Tg below room temperature

Another way for covalent immobilisation is to synthesise indicator chemistry with polymerizable entities such as methacrylate groups (Figure 4). These groups can then be copolymerized with monomers such as hydrophobic methyl methacrylate or hydrophilic acryl amide to give sensor copolymers. In order to obtain self-plasticized materials, methacrylate monomers with long alkyl chains (hexyl or dodecyl methacrylate) can be used. Thus, sensor copolymers are obtained which have a Tg below room temperature. Similarly, ionophores and ionic additives (quaternary ammonium ions and borates) can be derivatised to give methacrylate derivatives. 

For example, poly(vinyl alcohol) (PVOH) finds application as an effective adhesive for paper products such as the old-fashioned postage stamps or envelopes. Licking the stamp or envelope flap causes the adhesive to become sticky because water plasticizes the PVOH and lowers the Tg below room temperature. On pressing the stamp to a piece of paper, the polymer chains can entangle and hydrogen bond with the cellulose in the paper. As the water... 

The location of the glass transition temperature will depend on the nature of the polymer. Generally, a plastic differs from a rubbery material due to the location of its glass transition temperature. A plastic has a T above room temperature, while a rubber has a Tg below room temperature. As previously mentioned the flexibility of the chain will affect the value of T. Flexible groups will tend to lower the T, whife stiffening groups will act to increase it. Side groups can also affect the value. The... 

Poly(vinyl acetate) (PVAc), -[CH2-CH(OCOCH3) , is also prepared as an emulsion for adhesive applications, and is familiar to users as white glue. As mentioned already, the Tg of PVAc is above room temperature, which makes the polymer rigid and brittle at room temperature. For adhesive application, therefore, an external plasticizer, such as dibutyl phthalate, is added to lower the Tg below room temperature and to facilitate film formation from emulsions. 

In the preceding section it was demonstrated that multiphase systems comprising a phase with Tg below room temperature are distinguished by peculiarities in their deformation mechanism. While in the same subsection it was attempted to account for this peculiarity qualitatively, in this section it will be demonstrated that by means of eq. (3.4), which expresses the relationship between Tg and the microhardness, it is possible to describe the behaviour of the system in a quantitative manner. 

The cosolvent method, also known as solvent injection method permits vesicle formation for glassy or crystalline block copolymers. As a rule, the amphiphilic copolymer is dissolved in an appropriate organic solvent or solvent mixture, the role of which is to lower the Tg below room temperature next the solution is added dropwise to an aqueous buffer under vigorous stirring. Originally this method has been employed for PS-PAA and PS-PEO copolymers that self-assembled in vesicular structures by adding water to DMF or dioxane polymer solution [61,105] and then further applied to many other polymer systems [165],... 

The polymer was synthesized by polycondensation of an aryl dialkyl tri-azene compound containing a meta-COOH group in the aryl part and an OH-group in the alkyl part of the compound. Both the ablation characteristics (e.g., quality of ablation structure) and the properties of the polymer (e.g., low molecular weight (Mw), glass transition temperature (Tg) below room temperature, and the long synthesis time (>48 h)) were not satisfactory [120]. Therefore, we modified our approach to a two-step synthesis, shown in Scheme 2 [121, 122], which results in polymers of the general structure B in Scheme 1. 

Therefore, a solution of a resin with a Tg below room temperature never undergoes evaporation by the diffusion process. Considerable amounts (5-10%) of solvent can remain in a film for years. Diffusion is extremely slow through cured films having high Tg. 

Brittleness temperature The temperature at which a plastic or elastomer breaks in cantilever-bending impact under specific conditions. The brittleness temperature is related to that of the glass transition, for those plastics with TgS below room temperature, such as flexible PVC. Wickson EJ (ed) (1993) Handbook of polyvinyl chloride formulating. John Wiley and Sons Inc., New York. 

The research team of Cramail adopted a similar strategy to prepare aliphatic diols containing monoester, diester, ester-amide, monoamide and diamide linkages from methyl 10-undecenoate derivatives [15]. Resulting diols were condensed with a methyl diester, obtained by the self-metathesis of methyl 10-undecenoate, in the presence of TBD as a transesterification catalyst. This strategy lead to various fully aliphatic polyesters and polyester-amides with Mn values of 6-19 kDa, a glass transition temperature (Tg) below room temperature (RT) and T of 22-127 °C. 

Residual toluene can be removed from CK-1834 only with great difficulty and can easily depress the Tg below room temperature. 

One-component two-phase systems (semicrystalline polymers with Tg below room temperature)... 

All compounds (including aPP presented in the previous chapter) were used as purchased. For the polymers with a glass transition temperature Tg below room temperature (aPP, PIB, PBD, PIP, PE), the sample was slowly cooled down in the course of the NMR measurement, and the spectra were recorded after the glass transition temperature was reached. If Tg is above room temperature (PVC, PMMA), the samples were measured without prior treatment at ambient temperature. 

In common with most polymers that are completely or partly amorphous, ferroelectric polymers experience a phase change at the glass transition temperature Tg. Below Tg, the polymers are hard, rigid glasses. At Tgand above, the polymers become flexible and elastomeric. Brittle, rigid polymers have a Tg above room temperature for example, polystyrene has Tg = 100 °C. Rubbery or elastomeric materials have a Tg below room temperature. This is the case for PVDF and the copolymers, which have a Tg in the region of — 40 °C. 

Most materials considered to be pressure-sensitive have a Tg below room temperature. This fulfils two of the major requirements for a pressure-sensitive adhesive. Firstly, that it must undergo plastic flow on contact and secondly, it must... 

Table 1 lists the thermal properties of a series of type II aramid elastomers. Differential scanning calorimetry (DSC) measurements revealed that the aramid elastomers exhibited three transition points a glass transition, Tg, below room temperature (RT), and melting transitions, T , below RT and around 200 C. The DSC thermograms are typical of block copolymers consisting of crystalline... 

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