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
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 .