PVAc-PMMA blends

Fig. 21 Evolution profiles of some characteristic products recorded during the pyrolysis of the coalesced (left) and solution-cast (right) PMMA/PVAc blends...

Table 3 The assignments and intensities (relative to the weakest peak) of the characteristic and intense peaks in the pyrolysis mass spectra of physical and coalesced PMMA/PVAc blends at temperatures corresponding to maxima in the TIC curves (Fig. 21) [51]...

Fig. 23 DSC thermogram of the coprecipitated PC/PMMA/PVAc blend, first heating scan...

DSC scans recorded for PC/PMMA/PVAc blends obtained by solvent-casting and coprecipitation evidenced four distinct glass-transitions, one for each component polymer and one indicating that some of the PMMA and PVAc chains were mixing (see Fig. 23). 

We also observed that the PC chains possess a preferred ability to form inclusion compounds with y-CD in solution, when competing with PMMA and PVAc. From the XH NMR spectrum of the coalesced 1 1 1 PC/PMMA/PVAc blend (not shown), the molar ratio of PC PMMA PVAc was determined to actually be 1.6 1 1.4 compared to the initial molar ratio of 1 24 24, respectively, used in solution to form their common y-CD-IC. Despite the initial 1 24 24 PC PMMA PVAc molar ratio in solution, the PC component in the coalesced PC/PMMA/PVAc blend is still prevalent over the PMMA and PVAc components, which indicates that there may be additional factors that govern the inclusion process from a multiguest system. We believe that this very strong preference of the host y-CD molecules for PC chains, rather than the other two possible guests, is due to their different hydrophobicities. Although the final molar ratio of the coalesced ternary blend can be somewhat controlled by modifying the initial molar ratio of polymers in their common solution, our eventual aim is to be able to adjust, as desired, the constituent polymer ratios in coalesced ternary blends. 

The freeze drying of co-solutions of thermodynamically immiscible polymer pairs is a method of capturing kinetically the unlike molecules in molecular or segmental mixtures. PMMA/PVAc blends freeze-dried from co-solutions in benzene were reported homogeneous by dynamic mechanical and dilatometric observations. They showed a single T intermediate between those of the pure polymers [Miyata and Hata, 1970]. Further dilatometric and differential calorimetric data corroborated the findings of homogeneity [Ichihara et al., 1971]. 

Figure 3.45 compares the calculated and experimental results. L>a 4.2 X 10 cm s . This value is similar to that obtained [97] by the light scattering technique for the phase separation of PMMA/PVAc blends. 

All the PMMA PVAc blends cast from chloroform were transparent at room temperature and were found to undergo phase separation at elevated temperatures. The cloud point curves are shown in Figure 4.40. An increase in the molecular mass of the PVAc decreases the cloud point temperature as expected. The minimum in the cloud point curve appears close to a 50 50 PMMA PVAc mass ratio. This composition varies relatively little with molecular mass of PVACc as the latter is varied from 20 000 to 453 000. 

Figure 4.40 Plots of cloud points against composition for PMMA-PVAc blends. The weight-average molecular ma.ss (M .) of PMMA is 60 000. of PVAc I, 20 000 II, 170 000 III, 45.1 000...

The miscibility between several (meth)acrylate polymers and phenoxy (PHE) has been reported.[155,156] PEMA was noted to be partially miscible and PBMA to be phase separated in PHE blends. [155] An investigation of the effect of PMMA s tacticity on the phase behavior of PMMA/PHE blends showed aPMMA, sPMMA and iPMMA to all exhibit miscibility with PHE. [156] The miscibility of PMMA with a vinylidene chloride-acrylonitrile (20 wt% AN) copolymer was shown to be a function of the PMMA tacticity (aPMMA and iPMMA miscible with the copolymer and sPMMA immiscible). [157] Hsu et fl/.[158] reported the effect of tacticity of PMMA on the miscibility with PVAc. This study showed a limited effect of tacticity and solvent choice on the phase behavior of PMMA/PVAc blends and all blends were analyzed as being immiscible based on the observation of two Tgs. Modest areas of miscibility were established for MA, EA, nBA, and 2-ethylhexyl acrylate based acrylate-acrylic acid in the respective copolymers. No miscible combinations were found for MMA-AA or acrylate-MAA copolymers with vinyl acetateethylene (VAE) or PVAc. 

