Absorption glass transition

Water Absorption Glass Transition Melting Transition Thermal Stability Autoclave Stability Dielectric Constant, 10(2) Hz 10(5) Hz... 

More recently, test products were created of a blend of PMMA with a phenyl-substituted methacrylate these products have a glass-transition temperature of around 125°C, a significantly reduced water absorption compared to pure PMMA of about 0.32%, but also a higher birefringence (a stress-optic coefficient of 5.2 X 10 , compared with 0.3 X 10 for PMMA and 6.8 x 10 for BPA-PC). 

The TPX experimental product of Mitsubishi Petrochemical Ind. (221) is an amorphous, transparent polyolefin with very low water absorption (0.01%) and a glass-transition temperature comparable to that of BPA-PC (ca 150°C). Birefringence (<20 nm/mm), flexural modulus, and elongation at break are on the same level as PMMA (221). The vacuum time, the time in minutes to reach a pressure of 0.13 mPa (10 torr), is similarly short like that of cychc polyolefins. Typical values of TPX are fisted in Table 11. A commercial application of TPX is not known as of this writing. 

The highly polar nature of the TGMDA—DDS system results in high moisture absorption. The plasticization of epoxy matrices by absorbed water and its effect on composite properties have been well documented. As can be seen from Table 4, the TGMDA system can absorb as much as 6.5% (by weight) water (4). This absorbed water results in a dramatic drop in both the glass transition temperature and hot—wet flexural modulus (4—6). 

Thermoplastics grades have a norbomene content in the range 60-80% with Tg values from 60-180°C, in this range the glass transition being almost linearly related to the norbomene content. The modulus of elasticity increases with norbomene content and for commercial materials is in the range 2600-3200 MPa but density (1.02g/cm), tensile strength 66 MPa and water absorption (<0.01 %) is little affected by the monomer ratio. 

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

The simple relation (6.1) is quite useful. It allows an estimate of the gain or loss in yield strength if the glass transition temperature is changed, as for instance by the progress of the curing reaction, by radiation damage, or by absorption of water and of solvents. The ATe is determined fairly easily by thermoanalytical measurements. 

Partially aromatic PAs have a higher glass transition temperature and a higher melting temperature dian their aliphatic counterparts thus these polymers have a better dimensional stability.18 Due to the high Tg and the low water absorption as a result of die presence of die aromatic unit, the effect of water on the properties at room temperature is small. The barrier properties of partially aromatic PAs are also better. However, despite all these favorable properties, their commercial market is relatively small. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

MA Samus, G Rossi. Methanol absorption in ethylene-vinyl alcohol copolymers Relation between solvent diffusion and changes in glass transition temperature in glassy polymeric materials. Macromolecules 29 2275-2288, 1996. 

The absorption of moisture critically affects other important resin properties, particularly those associated with low-dielectric and thermomechanical applications. Results of a 96-h boiling water immersion test are presented in Table 2.2. The moisture absorbed decreased substantially with fluoromethylene chain length from n = 3 to n = 6, followed by only modest decreases for n = 8 and 10. This latter behavior was somewhat unexpected and may be the effect of decreased cross-link density counteracting the increased fluorine content. These 100°C measurements are just above the glass transition and the situation may be different at room temperature. These measurements are in progress. 

Replacement of isopropylidene units in polymer backbones by units of hexafluoroisopropylidene is known to enhance solubility, water and oil repellency, thermal stability, and glass transition temperature (Tg) and to decrease crystallinity and water absorption.1... 

Thus the quantum yield for acid production from triphenylsulfonium salts is 0.8 in solution and about 0.3 in the polymer 2 matrix. The difference between acid generating efficiencies in solution and film may be due in part to the large component of resin absorption. Resin excited state energy may not be efficiently transferred to the sulfonium salt. Furthermore a reduction in quantum yield is generally expected for a radical process carried out in a polymer matrix due to cage effects which prevent the escape of initially formed radicals and result in recombination (IS). However there are cases where little or no difference in quantum efficiency is noted for radical reactions in various media. Photodissociation of diacylperoxides is nearly as efficient in polystyrene below the glass transition point as in fluid solution (12). This case is similar to that of the present study since the dissociation involves a small molecule dispersed in a glassy polymer. 

In the above table, Mj, Vi, Yj and Hj are the contributions for group i for estimating the molecular weight, the molar volume, the glass-transition temperature, and the water absorption, respectively. The model equations for each of these properties are as follows ... 

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