Thin-film behavior of poly(methyl methacrylates). 1. Monolayers at the air-water interface

Abstract

The monolayer behavior of PMMA of varying tacticities at the air-water interface was studied. A difference in lateral cohesive energy is argued to be responsible for the fact that the pressure area isotherms of isotactic PMMA deviate strongly from those of syndiotactic PMMA. At low surface pressures the isotactic PMMA monolayer can be characterized as an expanded type monolayer, whereas syndiotactic PMMA forms a condensed type monolayer. At areas of about 20 AZ/monomeric unit a transition can be observed in the pressure-area isotherm of isotactic PMMA. This transition was studied as a function of molecular weight, temperature, and compression speed. From the results it is deduced that the transition corresponds to a two-dimensional pseudocrystallization process in which the isotactic PMMA assumes a double-helix conformation in the monolayer, similar to the three-dimensional crystal structure. From an Avrami analysis it is inferred that the kinetics of this crystallization can be described by an activated nucleation, followed by a one-dimensional growth.

Influence of the Polymethacrylate Chain Conformation in Langmuir–Blodgett–Kuhn Films on the Glass-Transition Temperature

“…[12] In the case of isotactic PMMA, this kind of transition results from a conformational change of the polymer chains towards a helical coil structure at the air/water interface. [13,14] The isotherm of the dPEMA showed a similar transition, however, slightly shifted to larger area values (DMMA L 0.25 nm 2 ), indicating a slightly higher requirement of molecular space. The area shift is a result of the different strength of the van der Waals interaction between the protonated and the perdeuterated species.…”

Development of an Ultrafast Low-Energy Electron Diffraction Setup

“…The chain-to-chain distances reported in the literature are 5.0(1.0)Å and 4.8(1.9)Å, respectively, with a repeating monomer unit length of about 2.5Å in direction of the polymer backbone. In the case of isotactic PMMA, linear as well as helical arrangements are found with a somewhat smaller interchain distance of the latter of 3.7(0.8)Å [110,115,116].…”

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

“…In contrast to atactic poly(methyl methacrylate) (a-PMMA), the syndiotactic species (s-PMMA) and the isotactic polymer (i-PMMA) are able to crystallize. The Langmuir isotherm of i-PMMA shows a transition at approximately 8 mN m -1 at 20°C which can be assigned to a crystallization process according to Shouten and Brinkhuis [20]. During this process, i-PMMA chains form a double helix in the monolayer parallel to the water surface.…”