Chapter 3
Confinement Effects on the Reactivity
in Ultrathin Polymer Films: Kinetics
and Temperature Dependence
of the Hydrolysis of NHS and TBA Esters
In this chapter, the effect of spatial confinement of the reactants on the kinetics
of the hydrolysis of poly(N-hydroxysuccinimidyl-methacrylate) (PNHSMA) and
polystyrene-block-poly(tert-butyl acrylate) (PS n -b-PtBA m ) ultrathin films (~90 nm)
on oxidized silicon substrates was systematically investigated. The activation energies determined according to the Arrhenius equation, and in particular the activation entropies calculated according to the transition state theory, revealed that
steric crowding in the surface-near region and tightness of the transition state is less
pronounced in polymer films compared to self-assembled monolayers (SAMs) that
expose the same reactive ester groups. Apparent rate constants calculated according
to infrared (IR) spectroscopy and contact angle (CA) data for both polymers and
SAMs directly demonstrated that polymer films are characterized by higher reactivity, as well as a high density of reactive functional groups at and near the polymer
surface. However, the reactivity of polymer films was reduced compared to reactivity
in solution because of restricted access and reduced mobility of the ester functional
groups in these films. Finally, it was found that polymer film thickness, thermal
pretreatment of the films, block copolymer composition for PS n -b-PtBA m , and local
surface composition did not affect the rate constants of hydrolysis.
3.1 Introduction
The ability to control the chemical and structural properties of surfaces is crucial for
advancements in selective and environmentally friendly catalysis [1], electronics [2],
chemical sensing [3], bio-chemistry [4], and applications in many other areas [5].
Studies of chemical reactions of surfaces may provide new routes to tailored surface
properties. Such reactions allow, for example, the tethering of biologically important
molecules to surfaces, which can be of significant importance in chemical biology
and microarray technology. In addition, chemical reactions occurring on organic
or polymeric surfaces play a crucial role in many applications, ranging from the
© Shanghai Jiao Tong University Press 2021
C. Feng et al., Microfabrication of Stimuli-Responsive Polymers,
https://doi.org/10.1007/978-981-33-6869-9_3
45
Confinement Effects on the Reactivity
in Ultrathin Polymer Films: Kinetics
and Temperature Dependence
of the Hydrolysis of NHS and TBA Esters
In this chapter, the effect of spatial confinement of the reactants on the kinetics
of the hydrolysis of poly(N-hydroxysuccinimidyl-methacrylate) (PNHSMA) and
polystyrene-block-poly(tert-butyl acrylate) (PS n -b-PtBA m ) ultrathin films (~90 nm)
on oxidized silicon substrates was systematically investigated. The activation energies determined according to the Arrhenius equation, and in particular the activation entropies calculated according to the transition state theory, revealed that
steric crowding in the surface-near region and tightness of the transition state is less
pronounced in polymer films compared to self-assembled monolayers (SAMs) that
expose the same reactive ester groups. Apparent rate constants calculated according
to infrared (IR) spectroscopy and contact angle (CA) data for both polymers and
SAMs directly demonstrated that polymer films are characterized by higher reactivity, as well as a high density of reactive functional groups at and near the polymer
surface. However, the reactivity of polymer films was reduced compared to reactivity
in solution because of restricted access and reduced mobility of the ester functional
groups in these films. Finally, it was found that polymer film thickness, thermal
pretreatment of the films, block copolymer composition for PS n -b-PtBA m , and local
surface composition did not affect the rate constants of hydrolysis.
3.1 Introduction
The ability to control the chemical and structural properties of surfaces is crucial for
advancements in selective and environmentally friendly catalysis [1], electronics [2],
chemical sensing [3], bio-chemistry [4], and applications in many other areas [5].
Studies of chemical reactions of surfaces may provide new routes to tailored surface
properties. Such reactions allow, for example, the tethering of biologically important
molecules to surfaces, which can be of significant importance in chemical biology
and microarray technology. In addition, chemical reactions occurring on organic
or polymeric surfaces play a crucial role in many applications, ranging from the
© Shanghai Jiao Tong University Press 2021
C. Feng et al., Microfabrication of Stimuli-Responsive Polymers,
https://doi.org/10.1007/978-981-33-6869-9_3
45