Condensation polymerization molecular weight distribution

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Example 13.4 Calculate the molecular weight distribution for a self-condensing polymerization with — + Stop the calculations... 

Failure to remove the alcohols generated in either of the equilibrium condensation steps will reduce the efficiency of the polymerization process. This effect can be explained by Le Chatelier s principle, which was discussed in Chapter 3. The volatile alcohols produced during polymerization act as a chemical stress on the product side of the reaction, which inhibits polymerization. Another implication of the equilibrium nature of this polymerization process is seen in the molecular weight distribution of the final polymer. All polyesters contain a few percent of low molecular weight oligomers, regardless of the polymerization process. 

Condensation polymerization of functional ferrocenes generally yields medium- or low-molecular-weight polymers with broad molecular-weight distributions.12 For example, ferrocenylcarbinol, 6.9, has been condensation-polymerized to polymers 6.10 and 6.11 in the presence of boron trifluoride etherate or zinc chloride (reaction (5)).910 Species 6.11... 

An interesting thing is that the polyether with low polydispersity from chain-growth condensation polymerization possessed higher crystallinity than the one with broad molecular weight distribution from conventional step-growth condensation polymerization. The XRD pattern of the former polymer showed a stronger intensity, and the DSC profile showed the... 

Enzymatic polymerization of lactones is a promising approach and has been investigated by several workers [45,46,71-78]. Poly(e-CL) with Mn=14,500 and a molecular weight distribution of 1.23 has recently been reported using Pseudomonas sp. lipase as the catalyst [71]. A complex mechanism involving both ring-opening and linear condensation polymerizations has been proposed for the enzymatic polymerization of lactones. 

Example 13.4 Calculate the molecular weight distribution for a self-condensing polymerization with k m - ko/(l + m). Stop the calculations when In = 5. Compare the results with those of the Flory distribution. 

Barrere and Landfester [184] prepared a hybrid miniemulsion in which isophorone diisocyanate was condensation polymerized with dodecanediol to form polyurethane at the same time that the polystyrene or polyBA was free radical polymerized. Unlike previous work, the polyurethane was not prepared in organic solvent in advance. Therefore, in this one-pot synthesis, polyaddition and free radical polymerization both take place in the same particle. HD was used as the costabihzer. After miniemulsification, the polycondensation was allowed to take place, and then a free radical initiator was added to polymerize the styrenic or acrylic monomer. Molecular weight distributions were bimodal the PU had a substantially lower molecular weight than the polyacrylate. Neither intra- nor interparticle phase separation could be detected by TEM the particles appeared to be homogeneous. No measurements of grafting were made, but since there was no unsaturation in the PU, none was expected. 

The Flory distribution is a random distribution useful in several modes of polymerization. This distribution results from addition polymerization reactions when the only significant processes that interrupt macromolecular growth are either or both of chain transfer (to any species but the polymer) or termination by disproportionation. Likewise, this molecular weight distribution describes linear condensation polymerization when equal reactivity is assumed for all ends only when the reaction involves an equilibrium between polymerization and depolymerization. The model describes the distribution with one parameter which is the number average molecular weight. The distribution equation is ... 

ADMET differs from ROMP in one major respect. Whereas ROMP is a chain-growth polymerization, ADMET is a step-growth, condensation process.58 Manifestation of this difference lies in both the molecular weights and the molecular weight distributions of polymer chains that result from the two path-... 

Miller et al. combined condensation polymerizations with both nitroxide-mediated and ROP (Scheme 61) [363]. The condensation polymerization of 2,7-dibromo-9,9-dihexylfluorenes (DHF) was carried out in the presence of a Ni(COD)2 catalyst using (l-(4 -bromophenyl)l-(2", 2", 6", 6"-tetramethyl-l-piperidinyl-oxy)ethyl) as a capping agent/initiator for the CRP of St. This led to a central block of pDHF and outer blocks of pSt (Mn=36,000,Mw/Mn=l.52). Similarly, a diol functionalized with a bromine moiety was used as the end cap-per/initiator for the simultaneous polymerizations of CL and DHF in the presence of both Ni(COD)2 and Sn(Oct)2 (Mn=17,000-31,600, Mw/Mn=1.65-2.39) [363]. The molecular weight distribution narrowed as the content of the DHF in the feed decreased for the condensation/ROP combination. Combining ATRP... 

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