Confinement effect of chain dynamics in micrometer thick layers of a polymer melt below the critical molecular weight

2006 ◽  
Vol 124 (11) ◽  
pp. 114903 ◽  
Author(s):  
Ravinath Kausik ◽  
Carlos Mattea ◽  
Nail Fatkullin ◽  
Rainer Kimmich
Keyword(s):  
Molecular Weight ◽  
Polymer Melt ◽  
Confinement Effect ◽  
Chain Dynamics ◽  
Critical Molecular Weight ◽  
Thick Layers

scholarly journals Melt Blending Modification of Commercial Polystyrene with Its Half Critical Molecular Weight, High Ion Content Ionomer, Poly(styrene–ran–cinnamic Acid) Zn Salt, toward Heat Resistance Improvement

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 584
Author(s):  
Zixin Yu ◽  
Jie Wang ◽  
Peihua Li ◽  
Dachuan Ding ◽  
Xuan Zheng ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Heat Resistance ◽  
Cinnamic Acid ◽  
Average Molecular Weight ◽  
Softening Temperature ◽  
Melt Blending ◽  
Ion Content ◽  
Critical Weight ◽  
Critical Molecular Weight ◽  
Cross Links

A half-critical weight-average molecular weight ( M ¯ w ) (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 M ¯ w 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 M ¯ w 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 M ¯ w , high-ion-content ionomer.

The Structure of Angular Polycycloisoprene

1963 ◽  
Vol 36 (2) ◽  
pp. 558-560 ◽  
Author(s):  
F. T. Wallenberger
Keyword(s):  
Molecular Weight ◽  
Refractive Index ◽  
Chemical Structure ◽  
Polymer Melt ◽  
Stannic Chloride ◽  
Polymeric Product ◽  
Melt Temperature ◽  
Reaction Proceeds ◽  
Ring Polymers ◽  
Silent Electric Discharge

Abstract Lewis and Brö nsted acids, heat, silent electric discharge and cathode rays cause progressing isomerization of synthetic and natural cis-1,4-polyisoprene to yield a polymeric product which has the empirical formula, (C5H8)n identical with that of the initial rubber hydrocarbon. The reaction, commonly carried out in benzene with stannic chloride as catalyst, is accompanied by an increase in specific gravity, refractive index and polymer melt temperature and a decrease in unsaturation, intrinsic viscosity and molecular weight of the material. The resulting polymer, readily soluble in a variety of solvents, is known as cyclized rubber, cyclo-caoutchouc, or “Pliolite-NR”, manufactured by the Goodyear Tire and Rubber Company. Staudinger recognized as early as 1926 that the reaction proceeds by isomerization and intramolecular cyclization. D'lanni postulated formation of cyclohexane rings within the polymer chain, while Veersen extended D'lanni's proposal and suggested random protonation of bonds leading to intralinear, mono-, di-, and polycyclic ring polymers. Ideally, complete and stereoselective cyclization would lead to angular polycycloisoprene. Comprehensive reviews concerning the chemistry of the cyclization have been published by Reese and by Bloomfield. This communication provides the first chemical structure proof of the cyclized product. It is based on the cyclization of cis-1,4- and of trans-1,4-polyisoprene. The resulting products were identical and their properties in agreement with literature data. Hence cyclization must have proceeded through a common intermediate.

scholarly journals Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length

2010 ◽  
Vol 6 ◽  
Author(s):  
Florian K Wolf ◽  
Anna M Fischer ◽  
Holger Frey
Keyword(s):  
Molecular Weight ◽  
Ring Opening ◽  
Biomedical Applications ◽  
Weight Control ◽  
Glycolic Acid ◽  
Polymer Melt ◽  
Degree Of Polymerization ◽  
Star Block Copolymers ◽  
Grafting From ◽  
Low Solubility

Due to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (<1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of glycolide in the melt. With this strategy it is possible to combine high molecular weight with good molecular weight control (up to 16,000 g/mol, PDI = 1.4–1.7), resulting in PGA multi-arm star block copolymers containing more than 90 wt % GA. The successful linkage of PGA arms and PG core via this core first/grafting from strategy was confirmed by detailed NMR and SEC characterization. Various PG/glycolide ratios were employed to vary the length of the PGA arms. Besides fluorinated solvents, the materials were soluble in DMF and DMSO up to an average arm length of 12 glycolic acid units. Reduction in the T g and the melting temperature compared to the homopolymer PGA should lead to simplified processing conditions. The findings contribute to broadening the range of biomedical applications of PGA.

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