| Natural rubber becomes an irreplaceable material in national defense industry and aerospace according to its excellent comprehensive mechanical performance. It is the important strategic resources of country. The excellent properties are closely related to the structures of branch chain and terminal groups in natural rubber molecular chain. This study has the important significance of theory and practice. It is benefited to probe into the reason of natural rubber excellent properties. It is helpful to study the high quality rubber latex and improving the performance of synthetic rubber. This thesis has studied the terminal groups, branch chain and the change of branched chain in the process of storing.Through the handling method of deproteinization by urea, saponification and amination, the samples of deproteinization natural rubber (DPNR), saponification natural rubber (SPNR) and amino-saponification natural rubber (SPNR-a) has been prepared. The instruments such as Gel Permeation Chromatograph (GPC), Kjeldahl Auto Analyzer,Fourier Transform Infrared Spectrometer (FTIR) and Nuclear Magnetic Resonance (NMR)Spectrometer are used. The methods such as nuclear magnetic resonance hydrogen spectrum method and nitrogen atom labeling method are exerted to characterize the branch chain and characteristic groups. The researches show that during the process of formation and storing, characteristic groups could be formed with enzyme and oxygen. These abnormal groups reacted with non-rubber components and other molecular chain to form branch chain. The results illustrated that there are four characteristic groups mainly. They are epoxide group, hydroxyl, aldehyde groups and carboxyl groups. The contents of them are 0.14%、0.07%、0.11%、0.01% respectively. In addition of this, 3,4-polyisoprene has been detected in natural rubber molecular chain with a content of 0.36%.During the process of storing, characterization of natural rubber sample in different time, the content variation tendency of characteristic groups in natural rubber branch chain has been found. Generally, contents of characteristic groups increased as the extension of storing time. Epoxide group has a higher growth rate in the initiating and then, the rate slowed down and was stable at last. The rate of hydroxyl is hardly to growth in the beginning. The rate growths fast after two weeks and slows to be stable in the end. The contents of aldehyde groups and carboxyl groups are growth also during storing. The rate of carboxyl groups is faster than aldehyde.The co-terminal groups of natural rubber molecular chain are comprised of variable dimethylallyl linked with 2 trans-isoprene. There were no signal of methyl in dimethylallyl in 13C-NMR spectrum. And there were no signal of new structure either. The methyl of dimethylallyl changed to detected-groups was presumed. According to the fact that the reaction mechanism of branches in natural rubber molecular chain and the characteristic of higher reactivity in terminal of chain, a hypothesis that the terminal groups of dimethylallyl changed to aldehyde group and carboxyl group was put forward. The assumption also proved by the fact that the ω-terminal groups can link with protein stably.a-terminal groups are phosphate or pyrophosphate linked with Phospholipid by hydrogen bond. It is proved by the signal peak of pyrophosphate and the signal of hyamine in phosphatidylcholine. |
