Monomeric Melts

Trioxane and Tetraoxane. The cycHc symmetrical trimer of formaldehyde, trioxane [110-88-3] is prepared by acid-catalyzed Hquid- or vapor-phase processes (147—151). It is a colorless crystalline soHd that bods at 114.5°C and melts at 61—62°C (17,152). The heats of formation are — 176.9 kJ/mol (—42.28 kcal/mol) from monomeric formaldehyde and —88.7 kJ/mol (—21.19 kcal/mol) from 60% aqueous formaldehyde. It can be produced by continuous distillation of 60% aqueous formaldehyde containing 2—5% sulfuric acid. Trioxane is extracted from the distillate with benzene or methylene chloride and recovered by distillation (153) or crystallization (154). It is mainly used for the production of acetal resins (qv). 

It melts at 39°C and may be purified by vacuum sublimation. The Hquid boils at 233°C to give a monomeric vapor in which the Ti—Br distance is 231 pm. Titanium tetrabromide is soluble in dry chloroform, carbon tetrachloride, ether, and alcohol. Like titanium tetrachloride, TiBr forms a range of adducts with molecules such as ammonia, amines, nitrogen heterocycles, esters, and ethers. 

While the chemistry of radiation curable hot melt adhesives is the same as that used in liquid (syrup) adhesives and coatings discussed elsewhere in this volume, there is a fundamental difference between the objectives of reaction in the two types of systems. Syrups consist largely or entirely of reactive monomeric and/or oligomeric materials. Radiation is used to initiate the polymerization of virtually the entire mass. In contrast, hot melts generally contain polymers initially, and these polymers are capable of reaction via radiation to produce chain extension and... 

The most commonly used isocyanate in urethane adhesives is MDI. The pure material methylene diphenyl-isocyanate is a solid that melts around 37°C. Many variations of MDI are commercially available, and these variations fall into three major classes monomeric MDI, modified MDI s, and polymeric MDI s. 

Monomeric MDI Pure 4,4 -MDI 2.0 Solid (MP = 37 C) Flexible prepolymers Liquid 1-K adhesive Thermoplastic adhesives Curing hot melts Solvent-borne adhesives... 

Most moisture-curing hot-melt adhesives utilize a crystallizable backbone and are based almost exclusively on monomeric MDI at NCO/OH ratios of 1.5 to 2.2. Poly(hexamethylene adipate) polyol is the workhorse of the curing hot-melt adhesives. 

B. Petroff, A. Milchev, I. Gutzow. Thermodynamic functions of both simple (monomeric) and polymeric melts MFA approach and Monte Carlo simulation. J Macromol Sci B 55 763-794, 1996. 

The thionitrosyl group may be stabilized either by a dimethylamino substituent or by the use of a highly bulky ort/io-substituted aryl groups. Ai,A -Dimethylthionitrosoamine M2NNS is obtained as a low melting, deep purple solid from the reaction of 1,1-dimethylhydrazine with sulfur (Eq. 10.1) or by the reduction of Mc2NNSO with LiAlH4. This thermally unstable derivative is monomeric in solution. 

Additives may be monomeric, oligomeric or high polymeric (typically impact modifiers and processing aids). They may be liquid-like or high-melting and therefore show very different viscosity compared to the polymer melt in which they are to be dispersed. 

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

Fig. 9. Kinematic viscosity v = r /p (r viscosity, p density) divided by S2/M (S2 = mean square radius of gyration, M molecular mass) as a function of M for polyethylene melts at the same monomeric friction coefficient. (Reprinted with permission from [48]. Copyright 1987 American Chemical Society, Washington)...

Copolyesters of poly(3HB-co-3HV) have approximately the same degree of crystallinity as the homopolymer PHB and all copolymers show similar conformation characteristics as those observed for PHB [24,26,65]. They show a minimum in their melting point versus composition curve at a 3HV content of approximately 40 mol%. The apparent ability of the two different monomeric units to cocrystallize might result from the fact that the copolymers are prone to show isodimorphic behavior [21, 26, 66-70]. However, the considerable reduction of the heat of fusion upon 3HV inclusion, as reported by Bluhm et al. 

InthisequationTm is the melting point in Kelvin of polymers with a number average molecular weight Mn. Polymer of infinite molecular weight melts at Tm,. The molecular weight of the monomeric unit is Ma, R the gas... 

In these formulas the letter X stands for the average copolymer composition, while of denotes the dispersion of the SCD quantitatively characterizing its width. The second of these statistical characteristics is extremely significant for the thermodynamics of the melt of a heteropolymer specimen, being in a simple way AHmix = RT jof connected with the specific enthalpy of mixing Affmix per mole of monomeric units. Here T is the absolute temperature, R represents the gas constant, whereas / denotes the Flory /-parameter whose values are available from the literature for many pairs of monomeric units (see, for example, [7]). 

Crystallization from w-pentane gives colorless crystals of 1, which are soluble in all common aprotic organic solvents. Compound 1 is monomeric in benzene solution, sensitive towards hydrolysis, but stable in air for short periods of exposure. It melts at 171 °C without decomposition, but decomposes under MOCYD-conditions to elemental silicon at about 600 °C. At room temperature 1 is regarded to be indefinitely persistent in the solid state and in solution in toluene solution it survives unchanged after heating to 110° for several days. 

Three flame retardants were compared in this study, namely, a brominated polycarbonate oligomer (58% bromine), a brominated polystyrene (68% bromine), and a brominated triaryl phosphate ester (60% bromine plus 4% phosphorus). These are described in Table I. Figures 1 and 2 compare the thermal stability of the brominated phosphate with commercial bromine-containing flame retardants by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The brominated phosphate melts at 110°C and shows a 1% weight loss at 300°C. Brominated polycarbonate and brominated polystyrene are polymeric and are not as volatile at elevated temperatures as the monomeric flame retardants. 

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