Typical random copolymer structure

In order to study elastomeric networks, simulating the type of polymers used for tires, we switched to polymers with low glass transition temperatures and oligoether bis-maleimides. A typical random copolymer structure, built from the radical copolymerization of n-hexyl acrylate and 2-furfuryl methacrylate, is shown below. These reactions were conducted in toluene at 80°C with AIBN as initiator. After 8 h, the copolymers were recovered by precipitation in 70 to 80% yields. The compositions varied fi om 2 to 30% of the furanic monomer (monomer feed and copolymer composition were always very similar, suggesting that ri and ti must have both been close to unity). The corresponding Tgs went from -70 to 30°C for molecular weights of about 20,000. Both homopolymers were also prepared as reference materials. 

Hydrogenated poly(butadiene), an ethylene-butene random copolymer, is often used as die crystallizing block, in di- and triblock copolymers. In this context the copolymer is commonly referred to as polyethylene. This nomenclature can be misleading since it carries the connotation that hydrogenated poly(butadiene) behaves as a homopolymer with respect to crystallization. In fact, it behaves as a typical random copolymer that is located within the structure of an ordered copolymer. 

The homopolymer of DMP dissolves readily in methylene chloride but precipitates on standing as a crystalline polymer-CH2Cl2 complex, providing a method for distinguishing between block copolymers and mixtures of homopolymers. Random copolymers prepared by methods a and b form stable solutions in methylene chloride. Copolymers with a 1 1 ratio of DMP and DPP prepared by methods c and d also yield stable methylene chloride solutions. Since the NMR spectrum shows that the DMP portion of these materials is present as a block and the solubility in methylene chloride shows that DMP homopolymer is absent, these copolymers have the block structure. They can be separated by crystallization from m-xylene into an insoluble DPP-rich fraction and a soluble DMP-rich fraction, both fractions having the NMR spectra characteristic of block copolymers. A typical 1 1 copolymer prepared by adding DMP to growing DPP polymer yielded 35% of insoluble material... 

The elastomeric ethylene-propylene copolymers (EPR) [5, 6] are also random copolymers but have an amorphous structure with a typical rubber-like elasticity and high elongation upon deformation. Amorphous character is achieved if the structure of the polymer is essentially random with a minimum of molecular regularity and a moderately high ethylene content. Ethylene content in EPR s are typically about 65 mole%. 

Random copolymer PP typically contains 1.5 to 7% ethylene, by weight, as a comonomer. The polymer structure is similar to that of isotactic PP with the addition of random insertion of ethylene groups. 

As shown in Scheme 2.27, POEVE and PNIPAM have similar structures with both hydrophilic and hydrophobic parts in each monomer unit. Quite recently, our group examined another possibility for thermosensitive phase separation random copolymers of hydrophilic and hydrophobic monomers.Although random copolymers have been investigated previously, the achieved phase separation was broad, with hysteresis and low turbidity. By living cationic polymerization in the presence of added bases, our group successfully prepared random copolymers of IBVE and HOVE, both of which are typical hydrophobic and hydrophilic monomers, and which are not thermosensitive themselves. At low temperature, the polymers were soluble in water, but when the temperature was increased to a critical point, the transparent solution became opaque. The phase separation was quite sensitive (Scheme 2.27(a)) and the temperature of phase separation was governed by the monomer feed ratio. 

As mentioned above, PLA should be addressed as a random copolymer rather than as a homopolymer the properties of the former depend on the ratio between L-lactic acid and D-lactic acid units. A few studies describe the influence of the concentration of D-lactic acid co-units in the PLLA macromolecule on the crystallization kinetics [15, 37, 77-79]. The incorporation of D-lactic acid co-units reduces the radial growth rate of spherulites and increases the induction period of spherulite formation, as is typical for random copolymers. In a recent work, the influence of the chain structure on the crystal polymorphism of PL A was detailed [15], with the results summarized in Figure 5.13. It shows the influence of D-lactic acid units on spherulite growth rates and crystal polymorphism of PLA for two selected molar mass ranges. 

PAMPS and its random copolymer containing 18-crown-6 (PAMPS -co-crown), are used to further study the nonelectrostatic contribution to desorption force [56]. The primary structures of polymers are shown in Scheme 30.5. As shown in Fig. 30.12, the typical force curves of PAMPS with a plateau are obtained from amino-modified quartz in the buffer of water. The long plateau suggests that the desorption process of the PAMPS chain from the substrate is smooth and that it adopts a train-like conformation at the interface and the desorption force remains about 120 pN. The desorption-adsorption process is in equilibrium in the experimental time scale, which is confirmed by the constant desorption force when changing the stretching velocity. The desorption force of PAMPS from the amino-modified quartz has been... 

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