THERMOREVERSIBLE CROSS-LINKING MALEIC ANHYDRIDE GRAFTED CHLOROBUTYL RUBBER WITH HYDROGEN BONDS (COMBINED WITH IONIC INTERACTIONS)

2014 ◽  
Vol 87 (3) ◽  
pp. 459-470 ◽  
Author(s):  
Lin Li ◽  
Jin Kuk Kim
Keyword(s):  
Hydrogen Bonds ◽  
Maleic Anhydride ◽  
Ionic Interactions ◽  
Cross Linking ◽  
External Energy ◽  
Scanning Calorimetry ◽  
Ionic Bonds ◽  
Cross Links ◽  
Ionic Hydrogen Bonds ◽  
Chlorobutyl Rubber

ABSTRACT Thermoreversible cross-linking polymers are designed based on reversible cross-linking bonds. These bonds are able to reversibly dissociate and associate upon the input of external energy, such as heat or light. Reprocessibility is possible for this kind of material. The objective was to thermoreversibly cross-link maleic anhydride grafted chlorobutyl rubber (MAH-g-CIIR) via a reaction with octadecylamine, with an excess to obtain amide-salts, which form both hydrogen bonds and ionic interactions. X-ray diffraction experiments showed the presence of microphase-separated aggregates that acted as physical cross-links for both the MAH-g-CIIR precursor and amide-salts. The tensile properties were improved by converting MAH-g-CIIR to amide-salts, because of the combination of hydrogen bonding and ionic interactions. The cross-linked materials could be repeatedly compression molded at 155 °C into homogeneous films. The differential scanning calorimetry curves and Fourier transform infrared spectra indicate that hydrogen bonds are of a thermoreversible nature, but the recovery of ionic bonds is impossible. After treatment with heating-cooling for up to three cycles, the tensile strength of the thermoreversible cross-linking CIIR was greatly reduced. The gradual reduction in the effectiveness of the ionic-hydrogen bonds is the major contribution to the reprocessibility of these materials.

scholarly journals Chemistry of collagen cross-links: glucose-mediated covalent cross-linking of type-IV collagen in lens capsules

1993 ◽  
Vol 296 (2) ◽  
pp. 489-496 ◽  
Author(s):  
A J Bailey ◽  
T J Sims ◽  
N C Avery ◽  
C A Miles
Keyword(s):  
Type Iv Collagen ◽  
Cross Linking ◽  
Mechanical And Thermal Properties ◽  
Maximum Strain ◽  
Scanning Calorimetry ◽  
Melting Temperatures ◽  
Type Iv ◽  
Collagen Molecules ◽  
Cross Links

The incubation of lens capsules with glucose in vitro resulted in changes in the mechanical and thermal properties of type-IV collagen consistent with increased cross-linking. Differential scanning calorimetry (d.s.c.) of fresh lens capsules showed two major peaks at melting temperatures Tm 1 and Tm 2 at approx. 54 degrees C and 90 degrees C, which can be attributed to the denaturation of the triple helix and 7S domains respectively. Glycosylation of lens capsules in vitro for 24 weeks caused an increase in Tm 1 from 54 degrees C to 61 degrees C, while non-glycosylated, control incubated capsules increased to a Tm 1 of 57 degrees C. The higher temperature required to denature the type-IV collagen after incubation in vitro suggested increased intermolecular cross-linking. Glycosylated lens capsules were more brittle than fresh samples, breaking at a maximum strain of 36.8 +/- 1.8% compared with 75.6 +/- 6.3% for the fresh samples. The stress at maximum strain (or ‘strength’) was dramatically reduced from 12.0 to 4.7 N.mm.mg-1 after glycosylation in vitro. The increased constraints within the system leading to loss of strength and increased brittleness suggested not only the presence of more cross-links but a difference in the location of these cross-links compared with the natural lysyl-aldehyde-derived cross-links. The chemical nature of the fluorescent glucose-derived cross-link following glycosylation was determined as pentosidine, at a concentration of 1 pentosidine molecule per 600 collagen molecules after 24 weeks incubation. Pentosidine was also determined in the lens capsules obtained from uncontrolled diabetics at a level of about 1 per 100 collagen molecules. The concentration of these pentosidine cross-links is far too small to account for the observed changes in the thermal and mechanical properties following incubation in vitro, clearly indicating that another as yet undefined, but apparently more important cross-linking mechanism mediated by glucose is taking place.

scholarly journals Crystal Nucleation and Growth in Cross-Linked Poly(ε-Caprolactone) (PCL)

2021 ◽  
Author(s):  
Timur Mukhametzyanov ◽  
Jürn W.P. Schmelzer ◽  
Egor Yarko ◽  
Albert Abdullin ◽  
Marat Ziganshin ◽  
...  
Keyword(s):  
Average Distance ◽  
Maximum Growth ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Theoretical Interpretation ◽  
Cross Linking ◽  
Scanning Calorimetry ◽  
Transition Range ◽  
Cross Links

