Copolymer, composition melting temperature

With the establishment of the characteristics of the fusion process of random copolymers the melting temperature-composition relation of such copolymers can be examined. To analyze the problem distinction must again be made as to whether the crystalline phase is pure or if the B units enter the crystallite, either on an equilibrium basis or as a defect. Merely establishing the liquidus is not sufficient to resolve this problem. The Flory relation is only applicable to an ideal system whose crystalline phase is pure. Deviations from this relation can be due to lack of ideality, with either the raising or lowering of the expected equilibrium melting temperature. On the other hand the B units can be entering the lattice. This... 

Some of the principles as well as problems involved in the melting of random copolymers are found in olefin type copolymers. The melting temperatures of a large number of random type ethylene copolymers, as determined by differential scanning calorimetry, are plotted as a function of the mole percent branch points in Fig. 5.11. The samples represented in this figure are either molecular weight and compositional fractions or those with a narrow composition distribution with a most probable molecular weight distribution.(74) These samples were crystallized and heated rapidly. In this set of data there are two different copolymers that contain ethyl... 

With the establishment of some of the unique features of the fusion of random copolymers, their melting temperature-composition relations can now be examined. Copolymers formed by condensation polymerization are usually characterized by a sequence-propagation probability p that is independent of copolymer composition and the extent of conversion. For such systems the quantity p can be... 

Droscher et al prepared chemically similar poly(oxymethylene)-based copolymers (with 1,3-dioxalane, 1,3-dioxane, 1,3-dioxepane and 1,3,6-trioxocane as respective comonomers) which were of extended crystal form and presumed to be completely crystalline. For this series of copolymers, the melting temperature-composition relation at low co-unit content depended on the chemical nature of the comonomer used. The characteristic curve observed by Inoue " was not found. It was presumed that an appreciable concentration of co-units enter the lattice. An interesting feature developed at higher co-unit concentration. Depending on the co-unit type, the melting temperatures became invariant with composition, while the normal poly(oxymethylene) unit cell was maintained. 

The effect of different types of comonomers on varies. VDC—MA copolymers mote closely obey Flory s melting-point depression theory than do copolymers with VC or AN. Studies have shown that, for the copolymers of VDC with MA, Flory s theory needs modification to include both lamella thickness and surface free energy (69). The VDC—VC and VDC—AN copolymers typically have severe composition drift, therefore most of the comonomer units do not belong to crystallizing chains. Hence, they neither enter the crystal as defects nor cause lamellar thickness to decrease, so the depression of the melting temperature is less than expected. 

Fig. 3. Influence of vinyl alcohol—vinyl acetate copolymer composition on melting temperature (56), where A represents block copolymers B, blocky...

C and is easily processable, whereas the homopolymers do not melt before the onset of thermal degradation, at temperatures as high as 500°C.73,74 Varying copolymer composition permits the adjustment of melting temperature and of other properties (e.g., solubility) to desired values. This method is frequently used for aliphatic and aromatic-aliphatic polyesters as well. 

Figure 3.10 Melting temperatures of caprolactam-caprolactone random copolymers as function of molar composition.22...

The dynamic mechanical behavior indicates that the glass transition of the rubbery block is basically independent of the butadiene content. Moreover, the melting temperature of the semicrystalline HB block does not show any dependence on composition or architecture of the block copolymer. The above findings combined with the observation of the linear additivity of density and heat of fusion of the block copolymers as a function of composition support the fact that there is a good phase separation of the HI and HB amorphous phases in the solid state of these block copolymers. Future investigations will focus attention on characterizing the melt state of these systems to note if homogeneity exists above Tm. 

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]). 

Even though the nonisothermal crystallization leads to just small changes in the subsequent melting behavior of different types of triblock copolymers, isothermal experiments employed to calculate the equilibrium melting temperature, T, have shown that this parameter can exhibit significant changes depending on composition. It has been reported that in PS-fc-PB-fc-PCL tri-... 

Fig. 1. Melting temperature (—and enthalpy (—, AH) of poly(8CL-co-6VL) random copolymers at different compositions, as synthesized by coordination-insertion ROP initiated with Al(OzPr)3 in toluene at 0 °C. is the molar fraction of eCL in the copolyester. (Tjjj and AH were determined by DSC at a heating rate of 10 °C/min)...

Fig. 2. Melting temperatures of crystalline VF-TFE copolymers as a function of the molar composition (from Natta, G., etaL J. Polymer Sci., Part A, 3,4263 (1965))...

Natta, Porri, Carbonaro and Lugli (25) have prepared copolymers of 1,3-butadiene with 1,3-pentadiene in the whole range of compositions. The properties of the copolymers, in which all butadiene and pentadiene comonomer units are in the trans-1,4 configuration, clearly show the isomorphous replacement between the two types of units. The melting point/composition data show that the copolymer melting temperatures are a regular function of composition and are always comprised between those of trans-1,4-polybutadiene modification II and trans-1,4-polypentadiene. Also the X-ray diffraction spectra of the copolymers show that the trans-1,4-pentadiene units are isomorphous with the trans-1,4-butadiene units crystallized in the crystalline modification of the latter stable at high temperatures (form II). 

The terpolymerization of CPT-SO2 and acrylonitrile is shown in Table II. It was necessary to accelerate the polymerization by adding azobisisobutyronitrile (AIBN) as initiator. The nature of the propagating species may not be different with a different initiator. Polymerization ceased at a low conversion at 40 °C in toluene. The terpolymer composition calculated from elemental analysis of C, H, N, and S showed an equimolar ratio of CPT and S02. The terpolymers are white powders, soluble in DMF, can be cast into transparent film different from the CPT-SO2 copolymer, and showed melting temperature without decompo-... 

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