PEPS Blends

In a recent study [47] of the polymerization of styrene in carbon dioxide swollen high density polyethylene (HOPE) at 100 C and 240 bar using t-butyl peroxybenzoate as initiator has shown that more than 100 % mass uptake of polystyrene levels are reached within about 15 hr reaction time. The kinetics of this in-situ polymerization is shown in Figure 12. Polymerization is conducted at a temperature below the crystalline melting temperature of HDPE. The crystalline melting temperature of polyethylene in these PEPS blends is reported to be the same as the initial polyethylene, which is an indication of the styrene polymerization proceeding only in the amorphous regions of the swollen host polyethylene matrix. 

Fig. 7 Transmission electron micrographs from symmetric PE/PEP/PE-PEP blends (a) fluctuating lamellae (b) microemulsion phase. From [103]. Reproduced by permission of the Royal Society of Chemistry...

Fig. 4 The critical temperature Tc (a) critical composition 0) is constructed assuming the same b as is chosen for class II, while the example for class III blends (n 5 0, c = 0, f)< 0) is generated by taking a and b equal to those for the PHl/PEP mixture...

While the spinodal ciuves [82] depicted in Fig. 8 refer to ECT calculations for compressible blends of semiflexible polymers at a pressme of 1 atm, similar behavior emerges [83] from the SECT where the pressure is infinite. Thus, we analyze the molecular features contributing to this remarkable difference in miscibihties within the framework of the SECT because of its analytical tractability. In order to elucidate the contributing featiues to the observed miscibihty difference, it is convenient to assume first that both blend components are completely flexible. Then, the partial entropic structural parameters rpp and rhhpp are identical (Sect. 3.1), so that all of the calculated miscibility differences between PP/PEP and hhPP/PEP blends emerge from the differ-... 

Fig. 8 LCT spinodal curves for PP/PEP and hhPP/PEP blends at P = 1 atm. The site occupancy indices Mpp = 1560 and Mpep =4275 used in the calculations correspond to one of the blends studied by Graessley et al. [31], and Mhhpp = 1560 is selected to ensure the same molecular weights for the PP and hhPP components. Both blends are assumed to have the same interaction energies e,j in order to illustrate the sole influence of monomer structure and chain semiflexibility on the blend miscibilities. The self-interaction energies en = (l/2)(epp pp + ehhpp-hhpp) = 205.40 K and tri = cpep-pep = 207.49 K are obtained from our earlier fits to PVT data for the pure melts. The bending energies = 219 K, = 277 K, and = 460 K are taken form [80], while the heterocontact energy is an adjustable parameter...

Fig.66 Phase diagrams of a symmetric (peo = 0.51, Mn = 2700, Mw/Mn = 1.10) and b asymmetric (0peo = 0.32, Mn = 2100, Mw/Mn = 1.14) PEO-fc-PEP block copolymers blended with epoxy resin. Phase transitions which originate from swelling of PEO chains with epoxy and/or curing agent are drawn as single lines, without implication that there are no coexistence regions. From [197]. Copyright 2001 Wiley...

Fig. 6.22 Phase diagram for blends of PE and PEP homopolymers (A/j, - 392 and 409 respectively) with a PE-PEP diblock (iVc = 1925) (Bates et al. 1995). Open and filled circles denote experimental phase transitions between ordered and disordered states measured by SANS and rheology respectively. Phase boundaries obtained from self-consistent field calculations are shown as solid lines. The diamond indicates the Lifshitz point (LP), below which an unbinding transition (UT) separates lamellar and two-phase regions in mean field theory.

Fig. 6.23 Logarithmic plots of the correlation length ( ) and zero-angle scattering intensity (/(0)) as a function of temperature reduced with respect to the Lilshitz temperature Tlp) for a blend of PE and PEP homopolymers with a PE-PEP diblock (details as Fig. 6.22) at a copolymer volume fraction

Bates 1984 Fredrickson and Larson 1987 Fredrickson andFIelfand 1988). The relaxation of these fluctuations involves collective motion of many molecules, and thus it is slower than the relaxation time of individual molecules. In small-amplitude oscillatory shearing, the fluctuation waveform is deformed, producing a slowly relaxing stress. Presumably, this accounts for (a) the anomalous contribution to G and (b) a similar, but smaller, contribution to G" (Rosedale and Bates 1990 Jin and Lodge 1997). (Similar anomalies are observed in polymer blends.) An asymmetric version of this PEP-PEE polymer that forms cylindrical domains shows an even larger low-frequency anomaly (Almdal et al. 1992). 

Sorbitol, sucrose, pentaerythritol and other polyalcohols or polyamines are used for the preparation of PEP for rigid foams where structures with high cross-linking density are required, while glycerol is mainly used for flexible foam production. Some PEP producers modulate the rigidity of the foam by using blends of sorbitol and glycerol in different ratios. 

The influence of a block copolymer on the droplet breakup and coalescence in model immiscible PEP/PPO polymer blends was investigated by Ramie et fd. [18], who found that the addition of 0.1 wt% or 1.0 wt% of PEO-b-PPO-b-PEO [poly (ethylene oxide)-poly(propylene oxide) copolymer] triblock copolymers facilitated breakup and inhibited coalescence. The steady-state droplet size resulting from breakup was reduced only slightly by the addition of 0.1 wt% copolymer, but more substantially by addition of lwt%. However, the kinetics of coalescence were suppressed effectively even when 0.1 wt% of copolymer was added. In these systems, the copolymer seems to reduce the efficiency of both droplet collision and film drainage and/or rupture. 

Several of these values have been confirmed by other work as well. For blends of htPP and PEP a very similar value of Xjj was found by the determination of the phase diagrams for both blends and block copolymers [4] 0.0981 MPa at 25°C versus a value of 0.104 MPa from the SANS work. Microscopic and thermal analysis of blends of PP with polybutene showed that they had a UCST behavior consistent with the value shown in the table [5]. On the other hand, work on block copolymers of PP and PE [6] showed that X,2 for these blends must be at least 1.93 MPa, which is far greater than the values derived from the SANS studies of the blends [3]. 

Fig. 20. NEXAFS images at 288 eV (PEP appears dark) of a 25/75 PEP/PMMA blend cryomilled for 10 h and annealed at 150°C for different times (in min) (a) 1, (b) 2, (c) 5, and (d) 30. (Data acquired with the Stony Brook STXM.) Adapted from Ref 148.

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