Poly 4-methyl-hexene

MHE) and of isopropylvinylether with sec-butylvinylether. The binary mixtures of isotactic poly-4-methylpentene with isotactic poly-4-methyl-hexene and of isotactic poly-i-propylvinylether with isotactic poly-see-butylvinylether were also examined. 

Only two types of polymers are considered here. These are isotactic poly(5-methyl-hexene-l) (P5MH1), with a non-chiral side chain (for the sake of comparison) and mainly isotactic poly(4-methyl-hexene-l) (P4MH1). The side chain of the latter polymer is chiral since the two substituents of the carbon in the p position are a methyl and an ethyl group. Polymers that are made only of the S or the R conformers - in other words the true chiral polymers (P(S)4MH1 and P(R)4MH1), the racemic copolymer of the (R) and (S) monomers (P(R, S)4MH1) and of course the racemic blend of the two enantiomeric polymers - are available. 

Additional examples of isomorphism include poly(isopropyl vinyl ether)/poly(sec-butyl vinyl ether) (PiPVE/PsBVE) and isotactic poly(4-methyl pentene)/isotactic poly(4-methyl hexene) (iP4MP/iP4mH) [314]. PiPVE/PsBVE blends were cocrystalline over the entire composition range, whereas iP4MP/iP4mH blends were isomorphic only in the range of 0-25 wt% of either constituent. For these blends, the chain axes and chain symmetries are identical, thus isomorphic behavior is possible. HDPE/LLDPE blends have been noted to be cocrystalline within limits of the comonomer incorporation in LLDPE. A comprehensive study of this... 

Controlled block copolymerization of olefins with polar monomers was performed with a lanthanide complex by the successive polymerization of hexene (or pentene) and methylmethacrylate (or caprolactone). Polyhexene-block-poly(methyl methacrylate), polyhcxcnc-fo/ock-polycaprolactone, poly-pentene-fc/ock-poly(methyl methacrylate), and polypentene-Wock-polycapro-lactone were synthesized using a lanthanide complex as initiator [140-143]. 

The crystal polymorphism of the chiral but racemic P5MH1 is, to some extent, very reminiscent of that of isotactic polypropylene. It exists in two crystal modifications. One crystal modification is stable at high temperature, and was observed early on by Corradini et al [39]. Its structure has been redefined as a chiral, frustrated one based on a trigonal cell with three threefold helices per cell. We have also discovered a second crystal modification produced from solution. It has an orthorhombic unit cell that contains four chains in - again - three-fold helical conformation, for which one must assume coexistence of two right- and two left-handed helices. Contrary to the a and ft phases of iPP, the frustrated structure of poly( 5-methyl-hexene-1) is the more stable one [40]. 

Fig. 7 DSC melting and crystallization curves of isotactic poly(S)-4-methyl-hexene-l. Note the two melting peaks (at 193.5 and 227.4 °C, respectively, AH 2.5 and 1.5cal/gram) and two crystallization peaks (at 201 and 120 °C, respectively same AH), as well as the significant temperature gap ( 74 °C) between the lower crystallization and melting processes. (From [44])...

A value of 4> = 292 was found for poly [(S)-4-methyl hexene-1], whereas the value for the hydrogenated monomer chosen as model compound is only 9.9 (in each case, expressed in units of 10" deg dm" cm mol" ). The increased value for the polymer undoubtedly results from the contribution of the helical structure. 

A polymer of unspecified chain length is named with a prefix poly. The prefix is then followed by the name of the monomer. Also, it is customary to use the common names of monomers and polymers. For instance, common names for phenylethene and polyphenylethene are styrene and polystyrene. This, however, is not an inflexible rule. When the monomer is named by a single word, then the prefix poly is simply added like polyethylene for a polymer of ethylene or polystyrene for a polymer of styrene. If, however, the monomer is named by two words or is preceded by a number, like methyl methacrylate, parentheses are used. Examples are poly(methyl methacrylate) or poly(l-hexene). 

Further confirmation of the structure and tacticity of poly/5-methyl-l,4-hexadiene)was obtained from X-ray diffraction and u-NMR data of its hydrogenated polymer (Scheme 2). The hydrogenated polymer sample showed a highly crystalline pattern (Figure 7), with diffraction spots that were well defined. This pattern was identical to that of isotactic poly(5-methyl-l-hexene) as reported in the literature (26) (measured identity period, 6.2 A lit., 6.33 A). 

Figure 8. 13C-NMR spectra of (A) hydrogenated poly(5-methyl-l,4-hexadiene) and (B) poly(5-methyl-l-hexene).

Data concerning the chain conformations of isotactic polymers are reported in Table 2.1. In all the observed cases the torsion angles do not deviate more than 20° from the staggered (60° and 180°) values and the number of monomeric units per turn MIN ranges between 3 and 4. Chains of 3-substituted polyolefins, like poly(3-methyl-l-butene), assume a 4/1 helical conformation (T G )4,45,46 while 4-substituted polyolefins, like poly(4-methyl-1-pentene), have less distorted helices with 7/2 symmetry (T G )3.5-39 When the substituent on the side group is far from the chain atoms, as in poly(5-methyl-1-hexene), the polymer crystallizes again with a threefold helical conformation (Table 2.1). Models of the chain conformations found for the polymorphic forms of various isotactic polymers are reported in Figure 2.11. 

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