Cross-linking impact performance

The physical properties of the pad are heavily determined by its chemical constituents such as polyols, isocyanates, stoichiometric ratio of isocyanate to diol, and cross-link molecular structures (hard and soft segments). They also have a great impact on the mechanical properties of the pad (strength, hardness, stiffness. Young s modulus, etc.) and on the performance of the CMP process. 

The 3LAII and 3LC materials perform poorly under impact. For the 3LC materials, this poor performance appears to arise from the small particle size (152 nm outer diameter in the rubbery layer). The poor performance of the 3LAII materials can again be attributed to the relatively high level of cross-linking within the rubbery layers of the 3LAII particles. 

The possibilities for copolymers with specialized performance characteristics depend on the ability to effect copolymerization with the other monomer. To date efforts to effect copolymerization with such monomers as styrene and butadiene have been unsuccessful (r2=35 vs. rj =0.067 for styrene, and r2=8.8 vs. r =0.035 for butadiene). The possibilities nevertheless exist for modifying the basic polymer to effect such desirable properties as cross-linking, improvement in impact resistance, compatibility with processing aid modifiers, and UV stability. 

The hyper-branched aromatic polyamine system not only enhances the rate of the cross-linking reaction of poly(ester amide) resins, but also improves the performance characteristics of cured films, especially those of thermostability, flame retardancy, hardness, impact strength and chemical resistance. A short list of vegetable oil-based poly(ester amide)s with some of their properties is given in Table 5.2. 

Flexiblization. Aliphatic diepoxide reactive diluents enhance the flexibility or elongation by providing chain segments with greater free rotation between cross-links. Polyaminoamide hardeners, based on aliphatic polyamines and dimerized fatty acids, perform similarly. Liquid polysulfide polymers possessing terminal mercaptan functionality improve impact properties in conjimction with polyamine hardeners. 

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