amount of the metal‐ion uptake were affected by the temperature of the feed solution and the grafting degree. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Grafting of polyelectrolytes onto polyacrylamide by reactive processing

Low‐molecular‐weight high‐charge‐density cationic poly diallydimethyl ammonium chloride (polyDADMAC) was grafted onto nonionic polyacrylamide (PAM) using organic peroxide initiators in the molten state carried out in a batch mixer. The graft copolymer can be used as a high performance flocculant. Glycerol was selected as a plasticizer. The grafting reaction was characterized in terms of composition, temperature, degree of grafting, and grafting efficiency. It was found that free radicals on polymer chains were induced by the decomposition of the initiator. Grafting was produced by free radical recombination termination. The degree of grafting increases with an increase of the polyDADMAC/PAM feed ratio. However, the grafting efficiency was lower than 10 wt % in this highly viscous polymer melt system. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1412–1416, 1999