Structure and Crystallization Behavior of Poly(ethylene oxide) (PEO) Chains in Core–Shell Brush Copolymers with Poly(propylene oxide)-block-poly(ethylene oxide) Side Chains

Abstract

Core–shell brush copolymers featuring a poly­(p-hydroxystyrene) (PHOS) backbone and PPO-b-PEO (PPO and PEO stand for poly­(propylene oxide) and poly­(ethylene oxide)) side chains with different molecular compositions and exhibiting two inverse molecular architectures in regard to the side chains were investigated. Differential scanning calorimetry (DSC) and temperature-resolved wide- and small-angle X-ray scattering (WAXS/SAXS) were used to characterize the thermal and structural behavior. For the sample with the crystallizable PEO block linked directly to the backbone and a high PEO fraction (84.9 wt %), our results reveal a PEO crystallization/melting behavior similar to the one of bulk PEO. Surprisingly, the crystalline order, as determined by WAXS, persists up to 30 K above the melting point determined by DSC (T m = 54 °C). For the samples where the PPO block is directly linked to PHOS backbone and the PEO chains are dangling, our results indicate that the side arm architecture has remarkable effects on the thermal and structural behavior. With decreasing PEO fraction in the side arms, the calorimetric crystallization temperature, T c, and the melting point, T m, of the PEO domains are strongly suppressed, reaching values as low as −45 °C and −8 °C, respectively. Furthermore, PEO crystallizes in an asymmetric lamellar phase with a distorted PEO crystalline phase. Above T m the morphology changes from microphase-separated symmetric lamellae to hexagonally perforated lamellae with PEO domains immersed within a PHOS/PPO matrix with decreasing PEO fraction. Our results suggest that this specific brush copolymer architecture allows for tuning the ability of PEO blocks to crystallize.

The effect of poly(ethylene glycol) mixed with poly(l‐lactic acid) on the crystallization characteristics and properties of their blends

“…The degree of crystallinity ( X c ) was evaluated using Eqn : where Δ H cc and Δ H m are the cold crystallization and melting enthalpies (J g −1 ), respectively, that were calculated from the cold crystallization and fusion peaks in DSC second heating curves, is the melting enthalpy of the 100% crystalline polymer and f is the weight fraction of each polymer in the blend. The theoretical values of 100% crystalline polymer melting enthalpies () used to calculate X c were 197 J g −1 for PEG and 93.1 J g −1 for PLLA . The reported enthalpy values have been normalized to the weight fraction of each constituent in the blend.…”

“…focused on plasticizing amorphous poly[( l ‐lactide)‐ co ‐( d , l ‐lactide)] with four different commercially available adipates, in order to enhance its mechanical and thermal properties. One of the most promising candidates widely used in the plastics industry to improve processability and ductility of semicrystalline polymers is poly(ethylene glycol) (PEG) . PEG is a linear or branched hydroxyl‐terminated polyether, which is usually prepared by anionic ring‐opening polymerization of ethylene oxide .…”

Recent progress in block copolymer crystallization

“…Here, blocks are tethered/constrained in ways different than the single tether; however, the crystallization behavior is related. Recent work has been focused on the morphologies of highly branched copolymers, such as graft copolymers, brush copolymers, and hyperbranched copolymers . For this review, we have focused only on highly branched BCP architectures (molecular schematics in Figure ) where polymer chains are involved in the crystallization process.…”

“…Brush copolymers of varying architectures were used to study the crystallization of PEO, PCL, and stereo PLLA/PDLA side chains . In one PEO study, a poly(norbornene) backbone was grafted with PS and PEO chains in a BCP type architecture where PS chains were grafted on one half while PEO chains were grafted on the other to form bottlebrush block copolymers (BBCP) .…”

“…The SAXS morphological features were maintained above T m as measure by WAXD. In another brush copolymer PEO study, core‐shell type grafts of PEO‐ b ‐PPO were attached to a poly(hydroxystyrene) backbone . The placement of the PEO chain was switched between the core (inside) block and the shell (outside) block, and the M n PEO shell block was varied ( w PEO = 0.23‐0.85).…”