Polybutadiene thermal degradation

Discoloration. When PVC, free of plasticizer or stabilizer, is compression molded in air at 200°C under adequate pressure (c.g., 500-6000 psig), thermal degradation results in discoloration to a pink to brown colored film. When the modified PVC containing as little as 3% of grafted cis-1,4-polybutadiene was pressed under the same conditions, the resultant film was essentially colorless or no more than faintly discolored. 

The compression-molded part, by definition, does not have flow-induced orientation. Comparison of compression-molded part properties with those of an injection-molded part can show the effect of melt temperature on properties. In the compression-molded article without flow-induced orientation, the impact strength remains constant until a certain melt temperature is surpassed and then decreases. This thermal degradation effect can be attributed to the polybutadiene component, which acts as an initiation site for oxidative degradation of the matrices. 

MAJOR APPLICATION H-H PVC is mostly studied in academic field to understand its structure/property relationship, thermal degradation behavior, and mechanism. Its properties are compared to those of commercial head-to-tail PVC. Pure H-H PVC has no significant industrial applications. H-H PVCs containing 40-65 wt% of Cl, also called chlorinated polybutadiene rubber-resins, are used for coating, paint-based applications and the preparation of threads, tires, tubings, and films, etc. 

During torque rheometer stability studies of blends of PVC and ABS, we have observed a reduction in thermal stability for the blend over each component separately which causes a premature increase in melt viscosity. DSC, TGA and IR Spectroscopic analyses show that this lower stability is a result of thermal degradation in all three (SAN, PBD, and PVC) phases of the blend and most rapidly to the polybutadiene rubber phase. 

Studies on the thermal degradation under vacuum of reprecipitated polybutadiene at 395 °C indicate that the initial rate of the process (up to around 20% decomposition) is rather high (Figure 2.3), but later on it falls gradually, with a linear dependence on the quantity of volatile products. The activation energy of the thermal degradation of polybutadiene, calculated from its initial rates, is 259.2 kj/mol [5]. 

Figure 2.3 Dependence of the rate of thermal degradation of polybutadiene on the degree of decomposition at temperatures of 1 345 °C, 2 348 C, 3 351 C and 4 ...

The molecular mass of the wax-like compounds, which are volatile at the decomposition temperatures and comprise the basic mass (82-97%) of the products of the thermal degradation of polybutadiene is 739. The average yield of monomer on degradation of poly butadiene does not exceed 1.5% mass of the total quantity of volatile compounds, a result which may be associated with both the partial polymerisation of the monomer produced, which is kept at room temperature, and the formation of vinylcyclohexane ... 

The thermal degradation of diene polymers was the subject of several studies [456, 457]. The scheme for polyisoprene and polybutadiene degradation was postulated in part by Golub and Garguila [458, 460]. It is based on infra-red spectra and NMR studies of the products ... 

Cansarz, I. and Laskawski, W. 1979. Peroxide-initiated crosslinking of maleic anhydride-modified low-molecular-weight polybutadiene. II. Crosslinking degree and thermal degradation of cured polymers. Journal of Polymer Science, Polymer Chemistry Edition 17 1523-1529. 

Polyisobutylene of low molecular weight was synthesized by a Wurtz type reaction from l,4-dibromo-2,2,3,3 tetramethylbutane. Polyacrylates were obtained from alternating copolymerization of symmetric internal olefins or ethylene with maleic anhydride followed by quantitative esterification. Poly(vinyl halides) were prepared from cis-1,4-polybutadiene by chlorination (H-H PVC) or bromin-ation (H-H PrBr). The polymers were characterized and their chemical, thermal, degradation solution, melt and blending behavior was studied. 

The presence of one polymeric component with lower structural stability stimulates the oxidative degradation of the system [0501], For polybutadiene-coated cellulose fiber the start of thermal degradation of cellulose takes place either in the mass of cellulose or in polybutadiene outer layer (Fig. 15) [92F1]. The addition of palm filler in polypropylene decreases the system stability because of the instability of cellulose component (Fig. 16) [05A1]. 

Natural rubber/cw-1,4-polybutadiene (NR/BR) blends (70/30 mass ratio) have been widely used in the tire industry. Many nanocomposites based on organo-montmorillonite (OMMT)/rubber blends have been investigated. However, relatively little attention had been paid to binary rubber hybrids/ montmorillonite nanocomposites, and according to Zheng Gu et ah, no studies existed dealing with OMMT/NR/BR nanocomposites. So, the authors described the preparation of OMMT/NR/BR nanocomposites by direct mechanical blending and determined the cure characteristics, static mechanical properties, dynamic mechanical properties, and thermal stability of the nanocomposites. OMMT/NR/BR nanocomposites had exactly the same onset decomposition temperature and lower thermal degradation rate as the NR/BR blends. 

Grimbley and Lehrle [20] and Beck [21] have studied the thermal degradation mechanism of polybutadiene. This polymer was shown to degrade through parallel degradation with random scission plus secondary depropagation of oligomers formed by random scission. Only a small contribution was made by the transfer process. 

From the results obtained by thermal decomposition of both low-molecular weight vicinal dichlorides in the gas phase [74,75] and of the copolymers of vinyl chloride and /rthermal instability of PVC to the individual head-to-head structures. Crawley and McNeill [76] chlorinated m-1,4-polybutadiene in methylene chloride, leading to a head-to-head, and a tail-to-tail PVC. They found, for powder samples under programmed heating conditions, that head-to-head polymers had a lower threshold temperature of degradation than normal PVC, but reached its maximum rate of degradation at higher temperatures. 

ESRI methods have been developed in our Detroit laboratory for the study of heterophasic systems such as ABS [14,40,59,87-89] and HPEC [61,90], both containing bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770) as the stabilizer, and exposed to thermal treatment and UV irradiation. The HAS-NO provided the contrast necessary in the imaging experiments. The major objectives were to examine polymer degradation under different conditions to assess the effect of rubber phase, polybutadiene (PB) in ABS and ethylene-propylene rubber (EPR) in HPEC, on the extent of degradation and to evaluate the extent of... 

---