CHAIN STRUCTURE AND CONFIGURATION
2.7 MULTICOMPONENT POLYMERS
Table 2.7 Specialized nomenclature terms (20)
Link Covalent chemical bond between two monomeric units, or between two chains.
Chain Linear polymer formed by covalent linking of monomeric units.
Backbone Used in graft copolymer nomenclature to describe the chain onto which the graft is formed.
Side chain Grafted chain in a graft copolymer.
Cross-link Structure bonding two or more chains together.
Network Three-dimensional polymer structure, where (ideally) all the chains are connected through cross-links.
Multicomponent polymer, General terms describing intimate solutions, blends, or multipolymer, and bonded combinations of two or more polymers.
multicomponent molecule
Copolymer Polymers that are derived from more than one species of monomer.
Block Portion of a polymer molecule in which the monomeric units have at least one constitutional or
configurational feature absent from the adjacent portions.
Block copolymer Combination of two or more chains of constitutionally or configurationally different features linked in a linear fashion.
Graft copolymer Combination of two or more chains of constitutionally or configurationally different features, one of which serves as a backbone main chain, and at least one of which is bonded at some point(s) along the backbone and constitutes a side chain.
Polymer blend Intimate combination of two or more polymer chains of constitutionally or configurationally different features, which are not bonded to each other.
Conterminous At both ends or at points along the chain.
AB-cross-linked Polymer chain that is linked at both ends to the same or copolymer to constitutionally or configurationally different chain or chains; a polymer cross-linked by a second species of polymer.
Interpenetrating polymer Intimate combination of two polymers both in network network form, at least one of which is synthesized and/or
cross-linked in the immediate presence of the other.
Semi-interpenetrating Combination of two polymers, one cross-linked and one polymer networka linear, at least one of which was synthesized and/or
cross-linked in the immediate presence of the other.
Star polymer Three or more chains linked at one end through a central moiety.
Star block copolymer Three or more chains of different constitutional or configurational features linked at one end through a central moiety.
aAlso called a pseudo-interpenetrating polymer network. See D. Klempner, K. C. Frisch, and H. L. Frisch, J. Elastoplastics, 5, 196 (1973).
2.7 MULTICOMPONENT POLYMERS 53
Figure 2.10 Six basic modes of linking two or more polymers are identified (20). (a) A polymer blend, constituted by a mixture or mutual solution of two or more polymers, not chemically bonded together. (b) A graft copolymer, constituted by a backbone of polymer I with covalently bonded side chains of polymer II. (c) A block copolymer, constituted by linking two polymers end on end by covalent bonds. (d ) A semi-interpenetrating polymer network constituted by an entangled combination of two polymers, one of which is cross-linked, that are not bonded to each other. (e) An interpenetrating polymer network, abbreviated IPN, is an entangled combi-nation of two cross-linked polymers that are not bonded to each other. (f ) AB-cross-linked copolymer, constituted by having the polymer II species linked, at both ends, onto polymer I.
The ends may be grafted to different chains or the same chain. The total product is a network composed of two different polymers.
Although many of the block copolymers reported in the 1 terature are actu-ally highly blocked, some of the most important “graft copolymers” described in the literature have been shown to be only partly grafted, with much homopolymer being present. To some extent then, the term graft copolymer may also mean, “polymer B synthesized in the immediate presence of ploymer.
A.” Only by a reading of the context can the two meanings be distinguished.
2.7.3 AB–Cross-linked Copolymers
The polymers of Section 2.7.2 are soluble, at least in the ideal case. A conter-minously grafted copolymer has polymer B grafted at both ends, or at various points along the structure to polymer A, and hence it is a network and not soluble. See structure ( f ) in Figure 2.10, which is sometimes called a conter-minously grafted copolymer.
2.7.4 Interpenetrating Polymer Networks
This is an intimate combination of two polymers in network form. At least one of the polymers is polymerized and/or cross-linked in the immediate presence of the other (27). While ideally the polymers should interpenetrate on the mol-ecular level, actual interpenetration may be limited owing to phase separation.
(Phase separation in polymer blends, grafts, blocks, and interpenetrating polymer networks is the more usual case and is discussed in Chapters 4 and 13).
2.7.5 Other Polymer–Polymer Combinations
According to new nomenclature, a polymer blend is accorded the connective –blend–. Many of these blends are prepared by highly sophisticated methods and are actually on a parallel with blocks, grafts, and interpenetrating polymer networks.
Block copolymers may also be arranged in various star arrangements. In this case polymer A radiates from a central point, with a number of arms to be specified. Then polymer B is attached to the end of each arm.
2.7.6 Separation and Identification of Multicomponent Polymers The methods of separation and identification of multicomponent polymers are far different from the methods described previously for the statistical type of polymer. First, only the blends are separable by extraction techniques. The remainder are bound together by either chemical bonds or interpenetration.
The interpenetrating polymer networks and the conterminously grafted poly-mers are insoluble in all simple solvents and do not flow on heating. The graft and block copolymers, on the other hand, do dissolve and flow on heating above Tfand/or Tg.
Most, but not all, of the multicomponent polymer combinations exhibit some type of phase separation, as is discussed in Chapters 4 and 13. Where the polymers are stainable and observable under the electron microscope, char-acteristic morphologies are often manifest. The principal polymers that are
stainable include the diene types and those containing ester groups. For those combinations exhibiting phase separation, two characteristic glass tempera-tures are also usually observed.