Copolymer, composition glass transition temperature

Table II. Molecular weight of PMMA segments, composition, glass transition temperatures, tensile strength, and elongation at break of PMMA- -PIB- -PMMA block copolymers (precursor difunctional PIB with M = 17,5(K))...

Recently, we reported on the compatibUity of PVME with styrene/1- or 2-vinylntphthalene(VN) copolymer using glass transition temperature and Fourier-Transform infrared (FTIR) spectroscopy . The compatibility of the styreneATN derivative copolymers with PVME was found to become weaker as the composition of styrene in the copolymers is decreased. It was also found that the compatibility of the copolymers with PVME is better for 2-VN containing copolymers than for 1-VN containing copolymers . 

Table 1 shows that most acryflcs have low glass-transition temperatures. Therefore, in copolymers they tend to soften and flexibHize the overall composition. Plasticizers also lower the transition temperature. However, unlike incorporated acryflc comonomers, they can be lost through volatilization or extraction. 

The glass transition temperature of a random copolymer usually falls between those of the corresponding homopolymers since the copolymers will tend to have intermediate chain stiffness and interchain attraction. Where these are the only important factors to be considered a linear relationship between Tg and copolymer composition is both reasonable to postulate and experimentally verifiable. One form of this relationship is given by the equation... 

FIGURE 8 Relationship between the glass transition temperature and the composition of copolymers of e-caprolactone and lactic acid. 

Various substituted styrene-alkyl methacrylate block copolymers and all-acrylic block copolymers have been synthesized in a controlled fashion demonstrating predictable molecular weight and narrow molecular weight distributions. Table I depicts various poly (t-butylstyrene)-b-poly(t-butyl methacrylate) (PTBS-PTBMA) and poly(methyl methacrylate)-b-poly(t-butyl methacrylate) (PMMA-PTBMA) samples. In addition, all-acrylic block copolymers based on poly(2-ethylhexyl methacrylate)-b-poly(t-butyl methacrylate) have been recently synthesized and offer many unique possibilities due to the low glass transition temperature of PEHMA. In most cases, a range of 5-25 wt.% of alkyl methacrylate was incorporated into the block copolymer. This composition not only facilitated solubility during subsequent hydrolysis but also limited the maximum level of derived ionic functionality. 

The isomeric bibenzoic acids (BBs), would appear to share similar structural features with naphthalene dicarboxylic acid. Like the PET-naphthalate copolymers, PET-bibenzoates have been demonstrated to possess moduli and glass transitions temperatures which increase with increasing levels of rigid comonomer [37-39], Unlike the PET/PEN copolymers, when the symmetrical 4,4 - I f I f monomer is substituted into a PET backbone, virtually every composition of PET-BB is semicrystalline the 2,4- and 3,4- isomers of BB, when... 

The simplest dependency exists between composition and glass transition temperature Independent from the ratio A/B one finds two values for Tg, one for the block from monomer A and one for the block of B. More complex are the dependencies with the mechanical properties. Here, parameters like the ratio A/B, number of blocks, block length, and alternation of the blocks play a decisive role. This is shown in Examples 3-47 and 3-48 with triblock copolymers of buta-... 

The solution random copolymer generally contains about 32 percent cis-, 41 percent trans- and 27 percent vinyl-unsaturation compared to 8 per cent cis-, 74 percent trans- and 18 percent vinyl-unsaturation in emulsion copolymer of the same monomer composition. The principal effect of slightly higher vinyl unsatura-tion in solution copolymer is a small increase in the glass transition temperature (-58 C versus -62 C for the emulsion copolymer). However, both solution and emulsion polymerized copolymers exhibit satisfactory low temperature performance for general uses. 

The monomer compositions were copolymerized using several different cure cycles. All of the cure cycles in this series included an additional post cure at 290 °C for one hour. The exact monomer compositions used, their detailed cure cycles and the physical properties of the resulting copolymers are shown in Table 16. As in the previous examples, here too the glass transition temperature went down as the fracture toughness increased. As before the fracture toughness rose as the mole ratio of bisbenzocyclobutene to bismaleimide approached unity. The presence of phenothiazine appeared to increase the fracture toughness in all of the examples although, its effect appeared most pronounced when... 

More recently [79], a carboxy-terminated PBZT ([r ] = 4.8 dL/g) was reacted with m-phenoxybenzoic acid via a Friedel Craft procedure in a meth-anesulfonic acid/P2Os mixture. This provided an ABA block copolymer in which the outer blocks (A) are composed of flexible coil polyetherketone (PEK) and a center block (B) which contains the rigid-rod PBZT. Thermomechanical analysis showed that 20 PBZT/80 PEK and 10 PBZT/90 PEK compositions exhibited glass transition temperatures of 157 °C and 135°C respectively. Consolidation studies have not been investigated to date. 

The Teflon AF family consists of copolymers of tetrafluoroethylene, (TFE) and 2,2-bis-trifluoromethyl-4,5-difluoro-l,3-dioxole, (PDD), whose structure is shown in Figure 2.1. The properties of these amorphous copolymers vary with the relative amounts of the comonomers. At present the two commercial grades of Teflon AF are AF-1600 and AF-2400 with glass transition temperatures of 160 and 240°C respectively. The variation of glass transition temperature with composition is shown in Figure 2.2. Thus AF-1600 and AF-2400 contain 64 and 83 mol % PDD, respectively. 

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