Thin-film behavior of poly(methyl methacrylates). 6. Monolayer phase behavior in relation to stereocomplexation in mixed monolayers of i- and s-PMMA

Abstract

The stereocomplexation process in mixed monolayers of isotactic and syndiotactic poly(methy1 methacrylate) is efficient only when low molecular weight samples are used. This phenomenon can be explained by an increasing tendency for phase separation in the monolayer upon using higher molecular weight samples, leading to larger domain sizes and a limited mutual accessibility: especially the use of high molecular weight syndiotactic PMMA appears to result in strong aggregation processes of these chains caused by the strong cohesive intersegment interactions at the air-water interface. This hypothesis is corroborated by the observation that addition of stereoblock PMMA strongly enhances the efficiency of the stereocomplexation process, thus acting as a compatibilizer, dispersing the s-PMMA chains in the monolayer. IntroductionIn previous publications,lt2 we discussed stereocomplexation processes that can take place in monolayers of mixtures of isotactic and syndiotactic PMMA. Upon compression, the monolayers exhibit an isotherm transition that can be correlated to the formation of double helical stereocomplex structures of both components, similar to the formation of such complexes in solution and melt mixtures of these materials. Indications for stereocomplexation were inferred from, e.g., the stoichiometry, the tacticity dependence, the surface potential behavior, and IR measurements of transferred monolayers. The monolayer stereocomplexation was most effectively conducted at elevated temperatures, lower temperatures leading to incomplete conversions.2 In this paper, we will focus on the relation between this stereocomplexation process and the phase behavior in the monolayer blends.The behavior of monolayers of polymer mixtures has been the subject of many reports in the literature. Especially the group of Gabrielli dedicated much effort to studying mixed monolayer^;^^ Kawaguchi recently also addressed the monolayer behavior of a series of polymer mixtures: and many other authors reported on the miscibility behavior of specific polymers in monolayers. Most of these studies assess the miscibility of two components on the basis of deviations from addivity of the specific areas or the compressibility or on the basis of the collapse behavior of the mixed monolayers. The first approach may not be very sensitive in many cases, since often the effects are quite small; the latter approach gives information only about the collapse regime, with very high segment concentrations and strongly deformed conformations, and the results are not always unambiguous. In most cases, the mixtures are either classified as miscible or nonmiscible; more detailed information is usually not extracted. Phenomena such as the extent of segregation of the individual coils, limited interpenetration, and molecular weight effects have not been addressed in detail in these experimental studies; a direct correlation with theoretical results on the behavior of two-dimensional polymer mixtures is not often given.Langmuir-Blodgett monolayers o...

Compression-Induced Stereocomplexation of Polylactides at the Air/Water Interface

“…Stereocomplexation of polymers at the air/ water interface has only been studied only for polylactides 35,36 and for PMMA. [37][38][39][40][41][42] Indeed, Brinkhuis and Schouten have shown that a stereocomplex could be formed at the air/water interface by compressing a Langmuir film of a 2:1 isotactic:syndiotactic PMMA blend. [39][40][41] This stereocomplex consists of double-helical structures with a syndiotactic strand winding around an isotactic strand, the stoichiometry being 2:1 at the monomeric level.…”

“…In addition to polylactides (PLA), − stereocomplexation has also been reported for different polymer couples, the most studied of them being poly(α-methyl-α-ethyl-β-propiolactones), − poly(γ-benzyl glutamates), − and poly(methyl methacrylates) − (PMMA). Stereocomplexation of polymers at the air/water interface has only been studied only for polylactides , and for PMMA. − Indeed, Brinkhuis and Schouten have shown that a stereocomplex could be formed at the air/water interface by compressing a Langmuir film of a 2:1 isotactic:syndiotactic PMMA blend. − This stereocomplex consists of double-helical structures with a syndiotactic strand winding around an isotactic strand, the stoichiometry being 2:1 at the monomeric level.…”

Synthesis of Isotactic-block-Syndiotactic Poly(methyl Methacrylate) via Stereospecific Living Anionic Polymerizations in Combination with Metal-Halogen Exchange, Halogenation, and Click Reactions

“…Typical stereoregular poly(methyl methacrylate)s (PMMAs), i.e., isotactic ( it -) and syndiotactic ( st -) PMMAs, are known to associate in the solid state and specific solutions to form a crystalline polymer complex, i.e., a stereocomplex, in which inner single or double helixes of the it -PMMA chain are surrounded by an outer st -PMMA helical chain with a larger radius [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. The unique structures and properties of synthetic polymers have attracted attention from both fundamental and application viewpoints [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Furthermore, these stereoregular polymer chains have been incorporated into various well-defined polymers, such as block, star, graft, and end-functionalized polymers, to create novel properties and functions [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”

Molecular Weight Dependence of the Poly(l-lactide)/Poly(d-lactide) Stereocomplex at the Air−Water Interface

“…17 Research on Langmuir-Blodgett (LB) films of polymers has increased drastically in the past decade because of possible applications in nonlinear optical devices and other fields such as biosensors and microlithography. Meanwhile, the stereocomplexation of a polymer at the air-water interface had been studied in great detail for poly(methyl methacrylate) (PMMA), [18][19][20][21] which is another typical example of a macromolecular stereocomplex. Indeed, Brinkhuis et al [18][19][20][21] have shown that the stereocomplex could form at the air-water interface by compressing a Langmuir film of a 2:1 isotactic/ syndiotactic PMMA blend.…”

“…Meanwhile, the stereocomplexation of a polymer at the air−water interface had been studied in great detail for poly(methyl methacrylate) (PMMA), − which is another typical example of a macromolecular stereocomplex. Indeed, Brinkhuis et al − have shown that the stereocomplex could form at the air−water interface by compressing a Langmuir film of a 2:1 isotactic/syndiotactic PMMA blend. This stereocomplex consists of double-helical structures with a syndiotactic strand winding around an isotactic strand.…”