Hevea Bralizens Is Natural Rubber : A Review on the Macro- and Micro-Structure of the Hevea Hydrocarbon Chain in its Natural and Chemical Forms, Especially in the Mma Grafted Hevea Natural Rubbers By IR Spectroscopy Including the ATR FTIR Spectral Analyses

The Hevea natural rubber molecule can be considered to be polyisoprene, in which individual isoprene molecules are joined by 1, 4-addition. It is possible to represent this polyisoprene in terms of the cis and Trans isomeric forms. Natural rubber is obtained commercially from the sap of trees called Hevea Brasilensis. These trees yield latex containing approximately 35% rubber hydrocarbon and 60 % of the aqueous fluid and 4-5 % of the proteineous components, lipids, fatty acids and resinous residents. The hydrocarbon polymer consists of 97% cis-1, 4 units, 1% trans-1, 4-units and 3% 3, 4 units in a head-to-tail structure. It was established and reported that the average molecular weight of cis-1, 4-polyisoprene is approximately equal to 38 000 and nearly 558 isoprene units are there on average in a given polymer chain.

It was discussed that the infrared spectra and structures of the Hevea polyisoprene would be changed due to chemical reactions during the production /process like halogenations, grafting or even chemical substitution in the sulphur vulcanization. In addition to the tentative assignments, the R & D chemists also pointed out the possibility of the occurrence of the vibration modes with small differences in spectral bands for the interpretation of spectral bands produced by chemical reaction and modification during the process.

Thus, the manufacturing process of the MG50 latex , where 50 % 0f the methyl methacrylate ( MMA) was grafted, the main backbone of the Hevea polyisoprenoid chains remained almost the same, except where the molecular sites and configurations are chemically modified in terms of carboxylate, hydroxyl groups, and some minor cis- and trans- configuration changes. The individual spectral vibration or bending modes of molecular structure would be changed, but a little or without any significance, and the difference of the spectral bands are within the ± 2 cm -1. Any presence of the inorganic or metallic ions would not change these spectral mode significantly either, as shown in the IR spectral modes of the present MG50 latex.

The MMG grafted hydrocarbon poly-isoprenoid chains are stereo-structurally in tack, except changes in the chemical grafting occurred where the isomers configurations also evolved and changes slight, and some isomers are “ destroyed “ through the chemical reaction like carboxylate, ( - C O – OH ) or hydroxide ( - OH ) groupings, and some these are overlapped or overshadowed, for example, the sharp peak at 1274 cm - 1 with symmetrical stretching is assigned to the C =O bond , and also was reported that 1387, 1278 and 987 cm -1 as O – CH .It is interesting to note that the peaks 835 cm -1 and 1720 cm -1 , that are related to the – C = O or – CHO groups , or corresponding to carbonyl, aldehyde , ketone , carboxylic acid, or esters groups . 

Keywords: Hevea NR, macro and micro-structures of polyisoprene isomers, ATR and IR Spectral bands; Z1, 4, E-1, 4, 1.2, 3, 4 isomers; methyl methacrylate MMA, MG50 Latex, MG30 rubber, non-rubber components.