Olefin structures copolymerization

Polymeric phosphine oxides are made by a variety of condensation- and addition-polymerization methods. Radical-initiated copolymerization of compounds with RPCI2 structures with olefins produces polydichlorophosphanes, which on hydrolysis yield polyphosphine oxides (37). Where p-xylylene (produced by pyrolysis) is the olefin, this copolymerization affords quite tenacious high-temperature thermoplastic phosphine oxides (38). 

Methyl-2-furaldehyde gave a similar overall behaviour, but a penultimate effect was observed in its copolymerization with isopropenylbenzene whereby two molecules of the aldehyde could add together if the penultimate unit in the growing chain was from the olefin. This was borne out by the copolymers composition and spectra. The values of the reactivity ratios showed this interesting behaviour rx = 1.0 0.1, r2 = 0.0 0.1. An apparent paradox occurred the aldehyde, which could not homo-polymerize, had equal probability of homo- and copolymerization and the olefin, which homopolymerized readily, could only alternate. The structure arising from this situation was close to a regular sequence of the type ... 

We showed (7) earlier that copolymers of higher a-olefins, particularly 1-hexene, with 5-methyl-1,4-hexadiene can be sulfur-cured readily and that they contain unsaturation approximating the level of the methylhexadiene charged. In view of this and the excellent durability (8) during flexing exhibited by vulcanizates of such copolymers, we were interested in determining the copolymer structure and the reactivity ratios of 1-hexene and 5-methyl-l,4-hexadiene during copolymerization. 

In the polymer field, reactions of this type are subject to several limitations related to the structure and symmetry of the resultant polymers. In effect, the stereospecific polymerization of propylene is in itself an enantioface-diflferen-tiating reaction, but the polymer lacks chirality. As already seen in Sect. V-A there are few intrinsically chiral stractures (254) and even fewer that can be obtained from achiral monomers. With two exceptions, which will be dealt with at the end of this section, optically active polymers have been obtained only from 1- or 1,4-substituted butadienes, fiom unsaturated cyclic monomers, fiom substituted benzalacetone, or by copolymerization of mono- and disubstituted olefins. The corresponding polymer stmctures are shown as formulas 32 and 33, 53, 77-79 and 82-89. These processes are called asymmetric polymerizations (254, 257) the name enantiogenic polymerization has been recently proposed (301). 

A polysulfone is characterized by the presence of the sulfone group as part of its repeating unit. Polysulfones may be aliphatic or aromatic. Aliphatic polysulfones (R and Rr are alkyl groups) were synthesized by radical-induced copolymerization of olefins and sulfur dioxide and characterized many years ago. However, they never demonstrated significant practical utility due to their relatively unattractive physical properties, not withstanding the low cost of their raw materials (1,2). The polysulfones discussed in this article are those based on an aromatic backbone structure. The term polysulfones is used almost exclusively to denote aromatic polysulfones. 

The catalyst [Pd(Me-DUPHOS)(MeCN)2](BF4)2 was also effective in the alternating asymmetric copolymerization of aliphatic a-olefins with carbon monoxide [27,28]. The polymer synthesized in a CH3N02-CH30H mixture has both 1,4-ketone and spiroketal (10) units in the main chain. The propylene-CO copolymer consisting only of a 1,4-ketone structure shows [ ]D +22° (in (CF3)2CHOH), and the optical purity of the main chain chiral centers is over 90% as estimated by NMR analysis using a chiral Eu shift reagent. 

In this article, we would like to review recent advances in polymer hybrids based on polyolefins and to classify them into four methodologies, namely, PO macroinitiator, PO macromonomer, reactive PO and living copolymerization of olefins, with their well-defined structures and applications. 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

Although the structures of these copolymers were not indicated, it is probable that the olefin and polar monomer are alternating units in accordance with the scheme in Reaction 23. It is also probable that the presence of excess polar monomer in the copolymer, as indicated in some examples, results from copolymerization of the polar monomer-com-plexed polar monomer complex or with the olefin-complexed polar monomer complex or concurrent homopolymerization of the two complexes. 

The copolymerization of furan and 2-methylfuran with dienophiles such as maleic anhydride leads to polymer structures with furan pendent functionality. Furan, 2-methylfuran, and 2,5-dimethylfuran have been copolymerized with acrylic monomers (51,52) and acrylonitrile (52,53). The furan ring of furan, 2-methylfuran, and 2,5-dimethylfuran participates as a diene in a free radical copolymerization with acrylonitrile. The initial step for furan and for 2,5-dimethylfuran is the attachment of an acrylonitrile radical at the 2-position, but for 2-methylfuran, the attack is at the-5-position. Propagation proceeds by the attack of the furan radical on an acrylonitrile molecule, to leave one olefinic bond in the structure derived from the furan ring. If this bond is in the 4,5- or 2,3-position, it may be involved in a second additional reaction by the return of the propagating chain. 

The copolymerization parameter rt which indicates how much faster an ethene is incorporated in the growing polymer chain than an a-olefin, when the last inserted monomer was an ethene unit, lies between 1 and 60 depending on the kind of comonomer and catalyst. The copolymerization parameter r2 is the analogous ratio for the a-olefin. The product r r2 is important for the distribution of the comonomer and is close to unity when using C2 symmetric metallocenes, indicating a randomly distributed comonomer. It is less than unity with a more alternating structure for Cs-symmetric catalysts [62-65] (Table 5). 

Sections of polymer chains must be capable of packing together in ordered periodic arrays for crystallization to occur. This requires that the macromolecules be fairly regular in structure. Random copolymerization will prevent crystallization. Thus, polyethylene would be an ideal elastomer except for the fact that its very regular and symmetrical geometry permits the chains to pack together closely and crystallize very quickly. To inhibit crystallization and confer elastomeric properties on this polymer, ethylene is commonly copolymerized with substantial proportions of another olefin or with vinyl acetate. 

---