Copolymer compatibilizing agents

It has been found by Baird and others [74-77] that the presence of LCP may accelerate and presumably direct the crystallization of conventional polymers (PET, etc.). Porter [76] has shown that, by blending biphasic polymers such as the PET-poly HBA copolymers, miscibility may be achieved between the conventional phase of the biphasic polymer with another conventional polymer that component is miscible with, i.e., X7-G/PBT. The latter phenomena may offer direction in the search for useful compatibilizing agents for LCP/conven-tional polymer systems. 

Chain functionalized polymers or graft copolymers are of great technological importance. They are used as compatibilizing agents for immiscible polymer blends (8) and adhesive layers between polymer-polymer co-extruded surfaces (8). Currently, of all polymers sold, about 30% are in the form of compatibilized immiscible blends (9-12). Next we discuss a few examples of chain functionalization. 

The copolymer composition in miniemulsion copolymerization of vinyl acetate and butyl acrylate during the initial 70% conversion was found to be less rich in vinyl acetate monomer units [34]. Miniemulsion polymerization also allowed the synthesis of particles in which butyl acrylate and a PMMA macromonomer [83, 84] or styrene and a PMMA macromonomer [85] were copolymerized. The macromonomer acts as compatibilizing agent for the preparation of core/shell PBA/PMMA particles. The degree of phase separation between the two polymers in the composite particles is affected by the amount of macromonomer used in the seed latex preparation. 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

Intense commercial and academic interest in block copolymers developed during the 1960s and continues today. These materials attract the attention of industry because of their potential for application as thermoplastic elastomers, tough plastics, compatibilizing agents for polymer blends, agents for surface and interface mo dification, polymer micelles, etc. Academic interest arises, primarily, from the use of these materials as model copolymer systems where effects of thermodynamic incompatibility of the two (or more) components on properties in bulk and solution can be probed. The synthesis, characterization, and properties of classical linear block copolymers (AB diblocks, ABA triblocks, and segmented (AB)n systems) have been well documented in a number of books and reviews [1-7] and will not be discussed herein except for the sake of comparison. 

Extrapolation of the concept of the compatibility of polymers with different structures but similar solubility parameters to the construction of effective compatibilizing agents leads to the use of block and graft copolymers having segments with suitable solubility parameters to compatibilize polymers which differ both in structure and solubility parameter. Thus, an AB block or graft copolymer compatibilizes polymers A and C when C has a solubility parameter similar to that of B, polymers D and B when D has a solubility parameter similar to that of A, and polymers C and D when the solubility parameter of C is similar to that of B, and D has a solubility parameter similar to that of A. 

PPE/PP compatibilized with PO grafted with ethylenically unsaturated f-alkylcarbamate copolymers used as decomposable compatibilizing agents Campbell Presley, 1995... 

A copolymer of the two immiscible polymers themselves would seem to be ideally suited to act as a compatibilizing agent for an immiscible blend. If the copolymer is at the interface of the two phases, then the segments of the copolymer dissolve in the respective bulk phases of the same identity. The copolymer acts as emulsifying agent for the blend resulting in reduced interfacial energy and improved interphase adhesion. 

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. 

Examples of individual processes for forming copolymer compatibilizing agent described in Table 5.4 are summarized in the following sections. 

As shown in Table 5.35, blends of immiscible polyesters may be compatibilized through copolymer formation mediated by addition of a phosphite condensing agent. Block copolymer results when the phosphite-activated end-group of one PEST reacts with a nucleophilic end-group of another PEST. The reaction takes place at the phase interface. A secondary phosphite is a byproduct. The relative proportions of copolymer vs. simple chain-extended PEST may depend upon the relative solubihty of condensing agent in each of the immiscible polymer phases. 

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