Poor Properties

Three different kinds of behavior were observed on addition of the polyethers to PVC and CPVC. First, high-impact resins were sometimes produced without the addition of any other rubber (3, 4). Second, incompatible mixtures with poor properties were obtained. Third, certain polyethers, which in themselves did not lead to PVC s of high impact strengths, seemed to enhance the properties of an already modified CPVC (5). 

Figure 2 also illustrates the poor properties obtained when milling temperature is too low. When milling was carried out at 335°F (steam-heated mill), the impact strength that developed was lower than the maximum obtained after milling at 380° F and decreased as the concentration of PTHF was increased above 8 phr. 

Contrasted with the resins modified with chlorinated polyethylene, addition of the substituted epoxides to resins modified with PTHF led to blends with very poor properties. 

A wide range of materials is included in this class. The common feature is the use of chain extension reactions to provide products with acceptable commercial properties. The chain extension reaction effectively reduces the actual number of chain ends, thereby eliminating the generally poor properties observed when very low-molecular-weight polymers are cross-linked. The chain extension step involves the reaction of a difunctional polymeric polyol with difunctional organic isocyanates to give the polyurethane ... 

When preparing these zeolites, this dual effect must be considered. Any variation from the desired batch composition can present problems if the test is designed to react for a fixed period of time. Variations which slow down the reaction could produce a zeolite which has poor properties simply because it has not completely crystallized. If one has variations which speed up the reaction, one could produce a mixture of zeolite phases. 

Also at this stage, pharmaceutical profiling assays, such as solubility, permeability, and metabolic stability provide a multivariate property profile of HTS hits that contribute to the team s holistic selection of leads for synthetic optimization. The pharmaceutical-property profile is considered in relation to the ensemble of activity properties for making informed decisions. Conversely, an alert to poor properties can save the team effort and time on problematic structures, or forewarn of issues that must later be solved via synthetic modification, salt form, or formulation. 

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