Papers by Siddhartha Asthana
Journal of Polymer Science Part A-polymer Chemistry, 1996
8-Vinyloxy ethyl phthalimide (ImVE) was polymerized using 1-(isobutoxy) ethyl acetate as the init... more 8-Vinyloxy ethyl phthalimide (ImVE) was polymerized using 1-(isobutoxy) ethyl acetate as the initiator in the presence of ethyl aluminum dichloride and either ethyl acetate or ethyl benzoate. The resulting polymers have a narrow molecular weight distribution, and their molecular weight can be controlled within a narrow range by varying the monomer and initiator concentrations. Diblock copolymers with n-butyl vinyl ether can also be formed.
Journal of Polymer Science Part A-polymer Chemistry, 1998
The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polys... more The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polystyrene-b-polyisobutylene (PSt-b-PIB) arms emanating from cyclosiloxane cores is described. The synthesis involved the sequential living cationic block copolymerization of styrene (St) and isobutylene (IB), followed by quantitative allylic end-functionalization of the living PSt-b-PIB ϩ to produce PSt-b-PIBOCH 2 O CHACH 2 prearms, and finally linking by hydrosilation of these prearms with SiOHcontaining cyclosiloxanes (e.g., 2,4,6,8,10,12-hexamethylcyclohexasiloxane, D 6 H ). Two types of star-blocks, namely primary and higher-order star-blocks, were prepared: Primary star-blocks containing 3-9 PSt-b-PIB arms were obtained by using various cyclosiloxanes (D 6 H to D 12 H ) and a close to exact stoichiometry between the SiOH and allyl groups, [SiOH]/[CAC] ϳ 1, in the essential absence of moisture ([H 2 O] ϳ 100 ppm). Higher-order star-blocks consisting of 13-24 PSt-b-PIB arms radiating from complex coupled cyclosiloxanes were prepared by the use of SiOH/allyl ratios significantly larger than unity ([SiOH]/[CAC] ϭ 2-3) in the presence of controlled amounts of moisture ([H 2 O] ϳ 600 ppm). Reaction conditions (temperature, concentration, stoichiometry, solvent nature, catalyst concentration, etc.) for efficient syntheses have been developed. The products were characterized by 200 and 600 MHz 1 H-NMR spectroscopy and triple-detector (RI, UV, LLS) GPC. The microstructure of the condensed cores in the higher-order star-blocks was studied by 2D-NMR (HMQC) spectroscopy, and the number of cyclosiloxane rings in the cores (i.e., the content (wt %) of cores in the star-blocks) was determined.
Journal of Applied Polymer Science, 2002
The objective of these investigations was to increase the use temperature of novel star-block pol... more The objective of these investigations was to increase the use temperature of novel star-block polymers consisting of a crosslinked polydivinylbenzene (PDVB) core from which radiate multiple poly(isobutylene-b-polystyrene) (PIB-b-PSt) arms, abbreviated by PDVB(PIB-b-PSt)n. We achieved this objective by blending star-blocks with poly(phenylene oxide) (PPO) that is miscible with PSt. Thus, various PPO/PDVB(PIB-b-PSt)n blends were prepared, and their thermal, mechanical, and processing properties were investigated. The hard-phase glass-transition temperature of the blends could be controlled by the amount (wt %) of PPO. The blends displayed superior retention of tensile strengths at high temperatures as compared to star blocks. The melt viscosities of blends with low weight percentages of PPO were lower than those of star blocks. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2866–2872, 2002
Journal of Polymer Science Part A-polymer Chemistry, 1998
The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polys... more The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polystyrene-b-polyisobutylene (PSt-b-PIB) arms emanating from cyclosiloxane cores is described. The synthesis involved the sequential living cationic block copolymerization of styrene (St) and isobutylene (IB), followed by quantitative allylic end-functionalization of the living PSt-b-PIB ϩ to produce PSt-b-PIBOCH 2 O CHACH 2 prearms, and finally linking by hydrosilation of these prearms with SiOHcontaining cyclosiloxanes (e.g., 2,4,6,8,10,12-hexamethylcyclohexasiloxane, D 6 H ). Two types of star-blocks, namely primary and higher-order star-blocks, were prepared: Primary star-blocks containing 3-9 PSt-b-PIB arms were obtained by using various cyclosiloxanes (D 6 H to D 12 H ) and a close to exact stoichiometry between the SiOH and allyl groups, [SiOH]/[CAC] ϳ 1, in the essential absence of moisture ([H 2 O] ϳ 100 ppm). Higher-order star-blocks consisting of 13-24 PSt-b-PIB arms radiating from complex coupled cyclosiloxanes were prepared by the use of SiOH/allyl ratios significantly larger than unity ([SiOH]/[CAC] ϭ 2-3) in the presence of controlled amounts of moisture ([H 2 O] ϳ 600 ppm). Reaction conditions (temperature, concentration, stoichiometry, solvent nature, catalyst concentration, etc.) for efficient syntheses have been developed. The products were characterized by 200 and 600 MHz 1 H-NMR spectroscopy and triple-detector (RI, UV, LLS) GPC. The microstructure of the condensed cores in the higher-order star-blocks was studied by 2D-NMR (HMQC) spectroscopy, and the number of cyclosiloxane rings in the cores (i.e., the content (wt %) of cores in the star-blocks) was determined.
The continued push for improved productivity in the high pressure die cast (HPDC) industry places... more The continued push for improved productivity in the high pressure die cast (HPDC) industry places ever increasing performance and productivity demands on die lubricants. The majority of new technology developments in die lubricants have been spurred by developments in automotive castings. The relentless push for vehicle weight reduction and improved productivity requirements, coupled with the casting of larger and more complex parts, has brought forward the necessity of significant innovations in die lubricants. This paper discusses the impacts of these trends on die lubricants while examining how new die lubricant technologies address the changing industry needs.
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Papers by Siddhartha Asthana