SI polymer

Styrenic block copolymers (SBCs) are also widely used in HMA and PSA appHcations. Most hot melt appHed pressure sensitive adhesives are based on triblock copolymers consisting of SIS or SBS combinations (S = styrene, I = isoprene B = butadiene). Pressure sensitive adhesives typically employ low styrene, high molecular weight SIS polymers while hot melt adhesives usually use higher styrene, lower molecular weight SBCs. Resins compatible with the mid-block of an SBC improves tack properties those compatible with the end blocks control melt viscosity and temperature performance. 

The last decade has also seen the advent of commercial SIS polymers with 15-18% styrene content, but with higher diblock content (typically 30-55%). These are available from many of the major suppliers. The higher diblock content makes them ideal for label applications where low modulus PSAs provide easy die cuttabilty in processing, and rapid wet out and bonding to the substrate in the label application. The shear holding power characteristic would be reduced, but this would not be a critical factor for many label applications. 

Domier has developed a production route for continuous fiber-reinforced ceramics based on the impregnation and pyrolysis of Si-polymers. This process is related to the manufacturing of fiber-reinforced plastics and allows the cost-effective production of large and complex CMC-structures. 

Suitable polymers with high ceramic yield, low shrinkage, and good processing properties are the key to the successful development of CMC by the liquid processing route. The following Si-polymers are the main candidates for the conversion to ceramics in inert gas atmosphere at temperatures over 1000°C ... 

Fig. 1. Scheme of the CMC manufacturing process of the infiltration and pyrolysis of Si-polymers... 

Syntheses of Base-Soluble Si Polymers and Their Application to Resists... 

Organosilicone surfactants can be classified according to the position of the lyophilic moiety with respect to the Si-O-Si polymer. The abbreviations M, D, T and Q, referring to the number of oxygen atoms bonded to the silicon, are used to define the silicone portion as shown in Table 2.8.2. Insertion of the lyophilic moiety (A) into the silicone polymer itself leads to monofunctional, i.e. M(D A)M, and polyfunctional linear, i.e. MID A D M, type surfactants. Polyfunctional linear versions are also described as rake, comb- or graft-copolymers. Substitution at the ends of the silicone polymer yields surfactants... 

The constancy of tensile strength of the SIS polymers, above a certain minimum end-block size, can be explained best on the basis of efficiency of phase separation. Since the latter depends on the three parameters—Le.y incompatibility of the two blocks, composition ratios, and block size—the SIS polymers must undergo a much better phase separation at equivalent composition and block size than the SBS polymers, and the latter require a higher styrene content and a longer polystyrene end block to accomplish good phase separation. This is in accord with the generally accepted fact that polyisoprene is more incompatible with polystyrene than is the case for polybutadiene. 

The importance of efficient phase separation on the purity of the domains is illustrated even better in Table III, which shows the tensile strength of the SIS polymers as a function of composition and end-block... 

It is not surprising, therefore, that the added polystyrene causes no change in the strength of the SIS polymer since, at these styrene contents... 

THe network structure of these block polymers can also be altered by actually crosslinking the elastomeric polydiene chains, thus introducing a chemical network. In this approach it was necessary to use a crosslinking method which would not result in any measurable chain scission. Dicumyl peroxide (Dicup) was chosen for crosslinking an SIS polymer since this peroxide is known to accomplish exclusive crosslinking without any observable chain scission (3). The Dicup was dissolved in a THF solution of the polymer, and a cast film was prepared which was then vulcanized in a press at 155 °C for 35 min. A control sample, without Dicup was treated in the same way. 

Table VI. Properties of SIS Polymers Crosslinked by Dicumyl Peroxide...

SBS copolymers are used in a wide variety of applications because of their clarity, toughness, and ease of processing. A major application is hot melt adhesives where they are compounded with hydrocarbon resins and oil.72 The SIS polymers are very popular in... 

Fully saturated SBC polymers have also been investigated. Vinylcyclohex-ane-ethylene/propylene-vinylcyclohexane triblock copolymers have been prepared by complete hydrogenation of SIS polymers using a supported palladium catalyst [53]. Under the appropriate conditions, hydrogenation of the styrene blocks can also be accomplished using Ziegler-type catalysts [54]. 

---