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Coatings of Polymers and Plastics Part 7

Tham khảo tài liệu 'coatings of polymers and plastics part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Polymers for Coatings for Plastics 139 3.1.6 Silane There are a number of ways to introduce organosilane functionality onto polymer backbones. Silane functionality for coatings exists in the form shown in the following text. R1Si OR x R1 polymer backbone R CH3 or other small alkyl In acrylic resins this is accomplished by copolymerizing an acrylate or methacrylate containing organosilane. The most readily available of these is Y-trimethoxysilylpropyl methacrylate TMSPM . The advantages of silane func- CH2h-Si OCH3 3 tionality is the high degree of flexibility and hydrolytic stability in the Si-O-C or Si-O-Si bonds that are formed in the curing reaction. The curing reaction can be initiated by moisture or by reactions with hydroxyl functional crosslinkers as shown in Figure 14 22 23 . In moisture cure reactions the alkoxy silane Fig. 14 Hydroxyl functional crosslinkers. Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 140 Nordstrom functional group reacts first with water to form a silanol SiOH group. This occurs both with acid and base catalysis. The silanol group then self-reacts to form a siloxane bond Si-O-Si . The siloxane bond provides a great deal of flexibility to a crosslink structure and is very resistant to hydrolysis. Silane functionality also can provide a high crosslink density due to the multiple number of alkoxy groups attached all of which can participate in crosslinking reactions if the conditions are rigorous enough catalysis availability of moisture cure temperature . The disadvantages of organosilane functionality are high cost and softness low Tg that is inherent when the very flexible siloxane bonds are present. 3.2 Polyester Binders High-performance coatings for plastic substrates are often formulated with polyester resins that are then crosslinked with materials similar to those described for acrylic resins. Polyesters are prepared by a step growth polymerization mechanism from .