Diimide hydrogenation of isoprene–styrene diblock copolymers

Abstract

Isoprene-styrene diblock copolymers of various molecular weights were prepared by anionic polymerization with n-BuLi in cyclohexane. Hydrogenation of the unsaturated backbone of the block copolymers was performed with diimide generated in situ by the thermolysis of p-toluenesulfonylhydrazide (TSH). The reaction was carried out in xylene at 135°C. A molar ratio of TSH to double bonds equal to 4:1 was found to be the optimum ratio, which provided the highest percentage of hydrogenation. The percentage of hydrogenation analyzed by 1 H-NMR, IR spectroscopy, and iodine value (the Wijs method) were compared. Evidence from 1 H-NMR also revealed a change in the ratio of the cis-trans configuration after hydrogenation. The thermal stability of the hydrogenated products was improved as shown by the results from thermogravimetric analysis. From differential scanning calorimetry measurements, the glass-transition temperatures of the hydrogenated products were found to increase about 10 -20°C above those of the original block copolymers.

Modification of polyisoprene‐block‐poly(vinyl trimethylsilane) block copolymers via hydrosilylation and hydrogenation, and their gas transport properties

“…After thermal decomposition, the diimide saturates the double bonds. It is a homogeneous reaction that is used to hydrogenate diene‐containing polymers such as polybutadiene and polyisoprene under nitrogen . Noncatalyzed hydrogenation of the four PI‐ b ‐PVTMS polymers with p ‐TSH was performed as described in the experimental section to obtain H‐PI‐ b ‐PVTMS (Scheme ).…”

“…Chemical modification of polymers has been used for many years to improve properties and to add functional groups to polymers if these resulting functional polymers are expensive, difficult or impossible to synthesize in a direct way via conventional polymerization methods . In this study, our main goal was to modify the polyisoprene block of PI‐ b ‐PVTMS with suitable components via metal catalyzed hydrosilylation and noncatalytized hydrogenation . Thus, the intent is to alter the thermodynamic and repulsive interactions between blocks, resulting in different morphologies, which are directly related to the gas transport properties of the modified block copolymers .…”

Raman spectroscopic study of non‐catalytic hydrogenation of unsaturated rubbers

“…It was found in several cases that an excess of about a 4-5-fold excess of diimide compared with the unsaturated units was needed for complete hydrogenation of polyisoprene in homo-and copolymers. 1,10,15 In our case, a twofold excess of TSH was used to hydrogenate the unsaturated units of NR and ENRs. The FT-IR spectra of NR and ENRs show mainly two characteristic peaks at 1665 and 836 cm 1 , attributing to the (C C) and the C-H outof-plane deformation of the trisubstituted carbon-carbon double bonds of polyisoprene units, respectively.…”

“…The formation of an unstable complex between the carbon-carbon double bonds and the TSOH generated could be responsible for the cis-trans isomerization. 10 No signal of the addition of the by-product to the hydrogenated NR was detected.…”

Epoxidação "in situ" aplicada ao látex de borracha natural

“…Isto faz com que este tipo de borracha seja alvo de inúmeras pesquisas, onde a busca por metodologias que a modifiquem quimicamente tem despertado o interesse das pesquisas atuais, para assim, ampliar suas áreas de aplicação. Pesquisas focadas na modificação da estrutura interna de polímeros tem sido desenvolvidas englobando uma variedade de borrachas sintéticas [1][2][3][4][5][6][7][8] , dentre as quais destacam-se reações de maleinização [4] , sulfonação [5] , epoxidação [1][2][3] e hidrogenação [6][7][8] . Trabalhos de pesquisa desenvolvidos por nosso grupo [1,2] demonstraram que a epoxidação in situ via ácido perfórmico é fácil, rápida e eficaz quando a mesma é aplicada a borrachas em solução.…”