Copolymer in-situ

Moreover, commercially available triblock copolymers designed to be thermoplastic elastomers, not compatihilizers, are often used in Heu of the more appealing diblock materials. Since the mid-1980s, the generation of block or graft copolymers in situ during blend preparation (158,168—176), called reactive compatibilization, has emerged as an alternative approach and has received considerable commercial attention. 

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]. 

Fig. 48. Schematic of the interfacial reaction of reactive chains. Polymer chains on either side of the interface contain functional groups that can mutually react together, effectively forming a copolymer in situ...

Commonly, the most economical and efficient process for adding a copolymer to a blend of immiscible polymers is to form the copolymer in situ by a chemical reaction during the extrusion process during establishment of the immiscible phase morphology — the process known as Reactive Compatibilization. 

Fig. 13 Chain extension via NMP of polyAA-SGl by a hydrophobic monomer in water to form amphiphilic block copolymers in situ and to induce micellization by polymerization...

Key words biodegradability, sol-gel transition, thermosensitivity, hydrogel, block copolymer, in-situ gelation, drug debvery system. 

A disadvantage of forming copolymer in situ is that such a process often requires that each of the immiscible polymers bear an appropriate chemical functionality for reaction across a melt-phase boundary. 

Compounding polymer blends often involves the use of high processing temperatures in order to induce sufficient molecular mobility into the component which softens at the higher temperature. All esters are susceptible to transesterification reactions as is PCL when mixed with other polyesters or polycarbonates under such conditions. These processes provide added complications to blending processes by producing copolymers in situ. A recent patent refers to the use of such processes in blending PCL with polyesters or polycarbonate to produce antielectrostatic compounds [5]. To date, most studies of transesterification reactions have been made on aromatic polyesters but there have recently been a few additional studies on PCL blends with other polyesters these are discussed in Sect. 12 on blends with polyesters. 

In the polymer blend section, we considered mixtures of homopolymers and/or random copolymers. However, the combination of homopolymers and block copolymers is equally important. Suitable block copolymers at the interface between two incompatible polymers will lower the interfadal tension and, thus, improve the dispersion of one polymer in the other (see Reference 49 and references therein). For practical applications, the critical issues are the synthesis of suitable block copolymers and the concentration of the block copolymers at the interface. In practice, compatibilization is, therefore, often achieved by forming block or graft copolymers in situ during blend preparation by, for example, interfadal reactions. 

PS was grafted. Addition of DCP does not change this amount significantly (Fig. 6). Also addition of BA to PP/PS blends was found to generate copolymers in-situ. These copolymers contributed to the blend compatibilization. 

Reactive compatibilization introducing reactive molecules capable of forming the desired copolymers in-situ, directly during blending. 

The graft copolymer, in situ formed during reactive compatibilization, has to be isolated from the blend and well purified prior to characterization. Experiments of selective solvent extraction and hydrolysis always precede the spectroscopic characterization. It is fiequently a difficult task to efficiently isolate the species that bear the chemical grafts. 

This severe lack of compatibility between the polyamides and conventional rubbers necessitated the development of suitable techniques for reactive compatibilization [5, 8-10]. Reactive compatibilization is defined here as the melt blending process in which two polymers containing mutually reactive functionalities react with each other at the interface generating a block or graft copolymer in situ, which compatibilizes the blend by reducing the interfacial tension and improving the interfacial adhesion (Scheme 8.2). 

Colloidal stability of polyester particles formed in the dispersion polymerization of s-caprolactone and lactides was achieved by adding to the polymerizing mixture block or graft copolymers with tailored chemical structure and with molecular weight from a few thousands to about 50 000 or by producing such copolymers in situ, during polymerization. 

Charoensirisomboon P, Inoue T, Weber M. Interfacial behavior of block copolymers in situ-formed in reactive blending of dissimilar polymers. Polymer 2000 41(12) 4483-90. 

Furthermore, to elucidate the temperature-dependent phase transitions of thin films of the p(EO)-b-p(MAAZ) diblock copolymer, in situ GIWAXS and GISAXS measurements were carried out during heating and subsequent cooling mns. °... 

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