Compatibilizer catalysts

Reactive compatibilization of engineering thermoplastic PET with PP through functionalization has been reported by Xanthos et al. [57]. Acrylic acid modified PP was used for compatibilization. Additives such as magnesium acetate and p-toluene sulfonic acid were evaluated as the catalyst for the potential interchange or esterification reaction that could occur in the melt. The blend characterization through scanning electron microscopy, IR spectroscopy, differential scanning calorimetry, and... 

Reactive compatibilization is also carried out by adding a monomer which in the presence of a catalyst can react with one or both phases providing a graft copolymer in situ that acts as a compatibilizer. Beaty and coworkers added methyl methacrylate and peroxide to waste plastics (containing polyethylene [PE], polypropylene [PP], PS, and poly(ethylene terephthalate) [PET]). The graft copolymer formed in situ homogenized the blend very effectively [19]. 

The compatibilization of clay with LDPE and HDFE is accomplished by the in situ polymerization of MAH or its precursor maleic acid, in the presence of a radical catalyst. The latter must be capable of initiating the homopolymerization of MAH, i.e. it must be present in high concentration and/or have a half-life of less than 30 min at the reaction temperature, e.g. t-butyl per-benzoate (tBFB) at 150°C. In a one-step process, the clay and PE are mixed with MAH-tBPB in the desired PE/clay ratio. In the preferred two-step process, a 70/30-90/10 clay/PE concentrate is prepared initially in the presence of MAH-tBPB and then blended with additional PE to the desired clay loading. The compatibil-ized or coupled PE-MAH-clay composites have better physical properties, including higher impact strengths, than unfilled PE or PE-clay mixtures prepared in the absence of MAH-tBPB. 

An interesting class of styrene-based polymers is ethylene/styrene co-polymers, which have many promising applications as films or foams, as compatibilizers, and as modifiers for bitumens and asphalts. The preparation of these co-polymers by a variety of catalysts has been reported, including both heterogeneous and homogeneous catalysts, but the co-polymers thus obtained typically contained low levels (<4mol%) of styrene incorporation or were heterogeneous in nature. ... 

However, a reactive styrene acrylonitrile copolymer (SAN)/gly-cidl methacrylate copolymer was found to be an effective reactive compatibilizer for the blends. Ethyltriphenyl phosphonium bromide was used as the catalyst. Probably, the epoxide groups react either with carboxyl or with hydroxyl groups of the PLLA end groups. This so modified polymer acts as the compatibilizer. Compatibilized PLLA/ABS blends exhibit an improved impact strength and an im-... 

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

Kaneko [2] prepared compatibilizing agents consisting of methacrylate, (II), and styryl, (III), macromolecules. These materials were polymerized using titanium-based Ziegler-Natta catalysts. 

The MAO-activated 138 and 137, effective in the living homopolymerization of ethylene and propylene, also promote their block co-polymerization. This approach broadens remarkably the utility of living catalysts because it allows the preparation of block co-polymers with high glass or melting transition blocks from common commercial monomers such as ethylene and propylene. These materials could have applications as compatibilizers and elastomers.1232,1233 Using complex 138, propylene has been first homopolymerized to sPP for 2h in toluene at 0°C (Mn = 38400 Mw/Mn = 1.11). Then, an ethylene overpressure was applied, and in 1 additional h an sPP-/W< (j -poly(E-r -P) diblock co-polymer was obtained (Mn = 145 100, A/w/A/ = 1.12). The microstructure of this diblock co-polymer is shown in Scheme 48. This co-polymer has a Tm of 131 °C while the ethylene-propylene block (E = 33 mol%) has a TR of —45 °C.1175 A detailed morphological and thermodynamic characterization of these co-polymers has been reported.1234... 

Performance of other additives Fillers arc instrumental in improving the performance of other additives. Antistatics, blowing agents, catalysts, compatibilizers, coupling agents, organic flame retardants, impact modifiers, rheology modifiers, thermal and UV stabilizers are all influenced by a fillet s presence. 

Polymers prepared via CRP show promise for applications like photoresists [112], liquid-crystalline displays [147-149, 154], and photo catalysts [151]. Incorporating blocks prepared using CRP techniques into copolymers with conductive or luminescent blocks [240,241,243,251] may impart better processability and make them useful for a broader range of applications. Block or gradient copolymers with highly controlled compositions may also be industrially useful as blend compatibilizers or as surfactants [194],perhaps improving upon already existing materials. Well-defined or functional compatibilizers and stabilizers could potentially result in lower production costs if less material is needed to impart the desired properties. 

