Fourier transform infrared (FTIR), ' H NMR, and ',C NMR have been used to characterize the structure of natural rubber cyclized with p-toluenesulfonic acid. The samples studied were only partially cyclized. The cyclized portions contained both mobile and rigid domains. Crosslinking occurred during the cyclization reaction. The cyclized samples showed a distribution of functionalities including some oxidation products. All three types of olefinic segmented end groups were formed during cyclization (di-, tri-, and tetrasubstituted olefins). The loss of the exocyclic species leads to the formation of cross-linked networks.

With the use of solid state carbon-13 NMR, changes in the structure of natural rubber and cis-polybutadiene were observed spectroscopically. Cis-trans conversion has been shown to occur in the naturaal rubber by the rearrangement of the allylic free radical. At least four structurally different methyl groups have been detected in the crosslinking of natural rubber by dicumyl peroxide, which indicates that the simple combination of allyic free radical is an oversimplification of the curing process. Quaternary aliphatic carbons have been detected which results from double bond migration. Polybutadiene showed only methine and methylene carbons present in the crosslinked network with a small amount of methyl end-groups. The increase in the line width of the highly crosslinked elastomers was shown to be dominated by the carbon-hydrogen static dipolar interaction. Fourier-transform infrared analysis observed the formation of a molecular complex between dicumyl peroxide and polybutadiene. The formation of trans double bonds was observed in the infrared spectra of polybutadiene. Weak broad bands around 1320 cm−1 were observed in the difference spectrum of cured rubbers and were assigned to carbon-carbon crosslinks. From the structural interpretation of spectra obtained from solid state carbon-13 NMR and Fourier-transform infrared, models are proposed for the crosslinked networks of natural rubber and polybutadiene, obtained from peroxide vulcaniation.

Solid‐state 13C‐NMR spectroscopy has been used to investigate the structure of cellulose nitrates prepared from cotton linters. The solid‐state technique has the advantage that the entire range of substitution can be studied, which is not possible at present by solution methods. The spectra change progressively with increasing degree of substitution (DOS = 3 for cellulose trinitrate), and can be used to quantify the extent of substitution at C6, C2, and C3. Progressive nitration leads to elimination of the original C6 resonances of native cellulose by DOS = 1.39. The first nitration of C6 occurs in the amorphous regions, and this is complete by DOS = 0.50. Substitution at C6 is accompanied by decrystallization, as indicated by the decrease in the resonance assigned to crystalline C4, which also disappears at DOS = 1.39. A new resonance assigned to C1 appears at DOS = 0.28 at 101 ppm; the original C1 resonance for cellulose declines steadily and disappears by DOS = 2.65. This change is assigned to nitration of C2, based on the published solution spectra. Finally, development of intensity at 82 ppm at DOS = 1.83 is assigned to the effect of nitration at C3. There is no indication of any rearrangement of the unsubstituted regions analogous to those that occur on Mercerization of native cellulose.

Solid-state 13C NMR was used to characterize the structure changes produced in gamma irradiation in natural rubber. The structure of the irradiated natural rubber was found to be heterogeneous, consisting of a mobile phase and a semi-rigid phase. Cis-trans chain isomerization was detected in the mobile phase of the gamma-irradiated samples. The CP/MAS spectra of the more rigid phase contained resonances due to quaternary carbons arising from cross-links and vinyl end groups caused by main chain scission. The calculated values of β and G( X) agreed with earlier published results. Peroxide-cured natural rubber of an equivalent amount of network density showed a higher amount of trans structure than did the gamma-irradiated natural rubber.

Changes in the structure of natural rubber and cispolybutadiene have been observed using solid state carbon-13 NMR. Cis-trans isomerization has been shown to occur in the natural rubber by rearrangement of the allylic free radical. At least four different methyl groups have been detected in the cross-linking of natural rubber by dicumyl peroxide, which indicates that the simple combination of allylic free radical is an oversimplification of the curing process. Quater nary aliphatic carbons have been detected which suggest double bond migration. Polybutadiene showed only methine and methylene carbons in the cross-linked net work with a small amount of methyl end groups. The increase in the line width of the highly cross-linked elastomers has been shown to be due in part to the static dipolar interaction between carbons and protons and chemical shift dispersions. The formation of trans double bonds has been observed in the infrared spectra of cis-polybutadiene. Weak broad bands around 1320 cm -1 observed in the difference spectrum of cured rubbers may be due to carbon-carbon cross-links. From the structural interpretation of spectra obtained from solid state carbon-13 NMR and Fourier transform infra red spectroscopy, models are proposed for the crosslinked networks of natural rubber and cis-1, 4-polybutadiene formed by peroxide vulcanization.The range of end use applications of elastomeric materials is ex tended by their ability to be cross-linked. It is well known that the chemical microstructure of rubber influences its physical properties and the reaction mechanism of the curing process. The use of dicumyl peroxide as a curative for natural rubber and cis-polybutadiene produces a network that contains 0097-6156/84/0243-0205S07.75/0