Glass transition temperature of polyurethane

Effect of varying polyol molecular weight on the glass transition temperature of polyurethanes... 

YangBetal (2005) Qualitative separation of the effects of carbon nano-powder and moisture on the glass transition temperature of polyurethane shape memory polymer. Scr Mater... 

Table 6.6. Glass Transition Temperatures of Polyurethane/Polyacrylate SINs...

Pan, G. H., Huang, W. M., Ng, Z. C., Liu, N., Phee, S. J. (2008), Hie glass transition temperature of polyurethane shape memory polymer reinforced with treated/non-treated attapulgite (playgorskite) clay in dry and wet conditions. Smart Materials and... 

The isosorbide polyurethane based on the aliphatic diisocyanate P(I-HMDI) is flexible. It is a thermoplastic with a glass transition temperature of 110°C and softening temperature of 190°C. Both transitions are well below its degradation onset which occurs at approximately 260°C. It forms good films by evaporation from its solutions and colorless transparent compression moldings. 

Polyurethane Networks. Andrady and Sefcik (1983) have applied the same relationship as Rietsch et al. (1976), to the glass transition temperature of networks based on poly(propylene oxide) diols with a controlled molar mass distribution, crosslinked by aromatic triisocyanates. They obtained a Kr value of 25 K kg mol-1, about twice that for PS networks. They showed that the length distribution of elastically active chain lengths, directly related to the molar mass distribution of the starting poly(propylene oxide), has practically no effect on Tg. 

An important application for hydroformylated oils and fats is the production of polyurethanes. Hydroformylated fatty acids are hydrogenated to the corresponding diols and then converted to polyurethanes with diphenylmethane diisocyanate (Scheme 11). The polymer has a glass transition temperature of —33°C to —56°C, and the molecular weight is between 1,000 and 4,000 [12]. 

Figure 14. Plots of the glass transition temperature of the soft segment phase, Tffs, Young s modulus E, and SAXS intensity, l(cps), vs. post-annealing time for a commercial polyester polyurethane (MDI/BD based), R53 (Hooker Chemical Company) (fixed s = 0.042 A 1 for SAXS data) (97).

Dynamic mechanical property (DMP) measurements are used to evaluate the suitability of a polymer for a particular use in sound and vibration damping. Since the dynamic mechanical properties of a polyurethane are known to be affected by polymer morphology (4), it is important to establish the crystallization and melting behavior as well as the glass transition temperature of each polymer. Differential scanning calorimetry (DSC) was used to determine these properties and the data used to interpret the dynamic mechanical property results. 

Organometallic polyurethanes containing backbone polyether units have been reported.184,185 The incorporation of ferrocenyl segments into the backbone of polyurethanes enhanced thermal stability.186 There have been a number of studies on the incorporation of ferrocenyl units into the backbone of polyesters 101.187-191 A number of polymers of this class exhibited liquid crystalline properties.189-192 The thermal stability and glass transition temperatures of these polymers decreased with an increase in the length of the alkyl chains. 

Figure 7. Plot of glass transition temperature of the soft segment vs. time after quenching for polyester and polyether polyurethanes (9).

For simultaneous interpenetrating networks (SINs), two independent, non-interfering reactions are required. Thus, a chain and a step polymerization have been the method of choice for many such polymerizations. Typical examples have involved PS and polyurethanes [Hourston and Schafer, 1996 Mishra et ai, 1995], and PMMA. A key factor in the kinetics of such polymerizations is to keep the system above the glass transition temperature of both components. If the glass transition of either the polymer network I or polymer network II rich phase vitrifies, the polymerization in that phase may slow dramatically. 

Typical polyurethanes use a diol extender such as 1,4 butane diol. The NH groups form hydrogen bonds with C=0 groups on neighbouring chains, inside very small, hard blocks. The soft blocks are crosslinked polyethers or polyesters. A typical polyether is poly(propylene oxide) —[—O—CH2— C(CH2)H—] pre-polymerised to a molecular mass Mn of about 6000, a degree of polymerisation n = 140. The PPO has a glass transition temperature of about —60 °C, so the crosslinked PPO is a rubber. This rubbery phase is connected, via the polyurethane molecules, to the crystalline phase. 

The selection of plasticizers for polyurethane compositions depends on satisfying various tasks such as lowering viscosity, increase in potlife, lowering modulus and hardness of polyurethane, an increase in the low temperature resistartee (lowering the glass transition temperature of soft chains), or dissolution of components in reaction mixture. 

Figure 2 shows the results of differential scanning calorimetry studies of these polymers. The glass transition temperature of the polybutadiene resin, R-45HT, is about -75 C. The glass transition temperature increases as the percentage of excess TDI used to make the polyurethane... 

Fig. 2. Effect of concentration of excess TDI on glass transition temperature of resulting polyurethanes. ...

A noteworthy feature of the polyurethanes of Table 43.1 is that the model polymer, the first entry, is insoluble in water, dichloromethane and acetone, whereas both the polyrotaxanes derived from 36-crown-12 and 60-crown-20 , la and Id, respectively, are soluble in these three solvents [32]. The glass transition temperatures of the polyurethane rotaxanes of Table 43.1 obey the Fox equation (see Fig. 43.1) this is due to... 

Where a step polymerization is used, almost always it is for the first polymer synthesized in a sequential IPN. The reasons involve the slow diffusion into a preexisting network of most monomers used in step polymerization and the relatively high glass transition temperature of step-polymerized polymers. The latter reason is important because in order for diffusion and concomitant polymerization to occur rapidly, polymer network I should be above its glass transition at the temperature of polymerization of monomer mix II. Table 6.2 presents glycerol as a simple trifunctional cross-linker for step-polymerized materials, suitable for polyesters and polyurethanes. 

Additional thermal stability of polymers may arise from secondary valence forces. These are due to dipole-dipole interactions (8kcal/mol) and hydrogen bonding (6-10 kcal/mol). The latter effect is particularly important in strongly polar polymers such as polyamide and polyurethanes. These forces have pronounced effects on melting points and glass transition temperatures of the polymers. 

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