Polybutadiene Combs

Polybutadiene- comb- (polyethylene polypropene) Comb polymer with butadiene backbone and side chains of polyethylene and polypropene... 

Figure9.18 Predictions of the hierarchical model compared with storage and loss moduli data for polybutadiene combs at 7= 25 °C. From Park and Larson [49].

In several cases the melt viscosity of a series of lightly-branched polymers has been determined as a function of MW, and compared with that of linear polymers, and it has been found or may be deduced from the published data that there is a cross-over molecular weight, below which the branched polymer is less viscous, but above which it more viscous, than the linear polymer of equal MW. This behaviour is observed with some comb-shaped polystyrenes (35) and poly(vinyl acetate)s (59, 89), star polybutadienes (57, 58, 123), and randomly-branched polyethylenes (56,61). Jackson has found (141) that if the ratio ZJZC of the number of chain atoms at the cross-over point, Zx, to the number at the kink in the log 0 — logM curve, Zc, [as given in Ref. (52)], is plotted against nb, the number of branches, a reasonable straight line is obtained, as in Fig. 5.1. 

The data for the three types of star-branched polymers show a decrease in rj on branching, with the exception of the trichain and tetrachain polybutadiene of longer branch length, for which the reverse is true. The data for most of the randomly branched and comb-type poly-vinylacetates nearly all show higher values than the linear polymer, excepting for two samples containing short branches, for which the reverse is true. 

Polybutadiene having a comb-type structure was prepared by adding additional butadiene to metalated polybutadiene. The grafted portion of the polymer, however, has a predominantly vinyl structure because of the presence of TMEDA. 

Unsaturated elastomers can be readily metallated with activated organolithium compounds in the presence of chelating diamines or alkoxides of potassium or sodium. For example, polyisoprene, polybutadiene, styrene-butadiene copolymers, and styrene-isoprene copolymers can be metallated with n-butyllithium TMEDA complexes (1/1 or 1/2 ratio) to form allylic or benzylic anions. The resulting allylic anion can be employed as an initiator site to grow certain branched or comb polymer species. These polymers can include polystyrene, which would form hard domains, or polybutadiene, which forms soft domains. 

Figure 2. Universal calibration plot. The figure symbols correspond to the following , linear polystyrene (PS) O, "comb" type polystyrene +, "star" type polystyrene A, heterograft copolymer x, polymethylmethacrylate (PMMA) 9, polyvinylchloride v > graft copolymer (PS/PMMA) , polyphenyl si loxane , polybutadiene, (redrawn with permission from ref. 52).

Fig. 26. Universal calibration curve for SEC. Polystsrrene (linear) O polystyrene ( comb ) + polystyrene ( star ) A polystyrene-poly(methylmethacrylate) copolymer (heterograft) x poly(methylmethacrylate) (linear) poly(vinylchloride) V polystyrene-poly(methylmethacrylate) copolymer (graft-comb) Bpolylphenyl siloxane) A polystyrene-poly(methylmethacrylate) copolymer (statistical-linear) n polybutadiene. From Ref 31.

Femyhough, C.M., Young, R.N., Poche, D., Degroot, A.W., Bosscher, F., Synthesis and characterization of polybutadiene and pofy(ethylene-l-butene) combs. Macromolecules 2001, 34 7034—7041. 

Cycloolefin macromonomers have been recently used in ring-opening metathesis polymerization reactions to manufacture block and graft copolymers of novel macromolecular architectures [84]. For this purpose, a- and co-norbornenyl-polybutadiene macromonomers, a-NBPB (R = CH2) and co-NBPB (R = COO), were reacted in the presence of molybdenum alkylidene complex, Mo(NAr)(CHtBu)(OtBu)2, to form polynor-bornene-polybutadiene diblock copolymers (117), with comb-like structure [85] [Eq. (49)]. 

Fig. 3.26 Universal calibration curve for crosslinked polystyrene gels with tetrahydrofuran as solvent %y linear polystyrene 0 branched polystyrene (comb type) +, branched polystyrene (star type) A, branched block copolymer of styrene methyl methacrylate x, poly (methyl methacrylate) poly (vinyl chloride) V, graft copolymer of styrene methyl methacrylate , polybutadiene (reprinted with permission from Comprehensive Polymer Science, copyright 1989, Pergammon Press pic).

By means of anionic polymerization, it is possible to produce in the laboratory linear polymers that are nearly monodisperse and have many types of branching such as multi-armed stars and combs and H-shaped molecules. For example, there have been reports of studies of anionically polymerized polystyrene, polybutadiene, and polyisoprene. An example of the anionic polymerization of a branched polymer is the technique of Roovers and Toporowski [22] for making comb polystyrenes. The varieties of model branched polymer that can be produced today by means of block polymerization and coupling chemistries include stars, H-shaped molecules, super-H molecules (multi-armed stars at both ends of a backbone segment), and combs of various types [23]. So-called pom-pom polymers are of special interest, because their rheological behavior has been modeled by McLeish and Larson [24]. These molecules have several arms at each end of a central crossbar, and polybutadienes having this structure have been synthesized [25,26]. 

Figure 5.31 Van-Gurp Palmen plot (loss angle versus magnitude of complex modulus) of data for linear (circles), star-branched (triangles), and comb (squares) polymers prepared by the hydrogenation of anionically polymerized polybutadienes.The branching structure hasadistinct effect on the shape of the curve. From Lohse etal. [119].

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