The thiol–ene click reaction was applied to modify poly(isobutylene-co-isoprene) (IIR) by two dif... more The thiol–ene click reaction was applied to modify poly(isobutylene-co-isoprene) (IIR) by two different strategies using carboxylated thiols (mercaptanoic acids) with different alkyl spacer chain lengths. In the first approach, the direct radical-promoted addition of thiols across the 1,4-isoprene units proceeded with 80–90% conversion of the internal double bonds. An alternate method involving the conversion of sterically hindered 1,4-isoprene units to pendant double bonds through epoxidation and hydrolysis prior to the click reaction proceeded with 90–98% conversion of the alkene moieties. The carboxylated IIR derivatives were characterized by 1H NMR, FT-IR spectroscopy, and gel permeation chromatography analysis. Irrespective of the synthetic strategy used, the yields of the reactions decreased as the length of the alkyl spacer in the mercaptanoic acid increased. The outcomes of the reactions also depended on the amounts of solvent and free radical initiator used. Carboxylated butyl rubber derivatives were obtained by reacting the isoprene units in the isobutylene copolymer with alkylmercaptanoic acids comprising alkyl spacers of different lengths. The yield of the reactions varied from 80 to 90% for direct reaction of the copolymer containing 1,4-isoprene units, but increased to 90–98% if the 1,4-units were isomerized to terminal alkenes prior to the reactions.
We report on the linear viscoelastic properties of mixtures comprising multiarm star (as model so... more We report on the linear viscoelastic properties of mixtures comprising multiarm star (as model soft colloids) and long linear chain homopolymers in a good solvent. In contrast to earlier works, we investigated symmetric mixtures (with a size ratio of 1) and showed that the polymeric and colloidal responses can be decoupled. The adopted experimental protocol involved probing the linear chain dynamics in different star environments. To this end, we studied mixtures with different star mass fraction, which was kept constant while linear chains were added and their
The synthesis of carboxylated derivatives of poly(isobutylene-co-isoprene) (isobutylene-isoprene ... more The synthesis of carboxylated derivatives of poly(isobutylene-co-isoprene) (isobutylene-isoprene rubber, IIR) with substitution levels ranging from 1-4 mol% and different spacer lengths was accomplished by azide-alkyne Huisgen cycloaddition. Azido-functionalized IIR was first prepared by reacting brominated IIR to full conversion with sodium azide in a tetrahydrofuran/N,Ndimethylacetamide 90:10 mixture. The click reaction of the azido-functionalized IIR with acetylenic acids, using the copper(I) bromide/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system in tetrahydrofuran, gave the carboxylated IIRs. The products were characterized by 1 H NMR and FT-IR spectroscopy, and their molecular weight was determined by size exclusion chromatography analysis. The conversion to carboxylated groups reached up to 100%, as determined by NMR spectroscopy, but was highly dependent on the type of solvent and the amounts of catalyst and reactants used in the procedures.
Whereas mixtures of colloids and non-adsorbing polymers have been studied in great detail in the ... more Whereas mixtures of colloids and non-adsorbing polymers have been studied in great detail in the last two decades, binary colloidal mixtures have not received much attention. Yet, fragmental evidence from asymmetric mixtures of hard spheres indicates a wide-ranging, complex behavior from liquid to crystal to single glass and to double glass, and respective rich rheology. Recently, we addressed the question of softness by investigating a mixture of soft and virtually hard colloidal spheres. We found an unprecedented wealth of states including repulsive single glass (RG), liquid, arrested phase separation (APS) and double glass (DG). This is a consequence of the coupling of softness and osmotic forces due to the hard component. We now report on the rheology of the different states with emphasis on the nonlinear response during start-up of stress at constant rate, its relaxation upon flow cessation, and large amplitude oscillatory shearing. Distinct features are identified, whereas comparison with single-colloid (soft or hard) glasses reveals some phenomenological universalities in yielding, residual stresses and periodic intra-cycle stress response. In brief, the DG exhibits much larger yield and residual stresses as compared to the RG and APS, whereas the yield strain is the same for all states. Two-step yielding is unambiguously evidenced for the APS whereas both yield stress and strain exhibit a weak dependence on Péclet number. Large amplitude oscillatory tests reveal large value of the intrinsic nonlinear parameters, reflecting the role of colloidal interactions. Moreover, RG exhibits intra-cycle stress
Polybutadiene macromonomers with a high 1,4-microstructure content and a polymerizable isoprene e... more Polybutadiene macromonomers with a high 1,4-microstructure content and a polymerizable isoprene end group were synthesized by termination of living polybutadienyllithium chains. While different isoprene derivatives were investigated as terminating agents for the preparation of the macromonomers, 2-bromomethyl-1,3-butadiene provided the best results. The termination reaction was optimized in terms of solvent composition, reaction temperature and reactivity-modifying additives used. The addition of 10 eq of terminating agent in equal volumes of hexane and tetrahydrofuran at-110°C provided the macromonomer in 95% yield. Anionic copolymerization of the macromonomer with 1,3butadiene in hexane yielded branched polybutadiene with a narrow molecular weight distribution (M w /M n = 1.07), but seeded initiation was necessary to avoid side reactions leading to multimodal molecular weight distributions.
