Poly natural rubber

Coordination polymerization of isoprene using Ziegler-Natta catalyst systems (Section 6 21) gives a material similar in properties to natural rubber as does polymerization of 1 3 butadiene Poly(1 3 buta diene) is produced in about two thirds the quantity of SBR each year It too finds its principal use in tires... 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

It was found that the amount of chlorine that could be removed (84-87%) was in close agreement to that predicted by Flory on statistical grounds for structure Figure 12.10(a). It is of interest to note that similar statistical calculations are of relevance in the cyclisation of natural rubber and in the formation of the poly(vinyl acetals) and ketals from poly(vinyl alcohol). Since the classical work of Marvel it has been shown by diverse techniques that head-to-tail structures are almost invariably formed in addition polymerisations. 

A number of higher poly(vinyl ether)s, in particular the ethyl and butyl polymers, have found use as adhesives. When antioxidants are incorporated, pressure-sensitive adhesive tapes from poly(vinyl ethyl ether) are said to have twice the shelf life of similar tapes from natural rubber. Copolymers of vinyl isobutyl ether with methyl acrylate and ethyl acrylate (Acronal series) and with vinyl chloride have been commercially marketed. The first two products have been used as adhesives and impregnating agents for textile, paper and leather whilst the latter (Vinoflex MP 400) has found use in surface coatings. 

Class and Chu [34] have studied the tackification of natural rubber and SBR over a wide range of resin concentrations for several tackifiers. From their graphical data it can be estimated that 1 1 tackification (by weight) with a poly(/-butyl styrene) resin, MW 850 and Tg = 59°C, gives a PSA with Tg about — 13°C, and storage modulus, G about 8.8 x 10 Pa, well within the PSA window. 

Wi is the weight fraction of the elastomer, W2 the tackifier, W3 a further compatible additive, such as an oil, and so forth, for the remaining components in the formulated PSA. Application of the Fox equation to the poly (/-butylstyrene) tackified natural rubber adhesive (cited above) gives a value of —11°C, in good agreement with the interpolated value of — 13°C. 

Emulsion polymerization is the most important process for production of elastic polymers based on butadiene. Copolymers of butadiene with styrene and acrylonitrile have attained particular significance. Polymerized 2-chlorobutadiene is known as chloroprene rubber. Emulsion polymerization provides the advantage of running a low viscosity during the entire time of polymerization. Hence the temperature can easily be controlled. The polymerizate is formed as a latex similar to natural rubber latex. In this way the production of mixed lattices is relieved. The temperature of polymerization is usually 50°C. Low-temperature polymerization is carried out by the help of redox systems at a temperature of 5°C. This kind of polymerization leads to a higher amount of desired trans-1,4 structures instead of cis-1,4 structures. Chloroprene rubber from poly-2-chlorbutadiene is equally formed by emulsion polymerization. Chloroprene polymerizes considerably more rapidly than butadiene and isoprene. Especially in low-temperature polymerization emulsifiers must show good solubility and... 

The elasticity of a polymer is its ability to return to its original shape after being stretched. Natural rubber has low elasticity and is easily softened by hearing. Flowever, the vulcanization of rubber increases its elasticity. In vulcanization, rubber is heated with sulfur. The sulfur atoms form cross-links between the poly-isoprene chains and produce a three-dimensional network of atoms (Fig. 19.17). Because the chains are covalently linked together, vulcanized rubber does not soften as much as natural rubber when the temperature is raised. Vulcanized rubber is also much more resistant to deformation when stretched, because the cross-... 

The polymer in natural rubber consists almost entirely of ci -poly(isoprene) (1.6). The molecules are linear, with relative molar mass typically lying between 300 000 and 500 000. The macromolecular nature of rubber was established mainly by Staudinger in 1922, when he hydrogenated the material and obtained a product that retained its colloidal character, rather than yielding fragments of low relative molar mass. 

Polymers containing each of these configurations are known, the most common being the cis- A and the 1,4-isomers. The first of these, poly(c/ -l,4-isoprene), is the macromolecular constituent of natural rubber the second is the material known as gutta percha. The latter, unlike natural rubber, has no elastomeric properties, but has a leathery texture. It has been used for diverse applications such as golf-ball covers and as an insulating material for the trans-Atlantic cables of the late nineteenth century. 

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

Anthony, Caston, and Guth obtained considerably better agreement between the experimental stress-strain curve for natural rubber similarly vulcanized and the theoretical equation over the range a = 1 to 4. KinelP found that the retractive force for vulcanized poly-chloroprene increased linearly with a — l/a up to a = 3.5. 

EPR Ethylene-propylene rubber NR Natural rubber poly isoprene... 

The word "polymer" (first proposed by Berzelius in 1833) is made of "poly" from the ancient Greek word "mlvq" meaning "many" and "pepot " meaning "part". Polymers are molecules built up from numerous identical chemical "units" spatially repeated to form a chain. From the early times and still nowadays, a distinction is often made between "natural" and "synthetic" polymers, but it is somewhat artificial as natural polymers can now sometimes be synthesized (e.g., synthetic "natural rubber") and some synthetic polymers, which are never found in nature, can be synthesized by natural ways (enzymatic syntheses). 

A similar comparison can be made with cis-poly(isoprene), natural rubber, by taking advantage of the fact that the polymer is very slow to crystallize [164], Consequently, the comparison can be made between the supercooled, noncrystalline polymers at 0°C and the semi-crystalline polymer (31% crystalline) at the same temperature. The Tlc values for each of the five carbons involved were again found to be the same for the completely disordered polymer and the semicrystalline one, so that a similar conclusion can be made with regard to their chain structure. 

When we compared the viscosities of solutions of natural rubber and of guttapercha and of other elastomers and later of polyethylene vs.(poly)cis-butadiene, with such bulk properties as moduli, densities, X-ray structures, and adhesiveness, we were greatly helped in understanding these behavioral differences by the studies of Wood (6) on the temperature and stress dependent, melting and freezing,hysteresis of natural rubber, and by the work of Treloar (7) and of Flory (8) on the elasticity and crystallinity of elastomers on stretching. Molecular symmetry and stiffness among closely similar chemical structures, as they affect the enthalpy, the entropy, and phase transitions (perhaps best expressed by AHm and by Clapeyron s... 

Starch (1), Cellulose (2), Cellulose Methyl Ether (3), Oxy-cellulose (4), PVA (5), Partially Hydrolyzed PVAc (6), Silk (.2), Wool (7), Hide-Powder (8), Natural Rubber Latex ( ), Synthesized Poly-(ot-Amino Acids) (10), Nylon-6 (11), Nylon-3 (12), Ot-Amylase (13), Lysozyme (14), RNA (15), Polyacrylonitrile (16), Polyvinyl-sulfonate (17) ... 

C. J. Carman Earlier in your talk you showed the carbon Ti data and NOEF for partially crystalline and amorphous poly-isoprenes. Was this a natural rubber which had been allowed to crystallize to different degrees or was this a synthetic rubber ... 

Pang H, Liao B, Huang Y, Cong G (2002) Studies on the blends of CO2 copolymer. IV. Natural rubber/poly(propylene carbonate) systems. J Appl Polym Sci 86 2140-2144... 

Natural rubber and other 1,4-poly-1,3-dienes are cyclized by treatment with strong protonic acids or Lewis acids [Golub, 1969 Subramaniam, 1988]. The reaction involves protonation of the double bond (Eq. 9-40) followed by cyclization via attack of the carhocation on the double bond of an adjacent monomer unit (Eq. 9-41). Some bicyclic and polycyclic... 

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