Destabilized homopolymers

It was shown many years ago that if some methacrylic acid is copolymerized with methacrylonitrile, the discolouration reaction 

The conjugated carbon—nitrogen sequences formed are responsible for the observed colour. Radicals do not seem to be involved in this reaction. Identical effects are observed when acrylonitrile is copolymerized with acrylic acid. 

Propagation can apparently pass through methylvinylketone units, conjugation being preserved. 

The rates of production of volatile material from polyvinylacetate, polyvinylchloride and vinylacetate vinylchloride copolymers, covering the entire composition range, have been compared by thermal volatilization analysis. It has been found that, at both extremes of the composition range, incorporation of the comonomer unit induces de-stabilization. Minimum stability occurs for composition of approximately 40—50 mole % vinylacetate. The rate of volatilization as a function of the composition of the copolymers is given in Fig. 74. The results were confirmed by a study of the thermal degradation in tritolylphosphate solution. The stability of the copolymers is a minimum at 30—40 mole % vinylacetate. HC1 and acetic acid catalyse the degradation of the 

The UV spectrum is quite similar to that reported for pure PVC. The variation of absorbance at three wavelengths with mole % vinylacetate in the copolymer, for 5% degraded samples, is given in Fig. 75. It is apparent 

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The pKa values of the imidazole residues in the copolymers decreased with decreasing vinylimidazole content. The increased acidity was attributed to a destabilization of the protonated imidazoles by intramolecular interaction with the alkylated imidazole residues. There was also a slight decrease in pKa as the length of the alkyl imidazole side chain was increased. The imidazole pKa values were higher in water (4.99-5.92) than in 28.5% ethanol-water (4.94-5.80)(12) due to enhanced stability of the charged residues in the more polar medium. The pKa values for the copolymers were lower than the pKa values for PVIm in 28.5% ethanol-water (5.78-6.20). The pH-rate profiles for the copol3nners in the hydrolysis of S2 in 28.5% ethanol-water were similar to PVIm.(13) The copolymers were more efficient catalysts than a mixture of the component homopolymers due to the increased basicity of the copolymers. Lengthening the alkyl side chain from one to three carbons had little effect on the rate of hydrolysis. 

Since the cyanobiphenyl derivatives had proved to be excellent materials for electro-optic displays, equivalent homopolymer poly-siloxane liquid crystals, based on these low molar mass mesogens, were synthesized. Their properties are summarized in Table 1. Since the homopolymers only exhibited smectic phases, copolymers were prepared using destabilizing 2-methyl-substituted ester side-groups. As shown in Table 2, at sufficiently high ester-group concentrations, a... 

Conceptually, microphase formation is an inherently block copolymer phenomenon. Interestingly, however, copolymers in the disordered phase can sometimes be made to microphase separate by the addition of homopolymer [107-109]. This phenomenon is called induced microphase separation, and it was predicted by the weak segregation theory [107] of blends prior to its observation [108]. It occurs if the copolymers are near the MST, and if the added homopolymer has sufficiently high molecular weight. Relatively low molecular weight homopolymer has the opposite effect, tending to destabilize the microphase. When induced microphase separation occurs, the added homopolymer is solubilized within the domains. 

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