The crystal nucleation and overall crystallization kinetics of cross-linked poly(ε-caprolactone) was studied experimentally by fast scanning calorimetry in a wide temperature range. With an increasing degree of cross-linking, both the nucleation and crystallization half-times increase. Concurrently, the glass transition range shifts to higher temperatures. In contrast, the temperatures of the maximum nucleation and the overall crystallization rates remain the same independent of the degree of cross-linking. The cold crystallization peak temperature generally increases as a function of heating rate, reaching an asymptotic value near the temperature of the maximum growth rate. A theoretical interpretation of these results is given in terms of classical nucleation theory. In addition, it is shown that the average distance between the nearest cross-links is smaller than the estimated lamellae thickness, which indicates the inclusion of cross-links in the crystalline phase of the polymer.

scholarly journals Differentiation of physical and chemical cross-linking in gelatin methacryloyl hydrogels

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Lisa Rebers ◽  
Raffael Reichsöllner ◽  
Sophia Regett ◽  
Günter E. M. Tovar ◽  
Kirsten Borchers ◽  
...  
Keyword(s):  
Near Infrared ◽  
Cross Linking ◽  
Cross Link ◽  
Scanning Calorimetry ◽  
Link Density ◽  
Double Bond Conversion ◽  
Cross Links ◽  
Physical And Chemical ◽  
The Impact ◽  
Chemical Cross Linking

AbstractGelatin methacryloyl (GM) hydrogels have been investigated for almost 20 years, especially for biomedical applications. Recently, strengthening effects of a sequential cross-linking procedure, whereby GM hydrogel precursor solutions are cooled before chemical cross-linking, were reported. It was hypothesized that physical and enhanced chemical cross-linking of the GM hydrogels contribute to the observed strengthening effects. However, a detailed investigation is missing so far. In this contribution, we aimed to reveal the impact of physical and chemical cross-linking on strengthening of sequentially cross-linked GM and gelatin methacryloyl acetyl (GMA) hydrogels. We investigated physical and chemical cross-linking of three different GM(A) derivatives (GM10, GM2A8 and GM2), which provided systematically varied ratios of side-group modifications. GM10 contained the highest methacryloylation degree (DM), reducing its ability to cross-link physically. GM2 had the lowest DM and showed physical cross-linking. The total modification degree, determining the physical cross-linking ability, of GM2A8 was comparable to that of GM10, but the chemical cross-linking ability was comparable to GM2. At first, we measured the double bond conversion (DBC) kinetics during chemical GM(A) cross-linking quantitatively in real-time via near infrared spectroscopy-photorheology and showed that the DBC decreased due to sequential cross-linking. Furthermore, results of circular dichroism spectroscopy and differential scanning calorimetry indicated gelation and conformation changes, which increased storage moduli of all GM(A) hydrogels due to sequential cross-linking. The data suggested that the total cross-link density determines hydrogel stiffness, regardless of the physical or chemical nature of the cross-links.

THERMOREVERSIBLE COVALENT CROSS-LINKING OF MALEIC ANHYDRIDE GRAFTED BUTYL RUBBER WITH GLYCEROL

2015 ◽  
Vol 88 (3) ◽  
pp. 373-389 ◽  
Author(s):  
Lin Li ◽  
Shuai Zhao ◽  
Zhenguo Ma ◽  
Zhenxiang Xin
Keyword(s):  
Reaction Time ◽  
Maleic Anhydride ◽  
Reaction Temperature ◽  
Butyl Rubber ◽  
Cross Linking ◽  
Molar Ratios ◽  
Cross Links ◽  
The Cross ◽  
The Fourier Transform ◽  
Percentage Conversion

ABSTRACT The formation of thermoreversible hemi-ester cross-links of maleic anhydride grafted butyl rubber (MAn-g-IIR) using glycerol as a cross-linking agent in the absence of catalyst was studied in the present work. The effects of the molar ratios of glycerol to anhydride, the amount of the mixed solvent, the reaction temperature, and the reaction time on the percentage conversion of anhydride to ester were determined. The maximum percentage conversion calculated from the Fourier transform infrared spectroscopy spectra was 52.11. Reaction temperature played the most important role on the percentage conversion, followed by reaction time. Compared with the original MAn-g-IIR, tensile strength of the hemi-ester cross-linked MAn-g-IIR was significantly improved. These macromolecular regular clusters acted as strong and multiple cross-linking points that led to impressive mechanical properties. This confirmed the formation of hemi-ester cross-links. The covalently cross-linked MAn-g-IIR was reprocessable via compression molding at 179 °C and higher, indicating that the cross-links were indeed thermoreversible. The cross-linked materials could be repeatedly compression molded at 179 °C into homogeneous films for at least three cycles.

Intelligent rubber with tailored properties for self-healing and shape memory

2015 ◽  
Vol 3 (24) ◽  
pp. 12864-12872 ◽  
Author(s):  
Dong Wang ◽  
Jing Guo ◽  
Huan Zhang ◽  
Beichen Cheng ◽  
Heng Shen ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Shape Memory ◽  
Self Healing ◽  
Memory Functions ◽  
Cross Links ◽  
Ionic Hydrogen Bonds

Thermoreversible rubbers are prepared by the thiol-ene functionalized polybutadiene oligomers via dynamic ionic hydrogen bonds and covalent cross-links, exhibiting tailored properties for self-healing and shape memory functions.

