Long Chain Branching in Natural Hevea Rubber-Determination by Gel Permeation Chromatography

Abstract

The hevea brasiltensis rubber contains, besides the insoluble branched entities, linear and branched molecules in the soluble fraction. The branching characteristics found by analyzing fractions of different molecular weight of rubber coagulated from freshly tapped latex, stabilized with hydroxylamine hydrochloride are: (a) molecules with molecular weights above 6.5×104−1.0×105g/mol (depending on the branch points functionality) are branched and molecules below these limits are linear. (b) The relationship between number of branch points and the logarithm of molecular weight is linear. (c) The branching density is not independent of molecular weight, as has been assumed for several polymers, but it has a maximum. The maximum branching density found in the soluble fraction is between 10.2×10−6 and 31.6×10−6mol/g, which varies little with the molecular weight; it is possible that molecular species with higher values become insoluble. (d) Branching results ˜λ and gel content (36%) of the whole rubber gave a total of 93–98% of branched entities (sol and gel) and 2–7% of linear species.

Nitric oxide release using natural rubber latex as matrix

“…One of the most important of the non-hydrocarbon group's presents in NRL is the aldehyde group, which is thought to be responsible for crosslinking between the chains in NRL 27 and their concentration varying from clone to clone 28 . Other compounds, such as lipids, neutral glycolipids and phospholipids, amount to 1.4-3.2%.…”

Natural rubber (NR) biosynthesis: perspectives from polymer chemistry

“…it is well established that nr is composed of long-chain branched molecules (Campos-López and angulo-sánchez, 1976;angulo-sánchez and Cabaulero-Mata, 1981;Fuller and Fulton, 1990). Fulton and groves showed the presence of long-chain branching and gel in NR by field flow fractionation (FFF): the log r g -log MW conformational plot was shown to have a slope of 0.3 in the high MW range (Fulton and groves, 1997).…”

SEC‐MALS study of dynamic structuring of natural rubber: Comparative study of two Hevea brasiliensis genotypes

“…4,27 Kim et al 5,33 analyzed NR samples with SEC-MALS and showed that the soluble part injected into a SEC system contained very few branched macromolecules, contrary to earlier published studies. [34][35][36] Kim et al 5,33 showed that the soluble part of NR in solution in tetrahydrofuran (THF) was composed of a mixture of linear chains and assumed compact microaggregates (R g % 110-130 nm). They showed that, to more effectively ascertain the mesostructure of NR, a MALS detector needs to be used with SEC to avoid a misunderstanding of the structure, as is the case with most polymers.…”