Dynamic mechanical analysis, acrylate

Crosslinked polymer networks formed from multifunctional acrylates are completely insoluble. Consequently, solid-state nuclear magnetic resonance (NMR) spectroscopy becomes an attractive method to determine the degree of crosslinking of such polymers (1-4). Solid-state NMR spectroscopy has been used to study the homopolymerization kinetics of various diacrylates and to distinguish between constrained and unconstrained, or unreacted double bonds in polymers (5,6). Solid-state NMR techniques can also be used to determine the domain sizes of different polymer phases and to determine the presence of microgels within a poly multiacrylate sample (7). The results of solid-state NMR experiments have also been correlated to dynamic mechanical analysis measurements of the glass transition (1,8,9) of various polydiacrylates. 

Abbreviations y x AFM AIBN BuMA Ca DCP DMA DMS DSC EGDMA EMA EPDM FT-IR HDPE HTV IPN LDPE LLDPE MA MAA MDI MMA PA PAC PB PBT PBuMA PDMS PDMS-NH2 interfacial tension viscosity ratio atomic force microscopy 2,2 -azobis(isobutyronitrile) butyl methacrylate capillary number dicumyl peroxide dynamic mechanical analysis dynamic mechanical spectroscopy differential scanning calorimetry ethylene glycol dimethacrylate ethyl methacrylate ethylene-propylene-diene rubber Fourier transform-infra-red high density polyethylene high temperature vulcanization interpenetrating polymer network low density polyethylene linear low density polyethylene maleic anhydride methacrylic acid 4,4 -diphenylmethanediisocyanate methyl methacrylate poly( amide) poly( acrylate) poly(butadiene) poly(butylene terephtalate) poly(butyl methacrylate) poly(dimethylsiloxane) amino-terminated poly(dimethylsiloxane)... 

Fig. 9. Dynamic mechanical analysis plots of tan 5 against temperature for chlorinated polyethylene (52 % Cl) (4) and blends with poly(butyl acrylate) containing (3) 84.7% PBA, (2) 64.1 % PBA, and (1) 46.1 % PBA. The inset shows a plot of T, against weight percent chlorinated polyethylene where there is a marked deviation from linearity indicative of a specific interaction...

Demonstration of Dual Cure. To demonstrate thermal cure after UV cure three sets of films were prepared for Dynamic Mechanical Analysis (DMA). In the first set, four formulations were based on AM 1, AH 2, the epoxy acrylate, amd the urethane acrylate. Formulations used the test resin at 65% in TPGDA, and included 3% Darocur 1173 as a source of free radicals. DMA plots for the epoxy acrylate and urethane acrylate are shown in Figure 9. The elastic or storage modulus (E ) in the rubbery region is often used as a measure of crosslink density. The maximum of the tan delta plot, not shown, is... 

Other systems investigated by this group are butyl rubber, - natural rubber sensitized with acrylates,chloroprene, chlorobutyl rubber and nitrile rubber.More recently, Perera has examined the relationship between chemical changes in radiation-grafted natural rubber, determined using MAS NMR, and mechanical properties measured using dynamic mechanical analysis. 

Figure 22 Dynamic mechanical analysis of acrylic fibres in air, water and solutions of benzyl alcohol. Measurements performed in tension at a frequency of I Hz, heating rate 1°C min. Curves shown offset for clarity...

Several experimental approaches have been applied for determining the fiber Tg under hot wet conditions [199-203]. Aiken et al. [199] compared the Tg of a commercial acrylic yarn in the dry state and in water using dynamic-mechanical analysis, and observed a reduction from 92 to 72°C. Bell and Murayama [200] observed that the Tg of a commercial AN-NA copolymer decreased from 128°C when dry to 80°C in a 100% relative humidity atmosphere. Gur-Arieh and Ingamells [201] related the extension in length of Acrilan filaments to a Tg reduction and showed a shift from a 90°C in air to 57°C in water. Finally, Hori et al. [202] used DSC to show that the Tg of four kinds of acryhc fibers decreased with increasing water content and approached an almost constant value for all four fibers. 