The rapid depletion of Non-renewable fuel sources coupled with environmental degradation, has led... more The rapid depletion of Non-renewable fuel sources coupled with environmental degradation, has led us further into the exploration of alternate energy resources. Biodiesels originating from non-edible feedstocks have garnered much attention in a span of few years. The current study focuses on the addition of Carbon Nanotubes in Tamanu oil biodiesel in a Diesel engine. In this study, parameters such as brake thermal efficiency, unburned hydrocarbon, carbon monoxide, and NOx emissions have been studied. The performance of these biodiesel-diesel blends were charted and results are compared with diesel. It is noted that the inclusion of nano-additives in dosages of 30 and 60 ppm enhances brake thermal efficiency, the drawback being increased specific fuel consumption. The emissions of HC, NOx and emissions show a favorable trend with addition of CNT but CO2 emissions were observed to be on the higher side. Also graphs were plotted revealing the relevant combustion characteristics of the ...
The thiol–ene click reaction was applied to modify poly(isobutylene-co-isoprene) (IIR) by two dif... more The thiol–ene click reaction was applied to modify poly(isobutylene-co-isoprene) (IIR) by two different strategies using carboxylated thiols (mercaptanoic acids) with different alkyl spacer chain lengths. In the first approach, the direct radical-promoted addition of thiols across the 1,4-isoprene units proceeded with 80–90% conversion of the internal double bonds. An alternate method involving the conversion of sterically hindered 1,4-isoprene units to pendant double bonds through epoxidation and hydrolysis prior to the click reaction proceeded with 90–98% conversion of the alkene moieties. The carboxylated IIR derivatives were characterized by 1H NMR, FT-IR spectroscopy, and gel permeation chromatography analysis. Irrespective of the synthetic strategy used, the yields of the reactions decreased as the length of the alkyl spacer in the mercaptanoic acid increased. The outcomes of the reactions also depended on the amounts of solvent and free radical initiator used. Carboxylated butyl rubber derivatives were obtained by reacting the isoprene units in the isobutylene copolymer with alkylmercaptanoic acids comprising alkyl spacers of different lengths. The yield of the reactions varied from 80 to 90% for direct reaction of the copolymer containing 1,4-isoprene units, but increased to 90–98% if the 1,4-units were isomerized to terminal alkenes prior to the reactions.
