Hydrophobic Polymer Melt, Tethered to the Water SurfaceMonolayers of Polyisoprenes with Sulfonate Head Groups

Abstract

Hydrophobic polymers with low glass transition temperature (polyisoprenes) and a single head group (sulfonate) have been synthesized and characterized as insoluble monolayers on a water surface. The films are considerably thicker (10−50 nm) than conventional Langmuir monolayers of low molecular weight substances or polymers with surface-active repeating units. The thickness is inversely proportional to the area per head group. Films can be transferred via the Langmuir−Blodgett technique with transfer ratios close to 1. We use these monolayers as model systems to investigate the influence of the polymer chain statistics on the properties of solvent-free tethered polymers. We assume that each polymer chain is bound to the water phase with the head group and has the conformation of a distorted three-dimensional coil. The distortion increases with decreasing area per head group (A/n) and influences the isotherm of the polymer monolayers. We develop a theoretical description of this effect and conclude that, at a given area per head group, the surface pressure increases linearly with the chain length. In the case of Gaussian statistics, the slope of this line is proportional to the third power of the area per head group. In the case of non-Gaussian statistics, this slope can be expressed as a polynomial of A/n. The experimental data confirm these theoretical predictions. Deviations from Gaussian statistics can be neglected, and the description as a nonuniformly stretched brush (Semenov theory) comes closer to the experiment than the model of a uniformly stretched brush. Chains shorter than 300 repeat units systematically deviate from the theory.

Stratification in Monolayers of a Bidisperse Melt Polymer Brush As Revealed by Neutron Reflectivity

“…The theoretical scattering length density of h-PIN + (= 0.268 × 10 -6 Å -2 ) was calculated from the chemical composition, the volume of a repeat unit of 123.7 Å 3 , and tabulated values of the scattering length of the corresponding elements . The scattering length density of d-PIN + (= 6.94 × 10 -6 Å 2 ) was estimated from the analysis of the reflectivity experiments on monolayers of pure d-PIN + (experiment 1; see below).…”

“… R G β was calculated according to R G β = (number of repeat units) 0.5 × 6.23 Å; see Heger and Goedel . Note: in this calculation, the experimental value of h out of the two-box profile was used, not the value predicted by ASCF theory.…”

“…In these systems, two incompatible polymers are connected by a chemical bond and phase separate into nanometer-size domains. The size and shape of these domains is a result of the balance between the interfacial tension between the domains and the loss of entropy associated with the stretching of the closely packed polymer chains. − Although there is considerable interest in these systems, it has been very advantageous to study polymer brushes as monolayers at flat surfaces, for example, by spreading hydrophobic polymers with ionic headgroups at the surface of a water-filled Langmuir trough. − In such a monolayer, it is relatively easy to determine and tune the surface concentration of the polymer chains and to give the system a preferred orientation in space. In addition, the plane of tethering in these monolayers usually is less diffuse than in the case of phase-separated block copolymers.…”

Molecularly Designed Interfacial Viscoelasticity by Dendronized Polymers: From Flexible Macromolecules to Colloidal Objects

“…For polymers, the two-dimensional confinement in Langmuir films offers a particular opportunity to study the dynamics and spatial organization in the absence of entanglements . Colloidal objects self-assemble by mechanisms that are specific to the presence of interfaces, such as long-range lateral capillary interactions induced by particle shape or surface roughness. − The Langmuir–Pockels trough allows precise control over the surface concentration of insoluble systems and, therefore, enables a well-controlled study of their dynamics and self-assembly. , Subsequent Langmuir–Blodgett (LB) film transfer provides opportunities to exercise molecular or single-particle level control over the immobilization of these structures on solid substrates, − where they can be inspected by high-resolution methods such as atomic force microscopy (AFM), − high-resolution transmission electron microscopy (TEM), , and scanning probe microscopy (SPM) …”

Deuterated and partially deuterated polyisobutenes, synthesized via living carbocationic polymerization

“…Of special interest in our context are polymers with ionic end groups like the sulfonate end group depicted in Scheme 2. Polymers of this type can be used to generate thin monolayers of anchored polymers 30,31) and can form inverse micelles and physically cross-linked networks due to the aggregation of the ionic groups [32][33][34][35] . Polymerization of deuterated isobutenes should in principle be possible using procedures well established for non-deuterated monomers.…”