Functionalized polymers with homopolymers

Copolymers. There are two forms of copolymers, block and random. A nylon block copolymer can be made by combining two or more homopolymers in the melt, by reaction of a preformed polymer with diacid or diamine monomer by reaction of a complex molecule, eg, a bisoxazolone, with a diamine to produce a wide range of multiple amide sequences along the chain and by reaction of a diisocyanate and a dicarboxybc acid (193). In all routes, the composition of the melt is a function of temperature and more so of time. Two homopolyamides in a moisture-equiUbrated molten state undergo amide interchange where amine ends react with the amide groups. 

The transformation of the chain end active center from one type to another is usually achieved through the successful and efficient end-functionalization reaction of the polymer chain. This end-functionalized polymer can be considered as a macroinitiator capable of initiating the polymerization of another monomer by a different synthetic method. Using a semitelechelic macroinitiator an AB block copolymer is obtained, while with a telechelic macroinitiator an ABA triblock copolymer is provided. The key step of this methodology relies on the success of the transformation reaction. The functionalization process must be 100% efficient, since the presence of unfunctionalized chains leads to a mixture of the desired block copolymer and the unfunctionalized homopolymer. In such a case, control over the molecular characteristics cannot be obtained and an additional purification step is needed. 

Fig. 25 Semilogarithmic plots of the changes of ratio I1/I3 for pyrene in aqueous solutions of homopolymer PVCL and grafted copolymers at 20° C as a function of polymer concentration. Homopolymer PVCL (a), PVCL-g-6 (b), PVCL-g-13 (c), PVCL-g-16 (d), PVCL-g-18 (e), PVCL-g-34 (/). (Reprinted with permission from Ref. [180] copyright 2005 Elsevier)...

Table IV summarizes the glass transition temperature of a number of special functional oil-based homopolymers. Many of the polymers shown indeed have T s below the critical value. It is now believed that the synthetically epoxidized oils were fully epoxidized, producing materials with unusually high degrees of crosslinking, which tended to raise their T s beyond the desirable range.

Both methods require that the polymerization of the first monomer not be carried to completion, usually 90% conversion is the maximum conversion, because the extent of normal bimolecular termination increases as the monomer concentration decreases. This would result in loss of polymer chains with halogen end groups and a corresponding loss of the ability to propagate when the second monomer is added. The final product would he a block copolymer contaminated with homopolymer A. Similarly, the isolated macroinitiator method requires isolation of RA X prior to complete conversion so that there is a minimum loss of functional groups for initiation. Loss of functionality is also minimized by adjusting the choice and amount of the components of the reaction system (activator, deactivator, ligand, solvent) and other reaction conditions (concentration, temperature) to minimize normal termination. 

Qualitative and quantitative elemental analysis of polymers can be carried out by the conventional methods used for low-molecular-weight compounds. So a detailed description is not needed here. Elemental analysis or determination of functional groups is especially valuable for copolymers or chemically modified polymers. For homopolymers where the elemental analysis should agree with that of the monomer, deviations from the theoretical values are an indication of side reactions during polymerization. However, they can also sometimes be caused by inclusion or adsorption of solvent or precipitant, or, in commercial polymers, to the presence of added stabilizers. The preparation of the sample for... 

In conclusion, the AB benzocydobutene monomers can be polymerized to form polymers with a broad range of mechanical properties. The properties of the polymers depend not only upon the type of reactive functionalities but also the nature of the linking group between functionalities. Based upon the properties presented for these homopolymers, it would seem that a broad spectrum and combination of unique thermal and mechanical properties can be obtained from these relatively simple molecules. 

This technique is based on the use of a linear polymer with pendant functional groups that can be activated to initiate the polymerization of a second monomer. Based on this definition, the linear precursor polymer can be considered as a multifunctional macromolecular initiator. The importance of the grafting from technique by cationic polymerization of the second monomer increased considerably with the advent of living cationic polymerization. The advantage is the virtual absence of homopolymer formation via chain transfer to monomer. 

