Chain Folding in Semicrystalline Oxybutylene/Oxyethylene/Oxybutylene Triblock Copolymers Studied by Raman Spectroscopy

Abstract

The chain-folding behavior of short oxybutylene/oxyethylene/oxybutylene triblock copolymers with one crystallizable E block and two noncrystallizable B blocks has been studied by low-frequency Raman spectroscopy in combination with small-angle X-ray scattering and differential scanning calorimetry. The advantage of using Raman spectroscopy in this application is demonstrated. The results point to folded-chain conformations in which the oxyethylene blocks are orientated normal to the lamellar end plane. It is probable that the oxybutylene blocks are similarly orientated. Comparison is made with related results for short oxypropylene/oxyethylene/oxypropylene triblock copolymers.

Confinement Size Effect on Crystal Orientation Changes of Poly(ethylene oxide) Blocks in Poly(ethylene oxide)-b-polystyrene Diblock Copolymers

“…Several experimental observations such as the “break-out” crystallization have also been reported. The crystallization behaviors are affected by chain architectures, molecular weights, hardness of the confinements, and confined phase morphologies. ,− …”

“…The crystallization behaviors are affected by chain architectures, molecular weights, hardness of the confinements, and confined phase morphologies. 16,[18][19][20][21][22][23][24][25][26][27] In one of our recent investigations, a lamellar-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) (M h n PEO ) 8.7K g/mol and M h n PS ) 9.2K g/mol) diblock copolymer was studied. [13][14][15] A large-amplitude oscillating shear was used to generate the macroscopically aligned lamellar phase morphology, and the lamellae normal (n ˆ) was perpendicular to the shear plane.…”

Equilibrium Control of Crystal Thickness and Melting Point through Block Copolymerization

“…To meet this requirement, the crystalline block adopts an equilibrium degree of chain folding to increase its area per chain at the interface, while the amorphous block adopts a distorted random coil conformation or even a strongly stretched conformation for very short blocks. 8 The longer the amorphous block, the more folded the crystalline block becomes. The scaling prediction of the DGH theory 5 for the lamellar repeat distance d illustrated in Figure 1a is where N t and N a are the degrees of polymerization of the entire diblock and the amorphous block.…”

“…Since the two blocks are covalently connected, each must occupy the same area on both sides of the lamellar interface while filling space at bulk density. To meet this requirement, the crystalline block adopts an equilibrium degree of chain folding to increase its area per chain at the interface, while the amorphous block adopts a distorted random coil conformation or even a strongly stretched conformation for very short blocks . The longer the amorphous block, the more folded the crystalline block becomes.…”

“…Another requirement is that the material is not kinetically constrained in adopting the equilibrium structure shown in Figure a, as might occur if the blocks were microphase-separated in the melt. Such a situation commonly occurs in polymers containing poly(ethylene oxide) blocks, PEO, which exhibit a large Flory interaction parameter (χ) against the nonpolar amorphous blocks with which they are commonly paired. ,− Achieving the equilibrium structure is particularly difficult when the crystallizable block forms discrete domains in the melt (spheres, cylinders), but it is for precisely such caseswhere the amorphous block is long relative to the crystalline blockthat the extent of chain folding induced by the amorphous block is predicted to be greatest and for which eq 1 was developed. Even in diblocks comprised only of saturated hydrocarbons, melt microphase separation will still occur when the molecular weights are sufficiently large, such that χ N t exceeds that at the order−disorder transition .…”