We report on the linear viscoelastic properties of mixtures comprising multiarm star (as model so... more We report on the linear viscoelastic properties of mixtures comprising multiarm star (as model soft colloids) and long linear chain homopolymers in a good solvent. In contrast to earlier works, we investigated symmetric mixtures (with a size ratio of 1) and showed that the polymeric and colloidal responses can be decoupled. The adopted experimental protocol involved probing the linear chain dynamics in different star environments. To this end, we studied mixtures with different star mass fraction, which was kept constant while linear chains were added and their
The synthesis of carboxylated derivatives of poly(isobutylene-co-isoprene) (isobutylene-isoprene ... more The synthesis of carboxylated derivatives of poly(isobutylene-co-isoprene) (isobutylene-isoprene rubber, IIR) with substitution levels ranging from 1-4 mol% and different spacer lengths was accomplished by azide-alkyne Huisgen cycloaddition. Azido-functionalized IIR was first prepared by reacting brominated IIR to full conversion with sodium azide in a tetrahydrofuran/N,Ndimethylacetamide 90:10 mixture. The click reaction of the azido-functionalized IIR with acetylenic acids, using the copper(I) bromide/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system in tetrahydrofuran, gave the carboxylated IIRs. The products were characterized by 1 H NMR and FT-IR spectroscopy, and their molecular weight was determined by size exclusion chromatography analysis. The conversion to carboxylated groups reached up to 100%, as determined by NMR spectroscopy, but was highly dependent on the type of solvent and the amounts of catalyst and reactants used in the procedures.
Whereas mixtures of colloids and non-adsorbing polymers have been studied in great detail in the ... more Whereas mixtures of colloids and non-adsorbing polymers have been studied in great detail in the last two decades, binary colloidal mixtures have not received much attention. Yet, fragmental evidence from asymmetric mixtures of hard spheres indicates a wide-ranging, complex behavior from liquid to crystal to single glass and to double glass, and respective rich rheology. Recently, we addressed the question of softness by investigating a mixture of soft and virtually hard colloidal spheres. We found an unprecedented wealth of states including repulsive single glass (RG), liquid, arrested phase separation (APS) and double glass (DG). This is a consequence of the coupling of softness and osmotic forces due to the hard component. We now report on the rheology of the different states with emphasis on the nonlinear response during start-up of stress at constant rate, its relaxation upon flow cessation, and large amplitude oscillatory shearing. Distinct features are identified, whereas comparison with single-colloid (soft or hard) glasses reveals some phenomenological universalities in yielding, residual stresses and periodic intra-cycle stress response. In brief, the DG exhibits much larger yield and residual stresses as compared to the RG and APS, whereas the yield strain is the same for all states. Two-step yielding is unambiguously evidenced for the APS whereas both yield stress and strain exhibit a weak dependence on Péclet number. Large amplitude oscillatory tests reveal large value of the intrinsic nonlinear parameters, reflecting the role of colloidal interactions. Moreover, RG exhibits intra-cycle stress
Polybutadiene macromonomers with a high 1,4-microstructure content and a polymerizable isoprene e... more Polybutadiene macromonomers with a high 1,4-microstructure content and a polymerizable isoprene end group were synthesized by termination of living polybutadienyllithium chains. While different isoprene derivatives were investigated as terminating agents for the preparation of the macromonomers, 2-bromomethyl-1,3-butadiene provided the best results. The termination reaction was optimized in terms of solvent composition, reaction temperature and reactivity-modifying additives used. The addition of 10 eq of terminating agent in equal volumes of hexane and tetrahydrofuran at-110°C provided the macromonomer in 95% yield. Anionic copolymerization of the macromonomer with 1,3butadiene in hexane yielded branched polybutadiene with a narrow molecular weight distribution (M w /M n = 1.07), but seeded initiation was necessary to avoid side reactions leading to multimodal molecular weight distributions.
The rapid depletion of Non-renewable fuel sources coupled with environmental degradation, has led... more The rapid depletion of Non-renewable fuel sources coupled with environmental degradation, has led us further into the exploration of alternate energy resources. Biodiesels originating from non-edible feedstocks have garnered much attention in a span of few years. The current study focuses on the addition of Carbon Nanotubes in Tamanu oil biodiesel in a Diesel engine. In this study, parameters such as brake thermal efficiency, unburned hydrocarbon, carbon monoxide, and NOx emissions have been studied. The performance of these biodiesel-diesel blends were charted and results are compared with diesel. It is noted that the inclusion of nano-additives in dosages of 30 and 60 ppm enhances brake thermal efficiency, the drawback being increased specific fuel consumption. The emissions of HC, NOx and emissions show a favorable trend with addition of CNT but CO2 emissions were observed to be on the higher side. Also graphs were plotted revealing the relevant combustion characteristics of the ...
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