Propylene- crystallization rate

PiQ. 10. Propylene polymerization rate at constant pressure and temperature (pciHf = 1,4S0 mm. Hg, t — 70°C) obtained with two samples of unground a-TiCli whose crystals have different sizes (seeFigs. 7 andS). (a-TiCl 1.64 g./l., [AI(CjHb),] 2.94 X 10- mol./l.). 

The stereoregularity—i.e., distribution of the stereosequence length in these polymers—has a marked effect on the crystallization rates and the morphology of the crystalline aggregates. These differences, in turn, influence the dynamic mechanical properties and the temperature dependence of the dynamic mechanical properties. In order to interpret any differences in the dynamic mechanical properties of polymers and copolymers of propylene oxide made with different catalysts, it was interesting to study the differences in the stereosequence length in the propylene oxide polymers made with a few representative catalysts. 

The stereosequence length also has a marked effect on the isothermal crystallization kinetics of the propylene oxide polymers. These studies and analysis of results on crystallization kinetics will be described in detail in another communication. Here we summarize briefly the main conclusions of the effect of stereosequence length on the isothermal crystallization rates. 

Propylene oxidation rates per unit surface area also increased with crystal-... 

It is not only the crystallization rate, however, which is influenced by nucleating agents, but also the morphology. Isotactic poly(propylene) crystallizes monoclinically in the presence of / -/-butyl benzoic acid and pseudohexagonally when the quinacridone dyestuff. Permanent Red EBB, is added. 

PPSu presents lower crystallinity, crystallization rates, and melting point compared to its homologs PESu and PBSu This in turn results in a polymer with higher enzymatic hydrolysis rates and hence greater biodegradability. On the other hand, retardation in PPSu crystallization is due to its reduced symmetry caused by the propylene units. 

The overall nucleation and crystalhzation rates of PLA tmder heterogeneous conditions are relatively higher than in homogenous conditions. The nucleation and crystallization rates of propylene-ethylene copolymer are increased tmder isothermal conditions. Addition of nucleating agent accelerates crystallization. Avrami equation is in popular use in the analysis of isothermal crystallization kinetics of polymers ... 

Randall, J. C. Alamo, R. G Agarwal, P. K. Ruff, C. J. Crystallization rates of matched fractions of MgCl2-supported Ziegler-Natta and metallocene isotactic poly(propylene)s. 2. Chain microstructures from a supercritical fluid fractionation of a MgCl2-supported Ziegler-Natta isotactic poly(propylene). 

Choi WJ, Kim SC (2(X)4) Effects of talc orientation and non-isothermal crystallization rate on crystal orientation of polypropylene in injection-molded polypropyloie/ethylene-propylene rubber/talc blends. Polymer 45 2393-2401... 

The effect of poly(methyl methacrylate), PMMA, on the crystallization kinetics of poly(ethylene oxide) has been investigated using the Avrami equation to analyze the results (80). The crystallization-rate constant, k, decreased as the concentration of PMMA increased. This and other results indicated that, in the blends, crystallization proceeds by a predetermined nucleation and this is followed with a two-dimensional growth. There has been evidence of melt compatibility for these two polymers (81-84) see Section V. Crystallization behavior of blends of poly(ethylene oxide) with poly(propylene oxide) (85) and with poly(vinyl acetate) (83) have been studied, as well as star and block copolymers of ethylene oxide and styrene (86). 

Poly(propylene-ifaf-ethylene) Crystallization rates measured by ... 

Further evidence for the influence of chain entanglement in the crystallization process is found in the crystallization of an isotactic poly(styrene) sample that was prepared from a freeze-dried dilute benzene solution.(38a) Entanglements in such a sample will be miiumal. The overall crystallization rate in such samples, in terms of ii/2, is enhanced by a factor of seven to eight relative to conventional crystallization from the pure melt.(38a) Experiments with isotactic poly(propylene), freeze-dried from n-octane, showed a similar enhancement in the crystallization rate.(38b) This type of experiment complements the overall crystallization rate of polymers from dilute solution. 

An analysis of the overall crystallization rate with composition requires that the comparison be made either at constant undercooling or at one of the nucleation temperature quantities, T / T AT or T /T(AT). This requirement is essential because of the importance of nucleation to the crystallization process. The overall crystallization kinetics of a variety of polymer-diluent systems have been reported. Many different relations between the overall crystallization rate and composition have been observed. For example, as is shown in Fig. 13.17 there is a continuous decrease in the crystallization rate with dilution for linear polyethylene-a-chloronaphthalene mixtures.(42) The results for poly(trans-1,4-isoprene) in methyl oleate follow a similar pattem.(80) In contrast, the rates for poly(dimethyl siloxane) crystallizing from toluene, at compositions V2 = 0.32 to 0.79, are the same at all undercoolings, but are faster than that of the pure polymer.(78) Another example is found with poly(ethylene oxide)-diphenyl ether mixtures.(77) In this case the crystallization rates for the pure polymer and composition = 0.92 to 0.51 are the same. However, the rates for the more dilute mixtures, V2 = 0.04 and 0.30 are lower. For poly(decamethylene adipate)-dimethyl formamide mixture the rates for the pure polymer and V2 = 0.80 are the same.(77) The mixture of isotactic poly(propylene) with dotricontane shows interesting behavior.(81) At all undercoolings studied, the crystallization rate initially decreases with dilution, reaches a minimum in the range V2 — 0.7 (a maximum in ti/2) and then slowly increases with further dilution, up to V2 = 0.10. 

The polyols used are of three types polyether, polyester, and polybutadiene. The polyether diols range from 400 to about 10,000 g/mol. The most common polyethers are based on ethylene oxide, propylene oxide, and tetrahydrofuran or their copolymers. The ether link provides low temperature flexibility and low viscosity. Ethylene oxide is the most hydrophilic and thus can increase the rate of ingress of water and consequently the cure rate. However, it will crystallize slowly above about 600 g/mol. Propylene oxide is hydrophobic due to hindered access to the ether link, but still provides high permeability to small molecules like water. Tetrahydrofuran is between these two in hydrophobicity, but somewhat more expensive. Propylene oxide based diols are the most common. 

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