In general, the combination of compatibilizer (with or without catalyst) and rubber in the blend shows a synergistic effect, but the effect is not substantial and is somewhat inconsistent. The blend containing both MBS and MBS-MA rubbers (No. 18) is expected to have the rubber particles distributed in both the PC and PA phases, but it fails to show any further improvement. 

The same technique can be used to dye a material that is otherwise difficult to dye. An ethylene-propylene copolymer rubber was reacted first with maleic anhydride, then with an aromatic amine dye in an extruder to produce a dyed rubber.81 Dye sites can also be inserted into polyolefins by grafting them with dimethylaminoethyl methacrylate, using azo or peroxide catalysts in an extruder.82 jV-Vinylimidazole has been grafted to polyethylene in an extruder with the help of dicumylperoxide.83 The product was mixed with an acrylic acid-modified polypropylene and used to compatibilize polyethylene and polypropylene. This could be helpful in the recycling of mixed polyolefins from municipal solid waste. Recycling of cross-linked (thermoset) polymers is more of a problem because they cannot be remelted in an extruder. However, they can be if... 

Since the early 1990 s the constrained geometry metallocene catalysts have been used by Dow to produce either alternating or pseudo-random ethylene-co-styrene interpolymers (ESI) [Stevens et al., 1991]. ESI with up to 50 wt% styrene is semicrystalline, it is known to compatibilize PE/PS... 

When applicable, a common method for controlling a redistribution process is to initiate the reaction with a catalyst. Control may then be achieved by quenching the catalyst at the desired extent of reaction. Certain types of redistribution catalyst may thermally decompose under controlled processing conditions that make quenching unnecessary. In these cases, a predominance of block copolymer may be formed that serves as an effective compatibilizer for an immiscible polymer blend. Just as importantly, only a relatively small proportion of the polymer chains actually participates in the redistribution process so that phase separation and the properties attributable to the original sequence distribution are maintained. 

Hu and Lambla [1995] have blended EM Ac (90-65 parts) with mono-hydroxy-terminated PS (10-35 parts) in an internal mixer at 180-220°C in the presence of dibutyltin dilaurate or dibutyl-tin oxide catalyst. A compatibilizing copolymer arises from transesterification between pendent ester groups of EMAc and terminal hydroxy groups of PS. The effects on blend properties of PS molecular weight were reported. The effects of processing conditions and addition of solvent on conversion kinetics were studied. 

Immiscible polyacrylates have been compatibilized through transesterification between pendent ester groups on one polyacrylate with pendent ester groups on another polyacrylate. Selected examples are listed in Table 5.38. Dibutyltin oxide was used as transesterification catalyst. 

In reactive compatibilization the copolymers are produced at the interface. From the economic and the performance points of view, this method is more attractive than that by addition of a compatibilizer. Owing to the cost of TSE, these machines are operated with short residence time of 1-4 min. For this reason, to complete the reactive compatibilization one must use either high concentration of reactive groups (e.g., for chain-end groups, low MW reacting polymers), highly reactive functional groups, or efficient catalyst. Thus, the basic requirements for efficient reactive compatibilization are ... 

The 80%/20% binary blends PE/PS and PP/PS were subjected to F-C reaction for compatibilization performed under nitrogen atmosphere in a Banbury mixer. Different concentrations of catalyst (AICI3) and 0.3% of cocatalyst (styrene) were added to the completely melted and mixed physical blends. The blends and catalyst concentrations are weight based. High MW commercial grades of linear low density polyethylene (LLDPE), and injection-grade polypropylene and polystyrene were used as homopolymers. The compatibilization conditions and MW of the homopolymers are given in Table 20.1. Blend names are listed in nomenclature. 

The morphology of PP/PS blends was studied following the emulsification behavior as explained in Section 20.3.1.2. Figure 20.10 shows that the emulsification curve follows a typical trace, which was frequently reported for compatibilization of immiscible blends (28-30). It is clear that after a significant drop in particle size, an equilibrium value is reached at about 0.7% AICI3. This value has been taken as the cmc condition. It has to be remarked that the particle size decreases to one third of its initial value, reaching an equilibrium diameter of about 0.5 pm. Also, the particle size homogeneity increases with the catalyst content. It is shown by the decrease in error bars in Fig. 20.10. From these results, it is foreseen that the copolymer formed by the F-C reaction behaves as an efficient in situ compatibi-lizer for the PP/PS blend. 

The PE particles were fractured along with the PP matrix in a transparticle mode, consistently with PE-PP compatibilization via EPR copolymer. As the catalyst content increases, the PS particle diameter decreases and the fracture becomes progressively transparticle (Fig. 20.16b). This indicates that the PP-PS and PE-PS are being compatibilized. 

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