W. E. Baker

Comparison of the effectiveness of different basic functional groups for the reactive compatibilization of polymer blends

Abstract Reactive compatibilization of immiscible polymer blends has been attracting a very considerable research interest in the past few years. While a wide variety of functionalized polymers having acidic groups are commercially available, potentially reactive polymers containing basic functional groups have rarely been developed. In this study, glycidyl methacrylate (GMA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), t-butylaminoethyl methacrylate (TBAEMA), dimethylaminoethyl methacrylate (DMAEMA), and 2-isopropenyl-2-oxazoline (IPO) were melt grafted onto a polypropylene (PP) homopolymer. The effectiveness of these functionalized PPs as compatibilizers for PP ( acrylonitrile -co- butadiene -co- acrylic acid ) rubber (NBR) blends was evaluated in terms of improvement in impact properties and blend morphology. It has been found that IPO and GMA are effective in compatibilizing the PP/NBR blends, with a nine-fold improvement in impact energy over pure PP and an uncompatibilized PP/NBR blend. The other functional groups are much less effective for the blend system where carboxylic acid is the coreactive group.

Melt rheology of graft modified polypropylene

Abstract The low frequency rheological behaviour of a family of glycidyl methacrylate and styrene graft modified polypropylenes was studied. Two initiators were examined in the grafting process and were found to produce significantly different copolymers in terms of the degree of grafting, molecular weight, and rheological properties. Rheological evidence that β-scission occurred during the grafting process was found for the PP-g-GMA copolymers. A slight increase in the elastic response was observed for the samples prepared using L 231, most likely due to crosslinking via epoxy ring opening. The elastic response of the styrene grafted copolymers was enhanced significantly, and the copolymers behaved like typical crosslinked materials at higher levels of grafted styrene. The low frequency storage modulus (G′) increased, spanning more than 2 decades, with the addition of styrene as a comonomer for the grafting of GMA. At higher levels of grafting, both the PP-g-S and PP-g-(GMA-S) copolymers were sufficiently crosslinked that G′ was greater than G″, the loss modulus, over the entire frequency range examined. However, these samples contained no gel material as determined by Soxhlet extraction with xylene.

Coupling of reactive polystyrene and polyethylene in melts

Abstract Polystyrene (OPS) having oxazoline groups and polyethylene (CPE) having carboxyl groups were melt blended in a Rheomix mixer. The effects of composition on the torque, thermal transitions, solubility and phase structure of these resulting polymer alloys were investigated. Differential scanning calorimetry (d.s.c.) and scanning electron microscopy (SEM) data on these alloys is compared with the corresponding melt blends of the non-reactive polymers. The torque-time relationships, phase structure and thermal properties of these polymer alloys were found to be very different from the non-reactive blends, and this was more so in an alloy with 40% CPE. This is attributed to the coupling reaction between the OPS and CPE. Studies on extraction of this alloy in xylene support the presence of a crosslinked polymer. The Fourier transform infra-red (FTi.r.) spectra of alloys and their low molecular weight analogues show that amido-ester linkages similar to the model compounds are formed between OPS and CPE.

Basic functionalization of polypropylene and the role of interfacial chemical bonding in its toughening

A reactive polypropylene (PP) containing oxazoline functional groups was prepared by the melt grafting of 2-iso-propenyl-2-oxazoline onto a PP homopolymer and used to introduce varying amounts of interfacial chemical reaction in PP/acrylonitrile-co-butadiene-co-acrylic acid rubber (NBR) blends. A technique has been successfully developed to control the rubber particle sizes of PP/NBR blends such that various PP/NBR blends with the same rubber particle size can be obtained by using different combinations of processing conditions and the amount of interfacial reaction. It has been found that moderate levels of interfacial chemical bonding are required for a transition from a brittle to ductile failure to be observed in PP/NBR blends. Blends without any interfacial chemical bonding showed no improvement in impact energy whereas up to a 13.5-fold improvement in impact energy (notched Charpy test) was observed for reactive blends above the brittle-tough transitions.

In situ compatibilization of polyolefin and polystyrene using Friedel-Crafts alkylation through reactive extrusion

In our preliminary study, it has been revealed that a copolymer of PE-g-PS can be formed during melt blending of polyethylene/polystyrene (PE/PS) blends via a Friedel—Crafts benzene ring alkylation of the PS. This paper reports our further study on the in situ compatibilization of polyolefin and polystyrene using a single screw extruder. Polyethylene and polypropylene (PP), respectively, have been blended with polystyrene, in the presence of an AlCl3 catalyst system. The mechanical characterization of the PE/PS and PP/PS blends shows significant improvement in tensile elongation. Further characterization of the PE-g-PS copolymer formed in the blends as well as the ungrafted PE and PS suggests a competition between grafting and PS degradation. This in situ compatibilization technique has potential in recycling of mixed polymer wastes.

