Abstract
A half-critical weight-average molecular weight () (approximately 21,000 g mol−1), high-ion-content Zn-salt poly(styrene–ran–cinnamic-acid) (SCA–Zn) ionomer was successfully synthesized by styrene–cinnamic-acid (10.8 mol %) copolymerization followed by excess-ZnO melt neutralization. At 220 °C, the SCA–Zn’s viscosity was only approximately 1.5 magnitude orders higher than that of commercial polystyrene (PS) at 102 s−1, and the PS/SCA–Zn (5–40 wt %) melt blends showed apparently fine, two-phased morphologies with blurred interfaces, of which the 95/5 and 90/10 demonstrated Han plots suggesting their near miscibility. These indicate that any PS–(SCA–Zn) processability mismatch was minimized by the SCA–Zn’s half-critical despite its dense ionic cross-links. Meanwhile, the SCA–Zn’s Vicat softening temperature (VST) was maximized by its cross-linking toward 153.1 °C, from that (97.7 °C) of PS, based on its half-critical at which the ultimate glass-transition temperature was approximated. Below approximately 110 °C, the PS/SCA–Zn (0–20 wt %) were seemingly miscible when their VST increased linearly yet slightly with the SCA–Zn fraction due to the dissolution of the SCA–Zn’s cross-links. Nevertheless, the 60/40 blend’s VST significantly diverged positively from the linearity until 111.1 °C, revealing its phase-separated morphology that effectively enhanced the heat resistance by the highly cross-linked SCA–Zn. This work proposes a methodology of improving PS heat resistance by melt blending with its half-critical , high-ion-content ionomer.
Highlights
Owing to its relatively high strength and modulus, superior electrical insulation, satisfactory dyeability, and excellent processability, polystyrene (PS) has widely been used in construction, automotive, packaging, etc. industries
With respect to its molecular weight (Mw) –Tg relationship. Such a low Mw might maximally improve the processability of the potential SCA, despite the possible cinnamic acid (CA) introduction of interchain hydrogen bond cross-links, while essentially maintaining its highest possible Tg. This is because the ultimate Tg (i.e., Tg∞ ) at ca. the critical Mw of polymers decreases little with a reduction in their Mw by half
These results show that the SCA–Zn 40 wt % incorporation appreciably improved the heat resistance of the PS/SCA–Zn blend essentially at the expense of its mechanical properties due to the two phases insufficiently adhering to each other
Summary
Owing to its relatively high strength and modulus, superior electrical insulation, satisfactory dyeability, and excellent processability, polystyrene (PS) has widely been used in construction, automotive, packaging, etc. industries. Polymers 2020, 12, 584 toughness, which, along with its not high enough heat resistance (Vicat softening temperature, VST and glass transition temperature, Tg of both approximately 100 ◦ C), limits its extension to engineering applications. Numerous modifications are conducted to improve the heat resistance of PS, e.g., blending, copolymerization, grafting, filling, interpenetration, their combinations, etc. When PS is melt-blended with more rigid resins such as poly(bisphenol-A carbonate) (PC) [1], brominated PS [2], etc., the VST of the blends is enhanced effectively; the blending of PS with more flexible polymers such as elastomers [3,4], high-density polyethylene [5], poly(lactic acid) [6], etc. May increase the blends’ impact toughness, while their VST is reduced. Upon solution grafting with methyl methacrylate [15] and 1,4-dimethyl-2,5-dichloromethyl benzene [16]
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