Aminopropyl-terminated oligomers

Supercritical-fluid-fractionation techniques have been explored to separate the aminopropyl-terminated oligomers into fractions of narrow poly-dispersity. The fractions have been fully characterized in terms of their structure, molecular weight, molecular weight distribution, and functionality. The results of selected studies are presented in this section. 

Table 6. Characteristics of aminopropyl terminated poly-dimethylsiloxane oligomers synthesized in bulk, at 80 °C with 0.01 weight % tetramethylammonium hydroxide catalyst157-1641...

Table 10. Characteristics of aminopropyl-terminated poly(dimethyl-diphenyl)siloxane oligomers 66 171)...

The first example of siloxane-urea segmented copolymers were prepared by the direct reaction of aminopropyl-terminated polydimethyl siloxane oligomers and MDI (4,4 -diphenylmethane diisocyanate), in solution at room temperature as shown in the Reaction Scheme XI. 

The effect of structural variations in siloxane oligomers in the synthesis and properties of the resulting siloxane-urea copolymers have also been investigated 161). In these studies aminopropyl-terminated poly(dimethyl-diphenyl)siloxane and poly-... 

Table 14. Synthesis and characteristics of siloxane-urea segmented copolymers based on MDI and aminopropyl terminated PDMS oligomers 1571...

Poly(arylester)-polysiloxane multiblock copolymers have also been synthesized by the interfacial polymerization of aminopropyl terminated polysiloxane oligomers with bisphenol-A and a mixture of isophthaloyl and terephthaloyl chlorides117, 193-1951 as illustrated in Reaction Scheme XV. In these reactions the poly(arylester) blocks are formed in situ during the copolymerization, so the control of their block sizes is not very precise. It is also important to note that since aminopropyl terminated siloxane oligomers are employed, the linkages which connect the arylester and siloxane blocks are amide linkages. 

Siloxane-urea copolymers were synthesized by the reaction of the aminopropyl terminated PDMS oligomers with MDI or HMDI with no chain extenders (Reaction Scheme XI and Tables 14 and 15). Therefore, in these copolymers the hard segments consist of the aminopropyl end groups on the siloxane oligomers and MDI or HMDI backbones as shown below. The soft segment is pure polydimethylsiloxane. 

Some characteristics of aminopropyl terminated polydimethylsiloxane oligomers are illustrated in Scheme 5. 

In this paper we will discuss the synthesis of a, urhydroxybutyl terminated polydimethylsiloxane oligomers by cationic routes and a,u-aminopropyl terminated poly(dimethy1-diphenyl)siloxane oligomers by anionic methods respectively. Detailed procedures for the synthesis of aminopropyl, carhoxypropyl and glycidoxypropyl terminated polydimethylsiloxane oligomers have already been described elsewhere(1 1). ... 

Table II provides a summary of the results on the characteristics of aminopropyl terminated poly(dimethyl-diphenyl)-siloxane oligomers synthesized. These reactions were conducted in bulk at 160°C with K0H as the initiator. As can be seen from Table II the stoichiometric number average molecular weights sought and obtained are in very good agreement. The level of diphenylsiloxane incorporation was determined by UV spectroscopy. There is no absorption of dimethylsiloxane backbone in the spectral range of 240 to 280 nm. On the other hand, phenyl groups absorb very strongly over these wavelengths (Figure 3). For quantitative analysis we have used the absorption peak at 270 nm as the reference.

Characteristics of Aminopropyl Terminated Poly(Dimethyldiphenyl)siloxane Oligomers... 

Fig. 4. FTIR spectrum of a primary aminopropyl-terminated PDMS oligomer (Mn=1528)...

The reaction scheme for the preparation of aminopropyl-terminated di-fimctionalized oligomers is illustrated in Scheme II. The reaction proceeds by the anionic equilibration of the cyclic siloxane tetramer, D4, in the presence of l,3-bis(3-aminopropyl)tetramethyldisiloxane. The equilibration process begins immediately upon addition of the siloxanolate catalyst, and samples were removed as a function of time for the purpose of the kinetic study. 

Significant differences were observed in the rate of incorporation of D4 and l,3-bis(3-aminopropyl)disiloxane for similar concentrations of potassium, tet-ramethylammonium, and tetrabutylphosphonium siloxanolate catalysts. The rate differences affected the reaction times that were required to obtain a completely equilibrated reaction mixture with the desired molecular weight. The potassium catalyst required excessively long reaction times or high concentrations before sufficient incorporation of the aminopropyldisiloxane was realized. The tetramethylammonium and tetrabutylphosphonium catalysts were much more efficient for the preparation of controlled-molecular-weight aminopropyl-terminated polysiloxane oligomers. 

The traditional approach used in poly(imide-siloxane) synthesis is the reaction of aminopropyl-terminated dimethylsiloxane oligomers with aromatic dianhydrides and additional diamines (9-13). Typically, subambient temperatures and dipolar aprotic solvents are used. The resulting high-molecular-weight polyamic acid solution can be heated to effect imidization and solvent evaporation. This procedure is analogous to the synthetic method used to prepare conventional polyimides for films and coatings. 

The equilibration of the aminopropyl terminated disiloxane was conducted in a very similar manner to the epoxy terminated disiloxane and is shown in Scheme 5. The reaction in this case could not be followed by our GPC unit since we noticed significant absorption of the oligomers onto the columns. 

McGrath, J. E. Sormani, P. M. Elsbernd, C. S. Kilic, S., Kinetics, Mechanisms, and Synthesis Studies of Difunctional Aminopropyl Terminated Polydimeth)dsiloxane Oligomers. Macromol. Chem., Macromol. Symp. 1986, 6, 67-80. 

The polyimide siloxane copolymers are generally synthesized, as shown in Scheme 1, from a combination of a dianhydride and diamine monomer and an aminopropyl terminated polysiloxane to form the segmented polyamic acid. The polyamic acid is then cyclodehydrated by either thermal or solution imidization to give randomly segmented polyimide siloxane copolymers (4). This is indeed the classical approach of reacting one flexible oligomer with two monomers which form the "hard segment (9). 

Detailed procedures for the synthesis ofa,o>-organofunctionally terminated siloxane oligomers with well defined structures have been given 50,66-67). Tables 6 and 7 provide the data on the synthesis and characteristics of aminopropyl and hydroxybutyl terminated polydimethylsiloxane oligomers prepared via anionic and cationic ringopening polymerization of octamethylcyclotetrasiloxane (D in the presence of appropriate disiloxanes, respectively. 

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