Synthesis, Structure, and Crystallization Behavior of Amphiphilic Heteroarm Molecular Brushes with Crystallizable Poly(ethylene oxide) and n-Alkyl Side Chains

Abstract

A series of heteroarm amphiphilic molecular brushes (AMBs) with poly­(ethylene glycol) (PEG) and long chain n-alkyl side chains were synthesized via conventional free radical polymerization (FRP) of mainly 4-vinylbenzyl-PEG methyl ether and N-alkylmaleimide macromonomers. By varying PEG side chain degree of polymerization (DP = 12, 16, and 20) and n-alkyl chain lengths (C16 and C20), we produced AMBs with varying combinations of side chain lengths. This enabled the elucidation of the effect of side chain length on AMB phase behavior, semicrystalline morphologies, and crystallization kinetics via differential scanning calorimetry, polarized light optical microscopy, and X-ray diffraction experiments. Calculations of segregation strength together with SAXS measurements indicate that all materials have probably phase-segregated structure in the melt. Most of the AMB materials prepared were double crystalline, i.e., contained crystals from alkyl and PEG chains. AMB crystallization was constrained by AMB architecture, the frustration being most evident in AMBs with combinations of either low DPPEG or short alkyl chain lengths. Large, well-developed spherulites, implying breakout crystallization from a weakly segregated melt, were only observed for the AMBs with the combination of the longest PEG chain (DP = 20) and longest alkyl chain length (C20). A peculiar behavior was found when spherulitic growth rates and overall crystallization rates of the PEG chains, within this particular AMB sample, were determined to be a function of crystallization temperature. In both cases, a distinct minimum with decreasing temperature was observed, probably caused by the challenges encountered in crystal packing of the PEG side chains, tethered to an amorphous backbone, which also contained already crystallized C20 chains. This minimum is analogous to that observed in the crystallization of long chain n-alkanes or high molar mass polyethylenes with bromine pendant groups that has been attributed to a self-poisoning effect; this is the first observation of this phenomenon in AMBs.

Molecular dynamics and crystallization in polymers based on ethylene glycol methacrylates (EGMAs) with melt memory characteristics: from linear oligomers to comb-like polymers

“…[54][55][56] In the case of POEGMA-long, g POEGMA demonstrates a change in its E act (from 0.38 to 0.55 eV, Table 2) at higher temperatures. In a very recent work, Czaderna-Lekka et al 28 studied by BDS several poly(oligo(ethylene glycol) methyl ether methacrylate) (POEG-MEA) networks including samples with similar numbers of oxyethylene groups (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). They recorded a g process with a similar time scale to that of g POEGMA here, slightly lower E act B 0.26 eV (24.9 kJ mol À1 ) and attributed its origins to the dipole moments of the ending methoxyl groups.…”

“…Poly(oligo ethylene glycol methacrylate) (POEGMA), the material of interest here, belongs to a class of polymers demonstrating 'graft-like' structures composed of carbon-carbon backbones (hydrophobic) and multiple oligo(ethylene glycol) side-chains (branches) [1][2][3] which are hydrophilic. Such materials are usually addressed as brush-or comb-like polymers [4][5][6][7][8] being the nonlinear poly(ethylene glycol) (PEG) analogues. 2 For short side chains, which occur for less than B10 ethylene glycol units, the POEGMA homopolymers are considered thermoresponsive, as upon thermally induced dehydration they undergo a nanophase transition.…”

“…Brush copolymers consisting of an amorphous main chain and crystallizable side chains can phase separate into a variety of morphologies resulting in copolymers with interesting properties. 5,8,[15][16][17] The crystallization behavior of such brush polymers has been investigated in the past decades by various groups, and according to the generally most accepted model the main chain and a fraction of side chains in the vicinity of the main chain constitute the amorphous phase whereas the side chains are incorporated into crystalline lamella separated by amorphous domains. 5,16 It is widely accepted that factors such as the backbone rigidity, the nature of the linking groups, and the length of the side chains affect significantly the side chain crystallization.…”

Amphiphilic Molecular Brushes with Regular Polydimethylsiloxane Backbone and Poly-2-isopropyl-2-oxazoline Side Chains. 2. Self-Organization in Aqueous Solutions on Heating

“…In particular, significant progress has been made in the study of molecular brushes constructed from components, which differ greatly in chemical nature [52][53][54][55][56]. One of the demanded classes of such amphiphilic polymers is graft copolymers containing stimulisensitive chains.…”

“…In the literature, there is extensive material concerning the development of new synthesis ways of graft copolymers, their experimental study, and theoretical description [ 46 , 47 , 48 , 49 , 50 , 51 ]. In particular, significant progress has been made in the study of molecular brushes constructed from components, which differ greatly in chemical nature [ 52 , 53 , 54 , 55 , 56 ]. One of the demanded classes of such amphiphilic polymers is graft copolymers containing stimuli-sensitive chains.…”