Fig. 22 MDSC scans of the (a) first, and (b) second heating runs recorded for the 1 1 1 molar PC/PMMA/PVAc coalesced blend. The sample was held for 3 min at 170°C after the first heating [35]...

Acrylic polymers are recognized for their miscibility with a variety of polymers, viz. miscibility of PMA with PVAc [Kem, 1957]. PMMA is miscible with standard PC at T < LCST - 140°C. The miscibility range can be greatly increased by modifying the PC chain ends (LCST < 300°C) [Kambour, 1988]. Demixing PMMA/PC blends by the spinodal decomposition mechanism generated alloys with excellent mechanical properties [Kyu, 1990]. 

The compressive, ultrasonic velocity at 6 MHz at room temperature was used to study cast films of PMMA/PVAc, PMMA/PS, PVC/CR, and PS/EPDM blends [Singh and Singh, 1983 Shaw and Singh, 1987]. A linear correlation between the sound velocity and composition was observed for miscible blends, whereas immiscibility, viz. in PMMA/PS blends the dependence was irregular. The phase separation in PVC/CR was detected at w = 70 wt % of CR, as a sudden departure from the linear correlation. The ultrasonic absorption vs. composition gave even stronger evidence of immiscibility. Ultrasonics have been successfully used to study the phase behavior in polyurethanes [Volkova, 1981]. 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Table 3.4. STgValues for PECH/PMMA, PS/PPO and PMA/PVAc blends...

Blends of polychloroprene with PMMA do not show the chlorine radical migration effects observed in PVC/PMMA blends, nor the stabilization of the dehydrochlorination reaction, both of which are consistent with the nonradical mechanism proposed for HCl production in the former polymer, but there is a major effect of HQ in producing PMMA stabilization. Blends of PVC with PMMA also show the effect of HCl, but this is masked by the earlier destabilization due to Q radicals. Acetic acid from PVA also leads to anhydride rings in PMMA with similar effects. Blends of PVC with PVAC show mutual catalysis of the decomposition of each polymer by the primary decomposition product of the other. This is seen both in TVA studies similar to those illustrated for the PVC/PMMA system and from direct measurements of acid production, as illustrated in Figure 18, which show clearly the destabilization of each polymer. 

Some studies reported the polymer electrolytes based on the blend components of PVAc and other polymers, e.g. PVAc/PMMA, PVAc/... 

Direct insertion probe pyrolysis mass spectrometry (DPMS) utilises a device for introducing a single sample of a solid or liquid, usually contained in a quartz or other non-reactive sample holder, into a mass spectrometer ion source. A direct insertion probe consists of a shaft having a sample holder at one end [70] the probe is inserted through a vacuum lock to place the sample holder near to the ion source of the mass spectrometer. The sample is vaporized by heat from the ion source or by heat from a separate heater that surrounds the sample holder. Sample molecules are evaporated into the ion source where they are then ionized as gas-phase molecules. In a recent study, Uyar et al. [74] used such a device for studying the thermal stability of coalesced polymers of polycarbonate, PMMA and polylvinyl acetate) (PVAc) [75] and their binary and ternary blends [74] obtained from their preparation as inclusion compounds in cyclodextrins. 

Li Y, Shimizu H (2009) Compatibilization by homopolymer significant improvements in the modulus and tensile strength of PPC/PMMA blends by addition of a small amount of PVAc. ACS Appl Mater Interfaces 1(8) 1650-1655... 

In another study, it was successfully reported an intimate ternary blend system of poly(carbonate) (PC)/poly(methyl methacrylate ) (PMMA)/poly (vinyl acetate) (PVAc) obtained by the simultaneous coalescence of the three guest polymers from their common y-cyclodextrin (y-CD) inclusion complex (IC). The thermal transitions and the homogeneity of the coalesced ternary blend were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) [50]... 

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