Poly relative monomer conversion

Chain polymerizations are less often performed in die bulk, because of problems with the control of the reaction. [An interesting exception is poly(methyl methacrylate), a polymer that is soluble in its own monomer (not all polymers are), and which is synthesized commercially by chain (free radical) polymerization very slowly in bulk (Figure 3-44). The resulting polymer has outstanding optical properties (clarity) because there are very few impurities.] In bulk polymerizations there is a tendency for the reaction mass to form a gel (i.e., have an extraordinarily high viscosity) and hot spots can develop. At the extreme, the reaction rate can accelerate to runaway proportions (for reasons we will discuss when we consider kinetics) with potentially disastrous (explosive) consequences. Viscosity and heat control can be achieved, if necessary, by carrying out the polymerizations to a relatively low conversion, with the unreacted monomer being separated and recycled. Another way to control the viscosity and heat transfer problems of chain polymerizations is to perform the polymerization in solution A major concern with this method is that chain transfer to sol-... 

The unique signals at 4.23 (t, 0CH2) and 2.64 (t, C(0)CH2) were assigned to the protons of e-caprolactone. Signals at 4.06 (t, OCHl), (t, ROCH2), and 2.30 (t, C(O)Cffi) appeared after tiie onset of polymerization reactions mid were assigned to poly(e-caprolactone). The relative intensity of signals at 4.06 to 4.23 and 4.06 to 3.64 were used to calculate monomer conversion and Mi, respectively. 

Some polymers, such as poly(vinyl chloride) or poly(acrylonitrile), are insoluble in their own monomers. In bulk polymerization, therefore, the polymer is precipitated at relatively low conversions. Since newly produced free radicals still have monomer available to them, the polymerization continues, but the kinetics of polymerization is complicated. Part of the growing chain resides in the precipitated phase, and thus the probability of chain termination is small. On the other hand, the rate of diffusion of the monomer to the growing chain end is considerably reduced, so that the propagation reaction is also affected. 

Methacrylate monomers showed relatively low conversions in comparison with the acrylates. In particular, the low reactivity of CHMA seems to result from its small affinity to the poly(NMAAm) microspheres, which causes slow diffudon of the monomer to the active reaction sites. Aliphatic hydrocarbons such as n-hexane and cyclohexane are not even misdble with NMAAm monomer. Consequently the (THMA system produced a larger MeOH-soluble part. 

Another commercially available polymer, poly(isobutylene-co-p-methylstyrene-co-p-bromomethylstyrene), was used as a macroinitiator for the ATRP of St to produce a graft copolymer (160). After 23 h at 100°C, with 1 equivalent of catalyst relative to the number of moles of initiator, monomer conversion was 81% however, increasing the concentration of catalyst fivefold resulted in the same efficiency after only 11 h. No evidence of imreacted macroinitiator was found in the GPC analysis, indicating that nearly all of the chains contained some grafted sites. Results from mechanical analysis showed that when the wt% of St was high (28%), the graft copol5mier exhibited no special properties however, with only 6 wt% pSt, the polymer was elastomeric and could be reversibly stretched to 500% of its initial dimension (160). 

The results of several copolymerization experiments with 7 are given in Table 3.8, from which it is clear that the assumption of similarity between 7 and benzyl methacrylate is reasonable. From Fig. 3.4. it is predicted that both MMA and MAN should copolymerize with 7 almost ideally , whereas styrene will deviate considerably from ideality . These predictions are verified by the results in Table 3.8. If the azo monomer is incorporated into the polymer in the same proportion as it is present in the initial monomer mixture, then it is possible to convert the, relatively valuable, azo monomer essentially 100% into polymer without changing the composition of the copolymer with conversion an important consideration for the technical utilisation of such products as the starting materials for graft copolymers. If the poly-... 

Thus, by lowering solvent polarity (CH2Cl2/CCl4 mixtures) or by the addition of a common ion salt (rtBtuNI), these researchers obtained poly(pMOS) of unimodal and relatively narrow MWDs, whose shape and position corresponded to those of the lower polymer population in the two-peaked distribution. Under these conditions the number-average molecular weights increase with conversion. Upon sequential addition of fresh monomer feeds, and block copolymers of pMOS and isobutyl vinyl ether (IBVE) are obtained [52], Similar results were also obtained for the polymerization of IBVE [53,54]. 

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