This study compared methacrylate and acrylate polymers to structural analogs with fluorinated ester groups. Two types of relaxations were characterized, the primary relaxation associated with the glass transition and secondary relaxations associated with side group motion and localized segmental motion. Dielectric analysis was used to characterize the response of dipoles to an electric field as a fimction of temperature. Mechanical properties were analyzed via dynamic mechanical analysis and stress relaxation measurements. Relaxation behavior was interpreted in terms of intermolecular and intramolecular mechanisms. 

Dias et al., used, what they called, a hyphenated rapid real-time dynamic mechanical analysis (RT DMA) and time resolved near-infi ared spectroscopy to simultaneously monitor photopolymerization of acrylate coating compositions. This allowed them to determine the rate of conversion and the mechanical properties of the finished films. It is claimed that up to 374 near infrared spectra and to 50 dynamic analysis points can be accumulated within a second. They observed that modulus buildup does not linearly follow chemical conversion of acrylate bonds. The gel point is detected after passing a certain critical acrylate conversion. Their experimental data revealed a critical dependence of the mechanical property development during the later stage of acrylate conversion. 

It is well known that adhesives need to be low-modulus elastomers, so that the resin formulation has to be designed to give, after UV-curing, a soft material with a low glass transition temperature (Fg). Fig. 3 shows some typical elastic modulus E) and tan S profiles recorded by dynamic mechanical analysis for a UV-cured polyurethane-acrylate which is suitable for adhesives applications, based on its E and Tg values. It is quite soft, as shown by its Persoz hardness value of 50 s, on a scale that goes up to 400 s for glassy materials. 

Figure5.6 Dynamic mechanical analysis (tan 5 versus temperature) for poly(vinyl amine) blends with ethylene/acrylic acid copolymers (reproduced (replotted) from Robeson, L. M., Kuphal, J. A. and Vratsanos, M. S., J. Appl. Polym. Sci. (1996) 61, p. 1561, with permission by John Wiley Sons, Inc.)...

Yang, J.-M., Li, H.-M., Yang, M.-C., and Shih, C.-H., 1999, Characterization of acrylic bone cements using dynamic mechanical analysis. J. Biomed. Mater. Res. (Appl. Biomater.) 48 52-60. 

The use of differential scanning calorimetry to identify secondary transitions in thermoplastics is studied. The temperature and breadth of the secondary transition are related to the those of the alpha transition in a variety of methacrylate, acrylate and styrene polymers, as well as polycarbonate. The effect of thermal history and the position and sharpness of these endothermic transitions is discussed. Some comparisons are made between this technique and results obtained via dielectric analysis and dynamic mechanical analysis obtained in the laboratory. 7 refs. 

Our research focuses on the structure and transport properties of cross-linked PEO (XLPEO) networks prepared with varying cross-link density and network architecture. Networks were synthesized via photopolymerization of poly(ethylene glycol) diacrylatc cross-linker in the presence of water as a diluent or via copolymetization with acrylate monomers, leading to network stractures as depicted schematically in Figure 35.1. Dynamic mechanical analysis was used to characterize the viscoelastic properties of the networks, and the static and dynamic characteristics of these materials were related to their gas separation performance. 

Adsorption of rubber over the nanosilica particles alters the viscoelastic responses. Analysis of dynamic mechanical properties therefore provides a direct clue of the mbber-silica interaction. Figure 3.22 shows the variation in storage modulus (log scale) and tan 8 against temperature for ACM-silica, ENR-silica, and in situ acrylic copolymer and terpolymer-silica hybrid nanocomposites. 

Reaction-induced phase separation is certainly also the reason for which an inhomogeneous structure is observed for photocured polyurethane acrylate networks based on polypropylene oxide (Barbeau et al., 1999). TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10-200 nm, mostly constituted by clusters of small hard units (the diacrylated diisocyanate) connected by polyacrylate chains. In addition, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements. Post-reaction increases the crosslink density inside the hard domains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates the presence of a two-phase structure. 

Analysis of the dynamic mechanical properties of acrylic polymers has been the subject of numerous investigations [169,205 214]. In most of these investigations, the measurements were made using a Rheovibron, which utilizes the forced-resonance principle [203]. 

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