Melt grafting of t-butylaminoethyl methacrylate onto polyethylene

Abstract The preparation of a polymer containing secondary amino groups by grafting of t-butylaminoethyl methacrylate (t-BAEMA) onto linear low-density polyethylene (LLDPE) in the melt has been investigated. Using a peroxide initiator, the effects of feed composition and reaction time were studied. Materials containing up to 3 wt% grafted t-BAEMA, 5 wt% t-BAEMA homopolymer and displaying minor crosslinking were obtained by the choice of appropriate feed composition and reaction conditions. Attempts were made to increase the degree of grafting and to minimize the homopolymerization by adding a variety of compounds. The homopolymerization was considerably reduced and relatively high grafting efficiency achieved by using p-benzoquinone as a chain terminator. Carbon tetrabromide, a chain transfer agent, suppressed polyethylene crosslinking but decreased grafting and increased homopolymerization. n-Hexane, known to be able to accelerate radiation-induced solution grafting of t-BAEMA onto a PE film, only accelerated t-BAEMA homopolymerization rather than grafting for this peroxide-initiated melt grafting case. Other compounds containing nitrogen, phosphorous or sulphur, known to be chain terminators for maleic anhydride and methyl methacrylate homopolymerization, acted only as inert additives. Preliminary studies on the potential interpolymer melt reaction between this graft polymer and acid polymers are also reported.

Polyolefin/polystyrene in situ compatibilization using Friedel-Crafts alkylation

Polyolefin/polystyrene (PS) blends are difficult to compatibilize using in situ reactive compatibilization techniques, because neither of these polymers has any functional groups that one can use in the formation of a copolymer from these polymer components. In this study, the Friedel–Crafts alkylation was realized in a polyethylene/PS (PE/PS) melt blend, which resulted in improved compatibility between PE and PS. A number of Lewis acid compounds were tested as catalysts, among which the AlCl3 was the most efficient. It was found in this study that the presence of a cocatalyst, such as a cationically polymerizable monomer or a halogenated alkane, significantly enhances the formation of PE-g-PS copolymer. The effects of blending parameters, such as temperature and blending time, on the in situ copolymer formation were investigated. The mechanical properties of compatibilized PE/PS blends were improved considerably. Such an in situ compatibilization technique has potential in the recycling of mixed polymer wastes.

Peroxide‐initiated grafting of maleic anhydride onto linear and branched hydrocarbons

The structural features of the grafting of maleic anhydride onto low-molecular-weight compounds have been elucidated using several spectroscopic and analytical techniques. Conclusive evidence for the occurrence of singly grafted anhydride residues in multiply grafted products has been established using 2,3-13C2 labeled maleic anhydride. In homogeneous solution, at the low concentrations of maleic anhydride employed, there is little evidence for oligomeric or polymeric grafts to dodecane, pristane, or squalane. The results suggest that isothermal grafting of maleic anhydride to hydrocarbon polymers should also lead to a predominance of single grafts.

Melt grafting of a basic monomer on to polyethylene in a twin-screw extruder: reaction kinetics

Abstract The grafting of 2-(dimethylamino) ethyl methacrylate (DMAEMA) on to linear low-density polyethylene (LLDPE) using peroxide initiators was studied in an intermeshing co-rotating twin-screw extruder. The grafting reactions were carried out above the apparent ceiling temperature of the DMAEMA monomer. It was observed that above this ceiling temperature homopolymer propagation reactions are no longer occurring. The homopolymer initiation step was seen, however, to consume significant quantities of monomer, thus resulting in low grafting efficiencies ( GE ). Reducing the monomer concentration was shown to suppress the homopolymer initiation reaction and provide high grafting efficiencies with little loss in graft levels. It was also observed that initiator concentration controls the overall conversion and degree of grafting ( DG ) as well as crosslinking. Graft levels are therefore limited by the amount of crosslinking that can be tolerated in the final graft product.

Peroxide‐initiated comonomer grafting of styrene and maleic anhydride onto polyethylene: Effect of polyethylene microstructure

Maleic anhydride has been grafted onto various polyethylenes (PEs) using 2,5-dimethyl-2,5-(di-t-butylperoxy)hexane as a free radical initiator in the presence of styrene as a comonomer. Three polyethylenes, differing systematically in their levels of terminal unsaturation and branching, were selected to investigate the effect of these microstructural characteristics on the course of both grafting and crosslinking. It was observed that when polyethylenes containing high levels of terminal unsaturation were reacted in the presence of peroxide or peroxide–maleic anhydride, crosslinking events were enhanced. When styrene was added as comonomer to the reaction medium to eliminate these undesirable side reactions, crosslinking was still observed with those polyethylenes that contained a high concentration of terminal unsaturation. This is attributed to a low reactivity between styrene and the allylic radical generated on the polyethylene backbone, which is believed to be responsible for the increased crosslinking. However, in the presence of high concentrations of styrene, crosslinking was eliminated for PEs containing high degrees of branching.