Polymerization temperature effect

Grijpma, D.W., and Pennings, A.J., Polymerization Temperature Effects on the Properties of L-Lactide and e-Caprolactonc copolymers. 1991, Pol Bull, 25 335... 

Grijpma, D.W., Pennings, A.J., 1991. Polymerization temperature effects on the properties of L-lactide and e-caprolactone copolymers. Polymer Bulletin 25 (3), 335—341. 

Equation (6.32) allows us to conveniently assess the effect of temperature variation on the rate of polymerization. This effect is considered in the following example. 

Various inorganic, organic, and organometaUic compounds are known to cataly2e this polymerization (4,8,9). Among these, BCl is a very effective catalyst, although proprietary catalysts that signiftcandy lower polymerization temperature from the usual, sealed-tube reaction at 250°C are involved in the industrial manufacture of the polymer. A polycondensation process has also been developed for the synthesis of (4) (10—12). This involves elimination of phosphoryl chloride from a monomer prepared from (NH 2 04 and PCl. ... 

DMSO is an effective solvent for the polymerization as it affords good solubiUty for both the polymer and disodium bisphenol A [2444-90-8]. Typical polymerization temperatures for polysulfone are in the range 130—160°C. At temperatures below 130°C, the polymerization slows down considerably due to poor solubiUty of the disodium bisphenol A salt. 

Fig. 2. Effect of polymerization temperature on the crystalline melting point of chloroprene mbbers produced by emulsion polymerization ...

All these effects increase the overall polymerization rate and decrease the degree of polymerization. The effect of polymerization temperature on the variation of monomer conversion with the polymerization time is exemplified in Fig. 8 for the emulsion polymerization of styrene. 

Peroxyacetals 58106 and peresters such as 61107 are also effective transfer agents, however, at typical polymerization temperatures ( 60 CC) they are thermally unstable and also act as initiators. Compounds such as 62 which may give addition and 1,5-intramolecular substitution with fragmentation have also been examined for their potential as chain transfer agents (l,5-SHi mechanism).108... 

There have been no comprehensive studies of the effect of temperature on the course of RAFT polymerization. Temperatures reported for RAFT polymerization range from ambient to 140 °C. There is evidence with dithiobenzoates that at higher temperatures there is less retardation and also data that suggest narrower... 

Temperature dependence, for potential of zero charge on silver in contact with solution, 76 Temperature effects on the potential of zero charge, 23 upon polymerization, 406 Temperature variation of the potential of zero charge (Frumkin and Demaskin), 28... 

The effect of the temperature on the polymerization of 53 in methylene chloride is presented in Table 3. The upper half of the data in the table shows the temperature effect on the products in the initial stage of the reaction, and the lower half is that for the middle to final stages of the reaction. Obviously there is a drastic change in the reaction products between -20 and -30 ° Below —30 °C, the cyclic dimer is the predominant or even sole product after the reaction of 48 hours, while above —20 °C, the low molecular weight polymer is exclusively formed. The cyclic oligomers once formed in the initial stage of the reaction are converted to the polymer in the later stage of the reaction above —20 °C. 

Figure 2. Effect of polymerization temperature (0) and AlR, Nd(vers), molar ratio (O) on molecular weight. Et,Al/ Ndivers), molar ratio was kept at 40 1 when the temperature was varied, and the temperature was maintained at 60°C when Et,Al/Nd(vers), molar ratio was varied. Nd(vers), is the neodymium salt of Versatic 10, which is a mixture of isomeric tertiary carboxylic acids.

The most studied catalyst family of this type are lithium alkyls. With relatively non-bulky substituents, for example nBuLi, the polymerization of MMA is complicated by side reactions.4 0 These may be suppressed if bulkier initiators such as 1,1-diphenylhexyllithium are used,431 especially at low temperature (typically —78 °C), allowing the synthesis of block copolymers.432,433 The addition of bulky lithium alkoxides to alkyllithium initiators also retards the rate of intramolecular cyclization, thus allowing the polymerization temperature to be raised.427 LiCl has been used to similar effect, allowing monodisperse PMMA (Mw/Mn = 1.2) to be prepared at —20 °C.434 Sterically hindered lithium aluminum alkyls have been used at ambient (or higher) temperature to polymerize MMA in a controlled way.435 This process has been termed screened anionic polymerization since the bulky alkyl substituents screen the propagating terminus from side reactions. 

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