Basic Chemistry

Kaneka has been interested in acrylic polymers and their new polymerization methods, which can realize both high-moisture permeability and excellent weatherability of silylated telechelic polymers. The chemi­cal structure of the novel telechelic polyacrylate (NTP) is shown in Fig. 2. The backbone is completely composed of carbon-carbon bonds, similar to a silyl-terminated polyisobutylene, which can give high weatherability to NTP sealants. Furthermore, NTP can be formulated as a one-part system which no

CH3

FIG. 2—Chemical structure of NTP.

FIG. 3—Structural differences between typical (pendant) silylated polyacrylate and telechelic polyacrylate.

silyl-terminated polyisobutylene can provide, because of comparably high-water penetration resulting from the high polarity of the polyacrylate backbone.

Typical silylated polyacrylates have a chemical structure, as shown on the left side of Fig. 3, and are synthesized by well-known acrylic radical polymerization techniques. These silylated polyacrylate have the following drawbacks:

1. A wide molecular weight distribution (MWD, polydispersity), resulting in higher viscosity at a comparatively small number average molecular Weight (Mn).

2. Randomly placed silyl-functional groups in the molecule

3. Uncontrollable numbers of silyl-functional groups per molecule

Therefore, a new synthetic method has been investigated at Kaneka by which narrow MWD and the introduction of silyl-functional groups at the terminals has been obtained.

In recent years, many studies about living radical acrylic polymerization, useful for industrial compa­nies, were conducted. Kaneka has found one of these studies, Atom Transfer Radical Polymerization (ATRP) [3,4], a quite promising polymerization method to synthesize a telechelic polyacrylate with silyl functional groups.

Methyl dimethoxy silyl groups at the polymer terminals are very stable under ambient conditions. However, in the presence of both water and a catalyst, as shown in Fig. 4, the silyl groups are first hydrolyzed and then condensation reaction occurs to create cross-linked structures.

Various types of polyacrylate backbone can be designed with the selection of acrylic monomers, and those polymers can be used to meet the requirements of various applications [5].

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