Polymers cyclization

Isomeric polymers can also be obtained from a single monomer if there is more than one polymerization route. The head-to-head placement that can occur in the polymerization of a vinyl monomer is isomeric with the normal head-to-tail placement (see structures III and IV in Sec. 3-2a). Isomerization during carbocation polymerization is another instance whereby isomeric structures can be formed (Sec. 5-2b). Monomers with two polymerizable groups can yield isomeric polymers if one or the other of the two alternate polymerization routes is favored. Examples of this type of isomerism are the 1,2- and 1,4-polymers from 1,3-dienes (Secs. 3-14f and 8-10), the separate polymerizations of the alkene and carbonyl double bonds in ketene and acrolein (Sec. 5-7a), and the synthesis of linear or cyclized polymers from non-conjugated dienes (Sec. 6-6b). The different examples of constitutional isomerism are important to note from the practical viewpoint, since the isomeric polymers usually differ considerably in their properties. 

At temperatures above 700° C, the rings in the cyclized polymer eliminate hydrogen and become aromatic. At temperatures above 900° C, the material loses N2 and generates char made from carbon. Other side chain reactions are discussed in Part 2 of this book. 

Consequently, two possible reaction paths, i.e., an intramolecular hh addition of uncyclized head radical and an intermolecular hh addition of cyclized head radical should be considered for the incorporating process of hh linkage into the derived poly-AAc chain. The discrimination of these two reactions is not easy, but the possibility of the occurrence of an intermolecular hh addition of cyclized head radical may be omitted by considering the steric crowding in the resulting cyclized polymer. Thus, the following three types of typical cyclopolymers will be given schematically. ... 

When common rings are incorporated in cyclopolymers as sequence units, radical and cationic initiators are known generally to give highly cyclized polymers (24). However, anionic initiators give a little or almost no cyclized units in the main... 

All polycondensation reactions proceeded in solutions (homogeneously) and yielded well-cyclized polymers, some characteristics of which are given in Table 18. 

From the above spectral data, the polymer structure is believed to be a linearly cyclized form as described in Scheme 20. Also, it has been known that the resulting cyclized polymers with conjugated double bonds have both five- and six-membered ring structures with a certain ratio, which should depend on the polymerization conditions, monomer structures, and the kinds of catalysts used. ieo... 

The polymers from the three compounds will have ladder-type structures. However, the polymers from compounds B and C will have at least one and two skeletal bond(s) per repeating unit while a double-cyclization polymer will result from compound A. The presence of one or two consecutive single bonds between aromatic units will enhance polymer susceptibility to thermal degradation. In principle, therefore, under identical conditions the thermal stability of the resulting polymers will be A more than B more than C. 

Polyetherlmldes Thermoplastic cyclized polymers of aromatic diether dianhydrides and aromatic diamine. Has good chemical, creep, and heat resistance, and dielectric properties. Processed by extrusion, thermo forming, and compression, injection, and blowmolding. Used in auto parts, jet engines, surgical instruments, industrial apparatus, food packaging, cookware, and computer disks. Also called PEI. 

The cationic cyclization of polyisoprene with acid catalysts is well documented. The same reaction in polybutadienes requires much more severe conditions, higher temperatures and more acidic catalysts, and until recently has received much less attention. A cyclized polymer with a reduction of 35—40% of the initial unsaturation, can be prepared by treating cis-l,4-polybutadiene with an alkyl aluminium chloride-organic halide catalyst in xylene solution at >100 C."- Such polymers, containing polycyclic sequences apparently at random within the chains, have better skid resistance and tensile properties than the parent polymer. Cyclization has been reported to accompany other reactions in polydienes, for example the radiation-induced addition of carbon tetrachloride to 1,2-polybutadiene, and the direct addition of a o j unsaturated carboxylic acids (acrylic and cinnamic) to polydienes and polypentenamers. It is reported that the thermal isomerization of cis-transoidal poly(phenylacetylene) is accompanied by cyclization, and additionally chain scission and aromatization at temperatures >120°C. ... 

Kodaira et al. compared the cyclopolymerizability of acryloylmethyl allyl-amine (AMAL), which gives polymers containing a considerable-amount of pendant allyl groups, with that of methacryloylmethyl allylamine (MAMAL), which is known to yield a highly cyclized polymer containing a small amount of pendant methallyl groups. 

Polyimides n Thermoplastic aromatic cyclized polymers of trimellitic anhydride and aromatic diamine. Have good tensile strength, dimensional stability, dielectric and barrier properties, and creep, impact, heat, and... 

The increase in molecular weight seems to indicate that not only did intrachain cyclization occur, but that some amount of inter-chain combination also took place, despite the dilute reaction conditions. Thin films of cyclized polymer had an initial modulus of 2.5—3.5 x 10 psi, tensile strength of 2,300—4,7(K) j i and an dongation of 1—2%. Rubbery poly(3,4-isoprene) had an dongation of 435% with an initial modulus and tensile strength of less than 500 pa. 

Kodatra T, Liu Q-Q, Satoyama M, Urushisaki M, Utsumi H (1999) Cyclopolymerization -XXVI. Repeating unit structure of cyclopolymers derived from N-substituted-N-allyl-2-(methoxycarbonyl)allylamines and mechanism of intramolecular cyclization. Polymer 40 6947-6954, and references therein... 

---