Li-Ling Chang

Characterization of miscible poly(ethylene oxide)/poly(phenyl methacrylate) system and the analysis of asymmetric Tg–composition dependence

Abstract Miscibility in the binary blend comprising of semicrystalline poly(ethylene oxide) (PEO) and fully amorphous poly(phenyl methacrylate) (PPhMA) was discovered for the first time. Differential scanning calorimetry, optical and scanning electron microscopy, and infrared spectroscopy were performed to characterize and demonstrate miscibility in the PEO/PPhMA system (in amorphous domains). The glass transition behavior suggests that the intermolecular interactions between the pairs are not particularly strong. The Fourier-transform infrared spectroscopy results also revealed a weak-to-moderate interaction via the phenyl ring might be likely. The overall behavior of the blend is a miscible system with weak non-specific interactions, and the apparent asymmetry in the Tg–composition relationship has been analyzed with a detailed view of partially segregated PEO crystalline domains.

Surface morphology and Flory-Huggins interaction strength in UCST blend system comprising poly(4-methyl styrene) and isotactic polystyrene

Abstract The surface morphology and polymer–polymer interaction parameter (χ12) of UCST blend systems comprising isotactic polystyrene and poly(4-methyl styrene) (P4MS) were investigated using atomic-force microscopy (AFM) and differential scanning calorimetry (DSC). From the measured glass transition temperature and the specific heat increments (ΔCp) at Tg, it was found that the P4MS dissolved more easily in the iPS rich-phase than did the iPS in the P4MS rich-phase. AFM result also supported that the compatibility increased more in the regions of P4MS-rich compositions than in the regions of PS-rich compositions of the PS/P4MS blends. From the measured Tg’s and apparent weight fractions of iPS and P4MS dissolved in each phase, the values of the Flory–Huggins interaction parameter (χ12) were determined to be 0.0163–0.0232 depending on the composition. These results indicate that the χ12 is quite dependend on the apparent volume fraction of the polymers dissolved in each phase. The values of χ12 calculated from this work (method based on Tg’s of phases) were lower than those estimated using an earlier method based on the UCST or clarity temperatures. All values of χ12 are greater than the values of interaction parameter at the critical point (χ12)c. This fact indicates that the iPS/P4MS blend are immiscible for all blend compositions. The surface of the phase-separated blend system was mostly covered with the P4MS rich-phase owing to its lower surface free energy in comparison with that of the neat iPS. The mechanism of surface phase separation for the P4MS blends with aPS or iPS is governed by two factors: (1) difference in the solubility of the two polymers in the solvent and (2) surface free energy.

Model Compound Study on Network‐Forming Reactions Between Poly(4‐Vinyl Phenol) and an Epoxy

Abstract Quantitative solid‐state 13C‐NMR was used to investigate the chemical reactions in blends of poly(4‐vinyl phenol) (PVPh) with diglycidylether of bisphenol‐A (DGEBA) at high temperatures. The PVPh/DGEBA blends (in absence of cure agents or catalysts) upon heating developed a cross‐linked structure. However, the reacted product was hardened/cross‐linked and not amenable to solution‐NMR characterization. In order to gain more insight into the mechanisms proving the chemical reactions between the epoxide of DGEBA and phenol of PVPh, studies were performed using compounds containing an epoxide group to model the DGEBA monomer and compounds containing an phenol group to model the actual PVPh polymer. The 1H‐ and 13C‐solution‐NMR spectroscopy characterizations demonstrated that chemical reactions between the model compounds. The results showed that the opening of the epoxy ring occurred, transforming the original epoxide ring to a phenyl–ether carbon linkage. The use of the model compounds clearly revealed a mechanism where the phenol group of PVPh reacted with the epoxide of DGEBA leading to a gelled/cross‐linked structure.

Melting and morphology in melt-crystallized meta-linked poly(aryl ether ketone)

Abstract Unique thermal behavior and accompanying morphology in meta -linked poly(ether diphenyl ether ketone) (PEDEK m ) melt-crystallized at various conditions was analyzed. The two widely spaced and well-resolved melting peaks ( T m,1 and T m,2 ) in PEDEK m offered a unique model for proposing a more advanced interpretation on the complex and highly controversial issues of multiple melting and crystalline morphology commonly seen in semi-crystalline polymers. There are two main lamella types of different thickness populations, whose melting peaks labeled P1 and P2 may appear in series giving two melting endotherms at 302 and 322°C, respectively. However, despite the series appearance of two melting peaks upon scanning, only one type of lamellae preferentially exists in the melt-crystallized PEDEK m depending on processing temperatures/histories. When isothermally crystallized at lower temperatures (290°C or lower), PEDEK m possesses only the P1 crystal, which may or may not be melted/re-crystallized into thicker P2 crystal entity depending on heating rates or annealing temperature/time. A break-off temperature for lamellar thickness in PEDEK m is about 300°C. When crystallized at 300°C or higher, PEDEK developed only the P2 crystal, which is mainly a thickened and branched axialite. This study also demonstrated that the unit cell remained unchanged for either the P1 or P2 crystal entities.