Monomers with Same Functional Group

Copolymerizations between pairs of cyclic esters, acetals, sulfides, siloxanes, alkenes, lactams, lactones, A-carboxy-a-amino acid anhydrides, imines, and other cyclic monomers 

Some monomers with no tendency toward homopolymerization are found to have some (not high) activity in copolymerization. This behavior is found in cationic copolymerizations of tetrahydropyran, 1,3-dioxane, and 1,4-dioxane with 3,3-bis(chlorDmethyl)oxetane [Dreyfuss and Dreyfuss, 1969]. These monomers are formally similar in their unusual copolymerization behavior to the radical copolymerization behavior of sterically hindered monomers such as maleic anhydride, stilbene, and diethyl fumarate (Sec. 6-3b-3), but not for the same reason. The copolymerizahihty of these otherwise unreactive monomers is probably a consequence of the unstable nature of their propagating centers. Consider the copolymerization in which M2 is the cyclic monomer with no tendency to homopolymerize. In homopolymerization, the propagation-depropagation equihhrium for M2 is completely toward 

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The presence of monomers with two functional groups of the same kind limits chain growth and decreases the molecular weight. 

Applying these methodologies monomers such as isobutylene, vinyl ethers, styrene and styrenic derivatives, oxazolines, N-vinyl carbazole, etc. can be efficiently polymerized leading to well-defined structures. Compared to anionic polymerization cationic polymerization requires less demanding experimental conditions and can be applied at room temperature or higher in many cases, and a wide variety of monomers with pendant functional groups can be used. Despite the recent developments in cationic polymerization the method cannot be used with the same success for the synthesis of well-defined complex copolymeric architectures. 

The second type of step-growth polymerization involves the use of monomers with different functional groups in the same molecule, A-B type monomers. An example of this reaction is the production of nylon 11 from 11-aminoundecanoic acid. 

The number-average molecular weight of a polymer may be controlled by offsetting the stoichiometry of two dissimilar mutually reactive difunctional monomers. The polymer will have the same endgroup functionality as that of the monomer used in excess. For a generic polymer made from a difunctional monomer AA with A functional groups and an excess of difunctional monomer BB widt B functional groups, r is defined as... 

Stage 1 Difunctional monomers A, with functional groups called c, react by an alternating polyaddition reaction with an excess mixture of difunctional D and trifunctional T monomers, which all have the same functional groups, called h (and thus are equally reactive), to (mainly) h-terminated prepolymer PI. In some calculations tetra-functional Q monomers with equally reactive h functional groups were present as well. 

Stage 3 The unreacted functional c groups of P2 react in this last stage with a mixture of difunctional E and trifunctional F monomers, which have the same functional groups called e (and thus are equally reactive). The h groups are assumed not to react in this stage. 

The resulting polymers always have the same functional group X at both chain ends. Therefore, telechelic polymers can be readily synthesized by the two-component iniferter system. An example is the polymerization of several monomers with 4,4J-azobiscyanovaleric acid (16) and dithiodiglycolic acid (17) as the initiator and the chain transfer agent, respectively, to synthesize the polymers having carboxyl groups at both chain ends [69]. 

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

Instead of using an equimolar mixture, one may use a slight stoichiometric imbalance of one monomer. At some point in the polymerization, the deficient reactant is used up and the molecules have two end groups with the same functional groups (i.e., those of the monomer in excess). 

In such cases also, all linking steps are reactions of the same groups, so that the rate coefficient can once again be assumed to have approximately the same value for all. However, the two types of functional groups now are on different monomers and therefore are not necessarily present in stoichiometric amounts. For stoichiometric mixtures of monomers with different functionalities, the rate equation 10.8 and eqns 10.9 and 10.10 for fractional conversion remain valid. For nonstoichiometric mixtures, eqn 10.8 must be replaced by... 

Reactive flame retardants have the same functional groups as the monomer with which they react. They are covalently bound to the polymer and are therefore less likely to leach to the environment. Reactive type flame retardants offer advantages such as polymer strength permanency and solvent resistance. A disadvantage is that they are polymer specific [15]. 

Ethylene can be copolymerized with alkene compounds or monomers containing polar functional groups, such as vinyl acetate and acrylic acid. Branched ethylene/ alkene copolymers are essentially the same as LDPE, since in commercial practice a certain amount of propylene or hexene is always added to aid in the control of molecular weight. 

Sometimes it is necessary to dehberately ensure lower length of the obtained polymer (for example, for better process bility). For the reactions similar to (3.4) one of the methods to reach this aim is to add one of the reactants in slight excess. The polycondensation will then proceed up to a point when one reactant is completely used up and all the chain ends possess the same functional group (either COOH or OH). Another method to achieve desired chain length at polycondensation is the addition of a small amount of a monomer with only one functional group (chain terminator). 

The approach relies on the formation of a pre-polymerization complex between monomers carrying suitable functional groups and the template. A cross-linker is then added and the polymerization initiated. Then, the highly cross-linked polymer forms around the template-monomer complexes. The template is then removed from the polymer via extraction with a solvent, which disrupts the non-covalent interactions present in the pre-polymerization complex. Subsequent template re-binding takes place through the formation of the same non-covalent interactions. 

In polymerizations of monomers with the same functional groups on each molecule, like... 

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