Interchain copolymer formation

Interchain copolymer formation Copolymers of reactive polystyrene and polymers with amide, mercaptan, epoxy, hydroxy, anhydride or carboxylic acid groups, copolymer of polypropylene grafted with maleic anhydride and nylon-6, copolymer of polyolefines and polystyrene, copolymer of EVA grafted with methacrylates and grafted polystyrene... 

Bulk polymerizations, such as addition (free-radical- and ionic-based) and step-growth types. Grafting polymerization by small molecules. Interchain copolymer formation, based on chain cleavage, graft copolymerization, and end-group block copolymerization. 

The majority of commercially important, immiscible polymer blends rely for compatibilization on the presence of a copolymer of the blended polymers. Nowadays, such a copolymer is almost never synthesized in a separate step and then added as a distinct entity to the blend of immiscible polymers. Instead, a compatibUizing copolymer is most economically formed simultaneously with generation of interphase morphology during extrusion processing, a process referred to as Reactive Compatibilization. The Reactive Compatibilization process is logically a sub-category of the broader class of Interchain Copolymer Formation reactions performed by Reactive Extrusion [Brown, 1992],... 

There are hve basic processes for achieving interchain copolymer formation between two polymers during Reactive Compatibilization in an extruder. Table 5.4 shows these hve processes starting with idealized homopolymers A with structure AAAAAAAA and B with structure BBBBBBBB. Each process produces a specihc type of copolymer compatibilizing agent by particular types of chemical reactions. 

In a third type of ionic association (Process 5c) acidic groups such as carboxylic acids bound to one polymer may mediate interchain copolymer formation by protonation of basic groups on a second, immiscible polymer. In this case the compatibilizing agent is again most often a cross-linked copolymer. 

Na, Zn, or Al. Multivalent cations may form a bridging linkage between the ionizable groups of the two immiscible polymers resulting in interchain copolymer formation by ion-ion association. Monovalent cations such as Na" or may also be used to promote associaticMi through ion-dipole association. With either type of cation, a morphology is formed in which there are concentrated domains of associated ionic species (ion clusters) in a matrix of the immiscible homopolymers. 

The interchain copolymer formation involves reactive groups of both polymers that form block or graft copolymers, with MW equal to the sum of the two homopolymers. Because of the short residence time in an extruder, either high concentration of reactive groups, or highly reactive functional groups are required [13]. 

Reactive blending is a very effective technology for compatibilization of polymer blends composed of immiscible components. Interchain copolymer formation by reactive compounding is particularly useful for compatibilization of immiscible polymer blends so that a product may be obtained with combinations of desirable properties arising from both polymers. Compatibilization in this sense refers to operational compatibility as defined by Gaylord [22] in which the blend exhibits useful technological properties over the lifetime of a molded part. 

Mashita et al [29] described interchain copolymer formation in compatibilized PP blends with PP-g-MA, PET, and glycidyl methacrylate grafted ethylene vinyl acetate (EVAc-g-GMA). The compatibilized blends had markedly higher impact strength and tensile properties than blends with either non-fimctionalized PP or without EVAc-g-GMA. 

The above discussion clearly shows that the increase of anionic copolymer concentration or the strength of chain interaction can lead to a transition from intrachain contraction to interchain association. It can result in a mesoglobular phase in which a limited number of copolymer chains are associated together to form polymeric colloidal particles stable between microscopic single-chain globular phase and macroscopic phase separation (precipitation). It is not a surprise to see the formation of such stable mesoglob-... 

Considering the competition between intrachain contraction and interchain association, we have to discuss an overlooked viscoelastic effect in the formation of stable mesoglobules in dilute solutions. Otherwise, it would be difficult to understand why copolymer chains with a high content of hydrophobic comonomers could form smaller interchain aggregates. In the micro-phase separation, copolymer chains in solutions contract and associate. The collision between contracted and associated chains would not be effective if the collision (or contact) time (rc) is much shorter than the time (re) needed to establish a permanent chain entanglement between two ap-... 

Based on the perception that interchain interactions should be suppressed by introducing nonplanar units into the PFO chains, we decided to prepare random copolymers incorporating swivel-cruciform binaphthyl moieties into the polymer backbone [46], Furthermore, as shown in the previous examples on low molecular weight chromophores by Bazan and coworkers, the distorted nature of the binaphthyl unit should simultaneously facilitate the formation of a glassy, amorphous state. PFO and random copolymers 34, incorporating binaphthyl units,... 

Adhesive Emulsions. Thermoplastic, synthetic polymers can be prepared as emulsions for use as adhesives. For example, while EVAc hot-melt adhesives described in the previous section contain less than 40% VAc, when the content of VAc in the copolymer is increased to 60%, and the copolymer is prepared in the form of aqueous emulsions, a very useful and versatile adhesive polymer is obtained. Although the VAc homopolymer, poly(vinyl acetate), is a brittle solid, with a Tg = 28 °C, the ethylene units present in the EVAc copolymer act as an internal plasticizer, and lower the Tg to below room temperature. The plasticization results from the reduction of interchain interaction of the VAc polymer chains by the ethylene units interspersed among the strongly interacting VAc units. This reduction of the Tg has important consequences because the formation of a flexible adhesive film from the emulsion depends upon the Tg of the polymer. 

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