Effect of tacticity on the structure and glass transition temperature of polystyrene adsorbed onto solid surfaces

Abstract

We have carried out atomistic (all-atom) molecular dynamics simulations to investigate the effect of tacticity on the structure and glass transition temperature (T) of polystyrene (PS) thin films adsorbed on two distinct types of solid substrates. The systems consist of thin films made of atactic, isotactic, and syndiotactic PS chains supported by graphite or hydroxylated α-quartz substrates, which are known to be atomically flat but chemically and structurally different. We have observed a marked dependence of the film structure on substrate type as well as on tacticity. For instance, rings' orientation near substrate surfaces depends on substrate type for atactic PS and isotactic PS films, while no such dependence is observed for syndiotactic PS films whose interfacial structure seems to result from their propensity to adopt the trans conformation rather than their specific interaction with the substrates. Moreover, our results indicate that glass transition temperatures of substrate supported polystyrene films are higher compared to those of the corresponding free-standing films. More specifically, PS films on graphite exhibit larger T values than those on α-quartz, and we have noticed that syndiotactic PS has the largest T irrespective of the substrate type. Furthermore, the local T in the region of the film in contact with the substrates shows a strong tacticity and substrate dependence, whereas no dependencies were found for the local T in the middle of the film. Substrate-film interaction energy and chains' dynamics near substrate-film interfaces were subsequently investigated in order to substantiate the obtained Ts, and it was found that films with higher Ts are strongly adsorbed on the substrates and/or exhibit smaller interfacial chains' dynamics essentially due to steric hindrance.

Green analogs of polybutadienes from carbon dioxide and epoxy‐based feedstocks

“…We also observed some crystallization temperature ( T c ) and melting temperature ( T m ) peaks for the RUPC2, which might be due to the long pendant groups that might undergo some sort of rearrangement. PS exhibited a T g of 87°C, which is substantially closer to the value reported in the literature for PS 25–27 . The T g of RUPC2‐ g ‐PS was found to be 80°C, and this reduction was due to the presence of amorphous RUPC2, which had a low T g .…”

“…PS exhibited a T g of 87 C, which is substantially closer to the value reported in the literature for PS. [25][26][27] The T g of RUPC2-g-PS was found to be 80 C, and this reduction was due to the presence of amorphous RUPC2, which had a low T g . Also, the T g peak of RUPC2 is visible in the DSC plot of RUPC2-g-PS.…”

“…2,3,5 In addition, CO 2 , which is one of the primary greenhouse gases, is used as feedstock for the synthesis of these polymers. The catalyst (salen) Co(III)Cl in combination with PPN-Cl as a co-catalyst has been reported by Coates et al 27 to offer good reactivity and selectivity Epoxy dodecane and dodecene were utilized as monomers as the long alkyl chain imparts amorphicity and flexibility. The RUPCs were prepared at two different dodecane-to-dodecene ratios to insert different amounts of double bonds in the polycarbonate (see Table 1).…”

Development of rigid amorphous fraction in cold‐crystallized syndiotactic polystyrene films confined near the nanoscale: Novel analysis via ellipsometry

“…The thermal expansivities of PS with each of three types of tacticity were analyzed in the case of thin films on α-quartz and graphite surfaces, in which aPS, isotactic polystyrene (iPS), and sPS films showed similar thermal expansivity. [89] )…”

“…The thermal expansivities of PS with each of three types of tacticity were analyzed in the case of thin films on α ‐quartz and graphite surfaces, in which aPS, isotactic polystyrene (iPS), and sPS films showed similar thermal expansivity. [ 89 ] ) For a cold‐crystallized sPS film with some extent of CF and RAF, it holds that. where w R , w M , and w C are the mass fractions or weight fractions of RAF, MAF, and CF, respectively. From the third assumption above, the thermal expansivity of MAF in sPS films equals α g in the glassy state and α r in the rubbery state, where α g and α r are values obtained from measurements on aPS films at the same conditions.…”