Thermal properties of polyurethane elastomers from soybean oil-based polyol with a different isocyanate index

2018 ◽  
Vol 51 (2) ◽  
pp. 157-174 ◽  
Author(s):  
Kamila Mizera ◽  
Joanna Ryszkowska
Keyword(s):  
Thermal Stability ◽  
Wear Resistance ◽  
Thermal Properties ◽  
Hydrogen Bonds ◽  
Soybean Oil ◽  
Physicomechanical Properties ◽  
Cross Linking ◽  
Scanning Calorimetry ◽  
Polyurethane Elastomers ◽  
Isocyanate Index

The aim of this work was to determine the influence of used soybean oil (SO)-based polyol on the thermal properties of tested polyurethane elastomers (PUEs), with a different value of isocyanate index (INCO). The thermal properties determined by thermogravimetric analysis and differential scanning calorimetry show that the highest INCO causes an increase in hydrogen bonds in PUEs and higher thermal stability. A structural analysis and degree of phase separation (DPS) of the tested PUEs were carried out via Fourier transform infrared spectroscopy. This analysis showed that at INCO = 1.02, the largest number of urethane bonds arises in PUE. The physicomechanical properties of PUEs were also tested via density, resilience, hardness, and wear resistance. The results concluded that the increasing number of –NCO groups during production of PUEs with SO polyol changes the number of hydrogen bonds and DPS and causes the increase of properties such as thermal resistance, storage modulus, cross-linking density, and wear resistance.

scholarly journals Synthesis and Characterization of N-Substituted Polyether-Block-Amide Copolymers

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 773
Author(s):  
Jyun-Yan Ye ◽  
Kuo-Fu Peng ◽  
Yu-Ning Zhang ◽  
Szu-Yuan Huang ◽  
Mong Liang
Keyword(s):  
Titanium Isopropoxide ◽  
Decomposition Temperature ◽  
Phenyl Isocyanate ◽  
Cross Linking ◽  
Resonance Spectroscopy ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Degradation Temperature ◽  
Melt Polycondensation ◽  
Structural Regularity

A series of N-substituted polyether-block-amide (PEBA-X%) copolymers were prepared by melt polycondensation of nylon-6 prepolymer and polytetramethylene ether glycol at an elevated temperature using titanium isopropoxide as a catalyst. The structure, thermal properties, and crystallinity of PEBA-X% were investigated using nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, wide angle X-ray diffraction, and thermogravimetric analysis. In general, the crystallinity, melting point, and thermal degradation temperature of PEBA-X% decreased as the incorporation of N-methyl functionalized groups increased, owing to the disruption caused to the structural regularity of the copolymer. However, in N-acetyl functionalized analogues, the crystallinity first dropped and then increased because of a new γ form arrangement that developed in the microstructure. After the cross-linking reaction of the N-methyl-substituted derivative, which has electron-donating characteristics, with poly(4,4′-methylenebis(phenyl isocyanate), the decomposition temperature of the resulting polymer significantly increased, whereas no such improvements could be observed in the case of the electro-withdrawing N-acetyl-substituted derivative, because of the incompleteness of its cross-linking reaction.

Thermal properties of polybenzoxazine exhibiting improved toughness: Blending with cyclodextrin and its derivatives

2021 ◽  
pp. 095400832110130
Author(s):  
Hailong Li ◽  
Sipei Zhao ◽  
Li Pei ◽  
Zihe Qiao ◽  
Ding Han ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Hydrogen Bonds ◽  
High Performance ◽  
Practical Application ◽  
Scanning Calorimetry ◽  
Thermoset Resins ◽  
Chemical Structures ◽  
Microscopy Techniques ◽  
Fractured Surface ◽  
Scanning Electron

Polybenzoxazines are emerging as a class of high-performance thermoset polymers that can find their applications in various fields. However, its practical application is limited by its low toughness. The cyclic β-cyclodextrin and a newly synthesized derivative (β-cyclodextrin-MAH) were separately blended with benzoxazine to improve the toughness of polybenzoxazine. The results revealed that the maximum impact strength of the blend was 12.24 kJ·m−2 and 14.29 kJ·m−2 when 1 wt.% of β-Cyclodextrin and β-Cyclodextrin-MAH, respectively, were used. The strengths were 53% and 86% higher than that of pure polybenzoxazine. The curing reaction, possible chemical structures, and fractured surface were examined using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques to understand the mechanism of generation of toughness. The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and β-cyclodextrin and β-cyclodextrin-MAH resulted in the generation of toughness. Furthermore, the curves generated during thermogravimetric analysis did not significantly change, revealing the good thermal properties of the system. The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties. This can be a potential way of modifying the thermoset resins.

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