Polymer Aggregates with Crystalline Cores:  The System Polyethylene−Poly(ethylenepropylene)

Abstract

We have studied the aggregation behavior of polyethylene−poly(ethylenepropylene) (PE−PEP) diblock copolymers dissolved in decane. For this purpose PE−PEP diblock copolymers of various molecular weights, compositions, and degrees of deuteration were synthesized via an anionic route. The structure and morphology of the aggregates was studied by small angle neutron scattering varying both the contrast as well as the polymer labeling. We found a hierarchy of structures: The PE component crystallizes in lamellar sheets (thickness 40−80 Å) surrounded on both sides by a PEP brush which exhibits a close to parabolic density profile. Different aggregates form macroaggregates of needlelike shape with the PE lamellar planes in the long direction. This macroaggregation is well described by a paracrystalline structure factor. The structural parameters depending on composition and molecular weights can be well understood in terms of a free energy of formation based on a scaling model. A quantitative evaluation of the different contributions to the free energy reveals an important role of defect structures resulting from the ethylene side branches in the polyethylene component. Finally, we show in a semiquantitative approach that the van der Waals energy between the brushes is large enough to facilitate macroaggregation.

Wax Crystallization from Solution in Hierarchical Morphology Templated by Random Poly(ethylene-co-butene) Self-assemblies

“…) exp(-u 2 )∫ 0 u exp(t 2 ) dt, which results from the averaging for an isotropic ensemble of platelets 7 and exhibits the following asymptotic behavior: for u f ∞, 2D(u)/u f 1/u 2 and for u f 0, D(u)/u f 1. The scattering of the molecules in solution was added (eq 5 with an exponent P ) 5 / 3 ) giving an additional contribution to the intensity at high Q.…”

“…The geometrical and density parameters have been evaluated from the fit of the data for both contrast conditions in terms of an ensemble of finite extended disks forming a correlated arrangement (eqs [6][7][8]. The results are reported in Table 3 and reveal almost the same lateral extension of the disks as in the case of sample 4 while the amounts of polymer and wax contained by the layers is significantly higher.…”

“…The Q -2 power law and the peak presence at the same Q as for the polymer selfassembling patterns 14 prove a cocrystallization of the polymer and wax in thin correlated platelets which were mediated by the primordial 1-dimensional density modulated polymer structures. The fit of the data was performed again in terms of two embedded layers that form a correlated arrangement described by the paracrystalline structure factor (eqs [6][7][8]. In this case infinite extended disks have been considered as long as their lateral size was not approached within the Q range investigated.…”

Tailored Polymer Additives for Wax (Paraffin) Crystal Control

“…Small-angle neutron scattering (SANS) technique exploiting on one side the strength of contrast matching and, on other side, the wide length scale explored, from 1nm up to 1m, is a dedicated technique to investigate and elucidate complex morphologies such as those occurring in a wax-polymer-oil system (Richter et al, 1997;Leube et al, 2000;Monkenbusch et al, 2000;Schwahn et al, 2002aSchwahn et al, , 2002bAshbaugh et al, 2002;Radulescu et al, 2003Radulescu et al, , 2004Radulescu et al, , 2006Radulescu et al, , 2008Radulescu et al, , 2011. An eloquent example is that of diblock polymers (Fig.…”

Crystallization-induced aggregation of block copolymer micelles: influence of crystallization kinetics on morphology

“…The overall shape thus depends on the interplay between the interfacial energy of the crystalline block and the solvent, and the stretching within the amorphous block [4]. Thus, the micellar architecture is strongly influenced by the crystallization conditions, such as temperature [9], and composition of the block copolymers [3, 5-By changing composition, solvent, and structure of the crystalline block, spherical [7,[11][12][13], cylindrical [10,14,28], and lamellar micelles have been obtained [1,3,5,15,29]. Recently, Winnik et al reported the possibility to obtain cylindrical micelles with controlled dimensions and architectures of organometallic block copolymers containing the crystallizable polyferrocenyldimethylsilane as one block.…”