Methylene groups polybutadiene

It is of interest to point out that polypentenamer (obtained by ring opening polymerization of cyclopentene) that possesses a structure similar to that of 1,4-polybutadiene, with an extra methylene group in each monomeric unit, also undergoes cis—trans isomerization [47]. However, vinyl group formation according to... 

Cyclooctadienyl substituents at the methylene groups in c/s-1,4-polybutadiene can be introduced by the radical-induced reaction with cycloocta-1,5-diene. Metathesis degradation of the product with tra 5-oct-4-ene shows that the substitution reaction is accompanied by double-bond shift reactions (Hummel 1990a). 

At temperatures above their Tg, the resonance spectrum of noncrystalline polybutadiene (PB) (Fig. 8a) is clearly different from that of the semicrystalline polyethylene (Fig. 8c). Amorphous PB exhibits a narrow Lorentzian line shape with a width of 0.2 G. In contrast, the PE spectrum comprises two components, ie, narrow and broad line shapes. When the spectra of semicrystalline polymers are recorded in the glassy state (Figs. 8b and 8d), only abroad component is observed. This indicates that the line shape corresponds to molecular mobility and the line width reflects a correlation (or relaxation) time. Therefore, the broad and narrow components of semicrystalbne PE (Fig. 8c) are related to protons of methylene groups in rigid and mobile (amorphous) environments, respectively. On the basis of this, it was proposed that the degree of crystallinity could be determined by resolving the area of the broad component (rigid phase) from the spectrum. 

The singlet oxygen photooxidation of polymers with pendant double bonds depends on the presence of methylene groups iy close vicinity to the double bond. For example 1.2-polybutadiene <1 08 not react with singlet oxygen whereas 1.2-poly(l,4-hexadiene) is reactive ... 

The proximity of the methyl group to the double bond in natural rubber results in the polymer being more reactive at both the double bond and at the a-methylenic position than polybutadiene, SBR and, particularly, polychlor-oprene. Consequently natural rubber is more subject to oxidation, and as in this case (c.f. polybutadiene and SBR) this leads to chain scission the rubber becomes softer and weaker. As already stated the oxidation reaction is considerably affected by the type of vulcanisation as well as by the use of antioxidants. 

Hydroxy-terminated polybutadiene (8) (HTPB) has been treated with dinitrogen pentoxide in methylene chloride. The product (9) is an energetic oligomer but is unlikely to find application because of the inherent instability of /3-nitronitrates." Initial peroxyacid epoxidation of some of the double bonds of HTPB followed by reaction with dinitrogen pentoxide yields a product containing vtc-dinitrate ester groups and this product (NHTPB) is of much more interest as an energetic binder (see Section 3.10)." ... 

Prepolymers of polybutadiene diol (M. 2500), polytetramethylene oxide diol (M. 1400 and M. 2100), and prepolymer of polypropylene oxide diol (M. 1400) were used to obtain segmented elastomers SPU-1 to SPU-5. Prepolymers were prepared by reaction of appropriate diol with 2,4-toluene diisocyanate (2 moles per one mole of diol). Prepolymers of polytetramethylene oxide diol (elastomers SPU-1 and SPU-4) were cured by methylene-bis-o-chloroaniline, MOCA, or by mixture of MOCA and polytetramethylene oxide diol (SPU-2 and SPU-3). SPU-5 samples, prepared from prepolymer of polypropylene oxide diol, were cured by MOCA, and prepolymer of polybutadiene diol was cured by a mixture of MOCA and polytetramethylene oxide diol (SPU-6). Various concentrations of hard segments, Cj, in SPU were set by a ratio of mixture components and molecular weight of prepolymer (Table 10.14). Excess of NCO-groups was in the range 1.03-1.06 for SPU-1 to SPU-5 and 0.99 for SPU-6. All samples were cured at 80°C for 4 days. The... 

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