Functionalized, liquid polybutadiene derivatives have also been developed as hybrid flexiblizers for epoxy resins. Carboxyl-terminated butadiene/acrylonitrile polymers, butadiene homopolymers, and maleic anhydride-amino acid grafted butadiene homopolymers have been used as flexibilizers to impart good low-temperature strength and water resistance to DGEBA-based epoxy adhesives. An epoxy system toughened by polybutadiene with maleic anhydride is claimed to provide a hydrophobic backbone, low viscosity, softness, and high tensile strength and adhesion (Table 7.10). 

The self assembly of polymers in the solid state, using polystyrene scaffolds with pendant 2,6-diamino-pyridine (DAP) units has been extensively described by Rotello et al. [224] (Sect. 3.3). Two different polymers were investigated either a homopolymer, functionalized with the pendant DAP units, or a PS-PS diblock copolymer, in which one block only was functionalized with the DPA units via a p-chloromethylstyrene block (Fig. 67). In order to study the effect exerted by the hydrogen-bonding moieties onto the microphase separation, a series of polymers with different fractions of... 

There are several ways in which block copolymers can be made. The three main methods are (1) sequential addition of monomers, (2) the preparation of a functionalized polymer followed by the use of the functionalized polymer as a macroinitiator or chain-stopper for initiation or termination of polymerization of the second monomer, and (3) use of a multiple-headed initiator. The purity of the block copolymers produced in these processes is dependent upon the livingness (lack of side reactions that lead to termination) of the chemistry used to make them. If the integrity of the chain-ends is maintained throughout the polymerization because all possible termination mechanisms are absent or eliminated, then pure block copolymers can be produced. If, however, impurities get into the process or if there are side reactions that lead to chain termination, the resulting block copolymers are contaminated with some homopolymer. Depending upon the application, some contamination of homopolymer in the block copolymer may be acceptable. 

The fact that large-modulation SRGs are formed only above a certain threshold amount of functionalization was also shown by Andruzzi et al.J for amorphous as well as LC polymers. They investigated copolymers derived from two photochromic monomers, 6-(4-oxy-4 -cyanoazobenzene)h x-l-yl methacrylate and 8-(4-oxy-4 -cyanoazobenzene)oct-l-yl methacrylate, and a nonphotochromic comonomer, (-)-menthyl methacrylate. Considerable amplitudes were obtained for all polymers with more than 30% of azofunctionalization. The maximum amplitudes were observed for copolymers possessing 75-80% of dye content, not the fully functionalized homopolymers. 

These are chemically homogeneous multiarm star polymers (usually homopolymers) with only excluded volume interactions [21,22], Due to their synthesis procedure (high vacuum anionic polymerization), they are stable and nearly monodisperse [23]. Their softness can be tuned at the synthesis level (number and size of arms) [23,24] and/or by varying the temperature in different solvents [25,26], Moreover, these systems can be functionalized in various ways [27]. What made these systems truly ideal soft colloids were the breakthroughs in both theoretical description and synthesis. The former refers to the ability to describe analytically their internal structure [28] and their softness in terms of an effective interaction potential [24,29]. 

The glass transition temperature of the homopolymers was 95 °C. Alternatively, the ROP of the CL portion using Al(0 Pr)3 as the catalyst at 25 °C resulted in homopolymers with Mn=1800-14,000 and Mw/Mn=1.15-1.22 [366]. 6-Arm star polymers composed of random copolymers of 4-(acryloyloxy)-e-caprolac-tone with CL or L, L-lactide were also prepared, although the control over the polymerization was lost in the presence of L, L-lactide. These two approaches to polymerizing the same monomer led to polymers with novel pendant functionalities that may be useful for a wide variety of applications [366]. 

This presentation summarizes results on the synthesis, the dilute solution and bulk properties of dimethylamine and sulfozwitterionic end-functionalized polymers having different architectures (linear homopolymers, diblock and triblock copolymers and star polymers with different number of fimctional groups). 

---